Kryptografie/tmp

Preface

Do not talk unencrypted "Neboltai"

Acknowledgements

We would like to express our thanks to the following reviewers and people who have generously offered their time and interest (in alphabetical order): Brown, ScottBrulebois, CyrilBurghardt, KrzysztofDirksen-Thedens, MathisDulaunoy, AlexandreEndres, JohannesGühring PhilippGrigg, IanHaslinger, GunnarHorenbeck, MaartenHuebl, AxelKnecht, PascalKoetter, Patrick BenKovacic, DanielLenzhofer, StefanLorünser, ThomasMaass, MaxMehlmauer, ChristianMillauer, TobiasMirbach, AndreasO’Brien, HughPacher, ChristophPalfrader, PeterPape, Tobias (layout)Petukhova, Anna (Logo)Pichler, PatrickRiebesel, NicolasRoeckx, KurtRoesen, JensRublik, MartinSchiffbauer, MarcSchosser, AndreasSchüpany, MathiasSchulze, AndreasSchwartzkopff, MichaelSchwarz, René («DigNative»)Seidl, Eva (PDF layout)Van Horenbeeck, MaartenWagner, Sebastian («sebix»)Zangerl, Alexander The reviewers did review parts of the document in their area of expertise; all remaining errors in this document are the sole responsibility of the primary authors.

Abstract

Unfortunately, the computer security and cryptology communities have drifted apart over the last 25 years. Security people don’t always understand the available crypto tools, and crypto people don’t always understand the real-world problems. 

— Ross Anderson (Anderson, 2008) This guide arose out of the need for system administrators to have an updated, solid, well researched and thought-through guide for configuring SSL, PGP, SSH and other cryptographic tools in the post-Snowden age. Triggered by the NSA leaks in the summer of 2013, many system administrators and IT security officers saw the need to strengthen their encryption settings. This guide is specifically written for these system administrators. As Schneier noted in (Schneier, 2013), it seems that intelligence agencies and adversaries on the Internet are not breaking so much the mathematics of encryption per se, but rather use software and hardware weaknesses, subvert standardization processes, plant backdoors, rig random number generators and most of all exploit careless settings in server configurations and encryption systems to listen in on private communications. Worst of all, most communication on the internet is not encrypted at all by default (for SMTP, opportunistic TLS would be a solution). This guide can only address one aspect of securing our information systems: getting the crypto settings right to the best of the authors' current knowledge. Other attacks, as the above mentioned, require different protection schemes which are not covered in this guide. This guide is not an introduction to cryptography. For background information on cryptography and cryptoanalysis we would like to refer the reader to the references in appendix Links and Suggested Reading at the end of this document. The focus of this guide is merely to give current best practices for configuring complex cipher suites and related parameters in a copy & paste-able manner. The guide tries to stay as concise as is possible for such a complex topic as cryptography. Naturally, it can not be complete. There are many excellent guides (II & SYM, 2012) and best practice documents available when it comes to cryptography. However none of them focuses specifically on what an average system administrator needs for hardening his or her systems' crypto settings. This guide tries to fill this gap.

The guide was produced in an open source manner: every step of editing can be traced back to a specific author via our version control system.

I: Introduction

Audience

Sysadmins. Sysadmins. Sysadmins. They are a force-multiplier.

Related publications

Ecrypt II [ii2011ecrypt] Ecrypt II (II & SYM, 2012), ENISA’s report on Algorithms, key sizes and parameters (ENISA and Vincent Rijmen, Nigel P. Smart, Bogdan warinschi, Gaven Watson, 2013) and BSI’s Technische Richtlinie TR-02102 (für Sicherheit in der Informationstechnik (BSI), 2018) are great publications which are more in depth than this guide. However, this guide has a different approach: it focuses on copy & paste-able settings for system administrators, effectively breaking down the complexity in the above mentioned reports to an easy to use format for the intended target audience.

How to read this guide

This guide tries to accommodate two needs: first of all, having a handy reference on how to configure the most common services’ crypto settings and second of all, explain a bit of background on cryptography. This background is essential if the reader wants to choose his or her own cipher string settings. System administrators who want to copy & paste recommendations quickly without spending a lot of time on background reading on cryptography or cryptanalysis can do so, by simply searching for the corresponding section in Best Practice. It is important to know that in this guide the authors arrived at two recommendations: Cipher string A and Cipher string B. While the former is a hardened recommendation a latter is a weaker one but provides wider compatibility. Cipher strings A and B are described in Recommended cipher suites. However, for the quick copy & paste approach it is important to know that this guide assumes users are happy with Cipher string B. While Best Practice is intended to serve as a copy & paste reference, Theory explains the reasoning behind cipher string B. In particular Architectural overview explains how to choose individual cipher strings. We advise the reader to actually read this section and challenge our reasoning in choosing Cipher string B and to come up with a better or localized solution.

Disclaimer

A chain is no stronger than its weakest link, and life is after all a chain.  

— William James

Encryption works. Properly implemented strong crypto systems are one of the few things that you can rely on. Unfortunately, endpoint security is so terrifically weak that NSA can frequently find ways around it.  

— Edward Snowden answering questions live on the Guardian’s website This guide specifically does not address physical security, protecting software and hardware against exploits, basic IT security housekeeping, information assurance techniques, traffic analysis attacks, issues with key-roll over and key management, securing client PCs and mobile devices (theft, loss), proper Operations Security, social engineering attacks, protection against tempest (i_wikipedia_Tempest (codename)_, 2018) attack techniques, thwarting different side-channel attacks (timing–, cache timing–, differential fault analysis, differential power analysis or power monitoring attacks), downgrade attacks, jamming the encrypted channel or other similar attacks which are typically employed to circumvent strong encryption. The authors can not overstate the importance of these other techniques. Interested readers are advised to read about these attacks in detail since they give a lot of insight into other parts of cryptography engineering which need to be dealt with[1]) ]. This guide does not talk much about the well-known insecurities of trusting a public-key infrastructure (PKI)[2]. Nor does this text fully explain how to run your own Certificate Authority (CA). Most of this zoo of information security issues are addressed in the very comprehensive book Security Engineering by Ross Anderson (Anderson, 2008). For some experts in cryptography this text might seem too informal. However, we strive to keep the language as non-technical as possible and fitting for our target audience: system administrators who can collectively improve the security level for all of their users.

Security is a process, not a product.  

— Bruce Schneier This guide can only describe what the authors currently believe to be the best settings based on their personal experience and after intensive cross checking with literature and experts. For a complete list of people who reviewed this paper, see the <acknowledgements>. Even though multiple specialists reviewed the guide, the authors can give no guarantee whatsoever that they made the right recommendations. Keep in mind that tomorrow there might be new attacks on some ciphers and many of the recommendations in this guide might turn out to be wrong. Security is a process. We therefore recommend that system administrators keep up to date with recent topics in IT security and cryptography. In this sense, this guide is very focused on getting the cipher strings done right even though there is much more to do in order to make a system more secure. We the authors, need this document as much as the reader needs it.

Scope

In this guide, we restricted ourselves to:* Internet-facing services

• Commonly used services
• Devices which are used in business environments (this specifically excludes XBoxes, Playstations and similar consumer devices)
• OpenSSL

We explicitly excluded:* Specialized systems such as medical devices, most embedded systems, industrial control systems (ICS), etc.

• Wireless Access Points
• Smart-cards/chip cards

Methods

C.O.S.H.E.R - completely open source, headers, engineering and research.  

— A. Kaplan His mail signature for many years For writing this guide, we chose to collect the most well researched facts about cryptography settings and let as many trusted specialists as possible review those settings. The review process is completely open and done on a public mailing list. The document is available (read-only) to the public Internet on the web page and the source code of this document is on a public git server, mirrored on GitHub.com and open for public scrutiny. However, write permissions to the document are only granted to vetted people. The list of reviewers can be found in Acknowledgements. Every write operation to the document is logged via the git version control system and can thus be traced back to a specific author. We accept git pull requests on the github mirror for this paper. Public peer-review and multiple eyes checking of our guide is the best strategy we can imagine at the present moment [3]. We invite the gentle reader to participate in this public review process. Please read the Contributing document.

II: Best Practice

Webservers

Apache

Note that any cipher suite starting with EECDH can be omitted, if in doubt. (Compared to the theory section, EECDH in Apache and ECDHE in OpenSSL are synonyms [4])

Tested with Versions

• Apache 2.2.22, Debian Wheezy with OpenSSL 1.0.1e
• Apache 2.4.6, Debian Jessie with OpenSSL 1.0.1e
• Apache 2.4.10, Debian Jessie 8.2 with OpenSSL 1.0.1k
• Apache 2.4.7, Ubuntu 14.04.2 Trusty with OpenSSL 1.0.1f
• Apache 2.4.6, CentOS Linux 7 (Core) with OpenSSL 1.0.1e
• Apache 2.4.18, Ubuntu 16.04.3 LTS with OpenSSL 1.0.2g

Settings

Enabled modules SSL and Headers are required. Listing 1. SSL configuration for an Apache vhost SSLCertificateFile /etc/ssl/certs/ssl-cert-snakeoil.pem SSLCertificateKeyFile /etc/ssl/private/ssl-cert-snakeoil.key #SSLCertificateChainFile /etc/apache2/ssl.crt/server-ca.crt #SSLCACertificateFile /etc/apache2/ssl.crt/ca-bundle.crt SSLProtocol All -SSLv2 -SSLv3 SSLHonorCipherOrder On SSLCompression off Header always set Strict-Transport-Security "max-age=15768000" # Strict-Transport-Security: "max-age=15768000 ; includeSubDomains" Header always set Public-Key-Pins "pin-sha256=\"YOUR_HASH=\"; pin-sha256=\"YOUR_BACKUP_HASH=\"; max-age=7776000; report-uri=\"https://YOUR.REPORT.URL\"" SSLCipherSuite 'EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA256:EECDH:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!IDEA:!ECDSA:kEDH:CAMELLIA128-SHA:AES128-SHA'

	Add six earth month HSTS header for all users…​
	If you want to protect all subdomains, use the following header. ALL subdomains HAVE TO support HTTPS if you use this!
	CALL subdomains HAVE TO support HTTPS if you use this! At least use one Backup-Key and/or add whole CA, think of Cert-Updates!

Additional settings

You might want to redirect everything to https:// if possible. In Apache you can do this with the following setting inside of a VirtualHost environment: Listing 2. https auto-redirect vhost

<VirtualHost *:80>
    Redirect permanent / https://SERVER_NAME/
</VirtualHost>

References

Apache2 Docs on SSL and TLS

How to test

See appendix Tools

lighttpd

Tested with Versions

• lighttpd/1.4.31-4 with OpenSSL 1.0.1e on Debian Wheezy
• lighttpd/1.4.33 with OpenSSL 0.9.8o on Debian Squeeze (note that TLSv1.2 does not work in openssl 0.9.8 thus not all ciphers actually work)
• lighttpd/1.4.28-2 with OpenSSL 0.9.8o on Debian Squeeze (note that TLSv1.2 does not work in openssl 0.9.8 thus not all ciphers actually work)
• lighttpd/1.4.31, Ubuntu 14.04.2 Trusty with Openssl 1.0.1f

Settings

Listing 3. SSL configuration for lighttpd

$SERVER["socket"] == "0.0.0.0:443" {
    ssl.engine = "enable"
    ssl.use-sslv2 = "disable"
    ssl.use-sslv3 = "disable"
    ssl.pemfile = "/etc/lighttpd/server.pem"
    ssl.ca-file = "/etc/ssl/certs/server.crt"
    ssl.cipher-list = "EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA256:EECDH:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!IDEA:!ECDSA:kEDH:CAMELLIA128-SHA:AES128-SHA"
    ssl.honor-cipher-order = "enable"
    setenv.add-response-header  = ( "Strict-Transport-Security" => "max-age=15768000") # six months
    # use this only if all subdomains support HTTPS!
    # setenv.add-response-header  = ( "Strict-Transport-Security" => "max-age=15768000; includeSubDomains")
}

Starting with lighttpd version 1.4.29 Diffie-Hellman and Elliptic-Curve Diffie-Hellman key agreement protocols are supported. By default, elliptic curve "prime256v1" (also "secp256r1") will be used, if no other is given. To select special curves, it is possible to set them using the configuration options ssl.dh-file and ssl.ec-curve. Listing 4. SSL EC/DH configuration for lighttpd

# use group16 dh parameters
ssl.dh-file = "/etc/lighttpd/ssl/dh4096.pem"
ssl.ec-curve = "secp384r1"

Please read section A note on Diffie Hellman Key Exchanges for more information on Diffie Hellman key exchange and elliptic curves.

Additional settings

As for any other webserver, you might want to automatically redirect http:// traffic toward https://. It is also recommended to set the environment variable HTTPS, so the PHP applications run by the webserver can easily detect that HTTPS is in use. Listing 5. https auto-redirect configuration

$HTTP["scheme"] == "http" {
    # capture vhost name with regex condition -> %0 in redirect pattern
    # must be the most inner block to the redirect rule
    $HTTP["host"] =~ ".*" {
        url.redirect = (".*" => "https://%0$0")
    }
    # Set the environment variable properly
    setenv.add-environment = (
        "HTTPS" => "on"
    )
}

Additional information

The config option honor-cipher-order is available since 1.4.30, the supported ciphers depend on the used OpenSSL-version (at runtime). ECDHE has to be available in OpenSSL at compile-time, which should be default. SSL compression should by deactivated by default at compile-time (if not, it’s active). Support for other SSL-libraries like GnuTLS will be available in the upcoming 2.x branch, which is currently under development.

References

• How to redirect HTTP requests to HTTPS
• Lighttpd Docs: Secure HTTP
• Release 1.4.30 (How to mitigate BEAST attack)
• Lightpd issue: SSL Compression disabled by default

How to test

See appendix Tools

nginx

Tested with Version

• 1.4.4 with OpenSSL 1.0.1e on OS X Server 10.8.5
• 1.2.1-2.2+wheezy2 with OpenSSL 1.0.1e on Debian Wheezy
• 1.4.4 with OpenSSL 1.0.1e on Debian Wheezy
• 1.2.1-2.2 bpo60+2 with OpenSSL 0.9.8o on Debian Squeeze (note that TLSv1.2 does not work in openssl 0.9.8 thus not all ciphers actually work)
• 1.4.6 with OpenSSL 1.0.1f on Ubuntu 14.04.2 LTS

Settings

Listing 6. SSL settings for nginx

ssl on;
ssl_certificate cert.pem;
ssl_certificate_key cert.key;
ssl_session_timeout 5m;
ssl_prefer_server_ciphers on;
ssl_protocols TLSv1 TLSv1.1 TLSv1.2; # not possible to do exclusive
ssl_ciphers 'EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA256:EECDH:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!IDEA:!ECDSA:kEDH:CAMELLIA128-SHA:AES128-SHA';
add_header Strict-Transport-Security "max-age=15768000"; # six months
# add_header Strict-Transport-Security "max-age=15768000; includeSubDomains"; 

Use this only if all subdomains support HTTPS!

If you absolutely want to specify your own DH parameters, you can specify them via ssl_dhparam file; However, we advise you to read section A note on Diffie Hellman Key Exchanges and stay with the standard IKE/IETF parameters (as long as they are >1024 bits).

Additional settings

If you decide to trust NIST’s ECC curve recommendation, you can add the following line to nginx’s configuration file to select special curves: Listing 7. SSL EC/DH settings for nginx ssl_ecdh_curve secp384r1; You might want to redirect everything to https:// if possible. In Nginx you can do this with the following setting: Listing 8. https auto-redirect in nginx return 301 https://$server_name$request_uri; The variable $server_name refers to the first server_name entry in your config file. If you specify more than one server_name only the first will be taken. Please be sure to not use the $host variable here because it contains data controlled by the user.

References

• Module ngx_http_ssl_module
• Configuring HTTPS servers

How to test

See appendix Tools

Cherokee

Tested with Version

• Cherokee/1.2.104 on Debian Wheezy with OpenSSL 1.0.1e 11 Feb 2013

Settings

The configuration of the cherokee webserver is performed by an admin interface available via the web. It then writes the configuration to /etc/cherokee/cherokee.conf, the important lines of such a configuration file can be found at the end of this section.* General Settings

• • Network
    • SSL/TLS back-end: OpenSSL/libssl
  • Ports to listen
    • Port: 443, TLS: TLS/SSL port
• Virtual Servers, For each vServer on tab Security:
  • Required SSL/TLS Values: Fill in the correct paths for Certificate and Certificate key
• Advanced Options
  • Ciphers:
    EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA256:EECDH:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!IDEA:!ECDSA:kEDH:CAMELLIA128-SHA:AES128-SHA
    • Server Preference: Prefer
    • Compression: Disabled
• Advanced: TLS
  • SSL version 2 and SSL version 3: No
  • TLS version 1, TLS version 1.1 and TLS version 1.2: Yes

Additional settings

For each vServer on the Security tab it is possible to set the Diffie Hellman length to up to 4096 bits. We recommend to use >1024 bits. More information about Diffie-Hellman and which curves are recommended can be found in section A note on Diffie Hellman Key Exchanges. In Advanced: TLS it is possible to set the path to a Diffie Hellman parameters file for 512, 1024, 2048 and 4096 bits. HSTS can be configured on host-basis in section vServers / Security / HTTP Strict Transport Security (HSTS):* Enable HSTS: Accept

• HSTS Max-Age: 15768000
• Include Subdomains: depends on your setup

To redirect HTTP to HTTPS, configure a new rule per Virtual Server in the Behavior tab. The rule is SSL/TLS combined with a NOT operator. As Handler define Redirection and use /(.*)$ as Regular Expression and +https://$\{host}/$1+ as Substitution. Listing 9. SSL configuration for cherokee server!bind!2!port = 443 server!bind!2!tls = 1 server!tls = libssl vserver!1!hsts = 1 vserver!1!hsts!max_age = 15768000 vserver!1!hsts!subdomains = 1 vserver!1!rule!5!handler = redir vserver!1!rule!5!handler!rewrite!10!regex = /(.*)$ vserver!1!rule!5!handler!rewrite!10!show = 1 vserver!1!rule!5!handler!rewrite!10!substring = https://${host}/$1 vserver!1!rule!5!handler!type = just_about vserver!1!rule!5!match = not vserver!1!rule!5!match!right = tls vserver!1!ssl_certificate_file = /etc/ssl/certs/ssl-cert-snakeoil.pem vserver!1!ssl_certificate_key_file = /etc/ssl/private/ssl-cert-snakeoil.key vserver!1!ssl_cipher_server_preference = 1 vserver!1!ssl_ciphers = EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA256:EECDH:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!IDEA:!ECDSA:kEDH:CAMELLIA128-SHA:AES128-SHA vserver!1!ssl_compression = 0 vserver!1!ssl_dh_length = 2048

References

• Cookbook: SSL, TLS and certificates
• Cookbook: Redirecting all traffic from HTTP to HTTPS

How to test

See appendix Tools

MS IIS

To configure SSL/TLS on Windows Server IIS Crypto can be used. Simply start the Programm, no installation required. The tool changes the registry keys described below. A restart is required for the changes to take effect. "IIS Crypto Tool" Instead of using the IIS Crypto Tool the configuration can be set using the Windows Registry. The following Registry keys apply to the newer Versions of Windows (Windows 7, Windows Server 2008, Windows Server 2008 R2, Windows Server 2012 and Windows Server 2012 R2). For detailed information about the older versions see the Microsoft knowledgebase article How to restrict the use of certain cryptographic algorithms and protocols in Schannel.dll. [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\Schannel] [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\Schannel\Ciphers] [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\Schannel\CipherSuites] [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\Schannel\Hashes] [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\Schannel\KeyExchangeAlgorithms] [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\Schannel\Protocols]

Tested with Version

• Windows Server 2008
• Windows Server 2008 R2
• Windows Server 2012
• Windows Server 2012 R2
• Windows Vista and Internet Explorer 7 and upwards
• Windows 7 and Internet Explorer 8 and upwards
• Windows 8 and Internet Explorer 10 and upwards
• Windows 8.1 and Internet Explorer 11

Settings

When trying to avoid RC4 (RC4 biases) as well as CBC (BEAST-Attack) by using GCM and to support perfect forward secrecy, Microsoft SChannel (SSL/TLS, Auth,.. Stack) supports ECDSA but lacks support for RSA signatures (see ECC suite B doubts). Since one is stuck with ECDSA, an elliptic curve certificate needs to be used. The configuration of cipher suites MS IIS will use, can be configured in one of the following ways:# Group Policy: Prioritizing Schannel Cipher Suites

1. Registry: How to restrict the use of certain cryptographic algorithms and protocols in Schannel.dll
2. IIS Crypto
3. Powershell

Table Client support shows the process of turning on one algorithm after another and the effect on the supported clients tested using https://www.ssllabs.com. SSL 3.0, SSL 2.0 and MD5 are turned off. TLS 1.0 and TLS 1.2 are turned on. Table 1. Client support

Cipher Suite	Client
TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256+	only IE 10,11, OpenSSL 1.0.1e
TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256+	Chrome 30, Opera 17, Safari 6+
TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA+	FF 10-24, IE 8+, Safari 5, Java 7

Table Client support shows the algorithms from strongest to weakest and why they need to be added in this order. For example insisting on SHA-2 algorithms (only first two lines) would eliminate all versions of Firefox, so the last line is needed to support this browser, but should be placed at the bottom, so capable browsers will choose the stronger SHA-2 algorithms. TLS_RSA_WITH_RC4_128_SHA or equivalent should also be added if MS Terminal Server Connection is used (make sure to use this only in a trusted environment). This suite will not be used for SSL, since we do not use a RSA Key. Clients not supported:# Java 6

1. WinXP
2. Bing

Additional settings

It’s recommended to use ´Strict-Transport-Security: max-age=15768000` for detailed information visit the Microsoft knowledgebase article in custom Headers. You might want to redirect everything to https:// if possible. In IIS you can do this with the following setting by Powershell: Set-WebConfiguration -Location "$WebSiteName/$WebApplicationName" `

   -Filter 'system.webserver/security/access' `
   -Value "SslRequireCert"

References

• How to restrict the use of certain cryptographic algorithms and protocols in Schannel.dll
• How to disable PCT 1.0, SSL 2.0, SSL 3.0, or TLS 1.0 in Internet Information Services

How to test

See appendix Tools

SSH

This section documents the Secure Shell (SSH) protocol. SSH is used to remotely manage computer systems, secururly transfer files over untrusted networks and to create "ad-hoc" virtual-private networks. SSH is defined by the following Internet Standards (RFCs): Table 2. SSH Standards

RFC	Title	Link
4251	The Secure Shell (SSH) Protocol Architecture	https://tools.ietf.org/html/rfc4251
4252	The Secure Shell (SSH) Authentication Protocol	https://tools.ietf.org/html/rfc4252
4253	The Secure Shell (SSH) Transport Layer Protocol	https://tools.ietf.org/html/rfc4253
6668	SHA-2 Data Integrity Verification for the Secure Shell (SSH) Transport Layer Protocol	https://tools.ietf.org/html/rfc6668
8268	More Modular Exponentiation (MODP) Diffie-Hellman (DH) Key Exchange (KEX) Groups for Secure Shell (SSH)	https://tools.ietf.org/html/rfc8268
8308	Extension Negotiation in the Secure Shell (SSH) Protocol	https://tools.ietf.org/html/rfc8308
8332	Use of RSA Keys with SHA-256 and SHA-512 in the Secure Shell (SSH) Protocol	https://tools.ietf.org/html/rfc8332

OpenSSH

OpenSSH is the most popular implementation of the SSH protocol. It is maintained by the OpenBSD project and portable versions are disitributed with many unix-like operating-systems and Windows Server.

Tested with Version

• OpenSSH 6.6p1 (Gentoo)
• OpenSSH 6.6p1-2 on Ubuntu 14.04.2 LTS
• OpenSSH 7.2p2 on Ubuntu 16.04.3 LTS

Settings

Listing 10. Important OpenSSH 6.6 security settings # Package generated configuration file # See the sshd_config(5) manpage for details # What ports, IPs and protocols we listen for Port 22 # Use these options to restrict which interfaces/protocols sshd will bind to #ListenAddress :: #ListenAddress 0.0.0.0 Protocol 2 # HostKeys for protocol version 2 HostKey /etc/ssh/ssh_host_rsa_key #HostKey /etc/ssh/ssh_host_dsa_key #HostKey /etc/ssh/ssh_host_ecdsa_key HostKey /etc/ssh/ssh_host_ed25519_key #Privilege Separation is turned on for security UsePrivilegeSeparation yes # Lifetime and size of ephemeral version 1 server key KeyRegenerationInterval 3600 ServerKeyBits 1024 # Logging SyslogFacility AUTH LogLevel INFO # Authentication: LoginGraceTime 120 PermitRootLogin no # or 'without-password' to allow SSH key based login StrictModes yes RSAAuthentication yes PubkeyAuthentication yes #AuthorizedKeysFile %h/.ssh/authorized_keys # Don't read the user's ~/.rhosts and ~/.shosts files IgnoreRhosts yes # For this to work you will also need host keys in /etc/ssh_known_hosts RhostsRSAAuthentication no # similar for protocol version 2 HostbasedAuthentication no # Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication #IgnoreUserKnownHosts yes # To enable empty passwords, change to yes (NOT RECOMMENDED) PermitEmptyPasswords no # Change to yes to enable challenge-response passwords (beware issues with # some PAM modules and threads) ChallengeResponseAuthentication no # Change to no to disable tunnelled clear text passwords #PasswordAuthentication yes # Kerberos options #KerberosAuthentication no #KerberosGetAFSToken no #KerberosOrLocalPasswd yes #KerberosTicketCleanup yes # GSSAPI options #GSSAPIAuthentication no #GSSAPICleanupCredentials yes # Cipher selection Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160 KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1 X11Forwarding yes X11DisplayOffset 10 PrintMotd no PrintLastLog yes TCPKeepAlive yes #UseLogin no #MaxStartups 10:30:60 #Banner /etc/issue.net # Allow client to pass locale environment variables AcceptEnv LANG LC_* Subsystem sftp /usr/lib/openssh/sftp-server # Set this to 'yes' to enable PAM authentication, account processing, # and session processing. If this is enabled, PAM authentication will # be allowed through the ChallengeResponseAuthentication and # PasswordAuthentication. Depending on your PAM configuration, # PAM authentication via ChallengeResponseAuthentication may bypass # the setting of "PermitRootLogin without-password". # If you just want the PAM account and session checks to run without # PAM authentication, then enable this but set PasswordAuthentication # and ChallengeResponseAuthentication to 'no'. UsePAM yes

Curve25519 OpenSSH 6.6p1 now supports Curve25519.

Tested with Version

• OpenSSH 6.5 (Debian Jessie)

Settings

Listing 11. Important OpenSSH 6.5 security settings # Package generated configuration file # See the sshd_config(5) manpage for details # What ports, IPs and protocols we listen for Port 22 # Use these options to restrict which interfaces/protocols sshd will bind to #ListenAddress :: #ListenAddress 0.0.0.0 Protocol 2 # HostKeys for protocol version 2 HostKey /etc/ssh/ssh_host_rsa_key #HostKey /etc/ssh/ssh_host_dsa_key #HostKey /etc/ssh/ssh_host_ecdsa_key HostKey /etc/ssh/ssh_host_ed25519_key #Privilege Separation is turned on for security UsePrivilegeSeparation yes # Lifetime and size of ephemeral version 1 server key KeyRegenerationInterval 3600 ServerKeyBits 1024 # Logging SyslogFacility AUTH LogLevel INFO # Authentication: LoginGraceTime 120 PermitRootLogin no # or 'without-password' to allow SSH key based login StrictModes yes RSAAuthentication yes PubkeyAuthentication yes #AuthorizedKeysFile %h/.ssh/authorized_keys # Don't read the user's ~/.rhosts and ~/.shosts files IgnoreRhosts yes # For this to work you will also need host keys in /etc/ssh_known_hosts RhostsRSAAuthentication no # similar for protocol version 2 HostbasedAuthentication no # Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication #IgnoreUserKnownHosts yes # To enable empty passwords, change to yes (NOT RECOMMENDED) PermitEmptyPasswords no # Change to yes to enable challenge-response passwords (beware issues with # some PAM modules and threads) ChallengeResponseAuthentication no # Change to no to disable tunnelled clear text passwords #PasswordAuthentication yes # Kerberos options #KerberosAuthentication no #KerberosGetAFSToken no #KerberosOrLocalPasswd yes #KerberosTicketCleanup yes # GSSAPI options #GSSAPIAuthentication no #GSSAPICleanupCredentials yes # Cipher selection Ciphers aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac-ripemd160 KexAlgorithms diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1 X11Forwarding yes X11DisplayOffset 10 PrintMotd no PrintLastLog yes TCPKeepAlive yes #UseLogin no #MaxStartups 10:30:60 #Banner /etc/issue.net # Allow client to pass locale environment variables AcceptEnv LANG LC_* Subsystem sftp /usr/lib/openssh/sftp-server # Set this to 'yes' to enable PAM authentication, account processing, # and session processing. If this is enabled, PAM authentication will # be allowed through the ChallengeResponseAuthentication and # PasswordAuthentication. Depending on your PAM configuration, # PAM authentication via ChallengeResponseAuthentication may bypass # the setting of "PermitRootLogin without-password". # If you just want the PAM account and session checks to run without # PAM authentication, then enable this but set PasswordAuthentication # and ChallengeResponseAuthentication to 'no'. UsePAM yes

Tested with Version

• OpenSSH 6.0p1 (Debian wheezy)

Settings

Listing 12. Important OpenSSH 6.0 security settings # Package generated configuration file # See the sshd_config(5) manpage for details # What ports, IPs and protocols we listen for Port 22 # Use these options to restrict which interfaces/protocols sshd will bind to #ListenAddress :: #ListenAddress 0.0.0.0 Protocol 2 # HostKeys for protocol version 2 HostKey /etc/ssh/ssh_host_rsa_key #HostKey /etc/ssh/ssh_host_dsa_key #HostKey /etc/ssh/ssh_host_ecdsa_key #Privilege Separation is turned on for security UsePrivilegeSeparation yes # Lifetime and size of ephemeral version 1 server key KeyRegenerationInterval 3600 ServerKeyBits 768 # Logging SyslogFacility AUTH LogLevel INFO # Authentication: LoginGraceTime 120 PermitRootLogin no # or 'without-password' to allow SSH key based login StrictModes yes RSAAuthentication yes PubkeyAuthentication yes #AuthorizedKeysFile %h/.ssh/authorized_keys # Don't read the user's ~/.rhosts and ~/.shosts files IgnoreRhosts yes # For this to work you will also need host keys in /etc/ssh_known_hosts RhostsRSAAuthentication no # similar for protocol version 2 HostbasedAuthentication no # Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication #IgnoreUserKnownHosts yes # To enable empty passwords, change to yes (NOT RECOMMENDED) PermitEmptyPasswords no # Change to yes to enable challenge-response passwords (beware issues with # some PAM modules and threads) ChallengeResponseAuthentication no # Change to no to disable tunnelled clear text passwords #PasswordAuthentication yes # Kerberos options #KerberosAuthentication no #KerberosGetAFSToken no #KerberosOrLocalPasswd yes #KerberosTicketCleanup yes # GSSAPI options #GSSAPIAuthentication no #GSSAPICleanupCredentials yes # Cipher selection Ciphers aes256-ctr,aes128-ctr MACs hmac-sha2-512,hmac-sha2-256,hmac-ripemd160 KexAlgorithms diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1 X11Forwarding yes X11DisplayOffset 10 PrintMotd no PrintLastLog yes TCPKeepAlive yes #UseLogin no #MaxStartups 10:30:60 #Banner /etc/issue.net # Allow client to pass locale environment variables AcceptEnv LANG LC_* Subsystem sftp /usr/lib/openssh/sftp-server # Set this to 'yes' to enable PAM authentication, account processing, # and session processing. If this is enabled, PAM authentication will # be allowed through the ChallengeResponseAuthentication and # PasswordAuthentication. Depending on your PAM configuration, # PAM authentication via ChallengeResponseAuthentication may bypass # the setting of "PermitRootLogin without-password". # If you just want the PAM account and session checks to run without # PAM authentication, then enable this but set PasswordAuthentication # and ChallengeResponseAuthentication to 'no'. UsePAM yes

Older Linux systems won’t support SHA2. PuTTY (Windows) does not support RIPE-MD160. Curve25519, AES-GCM and UMAC are only available upstream (OpenSSH 6.6p1). DSA host keys have been removed on purpose, the DSS standard does not support for DSA keys stronger than 1024bit [5] which is far below current standards (see section #section:keylengths). Legacy systems can use this configuration and simply omit unsupported ciphers, key exchange algorithms and MACs.

References

The OpenSSH sshd_config — OpenSSH SSH daemon configuration file man page is the best reference:

How to test

Connect a client with verbose logging enabled to the SSH server $ ssh -vvv myserver.com and observe the key exchange in the output.

Cisco ASA

Tested with Versions

• 9.1(3)

Settings

crypto key generate rsa modulus 2048 ssh version 2 ssh key-exchange group dh-group14-sha1

When the ASA is configured for SSH, by default both SSH versions 1 and 2 are allowed. In addition to that, only a group1 DH-key-exchange is used. This should be changed to allow only SSH version 2 and to use a key-exchange with group14. The generated RSA key should be 2048 bit (the actual supported maximum). A non-cryptographic best practice is to reconfigure the lines to only allow SSH-logins.

References

CLI Book 1: Cisco ASA Series General Operations CLI Configuration Guide, 9.1

How to test

Connect a client with verbose logging enabled to the SSH server $ ssh -vvv myserver.com and observe the key exchange in the output.

Cisco IOS

Tested with Versions

Table 3. Tested Myservice Versions

Program Version	OS/Distribution/Version	Comment
15.0	IOS
15.1	IOS
15.2	IOS

Settings

crypto key generate rsa modulus 4096 label SSH-KEYS ip ssh rsa keypair-name SSH-KEYS ip ssh version 2 ip ssh dh min size 2048 line vty 0 15 transport input ssh

Same as with the ASA, also on IOS by default both SSH versions 1 and 2 are allowed and the DH-key-exchange only use a DH-group of 768 Bit. In IOS, a dedicated Key-pair can be bound to SSH to reduce the usage of individual keys-pairs. From IOS Version 15.0 onwards, 4096 Bit rsa keys are supported and should be used according to the paradigm "use longest supported key". Also, do not forget to disable telnet vty access.

References

Cisco SSH

This guide is a basic SSH reference for all routers and switches. Pleaes refer to the specific documentation of the device and IOS version that you are configuring.

How to test

Connect a client with verbose logging enabled to the SSH server $ ssh -vvv switch.example.net and observe the key exchange in the output.

Mailservers

This section documents the most common mail servers. Mail servers may usually be grouped into three categories:* Mail Submission Agent (MSA)

• Mail Transfer Agent (MTA) / Mail Exchanger (MX)
• Mail Delivery Agent (MDA)

An email client (mail user agent, MUA) submits mail to the MSA. This is usually been done using the Simple Mail Transfer Protocol (SMTP). Afterwards, the mail is transmitted by the MTA over the Internet to the MTA of the receiver. This happens again via SMTP. Finally, the mail client of the receiver will fetch mail from an MDA usually via the Internet Message Access Protocol (IMAP) or the Post Office Protocol (POP). As MSAs and MTAs both use SMTP as transfer protocols, both functionalities may often be implemented with the same software. On the other hand, MDA software might or might not implement both IMAP and POP.

TLS usage in mail server protocols

Email protocols support TLS in two different ways. It may be added as a protocol wrapper on a different port. This method is referred to as Implicit TLS or as protocol variants SMTPS, IMAPS and POP3S. The other method is to establish a cleartext session first and switch to TLS afterwards by issuing the STARTTLS command. SMTP between MTAs usually makes use of opportunistic TLS. This means that an MTA will accept TLS connections when asked for it but will not require it. MTAs should always try opportunistic TLS handshakes outgoing and always accept incoming opportunistic TLS.

Recommended configuration

We recommend to use the following settings for Mail Transfer Agents:* correctly setup MX, A and PTR RRs without using CNAMEs at all

• the hostname used as HELO/EHLO in outgoing mail shall match the PTR RR
• enable opportunistic TLS, using the STARTTLS mechanism on port 25
• Implicit TLS on port 465 may be offered additionally
• use server and client certificates (most server certificates are client certificates as well)
• either the common name or at least an alternate subject name of the certificate shall match the PTR RR (client mode) or the MX RR (server mode)
• do not use self signed certificates
• accept all cipher suites, as the alternative would be to fall back to cleartext transmission
• an execption to the last sentence is that MTAs MUST NOT enable SSLv2 protocol support, due to the DROWN attack.

For MSA operation we recommend:* listen on submission port 587 with mandatory STARTTLS

• optionally listen on port 465 with Implicit TLS
• enforce SMTP AUTH even for local networks
• ensure that SMTP AUTH is not allowed on unencrypted connections
• only use the recommended cipher suites if all connecting MUAs support them

For MDA operation we recommend:* listen on the protocol port (143 for IMAP, 110 for POP3) with mandatory STARTTLS

• optionally listen on Implicit TLS ports (993 for IMAPS, 995 for POP3S)
• enforce authentication even for local networks
• make sure that authentication is not allowed on unencrypted connections
• use the recommended cipher suites if all connecting MUAs support them
• turn off SSLv2 (see: DROWN attack)

Dovecot

Tested with Versions

Table 4. Tested Dovecot Versions

Program Version	OS/Distribution/Version	Comment
2.1.7	Debian Wheezy	without ssl_prefer_server_ciphers
2.2.9	Debian Jessie
2.2.13	Debian 8.2 Jessie
2.0.19apple1	OS X Server 10.8.5	without ssl_prefer_server_ciphers
2.2.9	Ubuntu 14.04 Trusty
2.2.31	Ubuntu 16.04.3 LTS

Settings

Listing 13. Dovecot SSL Configuration # SSL protocols to use, disable SSL, use TLS only ssl_protocols = !SSLv3 !SSLv2 # SSL ciphers to use ssl_cipher_list = EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA256:EECDH:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!IDEA:!ECDSA:kEDH:CAMELLIA128-SHA:AES128-SHA # Prefer the server's order of ciphers over client's. (Dovecot >=2.2.6 Required) ssl_prefer_server_ciphers = yes # Diffie-Hellman parameters length (Default is 1024, Dovecot >=2.2.7 Required) # ToDo: for ReGenerating DH-Parameters: # manually delete /var/lib/dovecot/ssl-parameters.dat and restart # Dovecot to regenerate /var/lib/dovecot/ssl-parameters.dat ssl_dh_parameters_length = 2048 # Disable Compression (Dovecot >= 2.2.14 Required) # ssl_options = no_compression

Dovecot 2.0, 2.1: Almost as good as dovecot 2.2. Dovecot does not ignore unknown configuration parameters. Does not support ssl_prefer_server_ciphers.

Limitations

• Dovecot <2.2.14 does not support disabling TLS compression.In >2.2.14 [6] use: ssl_options = no_compression
• Dovecot <2.2.7 uses fixed DH parameters.In >2.2.7 [7] greater DH-Parameters are supported: ssl_dh_parameters_length = 2048.

References

• https://wiki2.dovecot.org/SSL

How to test

$ openssl s_client -crlf -connect example.com:993 $ openssl s_client -crlf -connect example.com:995 $ openssl s_client -crlf -starttls imap -connect example.com:143 $ openssl s_client -crlf -starttls pop3 -connect example.com:110 SSLyze offers scanning for common vulnerabilities and displays Protocols and Cipher-Suites. $ sslyze.exe --regular example.com:993 $ sslyze.exe --regular example.com:995 $ sslyze.exe --regular --starttls=imap example.com:143 $ sslyze.exe --regular --starttls=pop3 example.com:110

cyrus-imapd

Tested with Versions

Table 5. Tested cyrus-imapd Versions

Program Version	OS/Distribution/Version	Comment
2.4.17

Settings

To activate SSL/TLS configure your certificate with Listing 14. Activating TLS in cyrus tls_cert_file: /etc/ssl/certs/ssl-cert-snakeoil.pem tls_key_file: /etc/ssl/private/ssl-cert-snakeoil.key Do not forget to add necessary intermediate certificates to the .pem file. Limiting the ciphers provided may force (especially older) clients to connect without encryption at all! Sticking to the defaults is recommended. If you still want to force strong encryption use Listing 15. TLS cipher selection in cyrus tls_cipher_list: EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA256:EECDH:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!IDEA:!ECDSA:kEDH:CAMELLIA128-SHA:AES128-SHA cyrus-imapd loads hardcoded 1024 bit DH parameters using get_rfc2409_prime_1024() by default. If you want to load your own DH parameters add them PEM encoded to the certificate file given in tls_cert_file. Do not forget to re-add them after updating your certificate. To prevent unencrypted connections on the STARTTLS ports you can set Listing 16. Force encrypted connections in cyrus allowplaintext: no This way MUAs can only authenticate with plain text authentication schemes after issuing the STARTTLS command. Providing CRAM-MD5 or DIGEST-MD5 methods is not recommended. To support POP3/IMAP on ports 110/143 with STARTTLS and POP3S/IMAPS on ports 995/993 check the SERVICES section in cyrus.conf Listing 17. STARTTLS for POP3/IMAP and POP3S/IMAPS in cyrus SERVICES {

   imap  cmd="imapd -U 30"    listen="imap"  prefork=0 maxchild=100
   imaps cmd="imapd -s -U 30" listen="imaps" prefork=0 maxchild=100
   pop3  cmd="pop3d -U 30"    listen="pop3"  prefork=0 maxchild=50
   pop3s cmd="pop3d -s -U 30" listen="pop3s" prefork=0 maxchild=50

}

Limitations

cyrus-imapd currently (2.4.17, trunk) does not support elliptic curve cryptography. Hence, ECDHE will not work even if defined in your cipher list. Currently there is no way to prefer server ciphers or to disable compression. There is a working patch for all three features.

How to test

$ openssl s_client -crlf -connect example.com:993

Postfix

Tested with Versions

Table 6. Tested Postfix Versions

Program Version	OS/Distribution/Version	Comment
2.9.6	Debian Wheezy	with OpenSSL 1.0.1e
2.11.0	Ubuntu 14.04.02	with OpenSSL 1.0.1f
3.1.0	Ubuntu 16.04.3 LTS

Settings

Postfix has five internal lists of ciphers, and the possibility to switch between those with smtpd_tls_ciphers. However, we leave this at its default value for server to server connections, as many mail servers only support outdated protocols and ciphers. We consider bad encryption still better than plain text transmission. For connections to MUAs, TLS is mandatory and the ciphersuite is modified.

MX and SMTP client configuration:

As discussed in section [smtp_general], because of opportunistic encryption we do not restrict the list of ciphers or protocols for communication with other mail servers to avoid transmission in plain text. There are still some steps needed to enable TLS, all in main.cf: Listing 18. Opportunistic TLS in Postfix # TLS parameters smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key # log TLS connection info smtpd_tls_loglevel = 1 smtp_tls_loglevel = 1 # enable opportunistic TLS support in the SMTP server and client smtpd_tls_security_level = may smtp_tls_security_level = may # if you have authentication enabled, only offer it after STARTTLS smtpd_tls_auth_only = yes tls_ssl_options = NO_COMPRESSION

MSA:

For the MSA smtpd process which communicates with mail clients, we first define the ciphers that are acceptable for the “mandatory” security level, again in main.cf: Listing 19. MSA TLS configuration in Postfix smtp_tls_mandatory_protocols = !SSLv2, !SSLv3 smtp_tls_protocols = !SSLv2, !SSLv3 lmtp_tls_mandatory_protocols = !SSLv2, !SSLv3 lmtp_tls_protocols = !SSLv2, !SSLv3 smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3 smtpd_tls_protocols = !SSLv2, !SSLv3 smtpd_tls_mandatory_ciphers=high tls_high_cipherlist=EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA256:EECDH:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!IDEA:!ECDSA:kEDH:CAMELLIA128-SHA:AES128-SHA Then, we configure the MSA smtpd in master.cf with two additional options that are only used for this instance of smtpd: Listing 20. MSA smtpd service configuration in Postfix # ========================================================================== # service type private unpriv chroot wakeup maxproc command + args # (yes) (yes) (no) (never) (100) # ========================================================================== # ... submission inet n - - - - smtpd

   -o smtpd_tls_security_level=encrypt
   -o tls_preempt_cipherlist=yes

# ... For those users who want to use EECDH key exchange, it is possible to customize this via: The default value since Postfix 2.8 is “strong”. Listing 21. EECDH customization in Postfix smtpd_tls_eecdh_grade = ultra

Limitations

tls_ssl_options is supported from Postfix 2.11 onwards. You can leave the statement in the configuration for older versions, it will be ignored. tls_preempt_cipherlist is supported from Postfix 2.8 onwards. Again, you can leave the statement in for older versions.

References

• Refer to https://www.postfix.org/TLS_README.html for an in-depth discussion.

Additional settings

Postfix has two sets of built-in DH parameters that can be overridden with the smtpd_tls_dh512_param_file and smtpd_tls_dh1024_param_file options. The “dh512” parameters are used for export ciphers, while the “dh1024” ones are used for all other ciphers. The “bit length” in those parameter names is just a name, so one could use stronger parameter sets; it should be possible to e.g. use the IKE Group14 parameters (see section [DH] without much interoperability risk, but we have not tested this yet.

How to test

You can check the effect of the settings with the following command: $ zegrep "TLS connection established from.*with cipher" /var/log/mail.log | awk '{printf("%s %s %s %s\n", $12, $13, $14, $15)}' | sort | uniq -c | sort -n

     1 SSLv3 with cipher DHE-RSA-AES256-SHA
    23 TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384
    60 TLSv1 with cipher ECDHE-RSA-AES256-SHA
   270 TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384
   335 TLSv1 with cipher DHE-RSA-AES256-SHA

$ openssl s_client -starttls smtp -crlf -connect example.com:25

Exim

Tested with Versions

Table 7. Tested Exim Versions

Program Version	OS/Distribution/Version	Comment
4.82	Debian Jessie
4.82	Ubuntu 14.04.2	with OpenSSL 1.0.1e

It is highly recommended to read Encrypted SMTP connections using TLS/SSL first.

MSA mode (submission):

In the main config section of Exim add: Listing 22. Certificate selection in Exim (MSA) tls_certificate = /etc/ssl/exim.crt tls_privatekey = /etc/ssl/exim.pem Don’t forget to add intermediate certificates to the .pem file if needed. Tell Exim to advertise STARTTLS in the EHLO answer to everyone: Listing 23. TLS advertise in Exim (MSA) tls_advertise_hosts = * If you want to support legacy SMTPS on port 465, and STARTTLS on smtp(25)/submission(587) ports set Listing 24. STARTTLS and SMTPS in Exim (MSA) daemon_smtp_ports = smtp : smtps : submission tls_on_connect_ports = 465 It is highly recommended to limit SMTP AUTH to SSL connections only. To do so add Listing 25. SSL-only authentication in Exim (MSA) server_advertise_condition = ${if eq{$tls_cipher}{}{no}{yes}} to every authenticator defined. Add the following rules on top of your acl_smtp_mail: Listing 26. Submission mode in Exim (MSA) acl_smtp_mail = acl_check_mail acl_check_mail:

 warn hosts = *
   control = submission/sender_retain
 accept

This switches Exim to submission mode and allows addition of missing “Message-ID” and “Date” headers. It is not advisable to restrict the default cipher list for MSA mode if you don’t know all connecting MUAs. If you still want to define one please consult the Exim documentation or ask on the exim-users mailinglist. The cipher used is written to the logfiles by default. You may want to add log_selector = <whatever your log_selector already contains> +tls_certificate_verified +tls_peerdn +tls_sni to get even more TLS information logged.

Server mode (incoming):

In the main config section of Exim add: Listing 27. Certificate selection in Exim (Server) tls_certificate = /etc/ssl/exim.crt tls_privatekey = /etc/ssl/exim.pem Don’t forget to add intermediate certificates to the .pem file if needed. Tell Exim to advertise STARTTLS in the EHLO answer to everyone: Listing 28. TLS advertise in Exim (Server) tls_advertise_hosts = * Listen on smtp(25) port only: Listing 29. STARTTLS on SMTP in Exim (Server) daemon_smtp_ports = smtp It is not advisable to restrict the default cipher list for opportunistic encryption as used by SMTP. Do not use cipher lists recommended for HTTPS! If you still want to define one please consult the Exim documentation or ask on the exim-users mailinglist. If you want to request and verify client certificates from sending hosts set Listing 30. TLS certificate verification in Exim (Server) tls_verify_certificates = /etc/pki/tls/certs/ca-bundle.crt tls_try_verify_hosts = * tls_try_verify_hosts only reports the result to your logfile. If you want to disconnect such clients you have to use tls_verify_hosts = * The cipher used is written to the logfiles by default. You may want to add log_selector = <whatever your log_selector already contains> +tls_certificate_verified +tls_peerdn +tls_sni to get even more TLS information logged.

Client mode (outgoing):

Exim uses opportunistic encryption in the SMTP transport by default. Client mode settings have to be done in the configuration section of the smtp transport (driver = smtp). If you want to use a client certificate (most server certificates can be used as client certificate, too) set Listing 31. Certificate selection in Exim (Client) tls_certificate = /etc/ssl/exim.crt tls_privatekey = /etc/ssl/exim.pem This is recommended for MTA-MTA traffic. Do not limit ciphers without a very good reason. In the worst case you end up without encryption at all instead of some weak encryption. Please consult the Exim documentation if you really need to define ciphers.

OpenSSL:

Exim already disables SSLv2 by default. We recommend to add openssl_options = +all +no_sslv2 +no_sslv3 +no_compression +cipher_server_preference to the main configuration.

+all is misleading here since OpenSSL only activates the most common workarounds. But that’s how SSL_OP_ALL is defined.

You do not need to set dh_parameters. Exim with OpenSSL by default uses parameter initialization with the “2048-bit MODP Group with 224-bit Prime Order Subgroup” defined in section 2.2 of RFC 5114 (ike23). If you want to set your own DH parameters please read the TLS documentation of exim.

GnuTLS:

GnuTLS is different in only some respects to OpenSSL:* tls_require_ciphers needs a GnuTLS priority string instead of a cipher list. It is recommended to use the defaults by not defining this option. It highly depends on the version of GnuTLS used. Therefore it is not advisable to change the defaults.

• There is no option like openssl_options

Exim string expansion Most of the options accept expansion strings. This way you can e.g. set cipher lists or STARTTLS advertisement conditionally. Please follow the link to the official Exim documentation to get more information.

Limitations:

Exim currently (4.82) does not support elliptic curves with OpenSSL. This means that ECDHE is not used even if defined in your cipher list. There already is a working patch to provide support.

How to test

$ openssl s_client -starttls smtp -crlf -connect example.com:25

Cisco ESA/IronPort

Tested with Versions

Table 8. Tested Cisco ESA/IronPort Versions

Program Version	OS/Distribution/Version	Comment
	AsyncOS 7.6.1
	AsyncOS 8.5.6
	AsyncOS 9.0.0
	AsyncOS 9.5.0
	AsyncOS 9.6.0
	AsyncOS 9.7.0

Settings

Import your certificate(s) using the WEBUI (Network → Certificates). From AsyncOS 9.0 and up, SSL parameters for inbound SMTP, outbound SMTP and GUI access can be configured in one step via the WEBUI (System Administration → SSL Configuration, see figure IronPort Default SSL Settings). For all versions prior to 9.0, you have to connect to the CLI and configure the SSL parameters separately, as shown below using inbound SMTP as example. ironport.example.com> sslconfig sslconfig settings:

 GUI HTTPS method:  sslv3tlsv1
 GUI HTTPS ciphers: RC4-SHA:RC4-MD5:ALL
 Inbound SMTP method:  sslv3tlsv1
 Inbound SMTP ciphers: RC4-SHA:RC4-MD5:ALL
 Outbound SMTP method:  sslv3tlsv1
 Outbound SMTP ciphers: RC4-SHA:RC4-MD5:ALL

Choose the operation you want to perform: - GUI - Edit GUI HTTPS ssl settings. - INBOUND - Edit Inbound SMTP ssl settings. - OUTBOUND - Edit Outbound SMTP ssl settings. - VERIFY - Verify and show ssl cipher list. []> inbound Enter the inbound SMTP ssl method you want to use. 1. SSL v2. 2. SSL v3 3. TLS v1 4. SSL v2 and v3 5. SSL v3 and TLS v1 6. SSL v2, v3 and TLS v1 [5]> 3 Enter the inbound SMTP ssl cipher you want to use. [RC4-SHA:RC4-MD5:ALL]> EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA256:EECDH:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!IDEA:!ECDSA:kEDH:CAMELLIA128-SHA:AES128-SHA sslconfig settings:

 GUI HTTPS method:  sslv3tlsv1
 GUI HTTPS ciphers: RC4-SHA:RC4-MD5:ALL
 Inbound SMTP method:  tlsv1
 Inbound SMTP ciphers: EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EECDH:+CAMELLIA256:+AES256:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!SRP:!DSS:!RC4:!SEED:!ECDSA:CAMELLIA256-SHA:AES256-SHA:CAMELLIA128-SHA:AES128-SHA
 Outbound SMTP method:  sslv3tlsv1
 Outbound SMTP ciphers: RC4-SHA:RC4-MD5:ALL

Starting with AsyncOS 9.0 SSLv3 is disabled by default, whereas the default cipher set is still RC4-SHA:RC4-MD5:ALL (see figure IronPort Default SSL Settings).

"IronPort Default SSL Settings" Figure 1. IronPort Default SSL Settings After committing these changes in the CLI, you have to activate the use of TLS in several locations. For inbound connections, first select the appropriate certificate in the settings of each listener you want to have TLS enabled on (Network → Listeners, see figure IronPort Default SSL Settings). Afterwards, for each listener, configure all Mail Flow Policies which have their Connection Behavior set to “Accept” or “Relay” to at least prefer TLS (Mail Policies → Mail Flow Policies, see figure IronPort Default SSL Settings). It is recommended to also enable TLS in the default Mail Flow Policy, because these settings will be inherited by newly created policies, unless specifically overwritten. + TLS can be enforced by creating a new Mail Flow Policy with TLS set to “required”, creating a new Sender Group defining the addresses of the sending mail servers for which you want to enforce encryption (Mail Policies → HAT Overview) and using this new Sender Group in conjunction with the newly created Mail Flow Policy. "IronPort Listener Settings" Figure 2. IronPort Listener Settings "IronPort Mail Flow Policy Security Features" Figure 3. IronPort Mail Flow Policy Security Features TLS settings for outbound connections have to be configured within the Destination Controls (Mail Policies → Destination Controls). Choose the appropriate SSL certificate within the global settings and configure TLS to be preferred in the default profile to enable it for all outbound connections. After these two steps the Destination Control overview page should look like figure IronPort Destination Control overview on page . To enforce TLS for a specific destination domain, add an entry to the Destination Control Table and set “TLS Support” to “required”. "Destination Control overview" Figure 4. IronPort Destination Control overview

Limitations

All AsyncOS releases prior to version 9.5 use OpenSSL 0.9.8. Therefore TLS 1.2 is not supported in these versions and some of the suggested ciphers won’t work. Starting with AsyncOS 9.5 TLS 1.2 is fully supported. [8] You can check the supported ciphers on the CLI by using the option verify from within the sslconfig command: []> verify Enter the ssl cipher you want to verify. []> EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA256:EECDH:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!IDEA:!ECDSA:kEDH:CAMELLIA128-SHA:AES128-SHA DHE-RSA-CAMELLIA256-SHA SSLv3 Kx=DH Au=RSA Enc=Camellia(256) Mac=SHA1 DHE-RSA-CAMELLIA128-SHA SSLv3 Kx=DH Au=RSA Enc=Camellia(128) Mac=SHA1 DHE-RSA-AES256-SHA SSLv3 Kx=DH Au=RSA Enc=AES(256) Mac=SHA1 DHE-RSA-AES128-SHA SSLv3 Kx=DH Au=RSA Enc=AES(128) Mac=SHA1 CAMELLIA128-SHA SSLv3 Kx=RSA Au=RSA Enc=Camellia(128) Mac=SHA1 AES128-SHA SSLv3 Kx=RSA Au=RSA Enc=AES(128) Mac=SHA1

How to test

$ openssl s_client -starttls smtp -crlf -connect example.com:25

Virtual Private Networks

Virtual Private Networks (VPN) provide means of connecting private networks over external / public transport networks. Since we do not control the transport networks we have to to take care about data integrity and privacy.

Some providers also offer VPNs for connecting company networks via MPLS or simular technologies. The provider promises you that nobody else has access to your data trnfserred over their lines. You have to decide if this promise does fit to your information security requirements.

Basically there are two ways to ensure the privacy and integrity of the data sent via external lines. First you could utilize the built-in security of the Internet Protocol (IPsec). The other way are specific applications that encrypt the data before sending it over the line. IPsec is an Internet standard (TODO RFC 6071). This guarantees the interoperability between implementations of different vendors. You can establish a secure connection with your customer or your supplier. On the other hand VPN applications mostly utilize TLS to secury the communication between the partners. TODO: Descision criteria IPsec vs. VPN application.

IPsec

IPsec is the Internet standard to encrypt the transport of data between private networks.

Technology

We describe only the use the Internet Key Exchange (IKE) version 2 in this dodument. IKEv1 has some usage and security problems and should not be used any more. (TODO: reference).

Authentication

IPsec authentication should optimally be performed via RSA signatures, with a key size of 2048 bits or more. Configuring only the trusted CA that issued the peer certificate provides for additional protection against fake certificates. If you need to use Pre-Shared Key (PSK) authentication:* Choose a random, long enough PSK (see below)

• Use a separate PSK for any IPsec connection
• Change the PSKs regularly
• Think aboute a secure way to exchange the PSK. Sending an SMS it not secure.

The size of the PSK should not be shorter than the output size of the hash algorithm used in IKE.footnote[It is used in a HMAC, see RFC2104  and the discussion starting in TODO: verify http://www.vpnc.org/ietf-ipsec/02.ipsec/msg00268.html.]. For a key composed only of upper- and lowercase letters, numbers, and two additional characters[9], table #tab:IPSEC_psk_len gives the minimum lengths in characters.

Cryptographic Suites:

IPSEC Cryptographic Suites are pre-defined settings for all the items of a configuration; they try to provide a balanced security level and make setting up VPNs easier. [10] When using any of those suites, make sure to enable “Perfect Forward Secrecy“ for Phase 2, as this is not specified in the suites. The equivalents to the recommended ciphers suites in section Recommended cipher suites are shown in table #tab:IPSEC_suites.

Phase 1:

TODO: Phase 1 and 2 are phrases from IKEv1. Re-write for IKEv2. Alternatively to the pre-defined cipher suites, you can define your own, as described in this and the next section. Phase 1 is the mutual authentication and key exchange phase; table #tab:IPSEC_ph1_params shows the parameters. Use only “main mode“, as “aggressive mode“ has known security vulnerabilities [11].

Phase 2:

Phase 2 is where the parameters that protect the actual data are negotiated; recommended parameters are shown in table #tab:IPSEC_ph2_params.

References

• Fergusen, N. and Schneier, B.: A Cryptographic Evaluation of IPsec: https://www.schneier.com/paper-ipsec.pdf

Check Point Next Generation Firewall

Tested with Versions

Table 9. Tested CheckPoint Versions

Program Version	OS/Distribution/Version	Comment
R77	Secure Platform

Settings

Please see section IPsec for guidance on parameter choice. In this section, we will configure a strong setup according to Configuration A. This is based on the concept of a VPN Community, which has all the settings for the gateways that are included in that community. Communities can be found in the IPSEC VPN tab of SmartDashboard. "VPN Community encryption properties" [fig:checkpoint_1] Either choose one of the encryption suites in the properties dialog (figure [checkpoint_1], or proceed to Custom Encryption..., where you can set encryption and hash for Phase 1 and 2 (figure [checkpoint_2]. "Custom Encryption Suite Properties" [checkpoint_2] The Diffie-Hellman groups and Perfect Forward Secrecy Settings can be found under Advanced Settings / Advanced VPN Properties (figure [checkpoint_3]. "Advanced VPN Properties" [checkpoint_3]

Additional settings

For remote Dynamic IP Gateways, the settings are not taken from the community, but set in the Global Properties dialog under Remote Access / VPN Authentication and Encryption. Via the Edit... button, you can configure sets of algorithms that all gateways support (figure [checkpoint_4]). "Remote Access Encryption Properties" [checkpoint_4] Please note that these settings restrict the available algorithms for all gateways, and also influence the VPN client connections.

References

• Check Point VPN R77 Administration Guide (may require a UserCenter account to access)

TLS Based Applications

Tested with Versions

Table 10. Tested OpenVPN Versions

Program Version	OS/Distribution/Version	Comment
2.3.10	Ubuntu Xenial 16.04.1 LTS	linked against openssl (libssl.so.1.0.0)
2.3.2	Debian Wheezy (backports)	linked against openssl (libssl.so.1.0.0)
2.2.1	Debian Wheezy	linked against openssl (libssl.so.1.0.0)
2.3.2	Windows

General

We describe a configuration with certificate-based authentication; see below for details on the easyrsa tool to help you with that. OpenVPN uses TLS only for authentication and key exchange. The bulk traffic is then encrypted and authenticated with the OpenVPN protocol using those keys. Note that while the tls-cipher option takes a list of ciphers that is then negotiated as usual with TLS, the cipher and auth options both take a single argument that must match on client and server. OpenVPN duplexes the tunnel into a data and a control channel. The control channel is a usual TLS connection, the data channel currently uses encrypt-then-mac CBC, see https://github.com/BetterCrypto/Applied-Crypto-Hardening/pull/91#issuecomment-75365286

Client Configuration

Client and server have to use compatible configurations, otherwise they can’t communicate. The cipher and auth directives have to be identical.

Justification for special settings

OpenVPN 2.3.1 changed the values that the tls-cipher option expects from OpenSSL to IANA cipher names. That means from that version on you will get Deprecated TLS cipher name warnings for the configurations above. You cannot use the selection strings from section Recommended cipher suites directly from 2.3.1 on, which is why we give an explicit cipher list here. In addition, there is a 256 character limit on configuration file line lengths; that limits the size of cipher suites, so we dropped all ECDHE suites. The configuration shown above is compatible with all tested versions.

References

• OpenVPN Documentation: Security Overview https://openvpn.net/index.php/open-source/documentation/security-overview.html

Additional settings

Key renegotiation interval

The default for renegotiation of encryption keys is one hour (reneg-sec 3600). If you transfer huge amounts of data over your tunnel, you might consider configuring a shorter interval, or switch to a byte- or packet-based interval (reneg-bytes or reneg-pkts).

Insecure ciphers

Sweet32[12] is an attack on 64-bit block ciphers, such as 3DES and Blowfish in OpenVPN. The following ciphers are affected, and should no longer be used:* BF-*

• DES* (including 3DES variants)
• RC2-*

The following ciphers are not affected:* AES-*

• CAMELLIA-*
• SEED-*

According to mitigation section on Sweet32 website[13] users users should change the cipher from the DES or Blowfish to AES (cipher AES-128-CBC). If cipher change is not possible users can mitigate the attack by forcing frequent rekeying (reneg-bytes 64000000).

Fixing “easy-rsa”

When installing an OpenVPN server instance, you are probably using easy-rsa to generate keys and certificates. The file vars in the easyrsa installation directory has a number of settings that should be changed to secure values: This will enhance the security of the key generation by using RSA keys with a length of 4096 bits, and set a lifetime of one year for the server/client certificates and five years for the CA certificate.

4096 bits is only an example of how to do this with easy-rsa. See also section Keylengths for a discussion on keylengths.

In addition, edit the pkitool script and replace all occurrences of sha1 with sha256, to sign the certificates with SHA256.

Limitations

Note that the ciphersuites shown by openvpn --show-tls are known, but not necessarily supported [14]. Which cipher suite is actually used can be seen in the logs: Control Channel: TLSv1, cipher TLSv1/SSLv3 DHE-RSA-CAMELLIA256-SHA, 2048 bit RSA

PPTP

PPTP is considered insecure, Microsoft recommends to _use a more secure VPN tunnel_[15]. There is a cloud service that cracks the underlying MS-CHAPv2 authentication protocol for the price of USD 200[16], and given the resulting MD4 hash, all PPTP traffic for a user can be decrypted.

Cisco ASA

The following settings reflect our recommendations as best as possible on the Cisco ASA platform. These are - of course - just settings regarding SSL/TLS (i.e. Cisco AnyConnect) and IPsec. For further security settings regarding this platform the appropriate Cisco guides should be followed.

Tested with Versions

Table 11. Tested Cisco ASA Versions

Program Version	OS/Distribution/Version	Comment
9.1(3)	X-series model

Settings

crypto ipsec ikev2 ipsec-proposal AES-Fallback

protocol esp encryption aes-256 aes-192 aes
protocol esp integrity sha-512 sha-384 sha-256

crypto ipsec ikev2 ipsec-proposal AES-GCM-Fallback

protocol esp encryption aes-gcm-256 aes-gcm-192 aes-gcm
protocol esp integrity sha-512 sha-384 sha-256

crypto ipsec ikev2 ipsec-proposal AES128-GCM

protocol esp encryption aes-gcm
protocol esp integrity sha-512

crypto ipsec ikev2 ipsec-proposal AES192-GCM

protocol esp encryption aes-gcm-192
protocol esp integrity sha-512

crypto ipsec ikev2 ipsec-proposal AES256-GCM

protocol esp encryption aes-gcm-256
protocol esp integrity sha-512

crypto ipsec ikev2 ipsec-proposal AES

protocol esp encryption aes
protocol esp integrity sha-1 md5

crypto ipsec ikev2 ipsec-proposal AES192

protocol esp encryption aes-192
protocol esp integrity sha-1 md5

crypto ipsec ikev2 ipsec-proposal AES256

protocol esp encryption aes-256
protocol esp integrity sha-1 md5

crypto ipsec ikev2 sa-strength-enforcement crypto ipsec security-association pmtu-aging infinite crypto dynamic-map SYSTEM_DEFAULT_CRYPTO_MAP 65535 set pfs group14 crypto dynamic-map SYSTEM_DEFAULT_CRYPTO_MAP 65535 set ikev2 ipsec-proposal AES256-GCM AES192-GCM AES128-GCM AES-GCM-Fallback AES-Fallback crypto map Outside-DMZ_map 65535 ipsec-isakmp dynamic SYSTEM_DEFAULT_CRYPTO_MAP crypto map Outside-DMZ_map interface Outside-DMZ crypto ikev2 policy 1

encryption aes-gcm-256
integrity null
group 14
prf sha512 sha384 sha256 sha
lifetime seconds 86400

crypto ikev2 policy 2

encryption aes-gcm-256 aes-gcm-192 aes-gcm
integrity null
group 14
prf sha512 sha384 sha256 sha
lifetime seconds 86400

crypto ikev2 policy 3

encryption aes-256 aes-192 aes
integrity sha512 sha384 sha256
group 14
prf sha512 sha384 sha256 sha
lifetime seconds 86400

crypto ikev2 policy 4

encryption aes-256 aes-192 aes
integrity sha512 sha384 sha256 sha
group 14
prf sha512 sha384 sha256 sha
lifetime seconds 86400

crypto ikev2 enable Outside-DMZ client-services port 443 crypto ikev2 remote-access trustpoint ASDM_TrustPoint0 ssl server-version tlsv1-only ssl client-version tlsv1-only ssl encryption dhe-aes256-sha1 dhe-aes128-sha1 aes256-sha1 aes128-sha1 ssl trust-point ASDM_TrustPoint0 Outside-DMZ

Justification for special settings

New IPsec policies have been defined which do not make use of ciphers that may be cause for concern. Policies have a "Fallback" option to support legacy devices. 3DES has been completely disabled as such Windows XP AnyConnect Clients will no longer be able to connect. The Cisco ASA platform does not currently support RSA Keys above 2048bits. Legacy ASA models (e.g. 5505, 5510, 5520, 5540, 5550) do not offer the possibility to configure for SHA256/SHA384/SHA512 nor AES-GCM for IKEv2 proposals.

References

• http://www.cisco.com/en/US/docs/security/asa/roadmap/asaroadmap.html
• http://www.cisco.com/web/about/security/intelligence/nextgen_crypto.html

Openswan

Tested with Version

Table 12. Tested OpenS/WAN Versions

Program Version	OS/Distribution/Version	Comment
2.6.39	Gentoo

Settings

The available algorithms depend on your kernel configuration (when using protostack=netkey) and/or build-time options.

To list the supported algorithms $ ipsec auto --status | less and look for ’algorithm ESP/IKE’ at the beginning. aggrmode=no # ike format: cipher-hash;dhgroup # recommended ciphers: # - aes # recommended hashes: # - sha2_256 with at least 43 byte PSK # - sha2_512 with at least 86 byte PSK # recommended dhgroups: # - modp2048 = DH14 # - modp3072 = DH15 # - modp4096 = DH16 # - modp6144 = DH17 # - modp8192 = DH18 ike=aes-sha2_256;modp2048 type=tunnel phase2=esp # esp format: cipher-hash;dhgroup # recommended ciphers configuration A: # - aes_gcm_c-256 = AES_GCM_16 # - aes_ctr-256 # - aes_ccm_c-256 = AES_CCM_16 # - aes-256 # additional ciphers configuration B: # - camellia-256 # - aes-128 # - camellia-128 # recommended hashes configuration A: # - sha2-256 # - sha2-384 # - sha2-512 # - null (only with GCM/CCM ciphers) # additional hashes configuration B: # - sha1 # recommended dhgroups: same as above phase2alg=aes_gcm_c-256-sha2_256;modp2048 salifetime=8h pfs=yes auto=ignore

How to test

Start the vpn and using $ ipsec auto --status | less and look for ’IKE algorithms wanted/found’ and ’ESP algorithms wanted/loaded’.

References

• https://www.openswan.org/

tinc

Tested with Versions

Table 13. Tested tinc Versions

Program Version	OS/Distribution/Version	Comment
1.0.23	Gentoo	linked against OpenSSL 1.0.1e
1.0.23	Sabayon	linked against OpenSSL 1.0.1e

Defaults

tinc uses 2048 bit RSA keys, Blowfish-CBC, and SHA1 as default settings and suggests the usage of CBC mode ciphers. Any key length up to 8192 is supported and it does not need to be a power of two. OpenSSL Ciphers and Digests are supported by tinc.

Settings

Generate keys with $ tincd -n NETNAME -K8192 Old keys will not be deleted (but disabled), you have to delete them manually. Add the following lines to your tinc.conf on all machines

References

• tincd(8) man page
• tinc.conf(5) man page
• tinc mailinglist http://www.tinc-vpn.org/pipermail/tinc/2014-January/003538.html

PGP/GPG - Pretty Good Privacy

The OpenPGP protocol defines a set of asymmetric- and symmetric encryption algorithms, signature methods and compression protocols. GnuPG, a FOSS implementation of the OpenPGP standard, is widely used for mail encryption. GnuPG signs a message, encrypts it symmetrically and encrypts the symmetric key and the hash with Bob’s public key asymmetrically. Research on SHA-1 conducted back in 2005 (see: SHA-1 Broken) as well as the first practical successful collision in early 2017 (see: SHAttered) has made clear that collision attacks are a real threat to the security of the SHA-1 hash function. Since SHA-1 is defined as a must implementation by the OpenPGP specification, GnuPG is still using it. Currently settings should be adapted to preferably avoid using SHA-1. When using GnuPG, there are a couple of things to take care of:* keylengths (see: Keylengths)

• randomness (see: Random Number Generators)
• preference of symmetric encryption algorithm (see: Architectural overview)
• preference of hash function (see: Architectural overview)

Properly dealing with key material, passphrases and the web-of-trust is outside of the scope of this document. The GnuPG website has a good tutorial on GnuPG. After 31 December 2017 GnuPG version 2.0.x is no longer supported and shall not be used anymore. Use the new long term version 2.1 instead.

Hashing

Avoid SHA-1 by preferring better hashing methods. GnuPG. Edit $HOME/.gnupg/gpg.conf: Listing 32. Digest selection in GnuPG personal-digest-preferences SHA512 cert-digest-algo SHA512 default-preference-list AES256 CAMELLIA256 AES192 CAMELLIA192 AES CAMELLIA128 TWOFISH SHA512 SHA384 SHA256 BZIP2 ZLIB ZIP

Key Generation

Because of lack of forward secrecy (see: [pfs]) in OpenPGP it is preferable to use large asymmetric keys for long term communication protection. A RSA key of 4096 bits should provide enough confidentiality for the next 10 years (see: Cryptographic Key Length Recommendation). Listing 33. New key generation with GnuPG version 2.1 $ gpg --batch --full-gen-key $HOME/Desktop/params.txt` Listing 34. Parameters for key generation with GnuPG version 2.1 Key-Type: RSA Key-Length: 4096 Subkey-Type: RSA Subkey-Length: 4096 Name-Real: <your-name> Name-Email: <your-email-address> Passphrase: <password> Expires: 2y # My preferences: AES256, CAMELLIA256, AES192, CAMELLIA192, AES128, CAMELLIA128, TWOFISH, SHA512, SHA384, SHA256, BZIP2, ZLIB and ZIP Preferences: S9 S13 S8 S12 S7 S11 S10 H10 H9 H8 Z3 Z2 Z1

The preferences parameters S9 to Z1 correspond to AES256, CAMELLIA256, AES192, CAMELLIA192, AES, CAMELLIA128, TWOFISH, SHA512, SHA384, SHA256, BZIP2, ZLIB and ZIP. The parameters 3DES, SHA-1 and uncompressed are set automatically by GnuPG.

ECC - Elliptic Curve Cryptography

Since the release of GnuPG version 2.1 end-2014 ECC is supported. Older versions though are still widely used therefore ECC is not yet applicable in practice.

IPMI, ILO and other lights out management solutions

Consider creating an unrouted management VLAN and access that only via VPN.

We strongly recommend that any remote management system for servers such as ILO, iDRAC, IPMI based solutions and similar systems never be connected to the public internet.

Instant Messaging Systems

General server configuration recommendations

For servers, we mostly recommend to apply what’s proposed by the Peter’s manifesto. In short:* require the use of TLS for both client-to-server and server-to-server connections

• prefer or require TLS cipher suites that enable forward secrecy
• deploy certificates issued by well-known and widely-deployed certification authorities (CAs)

The last point being out-of-scope for this section, we will only cover the first two points.

ejabberd

Tested with Versions

• ejabberd 14.12, Debian 7 Wheezy
• ejabberd 14.12, Ubuntu 14.04 Trusty
• ejabberd 15.03, Ubuntu 14.04 Trusty
• ejabberd 16.01, Ubuntu 14.04 Trusty

Settings

ejabberd is one of the popular Jabber servers. In order to be compliant with the manifesto, you should adapt your configuration: Listing 35. TLS setup for ejabberd listen:

   -
       port: 5222
       module: ejabberd_c2s
       certfile: "/path/to/ssl.pem"
       starttls: true
       starttls_required: true
       protocol_options:
           - "no_sslv3"
           - "no_tlsv1"
           - "cipher_server_preference"
       max_stanza_size: 65536
       dhfile: "/path/to/dhparams.pem"
       shaper: c2s_shaper
       access: c2s
   -
       port: 5269
       module: ejabberd_s2s_in

s2s_use_starttls: required_trusted s2s_certfile: "/path/to/ssl.pem" s2s_dhfile: "/etc/ejabberd/dhparams.pem" # Available from version 15.03 s2s_protocol_options:

   - "no_sslv3"
   - "no_tlsv1"
   - "cipher_server_preference"

Available from version 15.06

Additional settings

It is possible to explicitly specify a cipher string for TLS connections. Listing 36. Specifying a cipher order and enforcing it listen:

   -
       port: 5222
       module: ejabberd_c2s
       certfile: "/path/to/ssl.pem"
       starttls: true
       starttls_required: true
       protocol_options:
           - "no_sslv3"
           - "no_tlsv1"
        - "cipher_server_preference"
       max_stanza_size: 65536
       dhfile: "/path/to/dhparams.pem"
       ciphers: "EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA256:EECDH:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!IDEA:!ECDSA:kEDH:CAMELLIA128-SHA:AES128-SHA"
   -
       port: 5269
       module: ejabberd_s2s_in

s2s_use_starttls: required_trusted s2s_certfile: "/path/to/ssl.pem" s2s_dhfile: "/etc/ejabberd/dhparams.pem" s2s_protocol_options:

   - "no_sslv3"
   - "no_tlsv1"
   - "cipher_server_preference"

s2s_ciphers: "EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA256:EECDH:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!IDEA:!ECDSA:kEDH:CAMELLIA128-SHA:AES128-SHA"

	Available from version 15.06
	Available from version 15.03

Weak Ciphers Note that we are setting the SSL option cipher_server_preference. This enforces our cipher order when negotiating which ciphers are used, as the cipher order of some clients chooses weak ciphers over stronger ciphers.

Starting with version 15.03[17], it is possible to use custom Diffie-Hellman-Parameters. This allows us to negotiate stronger Diffie-Hellman-keys, and also helps us avoid problems with using common weak Diffie-Hellman-Parameters. You can generate your own parameter file by running: $ openssl dhparam -out dhparams.pem 4096 By default, ejabberd provides an administration website (look for the ejabberd_http module). Enable TLS protection for it like this:

   port: 5280
   module: ejabberd_http
   web_admin: true
   http_poll: true
   http_bind: true
   captcha: true
   certfile: "/path/to/ssl.pem"
   tls: true

Tested with Versions

• Debian Wheezy 2.1.10-4+deb7u1

Settings

Older versions of ejabberd use a different configuration file syntax. In order to be compliant with the manifesto, you should adapt your configuration[18] as follows:

{listen,

   [
       {5222, ejabberd_c2s, [
       {access, c2s},
       {shaper, c2s_shaper},
       {max_stanza_size, 65536},
       starttls,
       starttls_required,
       {certfile, "/etc/ejabberd/ejabberd.pem"}
       ]},
   ]}.

{s2s_use_starttls, required_trusted}.

{s2s_certfile, "/etc/ejabberd/ejabberd.pem"}.

Additional settings

Older versions of ejabberd (< 2.0.0) need to be patched to be able to parse all of the certificates in the CA chain. Specifying a custom cipher string is only possible starting with version 13.12 (see configuration for version 14.12 above).

References

• ejabberd, your superpowerful messaging framework

How to test

IM Observatory is a useful website to test Jabber server configurations.

Chat privacy - Off-the-Record Messaging (OTR)

Off-the-Record Messaging Protocol works on top of the Jabber protocol. It adds to popular chat clients (Adium, Pidgin…​) the following properties for encrypted chats:* Authentication

• Integrity
• Confidentiality
• Forward secrecy

It basically uses Diffie-Hellman, AES and SHA1. Communicating over an insecure instant messaging network, OTR can be used for end to end encryption. There are no specific configurations required but the protocol itself is worth to be mentioned.

Charybdis

There are numerous implementations of IRC servers. In this section, we choose Charybdis which serves as basis for ircd-seven, developed and used by freenode. Freenode is actually the biggest IRC network[19]. Charybdis is part of the Debian & Ubuntu distributions. Listing 37. SSL relevant configuration for Charybdis/ircd-seven /* Extensions */ #loadmodule "extensions/chm_sslonly_compat.so"; loadmodule "extensions/extb_ssl.so"; serverinfo {

   ssl_private_key = "etc/test.key";
   ssl_cert = "etc/test.cert";
   ssl_dh_params = "etc/dh.pem";
   # set ssld_count as number of cores - 1
   ssld_count = 1;

}; listen {

   sslport = 6697;

};

SILC

SILC is instant messaging protocol publicly released in 2000. SILC is a per-default secure chat protocol thanks to a generalized usage of symmetric encryption. Keys are generated by the server meaning that if compromised, communication could be compromised. The protocol is not really popular anymore.

Databases

Oracle

No information available / known.

MySQL

Tested with Versions

• MySQL 5.5 on Debian Wheezy
• MySQL 5.7.20 on Ubuntu 16.04.3

References

MySQL Documentation on Configuring MySQL to Use Encrypted Connections.

How to test

After restarting the server run the following query to see if the ssl settings are correct: show variables like '%ssl%';

DB2

Tested with Version

We do not test this here, since we only reference other papers for DB2 so far.

Settings

ssl_cipherspecs:

In the link above the whole SSL-configuration is described in-depth. The following command shows only how to set the recommended ciphersuites. Listing 38. Recommended and supported ciphersuites db2 update dbm cfg using SSL_CIPHERSPECS TLS_RSA_WITH_AES_256_CBC_SHA256, TLS_RSA_WITH_AES_128_GCM_SHA256, TLS_RSA_WITH_AES_128_CBC_SHA256, TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256, TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256, TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256, TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256, TLS_RSA_WITH_AES_256_GCM_SHA384, TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384, TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384, TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384, TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384, TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA, TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA, TLS_RSA_WITH_AES_256_CBC_SHA, TLS_RSA_WITH_AES_128_CBC_SHA, TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA, TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA

References

IBM DB2 Documentation on Supported cipher suites.https://www.ibm.com/support/knowledgecenter/SSEPGG_9.7.0/com.ibm.db2.luw.admin.sec.doc/doc/c0053544.html

PostgreSQL

Tested with Versions

• Debian Wheezy and PostgreSQL 9.1
• Linux Mint 14 nadia / Ubuntu 12.10 quantal with PostgreSQL 9.1+136 and OpenSSL 1.0.1c

Settings

To start in SSL mode the server.crt and server.key must exist in the servers data directory $PGDATA.

Starting with version 9.2, you have the possibility to set the path manually.

References

It’s recommended to read Security and Authentication in the manual. PostgreSQL Documentation on Secure TCP/IP Connections with SSL. PostgreSQL Documentation on Client Authentication.

How to test

To test your ssl settings, run psql with the sslmode parameter: $ psql "sslmode=require host=postgres-server dbname=database" your-username

Proxy Solutions

Within enterprise networks and corporations with increased levels of paranoia or at least some defined security requirements it is common not to allow direct connections to the public internet. For this reason proxy solutions are deployed on corporate networks to intercept and scan the traffic for potential threats within sessions. For encrypted traffic there are four options:* Block the connection because it cannot be scanned for threats.

• Bypass the threat-mitigation and pass the encrypted session to the client, which results in a situation where malicious content is transferred directly to the client without visibility to the security system.
• Intercept (i.e. terminate) the session at the proxy, scan there and re-encrypt the session towards the client (effectively MITM).
• Deploy special Certificate Authorities to enable Deep Packet Inspection on the wire.

While the latest solution might be the most "up to date", it arises a new front in the context of this paper, because the most secure part of a client’s connection could only be within the corporate network, if the proxy-server handles the connection to the destination server in an insecure manner. Conclusion: Don’t forget to check your proxy solutions SSL-capabilities. Also do so for your reverse proxies!

Bluecoat / Symantec

Blue Coat Systems was a well-known manufacturer of enterprise proxy appliances. In 2016 it was acquired by Symantec. The products are now known as Symantec ProxySG and Advanced Secure Gateway (ASG). The description below is for the original Blue Coat SG Operating System (SGOS). BlueCoat Proxy SG Appliances can be used as forward and reverse proxies. The reverse proxy feature is rather under-developed, and while it is possible and supported, there only seems to be limited use of this feature "in the wild" - nonetheless there are a few cipher suites to choose from, when enabling SSL features.

Tested with Versions

Proxy Appliance	SGOS 6.5.x	Blue Coat, now Symantec

Only allow TLS 1.0,1.1 and 1.2 protocols:

$conf t $(config)ssl $(config ssl)edit ssl-device-profile default $(config device-profile default)protocol tlsv1 tlsv1.1 tlsv1.2

 ok

Select your accepted cipher-suites:

$conf t Enter configuration commands, one per line. End with CTRL-Z. $(config)proxy-services $(config proxy-services)edit ReverseProxyHighCipher $(config ReverseProxyHighCipher)attribute cipher-suite Cipher# Use Description Strength ------- --- ----------------------- --------

     1  yes            AES128-SHA256      High
     2  yes            AES256-SHA256      High
     3  yes               AES128-SHA    Medium
     4  yes               AES256-SHA      High
     5  yes       DHE-RSA-AES128-SHA      High
     6  yes       DHE-RSA-AES256-SHA      High
              [...]
    13  yes          EXP-RC2-CBC-MD5    Export

Select cipher numbers to use, separated by commas: 2,5,6

 ok

The same protocols are available for forward proxy settings and should be adjusted accordingly: In your local policy file add the following section: <ssl>

   DENY server.connection.negotiated_ssl_version=(SSLV2, SSLV3)

Disabling protocols and ciphers in a forward proxy environment could lead to unexpected results on certain (misconfigured?) webservers (i.e. ones accepting only SSLv2/3 protocol connections)

HAProxy

See https://www.haproxy.org/ See https://timtaubert.de/blog/2014/11/the-sad-state-of-server-side-tls-session-resumption-implementations/ See https://cbonte.github.io/haproxy-dconv/configuration-1.5.html#5.1-npn See https://cbonte.github.io/haproxy-dconv/configuration-1.5.html#3.2-tune.ssl.cachesize See https://kura.io/2014/07/02/haproxy-ocsp-stapling/ See https://kura.io/2015/01/27/hpkp-http-public-key-pinning-with-haproxy/ HAProxy can be used as loadbalancer and proxy for TCP and HTTP-based applications. Since version 1.5 it supports SSL and IPv6.

Tested with Versions

HAProxy 1.5.11 with OpenSSL 1.0.1e on Debian Wheezy

Settings

Listing 39. global configuration global

   ssl-default-bind-ciphers EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EECDH:+CAMELLIA256:+AES256:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!ECDSA:CAMELLIA256-SHA:AES256-SHA:CAMELLIA128-SHA:AES128-SHA
   ssl-default-bind-options no-sslv3 no-tls-tickets #disable SSLv3
   tune.ssl.default-dh-param 2048 #tune DH to 2048

Listing 40. frontend configuration frontend public

   bind *:80
   bind *:443 ssl crt server.pem
   mode http
   redirect scheme https code 301 if !{ ssl_fc } # redirect HTTP to HTTPS

Listing 41. backend configuration backend backend

   mode http
   server server 192.168.1.1:80 check
   http-request set-header X-Forwarded-Port %[dst_port]
   http-request add-header X-Forwarded-Proto https if { ssl_fc }
   rspadd Strict-Transport-Security:\ max-age=15768000;\ includeSubDomains #enable HSTS header for this backend

Enable NPN Support:

   bind *:443 ssl crt server.pem npn "http/1.1,http/1.0"

Append the npn command in the frontend configuration of HAProxy.

Enable OCSP stapling:

HAProxy supports since version 1.5.0 OCSP stapling. To enable it you have to generate the OCSP singing file in the same folder, with the same name as your certificate file plus the extension .ocsp. (e.g. your certificate file is named server.crt then the OCSP file have to be named server.crt.oscp)To generate the OCSP file use these commands: $ openssl x509 -in your.certificate.crt -noout -ocsp_uri # <- get your ocsp uri $ openssl ocsp -noverify -issuer ca.root.cert.crt -cert your.certificate.crt -url "YOUR OCSP URI" -respout your.certificate.crt.ocsp Reload HAProxy and now OCSP stapling should be enabled.Note: This OCSP signature file is only valid for a limited time. The simplest way of updating this file is by using cron.daily or something similar.

Enable HPKP:

Get certificate informations: $ openssl x509 -in server.crt -pubkey -noout | openssl rsa -pubin -outform der | openssl dgst -sha256 -binary | base64 Then you append the returned string in the HAProxy configuration. Add the following line to the backend configuration: rspadd Public-Key-Pins:\ pin-sha256="YOUR_KEY";\ max-age=15768000;\ includeSubDomains Reload HAProxy and HPKP should now be enabled.Note: Keep in mind to generate a backup key in case of problems with your primary key file.

How to test

See appendix Tools

Pound

Tested with Versions

Pound 2.6 See http://www.apsis.ch/pound See https://help.ubuntu.com/community/Pound

Settings

Listing 42. HTTPS Listener in Pound # HTTP Listener, redirects to HTTPS ListenHTTP

   Address 10.10.0.10
   Port    80
   Service
       Redirect "https://some.site.tld"
   End

End ## HTTPS Listener ListenHTTPS

   Address      10.10.0.10
   Port         443
   AddHeader    "Front-End-Https: on"
   Cert         "/path/to/your/cert.pem"
   ## See 'man ciphers'.
   Ciphers      "TLSv1.2:TLSv1.1:!SSLv3:!SSLv2:EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EECDH:+CAMELLIA256:+AES256:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!ECDSA:CAMELLIA256-SHA:AES256-SHA:CAMELLIA128-SHA:AES128-SHA"
   Service
       BackEnd
           Address 10.20.0.10
           Port 80
       End
   End

End

stunnel

Tested with Versions

• stunnel 4.53-1.1ubuntu1 on Ubuntu 14.04 Trusty with OpenSSL 1.0.1f, without disabling Secure Client-Initiated Renegotiation
• stunnel 5.02-1 on Ubuntu 14.04 Trusty with OpenSSL 1.0.1f
• stunnel 4.53-1.1 on Debian Wheezy with OpenSSL 1.0.1e, without disabling Secure Client-Initiated Renegotiation

Settings

Listing 43. HTTPS Listener in stunnel ciphers = EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EECDH:+CAMELLIA256:+AES256:+CAMELLIA128:+AES128:+SSLv3:!aNULL!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!DSS:!RC4:!SEED:!ECDSA:CAMELLIA256-SHA:AES256-SHA:CAMELLIA128-SHA:AES128-SHA curve = secp384r1 options = NO_SSLv2 options = NO_SSLv3 options = cipher_server_preference ; Secure Client-Initiated Renegotiation can only be disabled wit stunnel >= 4.54 ;renegotiation = no

Additional information

Secure Client-Initiated Renegotiation can only be disabled for stunnel versions >= 4.54, when the renegotiation parameter has been added (See changelog).

References

stunnel documentation: https://www.stunnel.org/static/stunnel.html stunnel changelog: https://www.stunnel.org/sdf_ChangeLog.html

How to test

See appendix Tools

Kerberos

This section discusses various implementations of the Kerberos 5 authentication protocol on Unix and Unix-like systems as well as on Microsoft Windows.

Overview

Kerberos provides mutual authentication of two communicating parties, e.g. a user using a network service. The authentication process is mediated by a trusted third party, the Kerberos key distribution centre (KDC). Kerberos implements secure single-sign-on across a large number of network protocols and operating systems. Optionally, Kerberos can be used to create encrypted communications channels between the user and service.

Recommended reading

An understanding of the Kerberos protocol is necessary for properly implementing a Kerberos setup. Also, in the following section some knowledge about the inner workings of Kerberos is assumed. Therefore we strongly recommend reading the excellent introduction Kerberos: An Authentication Service for Computer Networks first. No further overview over Kerberos terminology and functions will be provided, for a discussion and a selection of relevant papers refer to Kerberos Papers and Documentation. The Kerberos protocol over time has been extended with a variety of extensions and Kerberos implementations provide additional services in addition to the aforementioned KDC. All discussed implementations provide support for trust relations between multiple realms, an administrative network service (kerberos-adm, kadmind) as well as a password changing service (kpasswd). Sometimes, alternative database backends for ticket storage, X.509 and SmartCard authentication are provided. Of those, only administrative and password changing services will be discussed.

Protocol versions Only the Kerberos 5 protocol and implementation will be discussed. Kerberos 4 is obsolete, insecure and its use is strongly discouraged.

Providing a suitable Setup for secure Kerberos Operations

The aim of Kerberos is to unify authentication across a wide range of services, for many different users and use cases and on many computer platforms. The resulting complexity and attack surface make it necessary to carefully plan and continuously evaluate the security of the overall ecosystem in which Kerberos is deployed. Several assumptions are made on which the security of a Kerberos infrastructure relies:* Every KDC in a realm needs to be trustworthy. The KDC’s principal database must not become known to or changed by an attacker. The contents of the principal database enables the attacker to impersonate any user or service in the realm.

• Synchronisation between KDCs must be secure, reliable and frequent. An attacker that is able to intercept or influence synchronisation messages obtains or influences parts of the principal database, enabling impersonation of affected principals. Unreliable or infrequent synchronisation enlarges the window of vulnerability after disabling principals or changing passwords that have been compromised or lost.
• KDCs must be available. An attacker is able to inhibit authentication for services and users by cutting off their access to a KDC.
• Users’ passwords must be secure. Since Kerberos is a single-sign-on mechanism, a single password may enable an attacker to access a large number of services.
• Service keytabs need to be secured against unauthorized access similarly to SSL/TLS server certificates. Obtaining a service keytab enables an attacker to impersonate a service.
• DNS infrastructure must be secure and reliable. Hosts that provide services need consistent forward and reverse DNS entries. The identity of a service is tied to its DNS name, similarly the realm a client belongs to as well as the KDC, kpasswd and kerberos-adm servers may be specified in DNS TXT and SRV records. Spoofed DNS entries will cause denial-of-service situations and might endanger (i_mit_Realm configuration decisions_, 2013) the security of a Kerberos realm.
• Clients and servers in Kerberos realms need to have synchronized clocks. Tickets in Kerberos are created with a limited, strictly enforced lifetime. This limits an attacker’s window of opportunity for various attacks such as the decryption of tickets in sniffed network traffic or the use of tickets read from a client computer’s memory. Kerberos will refuse tickets with old timestamps or timestamps in the future. This would enable an attacker with access to a systems clock to deny access to a service or all users logging in from a specific host.

Therefore we suggest:* Secure all KDCs at least as strongly as the most secure service in the realm.

• Dedicate physical (i.e. non-VM) machines to be KDCs. Do not run any services on those machines beyond the necessary KDC, kerberos-adm, kpasswd and kprop services.
• Restrict physical and administrative access to the KDCs as severely as possible. E.g. ssh access should be limited to responsible adminstrators and trusted networks.
• Encrypt and secure the KDCs backups.
• Replicate your primary KDC to at least one secondary KDC.
• Prefer easy-to-secure replication (propagation in Kerberos terms) methods.Especially avoid LDAP replication and database backends. LDAP enlarges the attack surface of your KDC and facilitates unauthorized access to the principal database e.g. by ACL misconfiguration.
• Use DNSSEC. If that is not possible, at least ensure that all servers and clients in a realm use a trustworthy DNS server contacted via secure network links.
• Use NTP on a trustworthy server via secure network links.
• Avoid services that require the user to enter a password which is then checked against Kerberos. Prefer services that are able to use authentication via service tickets, usually not requiring the user to enter a password except for the initial computer login to obtain a ticket-granting-ticket (TGT). This limits the ability of attackers to spy out passwords through compromised services.

Implementations

Cryptographic Algorithms in Kerberos Implementations

The encryption algorithms (commonly abbreviated ’etypes’ or ’enctypes’) in Kerberos exchanges are subject to negotiation between both sides of an exchange. Similarly, a ticket granting ticket (TGT), which is usually obtained on initial login, can only be issued if the principal contains a version of the password encrypted with an etype that is available both on the KDC and on the client where the login happens. Therefore, to ensure interoperability among components using different implementations as shown in Commonly supported Kerberos encryption types by implementation. Algorithm names, a selection of available etypes is necessary. However, the negotiation process may be subject to downgrade attacks and weak hashing algorithms endanger integrity protection and password security.

This means that the des3-cbc-sha1-kd or rc4-hmac algorithms should not be used, except if there is a concrete and unavoidable need to do so. Other des3-*, des-* and rc4-hmac-exp algorithms should never be used.

Along the lines of cipher string B, the following etypes are recommended: aes256-cts-hmac-sha1-96 camellia256-cts-cmac aes128-cts-hmac-sha1-96 camellia128-cts-cmac. Commonly supported Kerberos encryption types by implementation. Algorithm names according to RFC3961, except where aliases can be used or the algorithm is named differently altogether as stated (Raeburn, 2005)

ID	Algorithm	MIT	Heimdal	GNU Shishi	MS ActiveDirectory
1	des-cbc-crc	yes	yes	yes	yes
2	des-cbc-md4	yes	yes	yes	no
3	des-cbc-md5	yes	yes	yes	yes
6	des3-cbc-none	no	yes	yes	no
7	des3-cbc-sha1	no	yes[20]	no	no
16	des3-cbc-sha1-kd	yes[21]	yesfoonote:[named des3-cbc-sha1]	yes	no
17	aes128-cts-hmac-sha1-96	yes	yes	yes	yesfoonote:[since Vista, Server 2008]
18	aes256-cts-hmac-sha1-96	yes	yes	yes	yes[22]
23	rc4-hmac	yes	yes	yes	yes
24	rc4-hmac-exp	yes	no	yes	yes
25	camellia128-cts-cmac	yes[23]	no	no	no
26	camellia256-cts-cmac	yes[24]	no	no	no

Existing installations

The configuration samples below assume new installations without preexisting principals. For existing installations:* Existing setups should be migrated to a new master key if the current master key is using a weak enctype.

• When changing the list of supported_enctypes, principals where all enctypes are no longer supported will cease to work.
• Be aware that Kerberos 4 is obsolete and should not be used.
• Principals with weak enctypes pose an increased risk for password bruteforce attacks if an attacker gains access to the database.

To get rid of principals with unsupported or weak enctypes, a password change is usually the easiest way. Service principals can simply be recreated.

MIT krb5

KDC configuration

In /etc/krb5kdc/kdc.conf set the following in your realm’s configuration: Listing 44. Encryption flags for MIT krb5 KDC supported_enctypes = aes256-cts-hmac-sha1-96:normal camellia256-cts-cmac:normal aes128-cts-hmac-sha1-96:normal camellia128-cts-cmac:normal default_principal_flags = +preauth In /etc/krb5.conf set in the [libdefaults] section: Listing 45. Encryption flags for MIT krb5 client [libdefaults] allow_weak_crypto = false permitted_enctypes= aes256-cts-hmac-sha1-96 camellia256-cts-cmac aes128-cts-hmac -sha1-96 camellia128-cts-cmac default_tkt_enctypes= aes256-cts-hmac-sha1-96 camellia256-cts-cmac aes128-cts-hmac-sha1-96 camellia128-cts-cmac default_tgs_enctypes= aes256-cts-hmac-sha1-96 camellia256-cts-cmac aes128-cts-hmac-sha1-96 camellia128-cts-cmac

Upgrading a MIT krb5 database to a new enctype

To check if an upgrade is necessary, execute the following on the KDC in question: root@kdc.example.com:~# kdb5_util list_mkeys Master keys for Principal: K/M@EXAMPLE.COM KVNO: 1, Enctype: des-cbc-crc, Active on: Thu Jan 01 00:00:00 UTC 1970 *

In this case, an old unsafe enctype is in use as indicated by the star following the key line.

To upgrade, proceed as follows. First create a new master key for the database with the appropriate enctype. You will be prompted for a master password that can later be used to decrypt the database. A stash-file containing this encryption key will also be written. root@kdc.example.com:~# kdb5_util add_mkey -s -e aes256-cts-hmac-sha1-96 Creating new master key for master key principal 'K/M@EXAMPLE.COM' You will be prompted for a new database Master Password. It is important that you NOT FORGET this password. Enter KDC database master key: Re-enter KDC database master key to verify: Verify that the new master key has been successfully created. Note the key version number (KVNO) of the new master key, in this case 2. root@kdc.example.com:~# kdb5_util list_mkeys Master keys for Principal: K/M@EXAMPLE.COM KVNO: 2, Enctype: aes256-cts-hmac-sha1-96, No activate time set KVNO: 1, Enctype: des-cbc-crc, Active on: Thu Jan 01 00:00:00 UTC 1970 * Set the new master key as the active master key by giving its KVNO. The active master key will be indicated by an asterisk in the master key list. root@kdc.example.com:~# kdb5_util use_mkey 2 root@kdc.example.com:~# kdb5_util list_mkeys Master keys for Principal: K/M@EXAMPLE.COM KVNO: 2, Enctype: aes256-cts-hmac-sha1-96, Active on: Wed May 13 14:14:18 UTC 2015 * KVNO: 1, Enctype: des-cbc-crc, Active on: Thu Jan 01 00:00:00 UTC 1970 Reencrypt all principals to the new master key. root@kdc.example.com:~# kdb5_util update_princ_encryption Re-encrypt all keys not using master key vno 2? (type 'yes' to confirm)? yes 504 principals processed: 504 updated, 0 already current After verifying that everything still works as desired it is possible to remove unused master keys. root@kdc.example.com:~# kdb5_util purge_mkeys Will purge all unused master keys stored in the 'K/M@EXAMPLE.COM' principal, are you sure? (type 'yes' to confirm)? yes OK, purging unused master keys from 'K/M@EXAMPLE.COM'... Purging the following master key(s) from K/M@EXAMPLE.COM: KVNO: 1 1 key(s) purged.

III: Theory

Overview

Number theorists are like lotus-eaters - having tasted this food they can never give it up. 

— Leopold Kronecker This chapter provides the necessary background information on why chapter [practicalsettings] recommended cipher string B. We start off by explaining the structure of cipher strings in section [architecture] (architecture) and define PFS in [pfs]. Next we present Cipher String A and Cipher String B in section Recommended cipher suites. This concludes the section on cipher strings. In theory, the reader should now be able to construct his or her own cipher string. However, the question why certain settings were chosen still remains. To answer this part, we need to look at recommended keylengths, problems in specific algorithms and hash functions and other cryptographic parameters. As mentioned initially in section [relatedPublications], the ENISA (ENISA and Vincent Rijmen, Nigel P. Smart, Bogdan warinschi, Gaven Watson, 2013), ECRYPT 2 (II & SYM, 2012) and BSI (für Sicherheit in der Informationstechnik (BSI), 2018) reports go much more into these topics and should be consulted in addition. We try to answer the questions by explaining issues with random number generators (section Random Number Generators), keylengths (section Keylengths), current issues in ECC (section A note on Elliptic Curve Cryptography), a note of warning on SHA-1 (section A note on SHA-1) and some comments on Diffie Hellman key exchanges (section A note on Diffie Hellman Key Exchanges). All of this is important in understanding why certain choices were made for Cipher String A and B. However, for most system administrators, the question of compatibility is one of the most pressing ones. Having the freedom to be compatible with any client (even running on outdated operating systems) of course, reduces the security of our cipher strings. We address these topics in section TODO. All these sections will allow a system administrator to balance his or her needs for strong encryption with usability and compatibility. Last but not least, we finish this chapter by talking about issues in PKIs (section Public Key Infrastructures), Certificate Authorities and on hardening a PKI. Note that these last few topics deserve a book on their own. Hence this guide can only mention a few current topics in this area.

Cipher suites

Architectural overview

This section defines some terms which will be used throughout this guide. A cipher suite is a standardized collection of key exchange algorithms, encryption algorithms (ciphers) and Message authentication codes (MAC) algorithm that provides authenticated encryption schemes. It consists of the following components:

Key exchange protocol  
 
Authentication  
 
Cipher  
 
Message authentication code (MAC)  
 
Authenticated Encryption with Associated Data (AEAD)  
 

Listing 46. Composition of a typical cipher string +-----+ +-----+ +--------+ +--------+ | DHE +--+ RSA +--+ AES256 +--+ SHA256 + +-----+ +-----+ +--------+ +--------+

A note on nomenclature There are two common naming schemes for cipher strings – IANA names (see appendix Links) and the more well known OpenSSL names. In this document we will always use OpenSSL names unless a specific service uses IANA names.

Forward Secrecy

Forward Secrecy or Perfect Forward Secrecy is a property of a cipher suite that ensures confidentiality even if the server key has been compromised. Thus if traffic has been recorded it can not be decrypted even if an adversary has got hold of the server key.* Forward secrecy (Wikipedia)

• Pushing for Perfect Forward Secrecy, an Important Web Privacy Protection (EFF)
• SSL: Intercepted today, decrypted tomorrow (Netcraft)

Recommended cipher suites

In principle system administrators who want to improve their communication security have to make a difficult decision between effectively locking out some users and keeping high cipher suite security while supporting as many users as possible. The web-site Qualys SSL Labs gives administrators and security engineers a tool to test their setup and compare compatibility with clients. The authors made use of ssllabs.com to arrive at a set of cipher suites which we will recommend throughout this document.

Caution these settings can only represent a subjective choice of the authors at the time of writing. It might be a wise choice to select your own and review cipher suites based on the instructions in section [ChoosingYourOwnCipherSuites].

Configuration A: Strong ciphers, fewer clients

At the time of writing, our recommendation is to use the following set of strong cipher suites which may be useful in an environment where one does not depend on many, different clients and where compatibility is not a big issue. An example of such an environment might be machine-to-machine communication or corporate deployments where software that is to be used can be defined without restrictions. We arrived at this set of cipher suites by selecting:* TLS 1.2

• Perfect forward secrecy / ephemeral Diffie Hellman
• strong MACs (SHA-2) or
• GCM as Authenticated Encryption scheme

This results in the OpenSSL string: EDH+aRSA+AES256:EECDH+aRSA+AES256:!SSLv3 Table 14. Configuration A ciphers

ID	OpenSSL Name	Version	KeyEx	Auth	Cipher	MAC
0x009F	DHE-RSA-AES256-GCM-SHA384	TLSv1.2	DH	RSA	AESGCM(256)	AEAD
0x006B	DHE-RSA-AES256-SHA256	TLSv1.2	DH	RSA	AES(256) (CBC)	SHA256
0xC030	ECDHE-RSA-AES256-GCM-SHA384	TLSv1.2	ECDH	RSA	AESGCM(256)	AEAD
0xC028	ECDHE-RSA-AES256-SHA384	TLSv1.2	ECDH	RSA	AES(256) (CBC)	SHA384

Compatibility At the time of this writing only Win 7 and Win 8.1 crypto stack, OpenSSL >= 1.0.1e, Safari 6 / iOS 6.0.1 and Safari 7 / OS X 10.9 are covered by that cipher string.

Configuration B: Weaker ciphers but better compatibility

In this section we propose a slightly weaker set of cipher suites. For example, there are known weaknesses for the SHA-1 hash function that is included in this set. The advantage of this set of cipher suites is not only better compatibility with a broad range of clients, but also less computational workload on the provisioning hardware. All examples in this publication use Configuration B. We arrived at this set of cipher suites by selecting:* TLS 1.2, TLS 1.1, TLS 1.0

• allowing SHA-1 (see the comments on SHA-1 in section [SHA])

This results in the OpenSSL string: 'EDH+CAMELLIA:EDH+aRSA:EECDH+aRSA+AESGCM:EECDH+aRSA+SHA384:EECDH+aRSA+SHA256:EECDH:+CAMELLIA256:+AES256:+CAMELLIA128:+AES128:+SSLv3:!aNULL:!eNULL:!LOW:!3DES:!MD5:!EXP:!PSK:!SRP:!DSS:!RC4:!SEED:!ECDSA:CAMELLIA256-SHA:AES256-SHA:CAMELLIA128-SHA:AES128-SHA' Table 15. Configuration B ciphers

ID	OpenSSL Name	Version	KeyEx	Auth	Cipher	MAC
0x009F	DHE-RSA-AES256-GCM-SHA384	TLSv1.2	DH	RSA	AESGCM(256)	AEAD
0x006B	DHE-RSA-AES256-SHA256	TLSv1.2	DH	RSA	AES(256)	SHA256
0xC030	ECDHE-RSA-AES256-GCM-SHA384	TLSv1.2	ECDH	RSA	AESGCM(256)	AEAD
0xC028	ECDHE-RSA-AES256-SHA384	TLSv1.2	ECDH	RSA	AES(256)	SHA384
0x009E	DHE-RSA-AES128-GCM-SHA256	TLSv1.2	DH	RSA	AESGCM(128)	AEAD
0x0067	DHE-RSA-AES128-SHA256	TLSv1.2	DH	RSA	AES(128)	SHA256
0xC02F	ECDHE-RSA-AES128-GCM-SHA256	TLSv1.2	ECDH	RSA	AESGCM(128)	AEAD
0xC027	ECDHE-RSA-AES128-SHA256	TLSv1.2	ECDH	RSA	AES(128)	SHA256
0x0088	DHE-RSA-CAMELLIA256-SHA	SSLv3	DH	RSA	Camellia(256)	SHA1
0x0039	DHE-RSA-AES256-SHA	SSLv3	DH	RSA	AES(256)	SHA1
0xC014	ECDHE-RSA-AES256-SHA	SSLv3	ECDH	RSA	AES(256)	SHA1
0x0045	DHE-RSA-CAMELLIA128-SHA	SSLv3	DH	RSA	Camellia(128)	SHA1
0x0033	DHE-RSA-AES128-SHA	SSLv3	DH	RSA	AES(128)	SHA1
0xC013	ECDHE-RSA-AES128-SHA	SSLv3	ECDH	RSA	AES(128)	SHA1
0x0084	CAMELLIA256-SHA	SSLv3	RSA	RSA	Camellia(256)	SHA1
0x0035	AES256-SHA	SSLv3	RSA	RSA	AES(256)	SHA1
0x0041	CAMELLIA128-SHA	SSLv3	RSA	RSA	Camellia(128)	SHA1
0x002F	AES128-SHA	SSLv3	RSA	RSA	AES(128)	SHA1

Compatibility Note that these cipher suites will not work with Windows XP’s crypto stack (e.g. IE, Outlook),

Explanation For a detailed explanation of the cipher suites chosen, please see [ChoosingYourOwnCipherSuites]. In short, finding a single perfect cipher string is practically impossible and there must be a tradeoff between compatibility and security. On the one hand there are mandatory and optional ciphers defined in a few RFCs, on the other hand there are clients and servers only implementing subsets of the specification. Straightforwardly, the authors wanted strong ciphers, forward secrecy [25] and the best client compatibility possible while still ensuring a cipher string that can be used on legacy installations (e.g. OpenSSL 0.9.8).

Our recommended cipher strings are meant to be used via copy and paste and need to work "out of the box".* TLSv1.2 is preferred over TLSv1.0 (while still providing a useable cipher string for TLSv1.0 servers).

• AES256 and CAMELLIA256 count as very strong ciphers at the moment.
• AES128 and CAMELLIA128 count as strong ciphers at the moment
• DHE or ECDHE for forward secrecy
• RSA as this will fit most of today’s setups
• AES256-SHA as a last resort: with this cipher at the end, even server systems with very old OpenSSL versions will work out of the box (version 0.9.8 for example does not provide support for ECC and TLSv1.1 or above). Note however that this cipher suite will not provide forward secrecy. It is meant to provide the same client coverage(eg. support Microsoft crypto libraries) on legacy setups.

Compatibility

TODO Write this section. The idea here is to first document which server (and openssl) version we assumed. Once these parameters are fixed, we then list all clients which are supported for Variant A) and B). Therefore we can document compatibilities to some extent. The sysadmin can then choose roughly what he looses or gains by omitting certain cipher suites.

Random Number Generators

"A real fair random number generator" (Image license: CC-BY-NC) A good source of random numbers is essential for many crypto operations. The key feature of a good random number generator is the non-predictability of the generated numbers. This means that hardware support for generating entropy is essential. Hardware random number generators in operating systems or standalone components collect entropy from various random events mostly by using the (low bits of the) time an event occurs as an entropy source. The entropy is merged into an entropy pool and in some implementations there is some bookkeeping about the number of random bits available.

When Random Number Generators Fail

Random number generators can fail – returning predictable non-random numbers – if not enough entropy is available when random numbers should be generated. This typically occurs for embedded devices and virtual machines. Embedded devices lack some entropy sources other devices have, e.g.:* No persistent clock, so boot-time is not contributing to the initial RNG state.

• No hard-disk: No entropy from hard-disk timing, no way to store entropy between reboots.

Virtual machines emulate some hardware components so that the generated entropy is over-estimated. The most critical component that has been shown to return wrong results is an emulated environment is the timing source (Engblom, 2011). Typically the most vulnerable time where low-entropy situations occur is shortly after a reboot. Unfortunately many operating system installers create cryptographic keys shortly after a reboot (Heninger, Durumeric, Wustrow, & Halderman, 2012). Another problem is that OpenSSL seeds its internal random generator only seldomly from the hardware random number generator of the operating system. This can lead to situations where a daemon that is started at a time when entropy is low keeps this low-entropy situation for hours leading to predictable session keys (Heninger, Durumeric, Wustrow, & Halderman, 2012). For systems where – during the lifetime of the keys – it is expected that low-entropy situations occur, RSA keys should be preferred over DSA keys: For DSA, if there is ever insufficient entropy at the time keys are used for signing this may lead to repeated ephemeral keys. An attacker who can guess an ephemeral private key used in such a signature can compromise the DSA secret key. For RSA this can lead to discovery of encrypted plaintext or forged signatures but not to the compromise of the secret key (Heninger, Durumeric, Wustrow, & Halderman, 2012).

Keylengths

On the choice between AES256 and AES128: I would never consider using AES256, just like I don't wear a helmet when I sit inside my car. It's too much bother for the epsilon improvement in security. Recommendations on keylengths need to be adapted regularly. Since this document first of all is static and second of all, does not consider itself to be authoritative on keylengths, we would rather refer to existing publications and websites. Recommending a safe key length is a hit-and-miss issue. Furthermore, when choosing an encryption algorithm and key length, the designer/sysadmin always needs to consider the value of the information and how long it must be protected. In other words: consider the number of years the data needs to stay confidential. The ECRYPT II publication gives a fascinating overview of strengths of symmetric keys in chapter 5 and chapter 7. Summarizing ECRYPT II, we recommend 128 bit of key strength for symmetric keys. In ECRYPT II, this is considered safe for security level 7, long term protection. In the same ECRYPT II publication you can find a practical comparison of key size equivalence between symmetric key sizes and RSA, discrete log (DLOG) and EC keylengths. ECRYPT II arrives at the interesting conclusion that for an equivalence of 128 bit symmetric size, you will need to use an 3248 bit RSA key (II & SYM, 2012). There are a couple of other studies comparing keylengths and their respective strengths. The website https://www.keylength.com/ compares these papers and offers a good overview of approximations for key lengths based on recommendations by different standardization bodies and academic publications. Figure #fig:keylengths.com[1] shows a typical comparison of keylengths on this web site. "Screenshot for 128 bit symmetric key size equivalents"

Summary

For asymmetric public-key cryptography we consider any key length below 3248 bits to be deprecated at the time of this writing (for long term protection). For elliptic curve cryptography we consider key lengths below 256 bits to be inadequate for long term protection. For symmetric algorithms we consider anything below 128 bits to be inadequate for long term protection.

Special remark on 3DES:

We want to note that 3DES theoretically has 168 bits of security, however based on the NIST Special Publication 800-57 [26]. Due to several security problems the effective key length should be considered 80 bits. The NIST recommends not to use 3DES any more and to migrate to AES as soon as possible.

A note on Elliptic Curve Cryptography

Everyone knows what a curve is, until he has studied enough mathematics to become confused through the countless number of possible exceptions. Elliptic Curve Cryptography (simply called ECC from now on) is a branch of cryptography that emerged in the mid-1980s. The security of the RSA algorithm is based on the assumption that factoring large numbers is infeasible. Likewise, the security of ECC, DH and DSA is based on the discrete logarithm problem (i_wikipedia_Discrete logarithm_, 2013). Finding the discrete logarithm of an elliptic curve from its public base point is thought to be infeasible. This is known as the Elliptic Curve Discrete Logarithm Problem (ECDLP). ECC and the underlying mathematical foundation are not easy to understand - luckily, there have been some great introductions on the topic. [27] [28] [29]. ECC provides for much stronger security with less computationally expensive operations in comparison to traditional asymmetric algorithms (See the Section Keylengths). The security of ECC relies on the elliptic curves and curve points chosen as parameters for the algorithm in question. Well before the NSA-leak scandal, there has been a lot of discussion regarding these parameters and their potential subversion. A part of the discussion involved recommended sets of curves and curve points chosen by different standardization bodies such as the National Institute of Standards and Technology (NIST) [30] which were later widely implemented in most common crypto libraries. Those parameters came under question repeatedly from cryptographers (Bernstein & Lange, 2013). At the time of writing, there is ongoing research as to the security of various ECC parameters (SafeCurves: choosing safe curves for elliptic-curve cryptography, 2013). Most software configured to rely on ECC (be it client or server) is not able to promote or black-list certain curves. It is the hope of the authors that such functionality will be deployed widely soon. The authors of this paper include configurations and recommendations with and without ECC - the reader may choose to adopt those settings as he finds best suited to his environment. The authors will not make this decision for the reader.

Warning One should get familiar with ECC, different curves and parameters if one chooses to adopt ECC configurations. Since there is much discussion on the security of ECC, flawed settings might very well compromise the security of the entire system!

A note on SHA-1

In the last years several weaknesses have been shown for SHA-1. In particular, collisions on SHA-1 can be found using 263 operations, and recent results even indicate a lower complexity. Therefore, ECRYPT II and NIST recommend against using SHA-1 for generating digital signatures and for other applications that require collision resistance. The use of SHA-1 in message authentication, e.g. HMAC, is not immediately threatened. We recommend using SHA-2 whenever available. Since SHA-2 is not supported by older versions of TLS, SHA-1 can be used for message authentication if a higher compatibility with a more diverse set of clients is needed. Our configurations A and B reflect this. While configuration A does not include SHA-1, configuration B does and thus is more compatible with a wider range of clients.

A note on Diffie Hellman Key Exchanges

A common question is which Diffie-Hellman (DH) parameters should be used for Diffie Hellman key-exchanges [31]. We follow the recommendations in ECRYPT II (II & SYM, 2012). Where configurable, we recommend using the Diffie Hellman groups defined for IKE, specifically groups 14-18 (2048–8192 bit MODP) (Kivinen & Kojo, 2003). These groups have been checked by many eyes and can be assumed to be secure. For convenience, we provide these parameters as PEM files on our webserver [32].

Public Key Infrastructures

Public-Key Infrastructures try to solve the problem of verifying whether a public key belongs to a given entity, so as to prevent Man In The Middle attacks. There are two approaches to achieve that: Certificate Authorities and the Web of Trust. Certificate Authorities (CAs) sign end-entities’ certificates, thereby associating some kind of identity (e.g. a domain name or an email address) with a public key. CAs are used with TLS and S/MIME certificates, and the CA system has a big list of possible and real problems which are summarized in section Hardening PKI and (Durumeric, Kasten, Bailey, & Halderman, 2013). The Web of Trust is a decentralized system where people sign each other’s keys, so that there is a high chance that there is a "trust path" from one key to another. This is used with PGP keys, and while it avoids most of the problems of the CA system, it is more cumbersome. As alternatives to these public systems, there are two more choices: running a private CA, and manually trusting keys (as it is used with SSH keys or manually trusted keys in web browsers). The first part of this section addresses how to obtain a certificate in the CA system. The second part offers recommendations on how to improve the security of your PKI.

Certificate Authorities

In order to get a certificate, you can find an external CA willing to issue a certificate for you, run your own CA, or use self-signed certificates. As always, there are advantages and disadvantages for every one of these options; a balance of security versus usability needs to be found.

Certificates From an External Certificate Authority

There is a fairly large number of commercial CAs that will issue certificates for money. Some of the most ubiquitous commercial CAs are Verisign, GoDaddy, and Teletrust. However, there are also CAs that offer certificates for free. The most notable examples are StartSSL, which is a company that offers some types of certificates for free, and CAcert, which is a non-profit volunteer-based organization that does not charge at all for issuing certificates. Finally, in the research and education field, a number of CAs exist that are generally well-known and well-accepted within the higher-education community. A large number of CAs is pre-installed in client software’s or operating system’s`‘trust stores’'; depending on your application, you have to select your CA according to this, or have a mechanism to distribute the chosen CA’s root certificate to the clients. When requesting a certificate from a CA, it is vital that you generate the key pair yourself. In particular, the private key should never be known to the CA. If a CA offers to generate the key pair for you, you should not trust that CA. Generating a key pair and a certificate request can be done with a number of tools. On Unix-like systems, it is likely that the OpenSSL suite is available to you. In this case, you can generate a private key and a corresponding certificate request as follows: $ openssl req -new -nodes -keyout <servername>.key -out <servername>.csr -newkey rsa:<keysize> -sha256 Country Name (2 letter code) [AU]:DE State or Province Name (full name) [Some-State]:Bavaria Locality Name (eg, city) []:Munich Organization Name (eg, company) [Internet Widgits Pty Ltd]:Example Organizational Unit Name (eg, section) []:Example Section Common Name (e.g. server FQDN or YOUR name) []:example.com Email Address []:admin@example.com Please enter the following 'extra' attributes to be sent with your certificate request A challenge password []: An optional company name []:

Setting Up Your Own Certificate Authority

In some situations it is advisable to run your own certificate authority. Whether this is a good idea depends on the exact circumstances. Generally speaking, the more centralized the control of the systems in your environment, the fewer pains you will have to go through to deploy your own CA. On the other hand, running your own CA maximizes the trust level that you can achieve because it minimizes external trust dependencies. Again using OpenSSL as an example, you can set up your own CA with the following commands on a Debian system: $ cd /usr/lib/ssl/misc $ sudo ./CA.pl -newca Answer the questions according to your setup. Now that you have configured your basic settings and issued a new root certificate, you can issue new certificates as follows: $ cd /usr/lib/ssl/misc $ sudo ./CA.pl -newreq Alternatively, software such as TinyCA that acts as a "wrapper" around OpenSSL and tries to make life easier is available.

Creating a Self-Signed Certificate

If the desired trust level is very high and the number of systems involved is limited, the easiest way to set up a secure environment may be to use self-signed certificates. A self-signed certificate is not issued by any CA at all, but is signed by the entity that it is issued to. Thus, the organizational overhead of running a CA is eliminated at the expense of having to establish all trust relationships between entities manually. With OpenSSL, you can self-sign a previously created certificate with this command: $ openssl req -new -x509 -key privkey.pem -out cacert.pem -days 1095 You can also create a self-signed certificate in just one command: $ openssl req -new -x509 -keyout privkey.pem -out cacert.pem -days 1095 -nodes -newkey rsa:<keysize> -sha256 The resulting certificate will by default not be trusted by anyone at all, so in order to be useful, the certificate will have to be made known a priori to all parties that may encounter it.

Hardening PKI

In recent years several CAs were compromised by attackers in order to get a hold of trusted certificates for malicious activities. In 2011 the Dutch CA Diginotar was hacked and all certificates were revoked (Elinor Mills, 2011). Recently Google found certificates issued to them, which were not used by the company (Damon Poeter, 2011). The concept of PKIs heavily depends on the security of CAs. If they get compromised the whole PKI system will fail. Some CAs tend to incorrectly issue certificates that were designated to do a different job than what they were intended to by the CA (Adam Langley, et. al., 2013). Therefore several security enhancements were introduced by different organizations and vendors (H. Tschofenig and E. Lear, 2013). Currently two methods are used, DANE (Hoffman & Schlyter, 2012) and Certificate Pinning (C. Evans and C. Palmer, 2013). Google recently proposed a new system to detect malicious CAs and certificates called Certificate Transparency (Adam Langley, Ben Laurie, Emilia Kasper, 2013). In addition, RFC 6844 describes Certification Authorization Records, a mechanism for domain name owners to signal which Certificate Authorities are authorized to issue certificates for their domain.

Certification Authorization Records

RFC 6844 describes Certification Authorization Records, a mechanism for domain name owners to signal which Certificate Authorities are authorized to issue certificates for their domain. When a CAA record is defined for a particular domain, it specifies that the domain owner requests Certificate Authorities to validate any request against the CAA record. If the certificate issuer is not listed in the CAA record, it should not issue the certificate. The RFC also permits Certificate Evaluators to test an issued certificate against the CAA record, but should exercise caution, as the CAA record may change during the lifetime of a certificate, without affecting its validity. CAA also supports an iodef property type which can be requested by a Certificate Authority to report certificate issue requests which are inconsistent with the issuer’s Certificate Policy.

Configuration of CAA records

BIND supports CAA records as of version 9.9.6. A CAA record can be configured by adding it to the zone file: $ORIGIN example.com

      CAA 0 issue "ca1.example"
      CAA 0 iodef "mailto:security@example.com"

If your organization uses multiple CA’s, you can configure multiple records:

     CAA 0 issue "ca1.example"
     CAA 0 issue "ca2.example"

"ca1.example" and "ca2.example" are unique identifiers for the CA you plan on using. These strings can be obtained from your Certificate Authority, and typically are its top level domain. An example is "letsencrypt.org" for the Let’s Encrypt CA operated by the Internet Security Research Group. Knot-DNS supports CAA records as of version 2.2.0.

Validation of CAA records

Once a CAA record is deployed, it can be validated using the following dig query: $ dig CAA google.com ; <<>> DiG 9.10.3-P4-Debian <<>> CAA google.com ;; ANSWER SECTION: google.com. 3600 IN CAA 0 issue "symantec.com" On older versions of Dig, which do not support CAA records, you can query the record type manually: $ dig +short -t TYPE257 google.com \# 19 0005697373756573796D616E7465632E636F6D

TLS and its support mechanisms

HTTP Strict Transport Security (HSTS)

HTTP Strict Transport Security (HSTS) is a web security policy mechanism. HSTS is realized through HTTP header by which a web server declares that complying user agents (web browsers) should interact with it by using only secure HTTPS connections. [33] HSTS header is bound to a DNS name or domain by which the server was accessed. For example if server serves content for two domains and it is HTTPS enabled only for one domain, the browser won’t enforce HSTS for the latter. HSTS reduces the risk of active man-in-the-middle attacks such as SSL stripping, and impersonation attacks with untrusted certificate. HSTS also helps to avoid unintentional mistakes such as insecure links to a secure web site (missing HTTPS links [34]), and mistyped HTTPS URLs. After the web browser receives a HSTS header in a correctly [35] prepared SSL session it will automatically use secure HTTPS links for accessing the server. This prevents unencrypted HTTP access (SSL striping, mistyped HTTPS URLs, etc.) when the server is accessed later by the client. When a server (that previously emitted a HSTS header) starts using an untrusted certificate, complying user agents must show an error message and block the server connection. Thus impersonation MITM attack with untrusted certificates cannot occur. For the initial setup HSTS header needs a trusted secure connection over HTTPS. This limitation can be addressed by compiling a list of STS enabled sites directly into a browser. [36]

HSTS Header Directives

HSTS header can be parametrized by two directives:* max-age=<number-of-seconds>

• includeSubdomains

max-age is a required directive. This directive indicates the number of seconds during which the user agent should enforce the HSTS policy (after the reception of the STS header field from a server). includeSubdomains is an optional directive. This directive indicates that the HSTS policy applies to this HSTS host as well as any subdomains of the host’s domain name.

HSTS Client Support

HSTS is supported [37] by these web browsers:* Firefox version >= v4.0

• Chrome version >= 4.0
• Android Browser >=4.4
• Opera version >= 12.0
• Opera mobile >= 16.0
• Safari >= 7.0
• Microsoft Internet Explorer >= 11 (with update provided 09. June 2015)
• Microsoft Edge >= 12

HSTS Considerations

Before enabling HSTS it is recommended to consider following:* Is it required to serve content or services over HTTP?

• Enabling includeSubdomains and SSL certificate management.
• Proper value of max-age.

It is recommended to serve all content using HTTPS, but there are exceptions to this rule as well. Consider running a private PKI [38]. CRLs and OCSP responses are published typically by HTTP protocol. If HSTS is enabled on the site where OCSP and CRLs are published the browser might fail fetching CRL or validating OCSP response. Similar reasoning goes for includeSubdomains. One needs to be sure that HTTPS can be enforced for all subdomains. Moreover the administrators are advised to watch for expiration of the SSL certificate and handle the renewal process with caution. If a SSL certificate is renewed after expiration or misses a (HSTS enabled) domain name, the connection to site will break (without providing override mechanism to the end user). Finally HSTS should be tested with lower max-age values and deployed with higher max-age values.

Testing HSTS

HSTS can be tested either using locally or through the Internet. For local testing it is possible to utilize Chrome Web browser UI by typing chrome://net-internals/#hsts [39] in the address bar. Testing over the Internet can be conducted by Qualys SSL Labs test https://www.ssllabs.com/ssltest/. Strict Transport Security (HSTS) information is located in the Protocol Details section.

References

• Websites Must Use HSTS in Order to Be Secure: https://www.eff.org/deeplinks/2014/02/websites-hsts
• OWASP: HTTP Strict Transport Security: https://www.owasp.org/index.php/HTTP_Strict_Transport_Security
• HSTS Browser Compatibility List: https://caniuse.com/stricttransportsecurity
• RFC 6797:HTTP Strict Transport Security (HSTS) - Examples: https://tools.ietf.org/html/rfc6797#section-6.2

HTTP Public Key Pinning (HPKP)

Much like HTTP Strict Transport Security (HSTS), HTTP Public Key Pinning (HPKP) is a Trust-On-First-Use (TOFU) mechanism. It protects HTTPS websites from impersonation using certificates issued by compromised certificate authorities. The data for Pinning is supplied by an HTTP-Header sent by the WebServer.

HPKP Header Directives

HPKP provides two different types of headers:* Public-Key-Pins

• Public-Key-Pins-Report-Only

HPKP header can be parametrized by following directives:* pin-sha256="<YOUR_PUBLICKEY_HASH⇒"

• max-age=<number-of-seconds>
• includeSubdomains
• report-uri="<https://YOUR.URL/TO-REPORT>"

pin-sha256 is a required directive. It can and should be used several (at least two) times for specifying the public keys of your domain-certificates or CA-certificates. Operators can pin any one or more of the public keys in the certificate-chain, and indeed must pin to issuers not in the chain (as, for example, a backup-pin). Pinning to an intermediate issuer, or even to a trust anchor or root, still significantly reduces the number of issuers who can issue end-entity certificates for the Known Pinned Host, while still giving that host flexibility to change keys without a disruption of service. OpenSSL can be used to convert the public-key of an X509-certificate as follows: $ openssl x509 -in <certificate.cer> -pubkey -noout |

openssl rsa -pubin -outform der |
openssl dgst -sha256 -binary |
openssl enc -base64

writing RSA key pG3WsstDsfMkRdF3hBClXRKYxxKUJIOu8DwabG8MFrU= This piped usage of OpenSSL first gets the Public-Key of <certificate.cer>, converts it do DER (binary) format, calculates an SHA256 Hash and finally encodes it Base64. The output (including the ending Equal-Sign) is exactly whats needed for the pin-sha256="<YOUR_PUBLICKEY_HASH⇒" parameter. To generate the hash for a prepared backup-key just create a certificate-signing-request and replace openssl x509 by openssl req -in <backup-cert.csr> -pubkey -noout as first OpenSSL command. Instead of using OpenSSL even web-services like https://report-uri.io/home/pkp_hash/ can be used to get a suggestion for the possible Public-Key-Hashes for a given website. max-age is a required directive (when using the Public-Key-Pins header). This directive specifies the number of seconds during which the user agent should regard the host (from whom the message was received) as a "Known Pinned Host". includeSubdomains is an optional directive. This directive indicates that the same pinning applies to this host as well as any subdomains of the host’s domain name. Be careful - you need to use a multi-domain/wildcard-certificate or use the same pub/private-keypair in all subdomain-certificates or need to pin to CA-certificates signing all your subdomain-certificates. report-uri is an optional directive. The presence of a report-uri directive indicates to the web-browser that in the event of pin-validation failure, it should post a report to the report-uri (HTTP-Post is done using JSON, Syntax see {RFC-7469 Section 3} [40]). There are WebServices like https://report-uri.io/ out there which can be used to easily collect and visualize these reports.

HPKP Client Support

HPKP is supported [41] by these web browsers:* Firefox version >= 35

• Chrome version between version 38 and 72
• Android Browser >= 44
• Opera version >= 25

Currently (20. Dec 2018) there is no HPKP support in: Apple Safari, Microsoft Internet Explorer and Edge. HPKP Support has been removed from Google Chrome and Chromium from version 72 onwards.

HPKP Considerations

Before enabling HPKP it is recommended to consider following:* Which Public-Keys to use for Pinning (Certificate + Backup-Certificate, CAs, Intermediate-CAs)

• Proper value of max-age. Start testing with a short Period, increase Period after deployment.
• Be careful when using includeSubdomains, are all your subdomains covered by the defined Public-Key-Hashes?

The administrators are advised to watch for expiration of the SSL certificate and handle the renewal process with caution. If a SSL certificate is renewed without keeping the public-key (reusing the CSR) for an HPKP enabled domain name, the connection to site will break (without providing override mechanism to the end user).

Testing HPKP

HPKP can be tested either using locally or through the Internet. There is a handy bash-script which uses OpenSSL for doing several SSL/TLS-Tests available at https://testssl.sh/ $ wget -q https://testssl.sh/testssl.sh $ wget -q https://testssl.sh/mapping-rfc.txt $ chmod 755 ./testssl.sh $ ./testssl.sh https://example.com # Sample Output, just HSTS and HPKP Section (Full report is quite long!): Strict Transport Security 182 days=15724800 s, includeSubDomains Public Key Pinning # of keys: 2, 90 days=7776000 s, just this domain

          matching host key: pG3WsstDsfMkRdF3hBClXRKYxxKUJIOu8DwabG8MFrU

For local testing it is possible to utilize Google Chrome web-browser, just open the Chrome net-internals-URL: chrome://net-internals/#hsts. For Mozilla Firefox there is an plug-in provided by the "Secure Information Technology Center Austria" available: https://demo.a-sit.at/firefox-plugin-highlighting-safety-information/ Testing over the Internet can be conducted by Qualys SSL Labs test https://www.ssllabs.com/ssltest/. Public Key Pinning (HPKP) information is located in the Protocol Details section. There is also a fast online HPKP-only check at https://report-uri.io/home/pkp_analyse.

References

• OWASP: Certificate and Public Key Pinning: https://www.owasp.org/index.php/Certificate_and_Public_Key_Pinning
• HPKP Browser Compatibility List: https://caniuse.com/\#feat=publickeypinning
• RFC 7469:Public Key Pinning Extension for HTTP - Examples: https://tools.ietf.org/html/rfc7469\#section-2.1.5

IV: Appendix

Tools

This section lists tools for checking the security settings.

SSL & TLS

Server checks via the web ssllabs.com offers a great way to check your webserver for misconfigurations. See https://www.ssllabs.com/ssltest/. Furthermore, ssllabs.com has a good best practices tutorial, which focuses on avoiding the most common mistakes in SSL. SSL Server certificate installation issues https://www.sslshopper.com/ssl-checker.html Check SPDY protocol support and basic TLS setup http://spdycheck.org/ XMPP/Jabber Server check (Client-to-Server and Server-to-Server) https://xmpp.net/ Luxsci SMTP TLS Checker https://luxsci.com/extranet/tlschecker.html DNSsec and DANE support of your domain and e-mail server? https://dane.sys4.de http://checktls.com is a tool for testing arbitrary TLS services. http://tls.secg.org is a tool for testing interoperability of HTTPS implementations for ECC cipher suites. http://www.whynopadlock.com/ Testing for mixed SSL parts loaded via http that can totally lever your HTTPS.

Browser Checks

Check your browser’s SSL capabilities: https://cc.dcsec.uni-hannover.de/ and https://www.ssllabs.com/ssltest/viewMyClient.html. Check Browsers SSL/TLS support and vulnerability to attacks: https://www.howsmyssl.com

Command Line Tools

https://sourceforge.net/projects/sslscan connects to a given SSL service and shows the cipher suites that are offered. http://www.bolet.org/TestSSLServer/ tests for BEAST and CRIME vulnerabilities. https://github.com/drwetter/testssl.sh checks a server’s service on any port for the support of TLS/SSL ciphers, protocols as well as some cryptographic flaws (CRIME, BREACH, CCS, Heartbleed). https://github.com/iSECPartners/sslyze Fast and full-featured SSL scanner. https://github.com/jvehent/cipherscan Fast TLS scanner (ciphers, order, protocols, key size and more) http://nmap.org/ nmap security scanner http://www.openssl.net OpenSSL s_client Monitoring TLS services with Zabbix (sorry, German) https://blog.sys4.de/zertifikate-uberwachen-mit-zabbix-de.html

Key length

http://www.keylength.com comprehensive online resource for comparison of key lengths according to common recommendations and standards in cryptography.

Random Number Generators

ENT is a pseudo random number generator sequence tester. Dieharder a random number generator testing tool. CAcert Random another random number generator testing service.

Guides

See: https://www.ssllabs.com/downloads/SSL_TLS_Deployment_Best_Practices.pdf.

Links

IANA official list of Transport Layer Security (TLS) Parameters Elliptic curves and their implementation (04 Dec 2010) A (relatively easy to understand) primer on elliptic curve cryptography Duraconf, A collection of hardened configuration files for SSL/TLSservices (Jacob Appelbaum’s github) Attacks on SSL a comprehensive study of BEAST, CRIME, TIME, BREACH, LUCKY 13 & RC4 Biases EFF How to deploy HTTPS correctly Bruce Almighty: Schneier preaches security to Linux faithful (on not recommending to use Blowfish anymore in favor of Twofish) Implement FIPS 183-3 for DSA keys (1024bit constraint) Elliptic Curve Cryptography in Practice Factoring as a Service Black Ops of TCP/IP 2012 SSL and the Future of Authenticity, Moxie Marlinspike - Black Hat USA 2011 ENISA - Algorithms, Key Sizes and Parameters Report (Oct.’13 Diffie-Hellman Groups standardized in RFC3526 TLS Security (Survey + Lucky13 + RC4 Attack) by Kenny Paterson Ensuring High-Quality Randomness in Cryptographic Key Generation Wikipedia: Ciphertext Stealing Wikipedia: Malleability (Cryptography) Ritter’s Crypto Glossary and Dictionary of Technical Cryptography

Suggested Reading

This section contains suggested reading material. Cryptography Engineering: Design Principles and Practical Applications, Ferguson, N. and Schneier, B. and Kohno, T. (ISBN-13: 978-0470474242) Security Engineering: A Guide to Building Dependable Distributed Systems, Anderson, R.J. (ISBN-13: 978-0470068526) Applied cryptography: protocols, algorithms, and source code in C, Schneier, B. (ISBN-13: 978-0471117094) Guide to Elliptic Curve Cryptography, Hankerson, D. and Vanstone, S. and Menezes, A.J. (ISBN-13: 978-0387952734) A Introduction To The Theory of Numbers, Godfrey Harold Hardy, E. M. Wrigh (ISBN-13: 978-0199219865) Malicious Cryptography: Exposing Cryptovirology, Young A., Yung, M. (ISBN-13: 978-0764549755)

Cipher Suite Name Cross-Reference

This table shows the cipher suite names as IANA defined them, the names OpenSSL uses, and the respective codes.

Code	IANA Name	OpenSSL Name
0x00,0x00	TLS_NULL_WITH_NULL_NULL
0x00,0x01	TLS_RSA_WITH_NULL_MD5	NULL-MD5
0x00,0x02	TLS_RSA_WITH_NULL_SHA	NULL-SHA
0x00,0x03	TLS_RSA_EXPORT_WITH_RC4_40_MD5	EXP-RC4-MD5
0x00,0x04	TLS_RSA_WITH_RC4_128_MD5	RC4-MD5
0x00,0x05	TLS_RSA_WITH_RC4_128_SHA	RC4-SHA
0x00,0x06	TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5	EXP-RC2-CBC-MD5
0x00,0x07	TLS_RSA_WITH_IDEA_CBC_SHA
0x00,0x08	TLS_RSA_EXPORT_WITH_DES40_CBC_SHA	EXP-DES-CBC-SHA
0x00,0x09	TLS_RSA_WITH_DES_CBC_SHA	DES-CBC-SHA
0x00,0x0A	TLS_RSA_WITH_3DES_EDE_CBC_SHA	DES-CBC3-SHA
0x00,0x0B	TLS_DH_DSS_EXPORT_WITH_DES40_CBC_SHA
0x00,0x0C	TLS_DH_DSS_WITH_DES_CBC_SHA
0x00,0x0D	TLS_DH_DSS_WITH_3DES_EDE_CBC_SHA
0x00,0x0E	TLS_DH_RSA_EXPORT_WITH_DES40_CBC_SHA
0x00,0x0F	TLS_DH_RSA_WITH_DES_CBC_SHA
0x00,0x10	TLS_DH_RSA_WITH_3DES_EDE_CBC_SHA
0x00,0x11	TLS_DHE_DSS_EXPORT_WITH_DES40_CBC_SHA	EXP-EDH-DSS-DES-CBC-SHA
0x00,0x12	TLS_DHE_DSS_WITH_DES_CBC_SHA	EDH-DSS-DES-CBC-SHA
0x00,0x13	TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA	EDH-DSS-DES-CBC3-SHA
0x00,0x14	TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA	EXP-EDH-RSA-DES-CBC-SHA
0x00,0x15	TLS_DHE_RSA_WITH_DES_CBC_SHA	EDH-RSA-DES-CBC-SHA
0x00,0x16	TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA	EDH-RSA-DES-CBC3-SHA
0x00,0x17	TLS_DH_anon_EXPORT_WITH_RC4_40_MD5	EXP-ADH-RC4-MD5
0x00,0x18	TLS_DH_anon_WITH_RC4_128_MD5	ADH-RC4-MD5
0x00,0x19	TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA	EXP-ADH-DES-CBC-SHA
0x00,0x1A	TLS_DH_anon_WITH_DES_CBC_SHA	ADH-DES-CBC-SHA
0x00,0x1B	TLS_DH_anon_WITH_3DES_EDE_CBC_SHA	ADH-DES-CBC3-SHA
0x00,0x1E	TLS_KRB5_WITH_DES_CBC_SHA
0x00,0x1F	TLS_KRB5_WITH_3DES_EDE_CBC_SHA
0x00,0x20	TLS_KRB5_WITH_RC4_128_SHA
0x00,0x21	TLS_KRB5_WITH_IDEA_CBC_SHA
0x00,0x22	TLS_KRB5_WITH_DES_CBC_MD5
0x00,0x23	TLS_KRB5_WITH_3DES_EDE_CBC_MD5
0x00,0x24	TLS_KRB5_WITH_RC4_128_MD5
0x00,0x25	TLS_KRB5_WITH_IDEA_CBC_MD5
0x00,0x26	TLS_KRB5_EXPORT_WITH_DES_CBC_40_SHA
0x00,0x27	TLS_KRB5_EXPORT_WITH_RC2_CBC_40_SHA
0x00,0x28	TLS_KRB5_EXPORT_WITH_RC4_40_SHA
0x00,0x29	TLS_KRB5_EXPORT_WITH_DES_CBC_40_MD5
0x00,0x2A	TLS_KRB5_EXPORT_WITH_RC2_CBC_40_MD5
0x00,0x2B	TLS_KRB5_EXPORT_WITH_RC4_40_MD5
0x00,0x2C	TLS_PSK_WITH_NULL_SHA
0x00,0x2D	TLS_DHE_PSK_WITH_NULL_SHA
0x00,0x2E	TLS_RSA_PSK_WITH_NULL_SHA
0x00,0x2F	TLS_RSA_WITH_AES_128_CBC_SHA	AES128-SHA
0x00,0x30	TLS_DH_DSS_WITH_AES_128_CBC_SHA
0x00,0x31	TLS_DH_RSA_WITH_AES_128_CBC_SHA
0x00,0x32	TLS_DHE_DSS_WITH_AES_128_CBC_SHA	DHE-DSS-AES128-SHA
0x00,0x33	TLS_DHE_RSA_WITH_AES_128_CBC_SHA	DHE-RSA-AES128-SHA
0x00,0x34	TLS_DH_anon_WITH_AES_128_CBC_SHA	ADH-AES128-SHA
0x00,0x35	TLS_RSA_WITH_AES_256_CBC_SHA	AES256-SHA
0x00,0x36	TLS_DH_DSS_WITH_AES_256_CBC_SHA
0x00,0x37	TLS_DH_RSA_WITH_AES_256_CBC_SHA
0x00,0x38	TLS_DHE_DSS_WITH_AES_256_CBC_SHA	DHE-DSS-AES256-SHA
0x00,0x39	TLS_DHE_RSA_WITH_AES_256_CBC_SHA	DHE-RSA-AES256-SHA
0x00,0x3A	TLS_DH_anon_WITH_AES_256_CBC_SHA	ADH-AES256-SHA
0x00,0x3B	TLS_RSA_WITH_NULL_SHA256	NULL-SHA256
0x00,0x3C	TLS_RSA_WITH_AES_128_CBC_SHA256	AES128-SHA256
0x00,0x3D	TLS_RSA_WITH_AES_256_CBC_SHA256	AES256-SHA256
0x00,0x3E	TLS_DH_DSS_WITH_AES_128_CBC_SHA256
0x00,0x3F	TLS_DH_RSA_WITH_AES_128_CBC_SHA256
0x00,0x40	TLS_DHE_DSS_WITH_AES_128_CBC_SHA256	DHE-DSS-AES128-SHA256
0x00,0x41	TLS_RSA_WITH_CAMELLIA_128_CBC_SHA	CAMELLIA128-SHA
0x00,0x42	TLS_DH_DSS_WITH_CAMELLIA_128_CBC_SHA
0x00,0x43	TLS_DH_RSA_WITH_CAMELLIA_128_CBC_SHA
0x00,0x44	TLS_DHE_DSS_WITH_CAMELLIA_128_CBC_SHA	DHE-DSS-CAMELLIA128-SHA
0x00,0x45	TLS_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA	DHE-RSA-CAMELLIA128-SHA
0x00,0x46	TLS_DH_anon_WITH_CAMELLIA_128_CBC_SHA	ADH-CAMELLIA128-SHA
0x00,0x67	TLS_DHE_RSA_WITH_AES_128_CBC_SHA256	DHE-RSA-AES128-SHA256
0x00,0x68	TLS_DH_DSS_WITH_AES_256_CBC_SHA256
0x00,0x69	TLS_DH_RSA_WITH_AES_256_CBC_SHA256
0x00,0x6A	TLS_DHE_DSS_WITH_AES_256_CBC_SHA256	DHE-DSS-AES256-SHA256
0x00,0x6B	TLS_DHE_RSA_WITH_AES_256_CBC_SHA256	DHE-RSA-AES256-SHA256
0x00,0x6C	TLS_DH_anon_WITH_AES_128_CBC_SHA256	ADH-AES128-SHA256
0x00,0x6D	TLS_DH_anon_WITH_AES_256_CBC_SHA256	ADH-AES256-SHA256
0x00,0x84	TLS_RSA_WITH_CAMELLIA_256_CBC_SHA	CAMELLIA256-SHA
0x00,0x85	TLS_DH_DSS_WITH_CAMELLIA_256_CBC_SHA
0x00,0x86	TLS_DH_RSA_WITH_CAMELLIA_256_CBC_SHA
0x00,0x87	TLS_DHE_DSS_WITH_CAMELLIA_256_CBC_SHA	DHE-DSS-CAMELLIA256-SHA
0x00,0x88	TLS_DHE_RSA_WITH_CAMELLIA_256_CBC_SHA	DHE-RSA-CAMELLIA256-SHA
0x00,0x89	TLS_DH_anon_WITH_CAMELLIA_256_CBC_SHA	ADH-CAMELLIA256-SHA
0x00,0x8A	TLS_PSK_WITH_RC4_128_SHA	PSK-RC4-SHA
0x00,0x8B	TLS_PSK_WITH_3DES_EDE_CBC_SHA	PSK-3DES-EDE-CBC-SHA
0x00,0x8C	TLS_PSK_WITH_AES_128_CBC_SHA	PSK-AES128-CBC-SHA
0x00,0x8D	TLS_PSK_WITH_AES_256_CBC_SHA	PSK-AES256-CBC-SHA
0x00,0x8E	TLS_DHE_PSK_WITH_RC4_128_SHA
0x00,0x8F	TLS_DHE_PSK_WITH_3DES_EDE_CBC_SHA
0x00,0x90	TLS_DHE_PSK_WITH_AES_128_CBC_SHA
0x00,0x91	TLS_DHE_PSK_WITH_AES_256_CBC_SHA
0x00,0x92	TLS_RSA_PSK_WITH_RC4_128_SHA
0x00,0x93	TLS_RSA_PSK_WITH_3DES_EDE_CBC_SHA
0x00,0x94	TLS_RSA_PSK_WITH_AES_128_CBC_SHA
0x00,0x95	TLS_RSA_PSK_WITH_AES_256_CBC_SHA
0x00,0x96	TLS_RSA_WITH_SEED_CBC_SHA	SEED-SHA
0x00,0x97	TLS_DH_DSS_WITH_SEED_CBC_SHA
0x00,0x98	TLS_DH_RSA_WITH_SEED_CBC_SHA
0x00,0x99	TLS_DHE_DSS_WITH_SEED_CBC_SHA	DHE-DSS-SEED-SHA
0x00,0x9A	TLS_DHE_RSA_WITH_SEED_CBC_SHA	DHE-RSA-SEED-SHA
0x00,0x9B	TLS_DH_anon_WITH_SEED_CBC_SHA	ADH-SEED-SHA
0x00,0x9C	TLS_RSA_WITH_AES_128_GCM_SHA256	AES128-GCM-SHA256
0x00,0x9D	TLS_RSA_WITH_AES_256_GCM_SHA384	AES256-GCM-SHA384
0x00,0x9E	TLS_DHE_RSA_WITH_AES_128_GCM_SHA256	DHE-RSA-AES128-GCM-SHA256
0x00,0x9F	TLS_DHE_RSA_WITH_AES_256_GCM_SHA384	DHE-RSA-AES256-GCM-SHA384
0x00,0xA0	TLS_DH_RSA_WITH_AES_128_GCM_SHA256
0x00,0xA1	TLS_DH_RSA_WITH_AES_256_GCM_SHA384
0x00,0xA2	TLS_DHE_DSS_WITH_AES_128_GCM_SHA256	DHE-DSS-AES128-GCM-SHA256
0x00,0xA3	TLS_DHE_DSS_WITH_AES_256_GCM_SHA384	DHE-DSS-AES256-GCM-SHA384
0x00,0xA4	TLS_DH_DSS_WITH_AES_128_GCM_SHA256
0x00,0xA5	TLS_DH_DSS_WITH_AES_256_GCM_SHA384
0x00,0xA6	TLS_DH_anon_WITH_AES_128_GCM_SHA256	ADH-AES128-GCM-SHA256
0x00,0xA7	TLS_DH_anon_WITH_AES_256_GCM_SHA384	ADH-AES256-GCM-SHA384
0x00,0xA8	TLS_PSK_WITH_AES_128_GCM_SHA256
0x00,0xA9	TLS_PSK_WITH_AES_256_GCM_SHA384
0x00,0xAA	TLS_DHE_PSK_WITH_AES_128_GCM_SHA256
0x00,0xAB	TLS_DHE_PSK_WITH_AES_256_GCM_SHA384
0x00,0xAC	TLS_RSA_PSK_WITH_AES_128_GCM_SHA256
0x00,0xAD	TLS_RSA_PSK_WITH_AES_256_GCM_SHA384
0x00,0xAE	TLS_PSK_WITH_AES_128_CBC_SHA256
0x00,0xAF	TLS_PSK_WITH_AES_256_CBC_SHA384
0x00,0xB0	TLS_PSK_WITH_NULL_SHA256
0x00,0xB1	TLS_PSK_WITH_NULL_SHA384
0x00,0xB2	TLS_DHE_PSK_WITH_AES_128_CBC_SHA256
0x00,0xB3	TLS_DHE_PSK_WITH_AES_256_CBC_SHA384
0x00,0xB4	TLS_DHE_PSK_WITH_NULL_SHA256
0x00,0xB5	TLS_DHE_PSK_WITH_NULL_SHA384
0x00,0xB6	TLS_RSA_PSK_WITH_AES_128_CBC_SHA256
0x00,0xB7	TLS_RSA_PSK_WITH_AES_256_CBC_SHA384
0x00,0xB8	TLS_RSA_PSK_WITH_NULL_SHA256
0x00,0xB9	TLS_RSA_PSK_WITH_NULL_SHA384
0x00,0xBA	TLS_RSA_WITH_CAMELLIA_128_CBC_SHA256
0x00,0xBB	TLS_DH_DSS_WITH_CAMELLIA_128_CBC_SHA256
0x00,0xBC	TLS_DH_RSA_WITH_CAMELLIA_128_CBC_SHA256
0x00,0xBD	TLS_DHE_DSS_WITH_CAMELLIA_128_CBC_SHA256
0x00,0xBE	TLS_DHE_RSA_WITH_CAMELLIA_128_CBC_SHA256
0x00,0xBF	TLS_DH_anon_WITH_CAMELLIA_128_CBC_SHA256
0x00,0xC0	TLS_RSA_WITH_CAMELLIA_256_CBC_SHA256
0x00,0xC1	TLS_DH_DSS_WITH_CAMELLIA_256_CBC_SHA256
0x00,0xC2	TLS_DH_RSA_WITH_CAMELLIA_256_CBC_SHA256
0x00,0xC3	TLS_DHE_DSS_WITH_CAMELLIA_256_CBC_SHA256
0x00,0xC4	TLS_DHE_RSA_WITH_CAMELLIA_256_CBC_SHA256
0x00,0xC5	TLS_DH_anon_WITH_CAMELLIA_256_CBC_SHA256
0x00,0xFF	TLS_EMPTY_RENEGOTIATION_INFO_SCSV
0xC0,0x01	TLS_ECDH_ECDSA_WITH_NULL_SHA	ECDH-ECDSA-NULL-SHA
0xC0,0x02	TLS_ECDH_ECDSA_WITH_RC4_128_SHA	ECDH-ECDSA-RC4-SHA
0xC0,0x03	TLS_ECDH_ECDSA_WITH_3DES_EDE_CBC_SHA	ECDH-ECDSA-DES-CBC3-SHA
0xC0,0x04	TLS_ECDH_ECDSA_WITH_AES_128_CBC_SHA	ECDH-ECDSA-AES128-SHA
0xC0,0x05	TLS_ECDH_ECDSA_WITH_AES_256_CBC_SHA	ECDH-ECDSA-AES256-SHA
0xC0,0x06	TLS_ECDHE_ECDSA_WITH_NULL_SHA	ECDHE-ECDSA-NULL-SHA
0xC0,0x07	TLS_ECDHE_ECDSA_WITH_RC4_128_SHA	ECDHE-ECDSA-RC4-SHA
0xC0,0x08	TLS_ECDHE_ECDSA_WITH_3DES_EDE_CBC_SHA	ECDHE-ECDSA-DES-CBC3-SHA
0xC0,0x09	TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA	ECDHE-ECDSA-AES128-SHA
0xC0,0x0A	TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA	ECDHE-ECDSA-AES256-SHA
0xC0,0x0B	TLS_ECDH_RSA_WITH_NULL_SHA	ECDH-RSA-NULL-SHA
0xC0,0x0C	TLS_ECDH_RSA_WITH_RC4_128_SHA	ECDH-RSA-RC4-SHA
0xC0,0x0D	TLS_ECDH_RSA_WITH_3DES_EDE_CBC_SHA	ECDH-RSA-DES-CBC3-SHA
0xC0,0x0E	TLS_ECDH_RSA_WITH_AES_128_CBC_SHA	ECDH-RSA-AES128-SHA
0xC0,0x0F	TLS_ECDH_RSA_WITH_AES_256_CBC_SHA	ECDH-RSA-AES256-SHA
0xC0,0x10	TLS_ECDHE_RSA_WITH_NULL_SHA	ECDHE-RSA-NULL-SHA
0xC0,0x11	TLS_ECDHE_RSA_WITH_RC4_128_SHA	ECDHE-RSA-RC4-SHA
0xC0,0x12	TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA	ECDHE-RSA-DES-CBC3-SHA
0xC0,0x13	TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA	ECDHE-RSA-AES128-SHA
0xC0,0x14	TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA	ECDHE-RSA-AES256-SHA
0xC0,0x15	TLS_ECDH_anon_WITH_NULL_SHA	AECDH-NULL-SHA
0xC0,0x16	TLS_ECDH_anon_WITH_RC4_128_SHA	AECDH-RC4-SHA
0xC0,0x17	TLS_ECDH_anon_WITH_3DES_EDE_CBC_SHA	AECDH-DES-CBC3-SHA
0xC0,0x18	TLS_ECDH_anon_WITH_AES_128_CBC_SHA	AECDH-AES128-SHA
0xC0,0x19	TLS_ECDH_anon_WITH_AES_256_CBC_SHA	AECDH-AES256-SHA
0xC0,0x1A	TLS_SRP_SHA_WITH_3DES_EDE_CBC_SHA	SRP-3DES-EDE-CBC-SHA
0xC0,0x1B	TLS_SRP_SHA_RSA_WITH_3DES_EDE_CBC_SHA	SRP-RSA-3DES-EDE-CBC-SHA
0xC0,0x1C	TLS_SRP_SHA_DSS_WITH_3DES_EDE_CBC_SHA	SRP-DSS-3DES-EDE-CBC-SHA
0xC0,0x1D	TLS_SRP_SHA_WITH_AES_128_CBC_SHA	SRP-AES-128-CBC-SHA
0xC0,0x1E	TLS_SRP_SHA_RSA_WITH_AES_128_CBC_SHA	SRP-RSA-AES-128-CBC-SHA
0xC0,0x1F	TLS_SRP_SHA_DSS_WITH_AES_128_CBC_SHA	SRP-DSS-AES-128-CBC-SHA
0xC0,0x20	TLS_SRP_SHA_WITH_AES_256_CBC_SHA	SRP-AES-256-CBC-SHA
0xC0,0x21	TLS_SRP_SHA_RSA_WITH_AES_256_CBC_SHA	SRP-RSA-AES-256-CBC-SHA
0xC0,0x22	TLS_SRP_SHA_DSS_WITH_AES_256_CBC_SHA	SRP-DSS-AES-256-CBC-SHA
0xC0,0x23	TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256	ECDHE-ECDSA-AES128-SHA256
0xC0,0x24	TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384	ECDHE-ECDSA-AES256-SHA384
0xC0,0x25	TLS_ECDH_ECDSA_WITH_AES_128_CBC_SHA256	ECDH-ECDSA-AES128-SHA256
0xC0,0x26	TLS_ECDH_ECDSA_WITH_AES_256_CBC_SHA384	ECDH-ECDSA-AES256-SHA384
0xC0,0x27	TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256	ECDHE-RSA-AES128-SHA256
0xC0,0x28	TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384	ECDHE-RSA-AES256-SHA384
0xC0,0x29	TLS_ECDH_RSA_WITH_AES_128_CBC_SHA256	ECDH-RSA-AES128-SHA256
0xC0,0x2A	TLS_ECDH_RSA_WITH_AES_256_CBC_SHA384	ECDH-RSA-AES256-SHA384
0xC0,0x2B	TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256	ECDHE-ECDSA-AES128-GCM-SHA256
0xC0,0x2C	TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384	ECDHE-ECDSA-AES256-GCM-SHA384
0xC0,0x2D	TLS_ECDH_ECDSA_WITH_AES_128_GCM_SHA256	ECDH-ECDSA-AES128-GCM-SHA256
0xC0,0x2E	TLS_ECDH_ECDSA_WITH_AES_256_GCM_SHA384	ECDH-ECDSA-AES256-GCM-SHA384
0xC0,0x2F	TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256	ECDHE-RSA-AES128-GCM-SHA256
0xC0,0x30	TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384	ECDHE-RSA-AES256-GCM-SHA384
0xC0,0x31	TLS_ECDH_RSA_WITH_AES_128_GCM_SHA256	ECDH-RSA-AES128-GCM-SHA256
0xC0,0x32	TLS_ECDH_RSA_WITH_AES_256_GCM_SHA384	ECDH-RSA-AES256-GCM-SHA384
0xC0,0x33	TLS_ECDHE_PSK_WITH_RC4_128_SHA
0xC0,0x34	TLS_ECDHE_PSK_WITH_3DES_EDE_CBC_SHA
0xC0,0x35	TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA
0xC0,0x36	TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA
0xC0,0x37	TLS_ECDHE_PSK_WITH_AES_128_CBC_SHA256
0xC0,0x38	TLS_ECDHE_PSK_WITH_AES_256_CBC_SHA384
0xC0,0x39	TLS_ECDHE_PSK_WITH_NULL_SHA
0xC0,0x3A	TLS_ECDHE_PSK_WITH_NULL_SHA256
0xC0,0x3B	TLS_ECDHE_PSK_WITH_NULL_SHA384
0xC0,0x3C	TLS_RSA_WITH_ARIA_128_CBC_SHA256
0xC0,0x3D	TLS_RSA_WITH_ARIA_256_CBC_SHA384
0xC0,0x3E	TLS_DH_DSS_WITH_ARIA_128_CBC_SHA256
0xC0,0x3F	TLS_DH_DSS_WITH_ARIA_256_CBC_SHA384
0xC0,0x40	TLS_DH_RSA_WITH_ARIA_128_CBC_SHA256
0xC0,0x41	TLS_DH_RSA_WITH_ARIA_256_CBC_SHA384
0xC0,0x42	TLS_DHE_DSS_WITH_ARIA_128_CBC_SHA256
0xC0,0x43	TLS_DHE_DSS_WITH_ARIA_256_CBC_SHA384
0xC0,0x44	TLS_DHE_RSA_WITH_ARIA_128_CBC_SHA256
0xC0,0x45	TLS_DHE_RSA_WITH_ARIA_256_CBC_SHA384
0xC0,0x46	TLS_DH_anon_WITH_ARIA_128_CBC_SHA256
0xC0,0x47	TLS_DH_anon_WITH_ARIA_256_CBC_SHA384
0xC0,0x48	TLS_ECDHE_ECDSA_WITH_ARIA_128_CBC_SHA256
0xC0,0x49	TLS_ECDHE_ECDSA_WITH_ARIA_256_CBC_SHA384
0xC0,0x4A	TLS_ECDH_ECDSA_WITH_ARIA_128_CBC_SHA256
0xC0,0x4B	TLS_ECDH_ECDSA_WITH_ARIA_256_CBC_SHA384
0xC0,0x4C	TLS_ECDHE_RSA_WITH_ARIA_128_CBC_SHA256
0xC0,0x4D	TLS_ECDHE_RSA_WITH_ARIA_256_CBC_SHA384
0xC0,0x4E	TLS_ECDH_RSA_WITH_ARIA_128_CBC_SHA256
0xC0,0x4F	TLS_ECDH_RSA_WITH_ARIA_256_CBC_SHA384
0xC0,0x50	TLS_RSA_WITH_ARIA_128_GCM_SHA256
0xC0,0x51	TLS_RSA_WITH_ARIA_256_GCM_SHA384
0xC0,0x52	TLS_DHE_RSA_WITH_ARIA_128_GCM_SHA256
0xC0,0x53	TLS_DHE_RSA_WITH_ARIA_256_GCM_SHA384
0xC0,0x54	TLS_DH_RSA_WITH_ARIA_128_GCM_SHA256
0xC0,0x55	TLS_DH_RSA_WITH_ARIA_256_GCM_SHA384
0xC0,0x56	TLS_DHE_DSS_WITH_ARIA_128_GCM_SHA256
0xC0,0x57	TLS_DHE_DSS_WITH_ARIA_256_GCM_SHA384
0xC0,0x58	TLS_DH_DSS_WITH_ARIA_128_GCM_SHA256
0xC0,0x59	TLS_DH_DSS_WITH_ARIA_256_GCM_SHA384
0xC0,0x5A	TLS_DH_anon_WITH_ARIA_128_GCM_SHA256
0xC0,0x5B	TLS_DH_anon_WITH_ARIA_256_GCM_SHA384
0xC0,0x5C	TLS_ECDHE_ECDSA_WITH_ARIA_128_GCM_SHA256
0xC0,0x5D	TLS_ECDHE_ECDSA_WITH_ARIA_256_GCM_SHA384
0xC0,0x5E	TLS_ECDH_ECDSA_WITH_ARIA_128_GCM_SHA256
0xC0,0x5F	TLS_ECDH_ECDSA_WITH_ARIA_256_GCM_SHA384
0xC0,0x60	TLS_ECDHE_RSA_WITH_ARIA_128_GCM_SHA256
0xC0,0x61	TLS_ECDHE_RSA_WITH_ARIA_256_GCM_SHA384
0xC0,0x62	TLS_ECDH_RSA_WITH_ARIA_128_GCM_SHA256
0xC0,0x63	TLS_ECDH_RSA_WITH_ARIA_256_GCM_SHA384
0xC0,0x64	TLS_PSK_WITH_ARIA_128_CBC_SHA256
0xC0,0x65	TLS_PSK_WITH_ARIA_256_CBC_SHA384
0xC0,0x66	TLS_DHE_PSK_WITH_ARIA_128_CBC_SHA256
0xC0,0x67	TLS_DHE_PSK_WITH_ARIA_256_CBC_SHA384
0xC0,0x68	TLS_RSA_PSK_WITH_ARIA_128_CBC_SHA256
0xC0,0x69	TLS_RSA_PSK_WITH_ARIA_256_CBC_SHA384
0xC0,0x6A	TLS_PSK_WITH_ARIA_128_GCM_SHA256
0xC0,0x6B	TLS_PSK_WITH_ARIA_256_GCM_SHA384
0xC0,0x6C	TLS_DHE_PSK_WITH_ARIA_128_GCM_SHA256
0xC0,0x6D	TLS_DHE_PSK_WITH_ARIA_256_GCM_SHA384
0xC0,0x6E	TLS_RSA_PSK_WITH_ARIA_128_GCM_SHA256
0xC0,0x6F	TLS_RSA_PSK_WITH_ARIA_256_GCM_SHA384
0xC0,0x70	TLS_ECDHE_PSK_WITH_ARIA_128_CBC_SHA256
0xC0,0x71	TLS_ECDHE_PSK_WITH_ARIA_256_CBC_SHA384
0xC0,0x72	TLS_ECDHE_ECDSA_WITH_CAMELLIA_128_CBC_SHA256
0xC0,0x73	TLS_ECDHE_ECDSA_WITH_CAMELLIA_256_CBC_SHA384
0xC0,0x74	TLS_ECDH_ECDSA_WITH_CAMELLIA_128_CBC_SHA256
0xC0,0x75	TLS_ECDH_ECDSA_WITH_CAMELLIA_256_CBC_SHA384
0xC0,0x76	TLS_ECDHE_RSA_WITH_CAMELLIA_128_CBC_SHA256
0xC0,0x77	TLS_ECDHE_RSA_WITH_CAMELLIA_256_CBC_SHA384
0xC0,0x78	TLS_ECDH_RSA_WITH_CAMELLIA_128_CBC_SHA256
0xC0,0x79	TLS_ECDH_RSA_WITH_CAMELLIA_256_CBC_SHA384
0xC0,0x7A	TLS_RSA_WITH_CAMELLIA_128_GCM_SHA256
0xC0,0x7B	TLS_RSA_WITH_CAMELLIA_256_GCM_SHA384
0xC0,0x7C	TLS_DHE_RSA_WITH_CAMELLIA_128_GCM_SHA256
0xC0,0x7D	TLS_DHE_RSA_WITH_CAMELLIA_256_GCM_SHA384
0xC0,0x7E	TLS_DH_RSA_WITH_CAMELLIA_128_GCM_SHA256
0xC0,0x7F	TLS_DH_RSA_WITH_CAMELLIA_256_GCM_SHA384
0xC0,0x80	TLS_DHE_DSS_WITH_CAMELLIA_128_GCM_SHA256
0xC0,0x81	TLS_DHE_DSS_WITH_CAMELLIA_256_GCM_SHA384
0xC0,0x82	TLS_DH_DSS_WITH_CAMELLIA_128_GCM_SHA256
0xC0,0x83	TLS_DH_DSS_WITH_CAMELLIA_256_GCM_SHA384
0xC0,0x84	TLS_DH_anon_WITH_CAMELLIA_128_GCM_SHA256
0xC0,0x85	TLS_DH_anon_WITH_CAMELLIA_256_GCM_SHA384
0xC0,0x86	TLS_ECDHE_ECDSA_WITH_CAMELLIA_128_GCM_SHA256
0xC0,0x87	TLS_ECDHE_ECDSA_WITH_CAMELLIA_256_GCM_SHA384
0xC0,0x88	TLS_ECDH_ECDSA_WITH_CAMELLIA_128_GCM_SHA256
0xC0,0x89	TLS_ECDH_ECDSA_WITH_CAMELLIA_256_GCM_SHA384
0xC0,0x8A	TLS_ECDHE_RSA_WITH_CAMELLIA_128_GCM_SHA256
0xC0,0x8B	TLS_ECDHE_RSA_WITH_CAMELLIA_256_GCM_SHA384
0xC0,0x8C	TLS_ECDH_RSA_WITH_CAMELLIA_128_GCM_SHA256
0xC0,0x8D	TLS_ECDH_RSA_WITH_CAMELLIA_256_GCM_SHA384
0xC0,0x8E	TLS_PSK_WITH_CAMELLIA_128_GCM_SHA256
0xC0,0x8F	TLS_PSK_WITH_CAMELLIA_256_GCM_SHA384
0xC0,0x90	TLS_DHE_PSK_WITH_CAMELLIA_128_GCM_SHA256
0xC0,0x91	TLS_DHE_PSK_WITH_CAMELLIA_256_GCM_SHA384
0xC0,0x92	TLS_RSA_PSK_WITH_CAMELLIA_128_GCM_SHA256
0xC0,0x93	TLS_RSA_PSK_WITH_CAMELLIA_256_GCM_SHA384
0xC0,0x94	TLS_PSK_WITH_CAMELLIA_128_CBC_SHA256
0xC0,0x95	TLS_PSK_WITH_CAMELLIA_256_CBC_SHA384
0xC0,0x96	TLS_DHE_PSK_WITH_CAMELLIA_128_CBC_SHA256
0xC0,0x97	TLS_DHE_PSK_WITH_CAMELLIA_256_CBC_SHA384
0xC0,0x98	TLS_RSA_PSK_WITH_CAMELLIA_128_CBC_SHA256
0xC0,0x99	TLS_RSA_PSK_WITH_CAMELLIA_256_CBC_SHA384
0xC0,0x9A	TLS_ECDHE_PSK_WITH_CAMELLIA_128_CBC_SHA256
0xC0,0x9B	TLS_ECDHE_PSK_WITH_CAMELLIA_256_CBC_SHA384
0xC0,0x9C	TLS_RSA_WITH_AES_128_CCM
0xC0,0x9D	TLS_RSA_WITH_AES_256_CCM
0xC0,0x9E	TLS_DHE_RSA_WITH_AES_128_CCM
0xC0,0x9F	TLS_DHE_RSA_WITH_AES_256_CCM
0xC0,0xA0	TLS_RSA_WITH_AES_128_CCM_8
0xC0,0xA1	TLS_RSA_WITH_AES_256_CCM_8
0xC0,0xA2	TLS_DHE_RSA_WITH_AES_128_CCM_8
0xC0,0xA3	TLS_DHE_RSA_WITH_AES_256_CCM_8
0xC0,0xA4	TLS_PSK_WITH_AES_128_CCM
0xC0,0xA5	TLS_PSK_WITH_AES_256_CCM
0xC0,0xA6	TLS_DHE_PSK_WITH_AES_128_CCM
0xC0,0xA7	TLS_DHE_PSK_WITH_AES_256_CCM
0xC0,0xA8	TLS_PSK_WITH_AES_128_CCM_8
0xC0,0xA9	TLS_PSK_WITH_AES_256_CCM_8
0xC0,0xAA	TLS_PSK_DHE_WITH_AES_128_CCM_8
0xC0,0xAB	TLS_PSK_DHE_WITH_AES_256_CCM_8
0xC0,0xAC	TLS_ECDHE_ECDSA_WITH_AES_128_CCM
0xC0,0xAD	TLS_ECDHE_ECDSA_WITH_AES_256_CCM
0xC0,0xAE	TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8
0xC0,0xAF	TLS_ECDHE_ECDSA_WITH_AES_256_CCM_8

The list of IANA cipher suite names was retrieved from https://www.iana.org/assignments/tls-parameters/tls-parameters-4.csv on Tue Jun 3 22:36:58 2014. The list of OpenSSL Ciphers was generated with OpenSSL 1.0.1e 11 Feb 2013.

Further Research

The following is a list of services, software packages, hardware devices or protocols that we considered documenting but either did not manage to document yet or might be able to document later. We encourage input from the community. Table 16. Further Protocols

DNSSec (mention BCPs)	DANE	Tor
S/Mime (check are there any BCPs? )	TrueCrypt, LUKS, FileVault	AFS
Kerberos	NNTP	NTPs tlsdate
Moxa , APC, und co…​ ICS
rsyslog	tftp	(s)ftp(s)
haproxy

Table 17. Further Protocols (Network centric)

IPv6 security
Wi-Fi, 802.1x	SIP	SRTP
Kerberos	NNTP	NTPs tlsdate
BGP / OSPF	LDAP	seclayer-tcp
RADIUS (RADSEC)	racoon	strongswan
l2tp
Ethernet to serial	DSL modems
UPnP, natPmp
HTTP Key Pinning (HTKP)
Monitoring: SNMPv3

Table 18. Further Applications

Lync	Tomcat
Microsoft SQL Server	Microsoft Exchange
IBM HTTP Server

Commerical Network Equipment Vendors Other ideas: SAML federated auth providers [42] Elastic Load Balancing (ELB)[43]

Software not covered by this guide

telnet: Usage of telnet for anything other than fun projects is highly discouraged Puppet DB: A Proxy or a tunnel is recommended if it needs to be facing public network interfaces.[44] rsync: Best use it only via SSH for an optimum of security and easiest to maintain.

Bibliography

Adam Langley, Ben Laurie, Emilia Kasper. (2013). Certificate Transparency. http://www.certificate-transparency.org https://datatracker.ietf.org/doc/rfc6962/ . Adam Langley, et. al. (2013). Go X.509 Verification Source Code. https://code.google.com/p/go/source/browse/src/pkg/crypto/x509/verify.go#173 . Anderson, R. (2008). Security engineering. Wiley.com. Retrieved from rja14/book.html http://www.cl.cam.ac.uk/ rja14/book.html Bernstein, D. J., & Lange, T. (2013). Security dangers of the NIST curves (Presentation slides). Retrieved from http://cr.yp.to/talks/2013.09.16/slides-djb-20130916-a4.pdf C. Evans and C. Palmer. (2013). Public Key Pinning Extension for HTTP. https://tools.ietf.org/html/draft-ietf-websec-key-pinning-09 . Damon Poeter. (2011). Fake Google Certificate Puts Gmail at Risk. http://www.pcmag.com/article2/0,2817,2392063,00.asp . Durumeric, Z., Kasten, J., Bailey, M., & Halderman, J. A. (2013). Analysis of the HTTPS Certificate Ecosystem. In Proceedings of the 13th Internet Measurement Conference. Retrieved from https://jhalderm.com/pub/papers/https-imc13.pdf Elinor Mills. (2011). Fraudulent Google certificate points to Internet attack. http://news.cnet.com/8301-27080_3-20098894-245/fraudulent-google-certificate-points-to-internet-attack/ . Engblom, J. (2011). Evaluating HAVEGE Randomness (Blog: Observations from Uppsala). Retrieved from http://jakob.engbloms.se/archives/1374 ENISA and Vincent Rijmen, Nigel P. Smart, Bogdan warinschi, Gaven Watson. (2013). ENISA - Algorithms, Key Sizes and Parameters Report. Retrieved from http://www.enisa.europa.eu/activities/identity-and-trust/library/deliverables/algorithms-key-sizes-and-parameters-report für Sicherheit in der Informationstechnik (BSI), B. (2018). BSI TR-02102 Kryptographische Verfahren. Retrieved from https://www.bsi.bund.de/EN/Publications/TechnicalGuidelines/tr02102/tr02102_node.html H. Tschofenig and E. Lear. (2013). Evolving the Web Public Key Infrastructure. https://tools.ietf.org/html/draft-tschofenig-iab-webpki-evolution-01.txt . Heninger, N., Durumeric, Z., Wustrow, E., & Halderman, J. A. (2012). Mining Your Ps and Qs: Detection of Widespread Weak Keys in Network Devices. In Proceedings of the 21st USENIX Security Symposium. Retrieved from https://factorable.net/weakkeys12.extended.pdf Hoffman, P., & Schlyter, J. (2012). The DNS-Based Authentication of Named Entities (DANE) Transport Layer Security (TLS) Protocol: TLSA. IETF. Retrieved from https://www.ietf.org/rfc/rfc6698.txt i_mit_Realm configuration decisions_. (2013). (Documentation). Retrieved from http://web.mit.edu/kerberos/krb5-latest/doc/admin/realm_config.html i_wikipedia_Discrete logarithm_. (2013). (Wikipedia). Retrieved from https://en.wikipedia.org/wiki/Discrete_logarithm i_wikipedia_Tempest (codename). (2018). (Wikipedia). Retrieved from https://en.wikipedia.org/wiki/Tempest(codename) II, E. C. R. Y. P. T., & SYM, D. (2012). ECRYPT II, 79–86. Retrieved from http://www.ecrypt.eu.org/ecrypt2/documents/D.SPA.20.pdf Katz, J., & Lindell, Y. (2008). Introduction to modern cryptography. Chapman & Hall/CRC. Retrieved from http://books.google.at/books?id=WIc_AQAAIAAJ Kivinen, T., & Kojo, M. (2003). More Modular Exponential (MODP) Diffie-Hellman groups for Internet Key Exchange (IKE). IETF. Retrieved from https://www.ietf.org/rfc/rfc3526.txt Postel, J. (1980). DoD standard Transmission Control Protocol. IETF. Retrieved from https://www.ietf.org/rfc/rfc761.txt Raeburn, K. (2005). Advanced Encryption Standard (AES) Encryption for Kerberos 5. IETF. Retrieved from https://www.ietf.org/rfc/rfc3962.txt SafeCurves: choosing safe curves for elliptic-curve cryptography. (2013). (Technical Background). Retrieved from http://safecurves.cr.yp.to/rigid.html Schneier, B. (2013). The NSA Is Breaking Most Encryption on the Internet (Blog: Schneier on Security). Retrieved from https://www.schneier.com/blog/archives/2013/09/the_nsa_is_brea.html Yarom, Y., & Falkner, K. (2013). Flush+ Reload: a high resolution, low noise, L3 cache side-channel attack. Cryptology ePrint Archive, Report 2013/448, 2013. http://eprint. iacr. org/2013/448/. 3. Retrieved from http://eprint.iacr.org/2013/448.pdf

Index

1. An easy to read yet very insightful recent example is the "FLUSH+RELOAD" technique for leaking cryptographic keys from one virtual machine to another via L3 cache timing attacks. (xref:bibliography-default-yarom2013flush[Yarom & Falkner, 2013 2. Interested readers are referred to https://bugzilla.mozilla.org/show_bug.cgi?id=647959 or http://www.h-online.com/security/news/item/Honest-Achmed-asks-for-trust-1231314.html which brings the problem of trusting PKIs right to the point 3. http://www.wired.com/opinion/2013/10/how-to-design-and-defend-against-the-perfect-backdoor/ 4. https://www.mail-archive.com/openssl-dev@openssl.org/msg33405.html 5. https://bugzilla.mindrot.org/show_bug.cgi?id=1647 6. https://www.dovecot.org/doc/NEWS-2.2 7. https://hg.dovecot.org/dovecot-2.2/rev/43ab5abeb8f0 8. https://www.cisco.com/c/dam/en/us/td/docs/security/esa/esa9-5/ESA_9-5_Release_Notes.pdf, Changed Behaviour, page 4 9. 64 possible values = 6 bits 10. RFC6379 , RFC4308  11. http://ikecrack.sourceforge.net/ 12. https://sweet32.info/ 13. https://sweet32.info/#impact 14. https://community.openvpn.net/openvpn/ticket/304 15. http://technet.microsoft.com/en-us/security/advisory/2743314 16. https://www.cloudcracker.com/blog/2012/07/29/cracking-ms-chap-v2/ 17. Early versions seem to have a few bugs - although officially supported, it did not work in tests with version 15.06. Version 16.01 is confirmed to work. 18. https://docs.ejabberd.im 19. IRC-Netze - Top 10 im Jahresvergleich 20. named old-des3-cbc-sha1 21. alias des3-cbc-sha1, des3-hmac-sha1 22. since 7, Server 2008R2 23. since 1.9 24. since 1.9 25. https://nikmav.blogspot.com/2011/12/price-to-pay-for-perfect-forward.html 26. https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-57pt1r4.pdf, page 51 27. https://arstechnica.com/security/2013/10/a-relatively-easy-to-understand-primer-on-elliptic-curve-cryptography 28. https://www.imperialviolet.org/2010/12/04/ecc.html 29. http://www.isg.rhul.ac.uk/~sdg/ecc.html 30. https://www.nist.gov 31. http://crypto.stackexchange.com/questions/1963/how-large-should-a-diffie-hellman-p-be 32. https://www.bettercrypto.org/static/dhparams/ 33. https://en.wikipedia.org/wiki/HTTP_Strict_Transport_Security 34. Thus, it might be useful for fixing HTTPS mixed-content related errors, see https://community.qualys.com/blogs/securitylabs/2014/03/19/https-mixed-content-still-the-easiest-way-to-break-ssl. 35. Website must load without SSL/TLS browser warnings (certificate is issued by a trusted CA, contains correct DNS name, it is time valid, etc.). 36. List of the preloaded sites can be found at https://www.chromium.org/hsts. This list is managed by Google/Chrome, but it is also used by Firefox https://wiki.mozilla.org/Privacy/Features/HSTS_Preload_List 37. https://caniuse.com/stricttransportsecurity 38. see Public Key Infrastructures 39. see https://blog.chromium.org/2011/06/new-chromium-security-features-june.html 40. https://tools.ietf.org/html/rfc7469\#section-3 41. https://caniuse.com/\#feat=publickeypinning 42. e.g., all the REFEDS folks (https://refeds.org/), including InCommon (http://www.incommon.org/federation/metadata.html https://wiki.shibboleth.net/confluence/display/SHIB2/TrustManagement) 43. https://lists.cert.at/pipermail/ach/2014-May/001422.html 44. https://lists.cert.at/pipermail/ach/2014-November/001626.html