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=== Umgang mit Schlüsselmaterial ===
Schlüsselmaterial identifiziert die kryptografischen Geheimnisse, aus denen ein Schlüssel besteht.
; Sämtliches Schlüsselmaterial muss als RESTRICTED-Daten behandelt werden
* Nur Personen mit spezieller Ausbildung und dem Bedarf an Wissen sollten Zugang zu Schlüsselmaterial haben.
* Das Schlüsselmaterial muss bei der Übertragung verschlüsselt werden.
* Schlüsselmaterial kann im Klartext gespeichert werden, aber nur mit einer angemessenen Zugangskontrolle (begrenzter Zugang).
; Dazu gehören
* OpenSSH server keys (<tt>/etc/ssh/ssh_host_*key</tt>)
* Client keys (<tt>~/.ssh/id_{rsa,dsa,ecdsa,ed25519}</tt> and <tt>~/.ssh/identity</tt>).
=== Ciphers and algorithms choice ===
; Recent OpenSSH servers and client support CHACHA20
* When CHACHA20 (OpenSSH 6.5+) is not available
* AES-GCM (OpenSSH 6.1+) and any other algorithm using EtM (Encrypt then MAC) [http://blog.djm.net.au/2013/11/chacha20-and-poly1305-in-openssh.html disclose the packet length] - giving some information to the attacker.
* NIST curves (<tt>ecdh-sha2-nistp512,ecdh-sha2-nistp384,ecdh-sha2-nistp256</tt>) are listed for compatibility, but the use of <tt>curve25519</tt> is [https://safecurves.cr.yp.to/ generally preferred]
; SSH protocol 2
* [https://en.wikipedia.org/wiki/Diffie–Hellman_key_exchange DH]
* [https://en.wikipedia.org/wiki/Elliptic_curve_Diffie–Hellman ECDH] key-exchange
* [https://en.wikipedia.org/wiki/Forward_secrecy forward secrecy]
; Group sizes
* [https://wiki.mozilla.org/Security/Guidelines/Key_Management Security/Guidelines/Key_Management]
The various algorithms supported by a particular OpenSSH version can be listed with the following commands
$ ssh -Q cipher
$ ssh -Q cipher-auth
$ ssh -Q mac
$ ssh -Q kex
$ ssh -Q key
=== Client key size and login latency ===
; Figure out the impact on performance of using larger keys
* Such as RSA 4096 bytes keys - on the client side
; Tests
Idle, i7 4500 intel CPU
* OpenSSH_6.7p1
* OpenSSL 1.0.1l
* ed25519 server keys
The following command is ran 10 times
time ssh localhost -i .ssh/id_thekey exit
; Results
{|| class="wikitable sortable"
|-
|| '''Client key '''
|| '''Minimum '''
|| '''Maximum '''
|| '''Average '''
|-
|| RSA 4096
|| 120ms
|| 145ms
|| 127ms
|-
|| RSA 2048
|| 120ms
|| 129ms
|| 127ms
|-
|| ed25519
|| 117ms
|| 138ms
|| 120ms
|-
|}
; Slower Machines
These numbers may differ on a slower machine
* This contains the complete login sequence
* Therefore is subject to variations
; Summery
* The latency differences are not significant
* It does not impact performance sufficiently
== Konfiguration ==
[[SSH/Kryptografie/Konfiguration]]
<noinclude>
=== Anhang ===
==== Siehe auch ====
{{Special:PrefixIndex/SSH}}
===== Dokumentation =====
===== Links =====
====== Projekt ======
====== Weblinks ======
# [https://wiki.mozilla.org/Security/Key_Management Key Management]
# [https://wiki.mozilla.org/Security/Server_Side_TLS Server Side TLS]
# [https://www.ietf.org/rfc/rfc4418.txt RFC4418 (umac)]
# [http://www.openssh.com/txt/draft-miller-secsh-umac-01.txt umac draft]
# [https://safecurves.cr.yp.to/ Safe curves]
# [http://blog.djm.net.au/2013/11/chacha20-and-poly1305-in-openssh.html DJM blog]
# [https://stribika.github.io/2015/01/04/secure-secure-shell.html Stribika blog]
# [http://2013.diac.cr.yp.to/slides/gueron.pdf AES-GCM performance study]
# [https://security.googleblog.com/2014/04/speeding-up-and-strengthening-https.html CHACHA20 vs AES-GCM performance study]
# [http://cvsweb.openbsd.org/cgi-bin/cvsweb/~checkout~/src/usr.bin/ssh/PROTOCOL.certkeys?rev=1.9&content-type=text/plain PROTOCOL.certkeys]
# [https://wiki.gnupg.org/rfc4880bis rfc44880bis from GnuPG]
# [https://weakdh.org/ Weak Diffie-Hellman and the Logjam Attack]
# [https://jbeekman.nl/blog/2015/05/ssh-logjam/ On OpenSSH and Logjam, by Jethro Beekman]
[[Kategorie:Kryptografie/Best Practice]]
[[Kategorie:Kryptografie/Best Practice]]
[[Kategorie:SSH]]
[[Kategorie:SSH]]
</noinclude>

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