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