topic kurze Beschreibung

Beschreibung

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 (/etc/ssh/ssh_host_*key)
• Client keys (~/.ssh/id_{rsa,dsa,ecdsa,ed25519} and ~/.ssh/identity).

Ciphers and algorithms choice

• When CHACHA20 (OpenSSH 6.5+) is not available, AES-GCM (OpenSSH 6.1+) and any other algorithm using EtM (Encrypt then MAC) disclose the packet length - giving some information to the attacker.
• Only recent OpenSSH servers and client support CHACHA20.

• NIST curves (ecdh-sha2-nistp512,ecdh-sha2-nistp384,ecdh-sha2-nistp256) are listed for compatibility, but the use of curve25519 is generally preferred.

• SSH protocol 2 supports DH and ECDH key-exchange as well as forward secrecy.
• Regarding group sizes, please refer to 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

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

Installation

Anwendungen

Fehlerbehebung

Syntax

Optionen

Parameter

Umgebungsvariablen

Exit-Status

Konfiguration

Dateien

Sicherheit

Dokumentation

RFC

Man-Pages

Info-Pages

Siehe auch

Links

Projekt-Homepage

Weblinks

• Key Management
• Server Side TLS
• RFC4418 (umac)
• umac draft
• Safe curves
• DJM blog
• Stribika blog
• AES-GCM performance study
• CHACHA20 vs AES-GCM performance study
• PROTOCOL.certkeys
• rfc44880bis from GnuPG
• Weak Diffie-Hellman and the Logjam Attack
• On OpenSSH and Logjam, by Jethro Beekman

Einzelnachweise

Testfragen

TMP