SSH/Kryptografie/Konfiguration

/etc/ssh/sshd_config

 # 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 supports Curve25519

Tested Version

OpenSSH 6.5 (Debian Jessie)

Kompatibilität

• 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

• Cisco SSH is a basic SSH reference for all routers and switches
• 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 myserver.com

and observe the key exchange in the output.