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| Zeile 136: |
Zeile 136: |
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| = TMP = | | = TMP = |
| == SSH Server ==
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| ; SSH is used to
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| * remotely manage computer systems
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| * secururly transfer files over untrusted networks
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| * create "ad-hoc" virtual-private networks
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|
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| === OpenSSH ===
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| * [https://www.openssh.com/ OpenSSH] is the most popular implementation of the SSH protocol
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| * It is maintained by the [https://openbsd.org/ OpenBSD] project
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| * portable versions are disitributed with many unix-like operating-systems and Windows Server
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|
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| ; Tested versions
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| * OpenSSH 6.6p1 (Gentoo)
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| * OpenSSH 6.6p1-2 on Ubuntu 14.04.2 LTS
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| * OpenSSH 7.2p2 on Ubuntu 16.04.3 LTS
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|
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| ==== Settings ====
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| ; Important OpenSSH 6.6 security settings
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| # Package generated configuration file
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| # See the sshd_config(5) manpage for details
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| # What ports, IPs and protocols we listen for
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| Port 22
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| # Use these options to restrict which interfaces/protocols sshd will bind to
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| #ListenAddress ::
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| #ListenAddress 0.0.0.0
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| Protocol 2
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| # HostKeys for protocol version 2
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| HostKey /etc/ssh/ssh_host_rsa_key
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| #HostKey /etc/ssh/ssh_host_dsa_key
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| #HostKey /etc/ssh/ssh_host_ecdsa_key
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| HostKey /etc/ssh/ssh_host_ed25519_key
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| #Privilege Separation is turned on for security
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| UsePrivilegeSeparation yes
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| # Lifetime and size of ephemeral version 1 server key
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| KeyRegenerationInterval 3600
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| ServerKeyBits 1024
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| # Logging
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| SyslogFacility AUTH
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| LogLevel INFO
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| # Authentication:
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| LoginGraceTime 120
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| PermitRootLogin no # or 'without-password' to allow SSH key based login
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| StrictModes yes
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| RSAAuthentication yes
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| PubkeyAuthentication yes
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| #AuthorizedKeysFile %h/.ssh/authorized_keys
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| # Don't read the user's ~/.rhosts and ~/.shosts files
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| IgnoreRhosts yes
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| # For this to work you will also need host keys in /etc/ssh_known_hosts
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| RhostsRSAAuthentication no
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| # similar for protocol version 2
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| HostbasedAuthentication no
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| # Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
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| #IgnoreUserKnownHosts yes
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| # To enable empty passwords, change to yes (NOT RECOMMENDED)
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| PermitEmptyPasswords no
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| # Change to yes to enable challenge-response passwords (beware issues with
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| # some PAM modules and threads)
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| ChallengeResponseAuthentication no
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| # Change to no to disable tunnelled clear text passwords
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| #PasswordAuthentication yes
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| # Kerberos options
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| #KerberosAuthentication no
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| #KerberosGetAFSToken no
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| #KerberosOrLocalPasswd yes
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| #KerberosTicketCleanup yes
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| # GSSAPI options
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| #GSSAPIAuthentication no
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| #GSSAPICleanupCredentials yes
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| # Cipher selection
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| Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr
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| 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
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| KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1
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| X11Forwarding yes
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| X11DisplayOffset 10
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| PrintMotd no
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| PrintLastLog yes
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| TCPKeepAlive yes
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| #UseLogin no
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| #MaxStartups 10:30:60
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| #Banner /etc/issue.net
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| # Allow client to pass locale environment variables
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| AcceptEnv LANG LC_*
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| Subsystem sftp /usr/lib/openssh/sftp-server
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| # Set this to 'yes' to enable PAM authentication, account processing,
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| # and session processing. If this is enabled, PAM authentication will
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| # be allowed through the ChallengeResponseAuthentication and
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| # PasswordAuthentication. Depending on your PAM configuration,
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| # PAM authentication via ChallengeResponseAuthentication may bypass
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| # the setting of "PermitRootLogin without-password".
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| # If you just want the PAM account and session checks to run without
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| # PAM authentication, then enable this but set PasswordAuthentication
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| # and ChallengeResponseAuthentication to 'no'.
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| UsePAM yes
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|
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| ; Curve25519
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| : OpenSSH 6.6p1 supports Curve25519
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|
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| ; Tested Version
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| : OpenSSH 6.5 (Debian Jessie)
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|
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| ==== Settings ====
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| ; Important OpenSSH 6.5 security settings
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| # Package generated configuration file
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| # See the sshd_config(5) manpage for details
| |
| # What ports, IPs and protocols we listen for
| |
| Port 22
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| # Use these options to restrict which interfaces/protocols sshd will bind to
| |
| #ListenAddress ::
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| #ListenAddress 0.0.0.0
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| Protocol 2
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| # HostKeys for protocol version 2
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| HostKey /etc/ssh/ssh_host_rsa_key
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| #HostKey /etc/ssh/ssh_host_dsa_key
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| #HostKey /etc/ssh/ssh_host_ecdsa_key
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| HostKey /etc/ssh/ssh_host_ed25519_key
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| #Privilege Separation is turned on for security
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| UsePrivilegeSeparation yes
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| # Lifetime and size of ephemeral version 1 server key
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| KeyRegenerationInterval 3600
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| ServerKeyBits 1024
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| # Logging
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| SyslogFacility AUTH
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| LogLevel INFO
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| # Authentication:
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| LoginGraceTime 120
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| PermitRootLogin no # or 'without-password' to allow SSH key based login
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| StrictModes yes
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| RSAAuthentication yes
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| PubkeyAuthentication yes
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| #AuthorizedKeysFile %h/.ssh/authorized_keys
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| # Don't read the user's ~/.rhosts and ~/.shosts files
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| IgnoreRhosts yes
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| # For this to work you will also need host keys in /etc/ssh_known_hosts
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| RhostsRSAAuthentication no
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| # similar for protocol version 2
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| HostbasedAuthentication no
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| # Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
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| #IgnoreUserKnownHosts yes
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| # To enable empty passwords, change to yes (NOT RECOMMENDED)
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| PermitEmptyPasswords no
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| # Change to yes to enable challenge-response passwords (beware issues with
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| # some PAM modules and threads)
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| ChallengeResponseAuthentication no
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| # Change to no to disable tunnelled clear text passwords
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| #PasswordAuthentication yes
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| # Kerberos options
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| #KerberosAuthentication no
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| #KerberosGetAFSToken no
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| #KerberosOrLocalPasswd yes
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| #KerberosTicketCleanup yes
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| # GSSAPI options
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| #GSSAPIAuthentication no
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| #GSSAPICleanupCredentials yes
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| # Cipher selection
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| Ciphers aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr
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| 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
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| KexAlgorithms diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1
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| X11Forwarding yes
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| X11DisplayOffset 10
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| PrintMotd no
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| PrintLastLog yes
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| TCPKeepAlive yes
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| #UseLogin no
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| #MaxStartups 10:30:60
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| #Banner /etc/issue.net
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| # Allow client to pass locale environment variables
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| AcceptEnv LANG LC_*
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| Subsystem sftp /usr/lib/openssh/sftp-server
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| # 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
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| # and ChallengeResponseAuthentication to 'no'.
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| UsePAM yes
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|
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| ==== Tested with Version ====
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| * OpenSSH 6.0p1 (Debian wheezy)
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|
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| ==== Settings ====
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| ; Important OpenSSH 6.0 security settings
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| # Package generated configuration file
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| # 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
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| Protocol 2
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| # HostKeys for protocol version 2
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| HostKey /etc/ssh/ssh_host_rsa_key
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| #HostKey /etc/ssh/ssh_host_dsa_key
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| #HostKey /etc/ssh/ssh_host_ecdsa_key
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| #Privilege Separation is turned on for security
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| UsePrivilegeSeparation yes
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| # Lifetime and size of ephemeral version 1 server key
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| KeyRegenerationInterval 3600
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| ServerKeyBits 768
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| # Logging
| |
| SyslogFacility AUTH
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| LogLevel INFO
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| # Authentication:
| |
| LoginGraceTime 120
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| PermitRootLogin no # or 'without-password' to allow SSH key based login
| |
| StrictModes yes
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| RSAAuthentication yes
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| PubkeyAuthentication yes
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| #AuthorizedKeysFile %h/.ssh/authorized_keys
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| # 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
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| # similar for protocol version 2
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| HostbasedAuthentication no
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| # Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
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| #IgnoreUserKnownHosts yes
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| # 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)
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| ChallengeResponseAuthentication no
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| # Change to no to disable tunnelled clear text passwords
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| #PasswordAuthentication yes
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| # Kerberos options
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| #KerberosAuthentication no
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| #KerberosGetAFSToken no
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| #KerberosOrLocalPasswd yes
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| #KerberosTicketCleanup yes
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| # GSSAPI options
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| #GSSAPIAuthentication no
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| #GSSAPICleanupCredentials yes
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| # Cipher selection
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| Ciphers aes256-ctr,aes128-ctr
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| MACs hmac-sha2-512,hmac-sha2-256,hmac-ripemd160
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| KexAlgorithms diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1
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| X11Forwarding yes
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| X11DisplayOffset 10
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| PrintMotd no
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| PrintLastLog yes
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| TCPKeepAlive yes
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| #UseLogin no
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| #MaxStartups 10:30:60
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| #Banner /etc/issue.net
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| # Allow client to pass locale environment variables
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| AcceptEnv LANG LC_*
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| 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'.
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| UsePAM yes
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|
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| ==== Kompatibilität ====
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| * Older '''Linux''' systems won’t support SHA2
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| * PuTTY (Windows) does not support RIPE-MD160
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| * Curve25519, AES-GCM and UMAC are only available upstream (OpenSSH 6.6p1)
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| * DSA host keys have been removed on purpose, the DSS standard does not support for DSA keys stronger than 1024bit [[https://bettercrypto.org/#_footnotedef_5 5]] which is far below current standards (see section #section:keylengths)
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| * Legacy systems can use this configuration and simply omit unsupported ciphers, key exchange algorithms and MACs
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|
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| ==== References ====
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| * [https://www.cisco.com/c/en/us/support/docs/security-vpn/secure-shell-ssh/4145-ssh.html Cisco SSH] is a basic SSH reference for all routers and switches
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| * Refer to the specific documentation of the device and IOS version that you are configuring
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|
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| ==== How to test ====
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| Connect a client with verbose logging enabled to the SSH server
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| $ ssh -vvv myserver.com
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| and observe the key exchange in the output.
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|
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| === Cisco ASA ===
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|
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| ==== Tested with Versions ====
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| * 9.1(3)
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|
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| ==== Settings ====
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| * crypto key generate rsa modulus 2048
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| * ssh version 2
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| * ssh key-exchange group dh-group14-sha1
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|
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|
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| * When the ASA is configured for SSH, by default both SSH versions 1 and 2 are allowed.
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| * In addition to that, only a group1 DH-key-exchange is used.
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| * This should be changed to allow only SSH version 2 and to use a key-exchange with group14.
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| * The generated RSA key should be 2048 bit (the actual supported maximum).
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| * A non-cryptographic best practice is to reconfigure the lines to only allow SSH-logins.
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|
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| ==== References ====
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| # [https://www.cisco.com/en/US/docs/security/asa/asa91/configuration/general/admin_management.html CLI Book 1: Cisco ASA Series General Operations CLI Configuration Guide, 9.1]
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|
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| ==== How to test ====
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| Connect a client with verbose logging enabled to the SSH server
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| $ ssh -vvv myserver.com
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| and observe the key exchange in the output.
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|
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| === Cisco IOS ===
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| ==== Tested Versions ====
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|
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| {| class="wikitable sortable options" style="border-spacing:0;width:9.259cm;"
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| |-
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| || Program Version
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| || OS/Distribution/Version
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| || Comment
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| |-
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| || 15.0
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| || IOS
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| ||
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| |-
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| || 15.1
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| || IOS
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| ||
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| |-
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| || 15.2
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| || IOS
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| ||
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| |-
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| |}
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|
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| ==== Settings ====
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| crypto key generate rsa modulus 4096 label SSH-KEYS
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| ip ssh rsa keypair-name SSH-KEYS
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| ip ssh version 2
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| ip ssh dh min size 2048
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| line vty 0 15
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| transport input ssh
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|
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| * 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.
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| * In IOS, a dedicated Key-pair can be bound to SSH to reduce the usage of individual keys-pairs.
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| * From IOS Version 15.0 onwards, 4096 Bit rsa keys are supported and should be used according to the paradigm "use longest supported key".
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| * Also, do not forget to disable telnet vty access.
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|
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| ==== How to test ====
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| Connect a client with verbose logging enabled to the SSH server
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| $ ssh -vvv switch.example.net
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| and observe the key exchange in the output.
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|
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|
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| [[Kategorie:Kryptografie:Best Practice]] | | [[Kategorie:Kryptografie:Best Practice]] |
| [[Kategorie:SSH]] | | [[Kategorie:SSH]] |