1 %%----------------------------------------------------------------------
3 \subsubsection{Tested with Version} OpenSSH 6.4
4 \subsubsection{Settings}
5 \paragraph*{sshd\_config}
6 \begin{lstlisting}[breaklines]
10 PermitEmptyPasswords no
11 PermitRootLogin no # or 'without-password' to allow SSH key based login
13 HostKey /etc/ssh/ssh_host_rsa_key
14 Ciphers aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr
15 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
16 KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group-exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1
19 \textbf{Note:} Older Linux systems won't support SHA2. PuTTY (Windows) does not support
20 RIPE-MD160. Curve25519, AES-GCM and UMAC are only available upstream (OpenSSH
21 6.1). DSA host keys have been removed on purpose, the DSS standard does not
22 support for DSA keys stronger than 1024bit
23 \footnote{\url{https://bugzilla.mindrot.org/show_bug.cgi?id=1647}} which is far
24 below current standards (see section \ref{section:keylengths}). Legacy systems
25 can use this configuration and simply omit unsupported ciphers, key exchange
27 %\subsubsection{Justification for special settings (if needed)}
28 \subsubsection{References}
29 The openssh sshd\_config man page is the best reference: \url{http://www.openssh.org/cgi-bin/man.cgi?query=sshd_config}
30 \subsubsection{How to test}
31 Connect a client with verbose logging enabled to the SSH server \\
32 \begin{lstlisting}[breaklines]
33 $ ssh -vvv myserver.com
34 \end{lstlisting}and observe the key exchange in the output.
37 %%----------------------------------------------------------------------
38 \subsection{Cisco ASA}
39 \subsubsection{Tested with Version} 9.1(3)
40 \subsubsection{Settings}
41 \begin{lstlisting}[breaklines]
42 crypto key generate rsa modulus 2048
44 ssh key-exchange group dh-group14-sha1
46 Note: When the ASA is configured for SSH, by default both SSH versions 1 and 2 are allowed. In addition to that, only a group1 DH-key-exchange is used. This should be changed to allow only SSH version 2 and to use a key-exchange with group14. The generated RSA key should be 2048 bit (the actual supported maximum). A non-cryptographic best practice is to reconfigure the lines to only allow SSH-logins.
47 \subsubsection{References}
48 \url{http://www.cisco.com/en/US/docs/security/asa/asa91/configuration/general/admin\_management.html }
49 \subsubsection{How to test}
50 Connect a client with verbose logging enabled to the SSH server \\
51 \begin{lstlisting}[breaklines]
52 $ ssh -vvv myserver.com
53 \end{lstlisting}and observe the key exchange in the output.
56 %----------------------------------------------------------------------
57 \subsection{Cisco IOS}
58 \subsubsection{Tested with Version} 15.0, 15.1, 15.2
59 \subsubsection{Settings}
60 \begin{lstlisting}[breaklines]
61 crypto key generate rsa modulus 4096 label SSH-KEYS
62 ip ssh rsa keypair-name SSH-KEYS
64 ip ssh dh min size 2048
70 Note: 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.
71 In IOS, a dedicated Key-pair can be bound to SSH to reduce the usage of individual keys-pairs.
72 From IOS Version 15.0 onwards, 4096 Bit rsa keys are supported and should be used according to the paradigm "use longest supported key". Also, do not forget to disable telnet vty access.
73 \subsubsection{References}
74 \url{http://www.cisco.com/en/US/docs/ios/sec\_user\_services/configuration/guide/sec\_cfg\_secure\_shell.html }
75 % add any further references or best practice documents here
76 \subsubsection{How to test}
77 Connect a client with verbose logging enabled to the SSH server \\
78 \begin{lstlisting}[breaklines]
79 $ ssh -vvv myserver.com
80 \end{lstlisting}and observe the key exchange in the output.