1 %%----------------------------------------------------------------------
3 \subsubsection{Tested with Version} OpenSSH 6.1
4 \subsubsection{Settings}
5 \paragraph*{sshd\_config}
6 \begin{lstlisting}[breaklines]
10 PermitEmptyPasswords no
13 HostKey /etc/ssh/ssh_host_rsa_key
14 Ciphers aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr
15 MACs 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{Additional settings}
28 The setting \texttt{ServerKeyBits 4096} has no effect until you re-generate new ssh host keys. There might be issues if you have users which rely on the fingerprint of the old ssh host key being stored in their clients' \texttt{.ssh/known\_hosts} file.
29 %\subsubsection{Justification for special settings (if needed)}
30 \subsubsection{References}
31 The openssh sshd\_config man page is the best reference: \url{http://www.openssh.org/cgi-bin/man.cgi?query=sshd_config}
32 \subsubsection{How to test}
33 Connect a client with verbose logging enabled to the SSH server \\
34 \begin{lstlisting}[breaklines]
35 $ ssh -vvv myserver.com
36 \end{lstlisting}and observe the key exchange in the output.
39 %%----------------------------------------------------------------------
40 \subsection{Cisco ASA}
41 \subsubsection{Tested with Version} 9.1(3)
42 \subsubsection{Settings}
43 \begin{lstlisting}[breaklines]
44 crypto key generate rsa modulus 2048
46 ssh key-exchange group dh-group14-sha1
50 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.
51 \subsubsection{References}
52 \url{http://www.cisco.com/en/US/docs/security/asa/asa91/configuration/general/admin\_management.html }
53 \subsubsection{How to test}
54 Connect a client with verbose logging enabled to the SSH server \\
55 \begin{lstlisting}[breaklines]
56 $ ssh -vvv myserver.com
57 \end{lstlisting}and observe the key exchange in the output.
60 %----------------------------------------------------------------------
61 \subsection{Cisco IOS}
62 \subsubsection{Tested with Version} 15.0, 15.1, 15.2
63 \subsubsection{Settings}
64 \begin{lstlisting}[breaklines]
65 crypto key generate rsa modulus 2048 label SSH-KEYS
66 ip ssh rsa keypair-name SSH-KEYS
68 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 \subsubsection{References}
73 \url{http://www.cisco.com/en/US/docs/ios/sec\_user\_services/configuration/guide/sec\_secure\_shell\_v2.html }
74 % add any further references or best practice documents here
75 \subsubsection{How to test}
76 Connect a client with verbose logging enabled to the SSH server \\
77 \begin{lstlisting}[breaklines]
78 $ ssh -vvv myserver.com
79 \end{lstlisting}and observe the key exchange in the output.