svn commit: r247485 - in stable/9: crypto/openssh crypto/openssh/openbsd-compat secure/lib/libssh secure/usr.sbin/sshd

[Ian Lepore]

On Sat, 2013-03-02 at 17:02 +0100, Dag-Erling Smørgrav wrote:
> Mike Tancsa <mike at sentex.net> writes:
> > The pcaps and basic wireshark output at
> >
> > http://tancsa.com/openssh/
> 
> This is 6.1 with aesni vs 6.1 without aesni; what I wanted was 6.1 vs
> 5.8, both with aesni loaded.
> 
> Could you also ktrace the server in both cases?
> 
> An easy workaround is to change the list of ciphers the server will
> offer to clients by adding a "Ciphers" line in /etc/ssh/sshd_config.
> The default is:
> 
> Ciphers aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour
> 
> Either remove the AES entries or move them further down the list.  The
> client will normally pick the first supported cipher.  As far as I can
> tell, SecureCRT supports all the same ciphers that OpenSSH does, so just
> moving arcfour{256,128} to the front of the list should work.
> 
> (AFAIK, arcfour is also much faster than aes)

The last time I tried to affect the chosen cypher by manipulating the
order of the list items in the config files was a couple years ago, but
I found then that you just can't do that.  The client side, not the
server, decides on the order, and it's based on compiled-in ordering
within the client code (not the client config).  From the server side
the only thing you can do to affect the order is leave items out of the
list (it will still try the remaining list items in the client-requested
order).

All of this was with "OpenSSH_5.4p1_hpn13v11 FreeBSD-20100308, OpenSSL
0.9.8q 2 Dec 2010" and may be completely out of date now.

-- Ian