On 10/18/2016 03:28 PM, Clint Dilks wrote:
So first
question is are people generally modifying the list of ciphers supported by
the ssh client and sshd?


I suspect that "generally" people are not. I do, because I can, and so that I can offer at least some advice to people who aim to do so.

On CentOS 6 currently it looks like if I remove all the ciphers they are
concerned about then I am left with Ciphers
aes128-ctr,aes192-ctr,aes256-ctr for both /etc/ssh/sshd_config and
/etc/ssh/ssh_config.

If you're going to go down this road, you should probably look at key exchanges and HMACs as well. On CentOS 7, I use:

KexAlgorithms curve25519-sha...@libssh.org,ecdh-sha2-nistp521,ecdh-sha2-nistp384,ecdh-sha2-nistp256,diffie-hellman-group-exchange-sha256 Ciphers chacha20-poly1...@openssh.com,aes256-...@openssh.com,aes128-...@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr MACs hmac-sha2-512-...@openssh.com,hmac-sha2-256-...@openssh.com,umac-128-...@openssh.com,hmac-sha2-512,hmac-sha2-256,umac-...@openssh.com

On CentOS 6, I believe you'd have to drop all of the @openssh.com items.

Is just using these three ciphers like to cause me
any problems?  Could having so few ciphers be creating a security concern
itself?

I don't think it'd be a security concern, just compatibility issues. So far, I've had minimal problems with restricted algorithms. I do have to make an exception for a slightly old WD MyBook World edition.

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