Re: sshd key exchange security

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On 09/11/2015 08:44 AM, Chris Adams wrote:
Once upon a time, Alice Wonder <alice@xxxxxxxxxxxxxx> said:
They recommend setting the following:

KexAlgorithms curve25519-sha256@xxxxxxxxxx

I don't even see that directive in my sshd config to set it, I
suppose it may be one that is manually added when needed but I want
to verify it actually means something in CentOS 7 ssh.

Also I'm a little worried that maybe curve25519 is one of the curves
that Red Hat (and thus CentOS 7) doesn't support due to patent
concerns.

That is supported in the CentOS 7 version of OpenSSH.  Look at the man
page for sshd_config and you'll see the KexAlgorithms option listed and
its valid values.  You can always see what your exact copy and config of
OpenSSH are using by running "sshd -T".

However, if you set it as above, you would _only_ be able to connect
with that algorithm, and not all SSH clients support that (even for
example OpenSSH on CentOS 6).


Thanks - what I ended up doing is:

KexAlgorithms curve25519-sha256@xxxxxxxxxx,diffie-hellman-group-exchange-sha256

Then I generated fresh 2048 and 4096 primes for the moduli file.

So far it seems all the ssh clients I have tried work.
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