Client fails kex after c38ea634893a1975dbbec798fb968c9488013f4a

[Neale Ferguson]

I have a Putty variant that works well with openSSH up until 7.4. After
git bisecting I found that after the application of
c38ea634893a1975dbbec798fb968c9488013f4a the client fails with host key
mismatch. The commit in question appears to remove vestiges of ssh-1
support but my client is using 2.0. I am trying to work out what in that
commit would lead to the symptoms. I have been through the patch and it
appears to be remove the ssh-1 option processing (-b etc.) but nothing
directly relating to key exchange processing.

I have verified that if I reverse the patch the client works and when I
put it back on it fails.

I assume it is a flow-on affect of something but I am struggling to
connect the dots. Any suggestions of what to look at?

The comment for this commit is:

Remove more SSH1 server code: * Drop sshd's -k option. *
    Retire configuration keywords that only apply to protocol 1, as well
as   the
    "protocol" keyword. * Remove some related vestiges of protocol 1
support.


Thanks, Neale