Comment 2 for bug 1310781

I've just come across a knock on effect of this bug when configuring the Ubuntu SSH server for <email address hidden> key exchange only, and using the latest Debian package openssh-client to connect.

Because Ubuntu's SSH server version doesnt match 6.6.1, the Debian SSH client disables <email address hidden> completely, getting rid of the (presumably) most secure algorithm available:

==========================================================================

debug1: Local version string SSH-2.0-OpenSSH_6.6.1p1 Debian-4
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.6p1 Ubuntu-2ubuntu1
debug1: match: OpenSSH_6.6p1 Ubuntu-2ubuntu1 pat OpenSSH_6.5*,OpenSSH_6.6* compat 0x14000000
...
debug2: compat_kex_proposal: original KEX proposal: <email address hidden>
debug2: Compat: skipping algorithm "<email address hidden>"
debug2: compat_kex_proposal: compat KEX proposal:
No supported key exchange algorithms found

==========================================================================

The compat value being hit is in compat.c:100.