bad bignum encoding for curve25519-sha256 at libssh.org

openssh (1:6.6p1-4) unstable; urgency=medium

  * Debconf translations:
    - Spanish (thanks, Matías Bellone; closes: #744867).
  * Apply upstream-recommended patch to fix bignum encoding for
    <email address hidden>, fixing occasional key exchange failures.

 -- Colin Watson <email address hidden> Mon, 21 Apr 2014 21:29:53 +0100

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.

Hello Colin, or anyone else affected,

Accepted openssh into trusty-proposed. The package will build now and be available at http://launchpad.net/ubuntu/+source/openssh/1:6.6p1-2ubuntu2 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, and change the tag from verification-needed to verification-done. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed. In either case, details of your testing will help us make a better decision.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

Sorry for the delay - I have enabled proposed and can confirm forced <email address hidden> works now :)

This bug was fixed in the package openssh - 1:6.6p1-2ubuntu2

---------------
openssh (1:6.6p1-2ubuntu2) trusty; urgency=medium

  * Apply upstream-recommended patch to fix bignum encoding for
    <email address hidden>, fixing occasional key exchange failures
    (LP: #1310781).
  * Force ssh-agent Upstart job to use sh syntax regardless of the user's
    shell (thanks, Steffen Stempel; LP: #1312928).
 -- Colin Watson <email address hidden> Fri, 02 May 2014 09:42:23 +0100

The verification of the Stable Release Update for openssh has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regresssions.