[Bug 1771359] Re: No matching cipher found even if client and server have matching cipher

[Joshua Powers]

Here are some change log entries confirming my suspicion:

openssh (1:7.4p1-1) unstable; urgency=medium

  * New upstream release (http://www.openssh.com/txt/release-7.4):
    - ssh(1): Remove 3des-cbc from the client's default proposal.  64-bit
      block ciphers are not safe in 2016 and we don't want to wait until
      attacks like SWEET32 are extended to SSH.  As 3des-cbc was the only
      mandatory cipher in the SSH RFCs, this may cause problems connecting
      to older devices using the default configuration, but it's highly
      likely that such devices already need explicit configuration for key
      exchange and hostkey algorithms already anyway.

openssh (1:7.3p1-1) unstable; urgency=medium

  * New upstream release (http://www.openssh.com/txt/release-7.3):
    - SECURITY: ssh(1), sshd(8): Fix observable timing weakness in the CBC
      padding oracle countermeasures.  Note that CBC ciphers are disabled by
      default and only included for legacy compatibility.

-- 
You received this bug notification because you are a member of Ubuntu
Foundations Bugs, which is subscribed to openssh in Ubuntu.
https://bugs.launchpad.net/bugs/1771359

Title:
  No matching cipher found even if client and server have matching
  cipher

Status in openssh package in Ubuntu:
  Incomplete

Bug description:
  Since Bionic upgrade (from Artful) I encounter problem to call HP
  switch with SSH.

  After the upgrade, trying to ssh some switch give me this message :

  $ ssh 192.168.0.1
  Unable to negotiate with 192.168.0.1 port 22: no matching cipher found. Their offer: aes128-cbc,3des-cbc,des-cbc

  So, I look for supported cipher :

  $ ssh -Q cipher
  3des-cbc
  aes128-cbc
  aes192-cbc
  aes256-cbc
  rijndael-cbc at lysator.liu.se
  aes128-ctr
  aes192-ctr
  aes256-ctr
  aes128-gcm at openssh.com
  aes256-gcm at openssh.com
  chacha20-poly1305 at openssh.com

  I see that aes128-cbc seem both supported. So I try... :

  $ ssh -c aes128-cbc 192.168.0.1

  ...and It's work !

  Workaround :

  I've added “ciphers aes128-cbc” to ~/.ssh/config file for each switch
  I manage.

  The ssh-client should detect automatically the good cipher ? No ?

  Thank you for your attention.

  ProblemType: Bug
  DistroRelease: Ubuntu 18.04
  Package: openssh-client 1:7.6p1-4
  ProcVersionSignature: Ubuntu 4.15.0-20.21-generic 4.15.17
  Uname: Linux 4.15.0-20-generic x86_64
  ApportVersion: 2.20.9-0ubuntu7
  Architecture: amd64
  CurrentDesktop: GNOME
  Date: Tue May 15 15:39:00 2018
  EcryptfsInUse: Yes
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=fr_FR.UTF-8
   SHELL=/bin/bash
  RelatedPackageVersions:
   ssh-askpass       N/A
   libpam-ssh        N/A
   keychain          N/A
   ssh-askpass-gnome 1:7.6p1-4
  SSHClientVersion: OpenSSH_7.6p1 Ubuntu-4, OpenSSL 1.0.2n  7 Dec 2017
  SourcePackage: openssh
  UpgradeStatus: Upgraded to bionic on 2018-04-24 (21 days ago)

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/openssh/+bug/1771359/+subscriptions