Subject: Bug#1202: [X2Go-Dev] kex error : no match for method mac algo client->server: server [hmac-sha2-256, hmac-sha2-512], client [hmac-sha1]

From: Mihai Moldovan <[email-masked]>
Date: Fri, 1 Sep 2017 08:56:00 +0200

Adding back the X2Go bugtracker, since this is valuable information for anyone
that might hit this issue.

On 09/01/2017 08:15 AM, J. M. van Bilsen wrote:
> that would be sufficient to tackle the problem. You are right I have to
> check if the package came from the mint or youre dist. Don worry I will
> be testing both but not this week. 
> 
> The reason I am looking for x2go is that we do not want to use other
> methods of remote connect. 

I'm happy to hear this. :)

I still don't feel good just closing bug reports without any work carried out.

More information: Linux Mint 18.1 seems to be based upon Ubuntu 16.04, and this
edition has x2goclient 4.0.5.1-1 available (exactly), so this seems to be a hit.
You're using very likely this version. So, now that we have this, I'm pretty
sure you're also on libssh 0.6.3-4.3, which is naturally based upon libssh 0.6.3.

The corresponding commit that introduced the SHA2-based MAC algorithms was
262c82ac0661bb0be46477006ed366e401c1620f (in libssh's source code repository.)

This commit first made it into libssh 0.7.0. Older libssh versions do not
include it and thus do not support SHA2-based MAC algorithms.

Given that Ubuntu 16.04 only ships libssh 0.6.3, that explains your trouble.

You basically have two options: either report this to Linux Mint and hope they
will update the update the libssh package for you and rebuild every package that
depends on it (including x2goclient), or build your own versions.

The first one is not likely to be successful, though I do not know Mint's update
philosophy. Debian and Ubuntu typically don't do such huge upgrades within a
released version line. If necessary, changes are backported to the older version
- but for libssh that might turn out to be quite complicated and not worth the
effort. Mint might be different, so it might be worth a shot to try.

The second one requires quite a lot of effort on your side, including staying up
to date and deploying self-modified packages.

Mihai