Ah, OK. In my testing, I had this in my server's /etc/ssh/sshd_config file to force

use of ECDSA keys during my testing:

# HostKey for protocol version 1
#HostKey /etc/ssh/ssh_host_key
# HostKeys for protocol version 2
#HostKey /etc/ssh/ssh_host_rsa_key
#HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
HostKey /etc/ssh/ssh_host_ed25519_key

If I then logged into the server with:

conch 192.168.1.2

, then having an ecdsa key in ~/.ssh/known_hosts

worked fine and I could log in. Before the latest patches, the ecdsa keys were not

being parsed properly and this never worked at all.

If I changed the config on the server to:

# HostKey for protocol version 1
#HostKey /etc/ssh/ssh_host_key
# HostKeys for protocol version 2
#HostKey /etc/ssh/ssh_host_rsa_key
#HostKey /etc/ssh/ssh_host_dsa_key
#HostKey /etc/ssh/ssh_host_ecdsa_key
#HostKey /etc/ssh/ssh_host_ed25519_key

I got a bad host key error with conch, same as if I tried to log into buildbot.twistedmatrix.com.

I put this:

import pudb; pudb.set_trace()

on this line inside _continue_KEX_ECDH_REPLY() :

https://github.com/twisted/twisted/blob/trunk/src/twisted/conch/ssh/transport.py#L1671

What I then found was that on this line:

hostkey, pubKey, signature, packet = getNS(packet, 3)

The host key is an RSA key. Then this line in the same function:

d = self.verifyHostKey(hostKey, fingerprint)

tries to compare the hostKey for 192.168.1.2 (which is RSA), against

the key in ~/.ssh/known_hosts which is ecdsa. It then fails and returns a bad host key error.

I also get this problem when trying to do conch buildbot.twistedmatrix.com

Craig

On Tue, Dec 20, 2016 at 5:13 PM, Glyph Lefkowitz <glyph@twistedmatrix.com> wrote:

Here's buildbot's key:

buildbot.twistedmatrix.com ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBBcw4pr6WdgDMw7PbkvsuEdCqKQTtpLYPGoe7qkuQucuexYBiCkO/BeoB0wANX2cVmxUP0llpYJQL4w3cAR0csA=

I think you should be able to validate that even if you can't auth :)

-g

On Dec 20, 2016, at 4:54 PM, Craig Rodrigues <rodrigc@crodrigues.org> wrote:

I'm not sure. I was able to use conch to log into a box where the ecdsa key looked like this in my ~/.ssh/known_hosts

192.168.1.2 ecdsa-sha2-nistp256 XXXXXXXXXX
--
Craig

On Tue, Dec 20, 2016 at 4:10 PM, Glyph Lefkowitz <glyph@twistedmatrix.com> wrote:
It works:

$ conch twistedmatrix.com echo hooray
hooray
$ conch --version
Twisted version: 16.6.0dev0
$

That's using an RSA host key though. It seems that the hosts I have using ECDSA keys (buildbot.twistedmatrix.com, for example) still don't work with conch. Is that expected at this point?

-glyph

On Dec 20, 2016, at 2:32 PM, Craig Rodrigues <rodrigc@crodrigues.org> wrote:

On Friday, December 2, 2016, Glyph Lefkowitz <glyph@twistedmatrix.com> wrote:
I think there might be a regression in 16.6.0.

For every version up to 16.6.0, I can do 'conch twistedmatrix.com' in a shell and it works fine.

I believe that I have fixed this in trunk.
Can you try this with conch in trunk?

This works for me in trunk:

1. Start with an empty ~/.ssh/known_hosts file , or one with an ecdsa key for myhost.com
2. ssh myhost.com
3. log out of myhost.com
3. see that ~/.ssh/known_hosts contains an ecdsa host key for myhost.com
4. conch myhost.com
5. successfully log into myhost.com with conch

Before the latest fixes, I would get a bad host key error in step 5.

Many thanks to the0id and acabhishek942 for providing the ecdsa fixes to conch.

--
Craig

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