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I got 2 Ubuntu machines, a new A and old B. The ssh configuration files are identical, but versions are different, as expected:

→ ssh -v localhost

A:

OpenSSH_8.9p1 Ubuntu-3, OpenSSL 3.0.2 15 Mar 2022

B:

OpenSSH_8.2p1 Ubuntu-4ubuntu0.5, OpenSSL **1.1.1f**  31 Mar 2020

And there's a third machine, C, an old server, which exhibits a behavior which I did not expect - the old machine B can establish a publickey ssh connection to it, while the new A can not (both A's and B's public keys are in authorized_keys for the user):

debug1: send_pubkey_test: no mutual signature algorithm
debug2: we did not send a packet, disable method
debug1: Next authentication method: password

Not really knowing if it will help, I went and installed a new version of openssl from source to C:

# openssl version
OpenSSL 1.1.1q  5 Jul 2022

, but that didn't change anything I did notice an extra line in the C's ssh config though:

GSSAPIDelegateCredentials no

but I doubt it has anything to do with the problem I experience..

What am I doing wrong?

Thank you all for your time!

alexakarpov
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  • Here is the issue: "no mutual signature algorithm" – Romeo Ninov Sep 06 '22 at 19:19
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    @RomeoNinov is correct about the relevant error message; search for it and you will probably find a solution. But also, why are you installing a new version of `openssl` when the problem is with `openssh`? – larsks Sep 06 '22 at 23:03
  • Good point @larsks; I guess I saw both mentioned in version info line and got confused – alexakarpov Sep 07 '22 at 00:15
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    Are you using RSA key(s) i.e. ~/.ssh/id_rsa? OpenSSH 8.8 up disables by default old/weak ssh-rsa signature algorithm, but if 'old C' is below 7.2 it supports only ssh-rsa not better rsa-sha2-*. See https://serverfault.com/questions/1092998/ssh-no-matching-host-key-type-found . **Try `-oPubKeyAcceptedAlgorithms=+ssh-rsa`**. – dave_thompson_085 Sep 07 '22 at 02:48

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