[Bug 1961833] Re: openssh 8.8 breaks login to Canonical servers

[Dan Streetman]

For reference to anyone coming here with this problem, when connecting
to a remote sshd server you can find what host key algorithms the remote
host uses by using -vv and check the debug output; look first for the
*peer* server KEXINIT proposal (not the earlier *local client* KEXINIT
proposal):

debug2: peer server KEXINIT proposal

a line or two after that, you should see the list of host key algorithms
the remote host is offering; if it contains *only* ssh-rsa then this bug
is relevant.

debug2: host key algorithms: ssh-rsa

Note that by default many systems support multiple algorithms, e.g. you
may see:

debug2: host key algorithms: ssh-rsa,ssh-dss,ecdsa-sha2-nistp256,ssh-
ed25519

in this case, even though the remote host does offer ssh-rsa, it also
supports other algorithms that jammy does support.

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https://bugs.launchpad.net/bugs/1961833

Title:
  openssh 8.8 breaks login to Canonical servers

Status in openssh package in Ubuntu:
  Won't Fix

Bug description:
  With 8.7p1-4 connecting to wendigo

  debug1: Next authentication method: publickey
  debug1: Offering public key: /home/jak/.ssh/id_rsa RSA SHA256:Dj1/l9g5RH00/wO7puC1WVxgpvmhmaQg3wEETwmOFPk agent
  debug1: Server accepts key: /home/jak/.ssh/id_rsa RSA SHA256:Dj1/l9g5RH00/wO7puC1WVxgpvmhmaQg3wEETwmOFPk agent

  With 8.8p1-1

  debug1: Offering public key: /home/jak/.ssh/id_rsa RSA SHA256:Dj1/l9g5RH00/wO7puC1WVxgpvmhmaQg3wEETwmOFPk agent                                                                                                                                                                             
  debug1: send_pubkey_test: no mutual signature algorithm   

  
  Needs further investigation, but blocks people a bit right now

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