[Bug 1389167] Re: HostbasedAuthentication produces spurious warnings

[Owen Dunn]

Digging a bit further, I think this arises because ssh-keysign punts off
all its host key processing to openSSL, but openSSL does not support
ED25519 keys.

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https://bugs.launchpad.net/bugs/1389167

Title:
  HostbasedAuthentication produces spurious warnings

Status in “openssh” package in Ubuntu:
  New

Bug description:
  Ubuntu 14.04.1 LTS
  openssh-client 1:6.6p1-2ubuntu2

  We have HostbasedAuthentication set up in our environment so that
  users can ssh between equivalent hosts without a password.

  ssh_config contains (relevantly)

  HostbasedAuthentication yes
  PreferredAuthentications publickey,hostbased,password,keyboard-interactive
  EnableSSHKeysign yes

  sshd_config contains (relevantly)

  HostbasedAuthentication yes

  This works:

  ocelot:~$ ssh othermc
  othermc:~$

  However, ssh-ing as an alternative user produces additional warning
  messages before the expected password prompt:

  ocelot:~$ ssh otheruser at othermc
  no matching hostkey found
  ssh_keysign: no reply
  key_sign failed
  otheruser at othermc's password:

  If instead of relying on EnableSSHKeysign in ssh_config I make the ssh
  binary setuid:

  chmod u+s /usr/bin/ssh

  ...the extra warnings go away and I get what I expect:

  ocelot:~$ ssh otheruser at othermc
  otheruser at othermc's password:

  This makes me suspect that there may be a problem with ssh-keysign.

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