[Bug 1668093] Re: ssh-keygen -H corrupts already hashed entries

[ChristianEhrhardt]

And the behavior is clearly against what the manpage says:
-H      Hash a known_hosts file.  This replaces all hostnames and addresses with hashed representations within the specified file; the original content is moved to a file with a .old suffix. These hashes may be used normally by ssh and sshd, but they do not reveal identifying information should the file's contents be disclosed.  This option will not modify existing hashed hostnames and is therefore safe to use on files that mix hashed and non-hashed names.

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Title:
  ssh-keygen -H corrupts already hashed entries

Status in openssh package in Ubuntu:
  Confirmed

Bug description:
  xenial @ 1:7.2p2-4ubuntu2.1 on amd64 has this bug. trusty @
  1:6.6p1-2ubuntu2.8 on amd64 does not have this bug. I have not tested
  any other ssh versions.

  The following should reproduce the issue:

  #ssh-keyscan XXXX > ~/.ssh/known_hosts
  # ssh root at XXXXX
  Permission denied (publickey).
  # ssh-keygen -H
  /root/.ssh/known_hosts updated.
  Original contents retained as /root/.ssh/known_hosts.old
  WARNING: /root/.ssh/known_hosts.old contains unhashed entries
  Delete this file to ensure privacy of hostnames
  # ssh root at XXXXXX
  Permission denied (publickey).
  # ssh-keygen -H
  /root/.ssh/known_hosts updated.
  Original contents retained as /root/.ssh/known_hosts.old
  WARNING: /root/.ssh/known_hosts.old contains unhashed entries
  Delete this file to ensure privacy of hostnames
  # ssh root at XXXXX
  The authenticity of host 'XXXXXX' can't be established.
  RSA key fingerprint is XXXXXX.
  Are you sure you want to continue connecting (yes/no)?

  # diff known_hosts.old known_hosts
  1c1
  < |1|BoAbRpUE3F5AzyprJcbjdepeDh8=|x/1AcaLxh45FlShmVQnlgx2qjxY= XXXXX
  ---
  > |1|nTPsoLxCugQyZi3pqOa2pc/cX64=|bUH5qwZlZPp8msMGHdLtslf3Huk= XXXXX

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