Bug#828475: openssh: Please migrate to openssl1.1 in Buster

[Moritz Muehlenhoff <jmm@debian.org>]

Hi,
we've discussed the topic of handling this particular bug at the Debian Security
Team sprint and discussing the various non-optimal solutions we feel embedding
libressl into the openssh package is the last disagreeable solution.

- We clearly need openssh in buster
- We clearly don't want OpenSSL 1.0.2 in buster
- It seems very unlikely that openssh will support the OpenSSL 1.1 APIs in
  the short term
- Using the compat patch seems risky
- OpenSSH only uses libcrypto, which is less exposed to high impact
  vulnerabilities compared to libssl. We can triage new openssl/libressl
  vulnerabilities to the extent they affect openssh in our current security
  triage workflows.

This is clearly not ideal, but we can revisit that for every release.
Who knows what happens until then, maybe enterprise distros fork by
openssh by then. Or maybe ongoing code changes in openssh reduce the
set of the compat shim to an extent which makes it sensible to revisit
the whole situation.

I've had a quick look at all openssl CVE IDs from 2017 affecting libcrypto
and I don't think any of the four (the others affects libssl only) would
be something we would have backported to a stable release (two of them
are likely not present in libressl anyway and probably specific to OpenSSL).

Cheers,
        Moritz