[Bug 1801762] Re: Dual-signed things should be easy to verify with one key

[TJ]

Julian - I hadn't realised there are two gpgv's!

Having found apt's own /usr/lib/methods/gpgv

I have been able to create a shell wrapper that can feed it the expected
request headers and parse the response headers to ensure a GPGVOutput:
GOODSIG ...

It's a proof of concept right now; if this approach is preferred then
I'll tidy it up and publish.

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https://bugs.launchpad.net/bugs/1801762

Title:
  Dual-signed things should be easy to verify with one key

Status in apt package in Ubuntu:
  New
Status in debmirror package in Ubuntu:
  New
Status in gnupg2 package in Ubuntu:
  New
Status in ubuntu-keyring package in Ubuntu:
  New
Status in ubuntu-release-upgrader package in Ubuntu:
  New

Bug description:
  As part of Ubuntu key rotation strategy, we rely on dual-signing
  (inline, or detached) such that validation with at least one key
  available in a keyring should be trusted, without using web-of-trust.

  However, it seems to be only correctly so far implemented by the apt's
  gpgv method.

  Ideally, we should ship an easy enough to use the helper that is `like
  gpgv` to use, and possibly reusing apt's gpgv code and/or exposing it
  via apt-key's verify.

  The problem seems to be that 1 good sig + 1 no public key available,
  results in gpgv exiting with 2, instead of 0 or 1.

  Ideally it should be easy enough to use gpgv/gpg to verify that at
  least one signature is good, and decrypt/extract signed contents only.

  More details and reproducers to follow.

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