Re: [PATCH 5/7] Add support for gnupg < 1.4

[Junio C Hamano <gitster@pobox.com>]

Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:

> On Wed, Apr 5, 2017 at 3:04 PM, Tom G. Christensen <tgc@jupiterrise.com> wrote:
>> This adds an OLD_GNUPG define to the Makefile which when activated will
>> ensure git does not use the --keyid-format argument when calling the
>> 'gpg' program.
>> This is consistent with how 'gpg' was used in git < 2.10.0 and slightly
>> decreases security.
>
> This changes the code Linus Torvalds added in b624a3e67f to mitigate
> the evil32 project generating keys which looked the same for 32 bit
> signatures.
>
> I think this change makes sense, but the Makefile should have a
> slightly scarier warning, something like:
>
> "Define OLD_GNUPG if you need support for gnupg <1.4. Note that this
> will cause git to only show the first 32 bits of PGP keys instead of
> 64, and there's a wide variety of brute-forced 32 bit keys in the wild
> thanks to the evil32 project (https://evil32.com). Enabling this will
> make GPG work old versions, but you might be fooled into accepting
> malicious keys as a result".

Very good point.  It surprised me somewhat to see that this is the
only change necessary (iow, there is no need to tweak anything in t/
directory).  Perhaps we would need a test or two (and need to figure
out a way to make them work with both old and more recent GnuPG)?