GPG: Deprecated hash + local "game over" exploit

Steve Kinney admin at
Sat Jul 1 13:17:29 PDT 2017


A couple of days ago Shawn pointed out offlist that my GPG installation
was using SHA1 when signing messages.  Although seven hash functions are
included in GnuPG 1.4.16, SHA1 is still the default.

For most purposes this is no cause for panic, but it's "untidy" at best
and might occasionally bite someone in the ass.

The simple cure is to append this to gpg.conf:

personal-digest-preferences SHA256 SHA512
digest-algo SHA256

I wonder when the gpg guise will get around to updating the default hash...

On a related note, gnupg-agent stores typed pass phrases for 10 minutes,
as a convenience when reading or signing multiple files or documents.
Only one little thing:  It stores typed pass phrases until the machine
is powered off, regardless of configuration settings per the gnupg-agent
man page.

Last time I checked, this bug was dismissed by Debian as a non-issue,
saying that exploiting it would require physical access to the machine
and "physical access is game over."  That's an excuse to leave the bug
in place, not a reason.  I am sure present company can provide several
examples of cases where the presence of gnupg-agent in its present
broken condition "is game over" for the user.

Four years ago I noticed this problem, exhausted "sane" remedies, and
found an effective work-around that denies gnupg-agent access to pass
phrases when using Enigmail or GPG itself.


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