Re: [openpgp] Deprecating SHA1

Phil Pennock <ietf-phil-openpgp@spodhuis.org> Fri, 23 October 2020 19:23 UTC

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Date: Fri, 23 Oct 2020 15:23:17 -0400
From: Phil Pennock <ietf-phil-openpgp@spodhuis.org>
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Subject: Re: [openpgp] Deprecating SHA1
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On 2020-10-23 at 14:51 +0200, Neal H. Walfield wrote:
>   - Does anyone see a safe way to accept SHA1 self-signatures today?
>     Or (ouch!), if we want to be safe, do we have to convince ~10% of
>     the sophisticated OpenPGP users to re-sign or regenerate their
>     keys?

At the start of this year, I reached out individually to maintainers
signing releases of some security critical software and had good luck
getting them to re-sign, by including instructions on how to do so.

I never got around to producing a blog-post, but the messaging worked,
everyone I reached out to followed through and fixed.  It's a small
sample set of about 5, and population biased towards caring about
security.  So while I wouldn't extrapolate to "everyone will do it", I
think with pressure "many people will".

The TLDR for folks using the widespread GnuPG software is that GnuPG
defaults to protecting you against a new self-sig, but expert-mode makes
it easy:

    gpg --expert --cert-digest-algo SHA256 --sign-key $YourKeyId

Crafted messages around that worked.  "Hey, it's one line and then
uploading your keys" -- I think getting 80% of that 10% is probably
fairly doable.  That then leaves 2% of total users with broken keys,
which is a more viable cut-off.

If services such as keys.openpgp.org started showing big scary red
warnings above keys which lack a sane self-sig, or warning on upload,
we'd get some pressure that way.

-Phil