Re: [openpgp] v5 in the crypto-refresh draft

Daniel Kahn Gillmor <dkg@fifthhorseman.net> Sat, 05 June 2021 17:55 UTC

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From: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
To: Peter Gutmann <pgut001@cs.auckland.ac.nz>, "openpgp@ietf.org" <openpgp@ietf.org>
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Date: Sat, 05 Jun 2021 13:37:10 -0400
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Subject: Re: [openpgp] v5 in the crypto-refresh draft
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On Sat 2021-06-05 12:22:38 +0000, Peter Gutmann wrote:
> Daniel Kahn Gillmor <dkg@fifthhorseman.net> writes:
>
>>Specific v5 changes
>
> Another thing I'd like to see changed in v5 is the incredibly annoying way
> OpenPGP handles its PRF.  For every PRF use on the planet except OpenPGP, you
> specify the number of iterations of the PRF to be applied.  For OpenPGP you
> specify the number of bytes to output and then have to work backwards through
> the PRF to figure out how many iterations this amounts to.  Making things even
> worse, the count is encoded in a weirdo fixed-point format that can't be
> passed as an integer count parameter to anything because it's not, or
> alternatively that if passed as an integer has to then be converted back into
> its oddball fixed-point format when written.  So:
>
>   Replace the S2K 'count' value with a 32-bit integer specifying the number of
>   PRF iterations to apply.

I don't think the S2K updates for v5 have made it into the
crypto-refresh draft yet.  So i appreciate this comment but i hope we
can delay it until we address new forms of S2K (see e.g. commit
6337518cd35ee416129959982a10df85548b2117 in the step-by-step branch,
which is not yet merged).

    --dkg