Re: [openpgp] AEAD Chunk Size

Peter Gutmann <> Sun, 31 March 2019 02:58 UTC

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From: Peter Gutmann <>
To: Jon Callas <>, "Neal H. Walfield" <>
CC: "" <>, Justus Winter <>, Jon Callas <>
Thread-Topic: [openpgp] AEAD Chunk Size
Date: Sun, 31 Mar 2019 02:58:44 +0000
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Subject: Re: [openpgp] AEAD Chunk Size
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Jon Callas <> writes:

>I think that if Peter wanted to remove AEAD, he’d just say that.

I'm not saying remove it, just get some data to support making a decision in
some way.  In particular, AEAD is a good thing, but there's no evidence that
chunking with AEAD, which complicates things greatly, is useful or necessary.

Here's three actual real-world data points: 

For the last twenty-eight years, PGP has had functionality equivalent to AEAD
in the form of encrypt+sign.  The only mechanism this supported was chunk-
size = data-size, and in twenty-eight years this never seems to have
caused/been seen as a problem. 

If you don't think encrypt+sign is equivalent functionality then we've also
had pseudo-AEAD in the form of MDC for eighteen years (draft-ietf-openpgp-
rfc2440bis-02) and chunking wasn't an issue then either.

Finally, CMS has had this for more than a decade (Authenticated-Enveloped-
Data) and it's not been a problem there either.

Why is it suddenly a big deal now, and only with OpenPGP, after twenty-eight
or eighteen years (depending on which one you choose) of equivalent mechanisms
not being a problem?  Is this because it really is, or just because AEAD can
do all sorts of cool things and people want to play with them?