Re: [openpgp] AEAD Chunk Size

"Neal H. Walfield" <neal@walfield.org> Thu, 28 February 2019 08:42 UTC

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Date: Thu, 28 Feb 2019 09:42:34 +0100
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From: "Neal H. Walfield" <neal@walfield.org>
To: Bart Butler <bartbutler@protonmail.com>
Cc: Vincent Breitmoser <look@my.amazin.horse>, "openpgp@ietf.org" <openpgp@ietf.org>
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Subject: Re: [openpgp] AEAD Chunk Size
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On Wed, 27 Feb 2019 22:34:09 +0100,
Bart Butler wrote:
> So ideally we’d prefer to keep the size byte, but to shrink its
> range in both directions. For example, the RFC could state that the
> chunk SHOULD be 16 kiB (or 256 kiB, hint hint), but decryption MUST
> be available for `c` values between 8-12 inclusive. This would also
> allow us to be backwards-compatible with messages that have already
> been created following the current version of the draft, which do
> exist given the benefit that AEAD provides and that OpenPGP.js has
> supported the current draft in experimental mode for most of the
> last year.

Could you please comment on the approximate number of messages that
have been sent with AEAD?  Is protonmail doing AEAD exclusively these
days?

As a compromise, I'd be willing to leave the byte, but have it be a
magic value whose value must be X (where X is say, 8 or 12).  Then you
can detect X=12 and not error out for your users.  But, I'm not yet
convinced that a range is a good idea.