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Re: [openpgp] AEAD Chunk Size

Derek Atkins <derek@ihtfp.com> Wed, 27 March 2019 15:50 UTC

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From: Derek Atkins <derek@ihtfp.com>
To: Tobias Mueller <muelli@cryptobitch.de>
Cc: "Neal H. Walfield" <neal@walfield.org>, Werner Koch <wk@gnupg.org>, openpgp@ietf.org, Vincent Breitmoser <look@my.amazin.horse>
References: <87d0n174w6.fsf@wheatstone.g10code.de> <87mumh33nc.wl-neal@walfield.org> <3GFS71V7BTJNZ.29C5TO8OY0O44@my.amazin.horse> <sjmy35isypu.fsf@securerf.ihtfp.org> <87r2bax5u2.wl-neal@walfield.org> <sjmlg1hskdq.fsf@securerf.ihtfp.org> <87pnqtwot9.wl-neal@walfield.org> <0f7f492bf18145f96e70886ba19ba290.squirrel@mail2.ihtfp.org> <87lg1gwelf.wl-neal@walfield.org> <61e3fb9d194d0b47f21be8e176daa0b9b6c5d0a5.camel@cryptobitch.de> <87sgvkihd1.wl-neal@walfield.org> <241225ce914a1843b48dab304c760151fe05b764.camel@cryptobitch.de> <87imwfj3oq.wl-neal@walfield.org> <65e588255c689d329546c3908dac112896d029ca.camel@cryptobitch.de>
Date: Wed, 27 Mar 2019 11:50:32 -0400
In-Reply-To: <65e588255c689d329546c3908dac112896d029ca.camel@cryptobitch.de> (Tobias Mueller's message of "Tue, 26 Mar 2019 18:45:09 +0100")
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Subject: Re: [openpgp] AEAD Chunk Size
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Tobias Mueller <muelli@cryptobitch.de> writes:

[snip]
> Note that there is *a single output* rather than multiple and that it
> doesn't allow for releasing partial plaintexts or authenticated
> prefixes.
> Do you see that any chunking protocol on top of that which is allowed
> for releasing plaintext early is not immediately covered by this
> definition?

In my mind, each chunk is its own AEAD ciphertext.  So the chunking is
happening *during* AEAD encryption, and not after encryption.  I.e., the
chunking and AEAD encryption should be tied together such that the chunk
header is part of the AEAD protection and the chunk data is the AEAD
encrypted data.

This approach does, IMHO, map directly into the RFC definition.

-derek

-- 
       Derek Atkins                 617-623-3745
       derek@ihtfp.com             www.ihtfp.com
       Computer and Internet Security Consultant

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