Re: [openpgp] AEAD Chunk Size

"Neal H. Walfield" <neal@walfield.org> Tue, 19 March 2019 08:32 UTC

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Date: Tue, 19 Mar 2019 09:32:04 +0100
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From: "Neal H. Walfield" <neal@walfield.org>
To: Bill Frantz <frantz@pwpconsult.com>, openpgp@ietf.org
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Subject: Re: [openpgp] AEAD Chunk Size
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On Tue, 19 Mar 2019 08:30:22 +0100,
Werner Koch wrote:
> On Mon, 18 Mar 2019 14:11, frantz@pwpconsult.com said:
> 
> > To protect against truncation attacks you can borrow an idea from the
> > database people and not commit your changes until you have a complete
> > message.
> 
> Right.  And you need to do that anyway because authenticated encryption
> doesn't tell you anything about the origin of the message and thus you
> need to check the signature of the message after it has been completely
> decrypted (at least with OpenPGP and CMS).  Anyone can send malicious
> content and AE doesn't protect against processsing such content.

I agree with you that AEAD + signed chunks is even better.  But,
streaming AEAD still provides a significant improvement relative to
the status quo: it protects against EFAIL-style exfiltration attacks.