Subject: [quicwg/base-drafts] Robert Wilton's HTTP/3 Comment 4 (#4807)

From: Lucas Pardue <[email-masked]>
Date: Thu, 21 Jan 2021 06:35:18 -0800

@rgwilton said

> 10.6.  Use of Compression
>
> >   Implementations communicating on a secure channel MUST NOT compress
> >   content that includes both confidential and attacker-controlled data
> >   unless separate compression contexts are used for each source of
> >   data.  Compression MUST NOT be used if the source of data cannot be
> >   reliably determined.
>
> This wasn't entirely clear to me.  I presume (perhaps wrongly) that the issue
> is about the use of compression before the confidential data has been
> encrypted.  I.e., I would presume that compressing a stream of data that
> includes both encrypted and non encrypted data is okay?  Perhaps this could be
> clarified.

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From: Mike Bishop <[email-masked]>
Date: Thu, 21 Jan 2021 07:57:22 -0800

The issue is about guess-and-check attacks, mentioned in the previous paragraph.  If there's a mixture of confidential and attacker-controlled data in the same context, the attacker can guess a value and then see if the resulting compressed data is shorter because their guess was compressed against the confidential value.  The requirement is that data from different sources be maintained in separate contexts so the attacker can't check its guesses against the confidential value.

Encryption is relevant here only because the attacker can't simply observe the data stream to get the confidential information.

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From: Robert Wilton <[email-masked]>
Date: Thu, 21 Jan 2021 09:20:46 -0800

On reading it again, the existing text is probably clear enough, so you can close this issue.

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From: Lars Eggert <[email-masked]>
Date: Thu, 21 Jan 2021 11:08:14 -0800

Closed #4807.

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