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Re: [TLS] TLS 1.3 - Support for compression to be removed

Tony Arcieri <bascule@gmail.com> Sun, 04 October 2015 18:10 UTC

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From: Tony Arcieri <bascule@gmail.com>
Date: Sun, 04 Oct 2015 11:09:49 -0700
Message-ID: <CAHOTMVL4A2AqfByfo-er_qZ6rgyVWWM_mBXeT9Wgd1Rk1cuMgw@mail.gmail.com>
To: Jeffrey Walton <noloader@gmail.com>
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Subject: Re: [TLS] TLS 1.3 - Support for compression to be removed
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On Sun, Oct 4, 2015 at 10:58 AM, Jeffrey Walton <noloader@gmail.com> wrote:

> > The takeaway for me is you can't mix compression, any fixed value an
> > attacker wishes to learn, and attacker-controlled data, or there will be
> a
> > compression side-channel.
>
> Is that necessarily true?
>
> Deflate violates semantic security by allowing the attacker to gain
> information across messages (even though any single message is
> secure). So perhaps its the mode of compression ot the way compression
> was implemented, and not compression itself.


The only property of compression that this class of side-channel attack
relies on is that the compression algorithm produces a smaller output for
message a || a than a || b (where a and b are of identical length), so
really it would seem to be a conceptual problem with mixing compression and
encryption.

If someone has produced a secure system for "compression side-channel
resistant encryption", I haven't seen it.

-- 
Tony Arcieri

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