Re: [TLS] Data volume limits

Watson Ladd <watsonbladd@gmail.com> Sat, 02 January 2016 01:20 UTC

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Date: Fri, 1 Jan 2016 20:20:42 -0500
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From: Watson Ladd <watsonbladd@gmail.com>
To: Brian Smith <brian@briansmith.org>
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Cc: Florian Weimer <fweimer@redhat.com>, "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] Data volume limits
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On Tue, Dec 29, 2015 at 2:10 PM, Brian Smith <brian@briansmith.org> wrote:
> Ilari Liusvaara <ilariliusvaara@welho.com> wrote:
>>
>> OTOH, you can't drop an attacker knowing older key without doing
>> new key exchange.
>
>
> I think it would be very unfortunate to have the complexity of key update
> (the new keys are derived from the old keys) without having the benefits of
> rekeying (the new keys are independent of the old keys).

What complexity? Sending a special packet with a different protocol
that triggers a change in record layer state is not that tricky, and
even DTLS is designed to handle this already. In fact one could even
use the epoch number implicitly.

What benefits? The concern isn't that an attacker obtains the key, but
that confidentiality is lost. If we're worried about attackers who can
read memory the answer is clear: write in a language that doesn't
permit this.
>
> Note that NIST Special Publication 800-133 [1] defines these separate terms,
> and I suggest we use them in this conversation to avoid confusion:
>
> Key update: A procedure in which a new cryptographic key is computed as a
> function of the (old) cryptographic key that it will replace.
>
> Rekey: A procedure in which a new cryptographic key is generated in a manner
> that is independent of the (old) cryptographic key that it will replace.
>
> [1]
> http://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-133.pdf.
>
> Cheers,
> Brian
> --
> https://briansmith.org/
>
>
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