Re: [TLS] proposal to encrypt ContentType for TLS 1.3

Martin Thomson <martin.thomson@gmail.com> Mon, 07 July 2014 21:01 UTC

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Date: Mon, 7 Jul 2014 14:01:34 -0700
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From: Martin Thomson <martin.thomson@gmail.com>
To: Fabrice Gautier <fabrice.gautier@gmail.com>
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Subject: Re: [TLS] proposal to encrypt ContentType for TLS 1.3
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On 7 July 2014 13:29, Fabrice Gautier <fabrice.gautier@gmail.com> wrote:
> If I'm reading this properly, there would be two types of records on
> the wire: TLSCiphertext and TLSPlaintext.
> However, I don't see a very reliable, documented way to distinguish
> between the two on the wire.

TLSPlaintext records appear before a ChangeCipherSpec and
TLSCiphertext records appears afterwards.  That is pretty unambiguous.

Yes, this does mean that it's going to be self-evident in individual
frames, interpreted individually, which is exactly Martin Rex's
objection.

> - In DTLS, records maybe dropped, received out of order, received
> multiple times, etc, so TLSPlaintext and TLSCiphertext records aybe
> intermixed, without a clear switchover point. This would make
> efficient DTLS difficult.

Doesn't the explicit sequence number in DTLS do that job adequately?
Yes, you don't know until you get the packet containing CCS (or a
retransmit thereof), but there's a fairly narrow range of values where
it could appear.