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Re: [TLS] draft-ietf-tls-renegotiation-01.txt and DTLS

Eric Rescorla <ekr@networkresonance.com> Thu, 03 December 2009 20:43 UTC

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Date: Thu, 03 Dec 2009 12:45:04 -0800
From: Eric Rescorla <ekr@networkresonance.com>
To: Marsh Ray <marsh@extendedsubset.com>
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Cc: Tolga Acar <Tolga.Acar@microsoft.com>, Kyle Hamilton <aerowolf@gmail.com>, "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] draft-ietf-tls-renegotiation-01.txt and DTLS
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At Thu, 03 Dec 2009 14:01:32 -0600,
Marsh Ray wrote:
> 
> Tolga Acar wrote:
> > I looked at DTLS and it doesn't seem like it is vulnerable as TLS is.
> >  The "uint16 epoch" and "uint48 sequence_number" in the record header
> > are input to the MAC and are validated per RFC4347 Section 4.1.2.1.
> > It seems to me that a MiTM would not have a  matching epoch+sequence
> > number, the MiTM can't change them (ok, may change, but MAC would not
> > validate), and it takes 2^48 for them to roll over.
> 
> Couldn't he possibly 'prep' the client by triggering the exchange of the
> appropriate number of dummy records before splicing him into the server
> connection?
> 
> Is there something about the DTLS sequence_number that makes it more
> resilient than the TLS record sequence number?

The sequence number still zeros at every handshake. AFAIK, the only
protection is the epoch, which, as discussed, is potentially manipulable.

-Ekr

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