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Re: [TLS] Updated DTLS draft

Martin Thomson <martin.thomson@gmail.com> Fri, 17 March 2017 00:04 UTC

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From: Martin Thomson <martin.thomson@gmail.com>
Date: Fri, 17 Mar 2017 11:03:54 +1100
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To: Matt Caswell <frodo@baggins.org>
Cc: Eric Rescorla <ekr@rtfm.com>, "tls@ietf.org" <tls@ietf.org>
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Subject: Re: [TLS] Updated DTLS draft
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On 17 March 2017 at 10:58, Matt Caswell <frodo@baggins.org> wrote:
> In DTLS1.3 the cookie is now (potentially) much larger and appears much later in
> the ClientHello, making it much more likely that it will not fall
> fully within the
> first fragment. This could mean a fully stateless solution is impossible.


I think that it is feasible to simply require that ClientHello be
contained in a single datagram.  QUIC does this and when we did the
sums it wasn't completely unreasonable, even assuming several key
shares and a big-ish cookie.  And then we made it possible to make the
cookie even smaller in -19.

That assumes that you are willing to assume a 1k MTU, which I know
IPv4 doesn't guarantee.  I'd be OK with adding a caveat on that point
in the form of "Consequently, DTLS might not work with a small MTU".

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