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Re: [TLS] a slightly different DTLSShortCiphertext

Eric Rescorla <ekr@rtfm.com> Mon, 05 March 2018 00:27 UTC

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From: Eric Rescorla <ekr@rtfm.com>
Date: Sun, 04 Mar 2018 16:26:53 -0800
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To: "Fossati, Thomas (Nokia - GB/Cambridge)" <thomas.fossati@nokia.com>
Cc: Martin Thomson <martin.thomson@gmail.com>, "tls@ietf.org" <tls@ietf.org>
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Subject: Re: [TLS] a slightly different DTLSShortCiphertext
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On Sun, Mar 4, 2018 at 4:12 PM, Fossati, Thomas (Nokia - GB/Cambridge) <
thomas.fossati@nokia.com> wrote:

> On 04/03/2018, 23:12, "Martin Thomson" <martin.thomson@gmail.com> wrote:
> > We are about to remove that bit from the QUIC packet.  I don't see any
> > advantage in adding it here.
> >
> > Can you explain in more detail who you think consumes this bit?
>
> Server or server-side middleware that doesn't know whether the packet
> that needs parsing belongs to a session that negotiated CID or not.  I'm
> not sure the analogy with QUIC holds here: AFAIU, in QUIC the server can
> always say "use CID when you are talking to me"; in DTLS, the server has
> to live with a mix of CID and non-CID sessions.
>

Well, this actually isn't strictly true: the server could refuse to
negotiate TLS 1.3
if the client didn't negotiate CID. And because you can distinguish TLS 1.3
from
TLS 1.2, ....


I genuinely can't see what advantage we get by not having its
> presence explicitly signalled.  Could you elaborate a bit on that?
>

Well, you're making every packet 1 byte bigger, for starters.

-Ekr


> Cheers, thanks
>
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