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Re: [TLS] Cookie reuse subsequent connections

Martin Thomson <martin.thomson@gmail.com> Mon, 30 October 2017 09:31 UTC

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From: Martin Thomson <martin.thomson@gmail.com>
Date: Mon, 30 Oct 2017 20:31:46 +1100
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To: Jānis Čoders <janis.coders@gmail.com>
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Subject: Re: [TLS] Cookie reuse subsequent connections
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What is most likely to happen is that the cookie will be invalid and
the connection will be rejected.

Many TLS servers assume that presence of a cookie means that they
previously sent a HelloRetryRequest on that connection.  For instance,
NSS packs a hash of the original ClientHello into the cookie so that
it can restore the handshake transcript.  Reusing the cookie will just
lead to the server restoring the handshake transcript from the wrong
handshake.  And that's even assuming that it accepts the cookie in the
first place.

On Mon, Oct 30, 2017 at 6:07 PM, Jānis Čoders <janis.coders@gmail.com> wrote:
> Hi, is there ANY security issue with reusing Cookie from previous TLS
> connection? In current draft there is text: "Clients MUST NOT use
> cookies in their initial ClientHello in subsequent connections." I
> can't think of any security implication, but can think of situations
> where it could be useful.
>
> --
> Ar cieņu,
> Jānis Čoders
>
> _______________________________________________
> TLS mailing list
> TLS@ietf.org
> https://www.ietf.org/mailman/listinfo/tls

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