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Re: [TLS] Protocol version for inappropriate_fallback alerts (was: Re: I-D Action: draft-ietf-tls-downgrade-scsv-01.txt)

Bodo Moeller <bmoeller@acm.org> Tue, 11 November 2014 15:52 UTC

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Date: Tue, 11 Nov 2014 16:52:21 +0100
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From: Bodo Moeller <bmoeller@acm.org>
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Cc: Florian Weimer <fweimer@redhat.com>
Subject: Re: [TLS] Protocol version for inappropriate_fallback alerts (was: Re: I-D Action: draft-ietf-tls-downgrade-scsv-01.txt)
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Florian Weimer <fweimer@redhat.com>:


> Section 3 still does not mention which version to put into the
> inappropriate_fallback alert message.


Good point; it can't hurt to be completely explicit about this.

Proposed new wording:

o If TLS_FALLBACK_SCSV appears in ClientHello.cipher_suites and the highest
protocol version supported by the server is higher than the version
indicated in ClientHello.client_version, the server MUST respond with a
fatal inappropriate_fallback alert *(unless it responds with a fatal
protocol_version alert because the version indicated in
ClientHello.client_version is unsupported). The record layer version number
MUST be set to ClientHello.cipher_suites for this alert (as it would for
the Server Hello message if the server was continuing the handshake)*.


Bodo

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