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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 19:52 UTC

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From: Bodo Moeller <bmoeller@acm.org>
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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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>
> But I do _not_ think that a MUST for ClientHello.client_version
> would be appropriate for an fatal alert that is sent instead
> of ServerHello.  For alerts that early in the handshake a server
> may for simplicity reuse the record layer protocol that was used
> for the in coming ClientHello.


God point.  If the record-layer version number differs from
ClientHello.client_version, the client should really be ready to accept
both version numbers. So what about the following?

[...]  The record layer version number for this alert MUST be set to either
ClientHello.client_version (as it would for the Server Hello message if the
server was continuing the handshake), or to the record layer version number
used by the client.


Bodo

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