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Re: [TLS] POODLE applicability to TLS 1.0+ (was Re: Working Group Last Call for draft-ietf-tls-downgrade-scsv-00)

Bodo Moeller <bmoeller@acm.org> Tue, 21 October 2014 05:32 UTC

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Date: Tue, 21 Oct 2014 07:32:33 +0200
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From: Bodo Moeller <bmoeller@acm.org>
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Subject: Re: [TLS] POODLE applicability to TLS 1.0+ (was Re: Working Group Last Call for draft-ietf-tls-downgrade-scsv-00)
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Brian Smith <brian@briansmith.org>:

2. The downgrade-scsv draft should be changed to say that implementations
> MUST always send the TLS_FALLBACK_SCSV when ClientHello.client_version
> indicates TLS 1.1 or lower if the client supports TLS 1.2.
>

Maybe, but note that this doesn't actually help against the concrete
problem with old buggy NSS servers (because these don't handle
TLS_FALLBACK_SCSV).

I think that an RFC 2119 "SHOULD" is right for this; if applications ignore
that recommendation willy-nilly, they could also ignore a "MUST". For
strong protection against bugs in old protocol versions, the only option is
to disallow those versions completely.

Bodo

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