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Re: [TLS] Last Call: <draft-ietf-tls-downgrade-scsv-03.txt>

Henrik Grubbström <grubba@gmail.com> Thu, 22 January 2015 14:39 UTC

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Date: Thu, 22 Jan 2015 15:39:52 +0100
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Subject: Re: [TLS] Last Call: <draft-ietf-tls-downgrade-scsv-03.txt>
From: Henrik Grubbström <grubba@gmail.com>
To: Hubert Kario <hkario@redhat.com>
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On Thu, Jan 22, 2015 at 12:07 PM, Hubert Kario <hkario@redhat.com> wrote:
> On Wednesday 21 January 2015 16:45:31 Michael D'Errico wrote:
>> Martin Rex wrote:
>> > Rubber-Stamping the fallback-scsv hack onto the standards track is
>> > IMHO a very bad idea.
>>
>> I apologize if this has been discussed before (I have about 1400
>> unread TLS mailing list messages in my queue), but it seems that
>> a simpler SCSV or extension could just ask the server to echo its
>> highest supported version:
>>
>>      ClientHello w/SCSV    ----->
>>                            <-----    ServerHello w/version extension
>
> that's not allowed by the RFC's, the server can send back only the extension
> id's client has sent

Not quite; cf RFC 5746 (Renegotiation Indication Extension), where the
client may use the SCSV TLS_EMPTY_RENEGOTIATION_INFO_SCSV instead of
the renegotiation_info extension in its ClientHello, but the server
will reply with the renegotiation_info extension.

/grubba

-- 
Henrik Grubbström                                       grubba@grubba.org
Roxen Internet Software AB                              grubba@roxen.com

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