Re: [TLS] SCSV vs RI when both specified - consensus?

Nasko Oskov <noskov@microsoft.com> Mon, 21 December 2009 18:21 UTC

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From: Nasko Oskov <noskov@microsoft.com>
To: Marsh Ray <marsh@extendedsubset.com>, Michael D'Errico <mike-list@pobox.com>
Thread-Topic: [TLS] SCSV vs RI when both specified - consensus?
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Date: Mon, 21 Dec 2009 18:20:16 +0000
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Subject: Re: [TLS] SCSV vs RI when both specified - consensus?
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Marsh Ray wrote:
>Michael D'Errico wrote:
>> I agree we need to publish ASAP, but if consensus is (1), then I need 
>> to change my (running) code since it currently does (2).
>
>
>Is everybody OK with this wording? (it's the more lenient choice):
>
>> Clients MUST NOT put multiple occurrences of an RI extension in the 
>> same Client Hello message. A client MAY specify the SCSV in the same 
>> Client Hello message as an RI extension (the SCSV will be effectively 
>> ignored).
>>
>> A server receiving a Client Hello containing multiple RI extensions 
>> MUST generate a fatal "decode_error" alert and terminate the 
>> connection. A server receiving a Client Hello containing the SCSV and 
>> an RI extension is to interpret the RI as usual and ignore the SCSV.

I generally agree with this wording. I find the sentence describing multiple
RI extensions behavior redundand, since this is already part of RFC5246:

Section 7.4.1.4:
    There MUST NOT be more than one extension of the same type.


>We'll have to fix the conflict with the current:
>> This SCSV is not a true cipher suite and cannot be negotiated. It 
>> merely has exactly the same semantics as an empty "renegotiation_info"
>> extension.
>
>to something like:
>> This SCSV is not a true cipher suite and cannot be negotiated, it has 
>> similar semantics as an empty "renegotiation_info" extension.

Agreed.

Nasko