Re: [TLS] Last Call: <draft-ietf-tls-downgrade-scsv-03.txt> (TLS Fallback Signaling Cipher Suite Value (SCSV) for Preventing Protocol Downgrade Attacks) to Proposed Standard

Bodo Moeller <bmoeller@acm.org> Mon, 12 January 2015 11:52 UTC

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Date: Mon, 12 Jan 2015 12:52:23 +0100
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Subject: Re: [TLS] Last Call: <draft-ietf-tls-downgrade-scsv-03.txt> (TLS Fallback Signaling Cipher Suite Value (SCSV) for Preventing Protocol Downgrade Attacks) to Proposed Standard
From: Bodo Moeller <bmoeller@acm.org>
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Cc: Nikos Mavrogiannopoulos <nmav@redhat.com>, "tls@ietf.org" <tls@ietf.org>
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Nikos Mavrogiannopoulos <nmav@redhat.com>om>:

>
> [...] However, if you think that
> this has to be on standards track, please provide at least some
> argumentation for it.
>

draft-ietf-tls-downgrade-scsv-03 mandates server-side behavior (in response
to certain Client Hello messages) that requires wide deployment to achieve
the desired effect, hence Standards Track seems appropriate and
Informational status would be insufficient.

I don't agree with your assessment that "Making this a proposed standard,
would imply that the flawed technique is into standards track."
draft-ietf-tls-downgrade-scsv-03
does not say that clients should implement a downgrade dance, it merely
recommends sending a certain signal *if* they choose to do so.

Also note that the point that some clients may use downgraded retries for
compatibility with buggy servers *is* already acknowledged by Standards
Track RFCs, e.g. RFC 5246 Appendix E.1:  "Note: some server implementations
are known to implement version negotiation incorrectly. [...]
Interoperability with such buggy servers is a complex topic beyond the
scope of this document, and may require multiple connection attempts by the
client."

Bodo