Subject: [Uta] Richard Barnes' Discuss on draft-ietf-uta-tls-bcp-09: (with DISCUSS and COMMENT)

From: "Richard Barnes" <[email-masked]>
Date: Wed, 18 Feb 2015 19:34:33 -0800

Richard Barnes has entered the following ballot position for
draft-ietf-uta-tls-bcp-09: Discuss

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DISCUSS:
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I really can't abide by the abdication in Section 5.2.  Getting a cert is
hard.  Running reasonably recent software and configuring it properly is
not.  The possibility that a connection will not be authenticated is no
excuse for using bad versions of TLS or using insecure ciphersuites.

I appreciate that normally deference to WG consensus is appropriate, but
this is a recommendation that could be actively harmful to the Internet
by encouraging the continued use of broken code.

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COMMENT:
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These COMMENTs are right on the edge of being  DISCUSS points, because I
think there are some pretty critical references missing.  Please consider
this a COMMENT of Unusual Strength.

Section 1. "which together are the most widely deployed ciphers"

Actually, at least in the web context, this isn't totally true. 
According to Firefox telemetry, AES-GCM has been the most widely deployed
cipher since at least 3Q14, and is currently used in the majority of TLS
handshakes that Firefox does (52%) [1].

Section 3.1.1. Implementations MUST NOT negotiate SSL version 3

A reference to draft-ietf-tls-sslv3-diediedie seems in order here.

Section 3.1.

It would be good for this section to mention that servers MUST implement
TLS version negotiation.  That is, they MUST NOT abort the handshake if
the version offered by the client is higher than the version the server
supports.  This is, after all, the root cause of fallback.  

Section 3.1.3. 

I'm surprised that there's not even a SHOULD CONSIDER [RFC6919] for SCSV
here.  Did the WG discuss having any requirement for SCSV?

Also, if you want a cite for the 3% number, it's in the proceedings of
IETF 91 [2].

Section 3.3.

You might point out HPACK [3] as an example of compression that is
sensitive to things like CRIME.

Section 3.5.

Shouldn't this refer more specifically to draft-ietf-tls-session-hash
[4]?  As it is, the recommendations in this section are kind of vacuous;
e.g., TLS without session-hash provides no way to "bind the master secret
to the full handshake".

Section 4.4. "Modular vs. Elliptic Curve"

I think that "finite field" or "modp" are more common than "modular".

[1] http://mzl.la/1AmwXsm
[2] http://www.ietf.org/proceedings/91/slides/slides-91-saag-3.pdf
[3] https://tools.ietf.org/html/draft-ietf-httpbis-header-compression
[4] https://tools.ietf.org/html/draft-ietf-tls-session-hash