Re: [TLS] I-D Action: draft-ietf-tls-prohibiting-rc4-01.txt

mrex@sap.com (Martin Rex) Thu, 02 October 2014 17:54 UTC

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To: =?ISO-8859-1?Q?Hanno_B=F6ck?= <hanno@hboeck.de>
Date: Thu, 2 Oct 2014 19:54:46 +0200 (CEST)
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From: mrex@sap.com (Martin Rex)
Archived-At: http://mailarchive.ietf.org/arch/msg/tls/sqLifZp3BY5huDjOjd1vBeSnQvs
Cc: tls@ietf.org
Subject: Re: [TLS] I-D Action: draft-ietf-tls-prohibiting-rc4-01.txt
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Hanno Böck wrote:
> 
> I really don't want to hold anything here and would welcome if this
> gets finally out, however there's one thing that bothers me:
> There is currently no such RFC for RC2 or DES. Both are - considering
> current RFCs - perfectly valid ciphers according to RFC 2246.
> 
> It doesn't really make sense to forbid RC4 (likely weak, but no
> public practical attacks yet) while still allowing RC2(40 bit)/DES
> (practically broken).

not quite.

TLS cipher suites with three symmetric encryption algorithms
that are described in the TLSv1.1 spec (rfc4346) no longer appear
in TLSv1.2 (rfc5246):   RC2, (single-)DES, and IDEA

For two of these three TLS cipher(suites), a seperate RFC was issued:

  http://tools.ietf.org/html/rfc5469

RC2 may have been left out since it existed only as RC2-40 in SSLv3&TLS.


I prefer the rfc5469 approach by a significant margin over the
science-defying dogmatic, radical extremist approach of the rc4 I-D.
Attacking a single-DES TLS session is *VERY* practical.

Attacking a dozen RC4-encrypted TLS-sessions is infeasible based on
all that we currently know.


-Martin