Subject: [Dime] RFC3588bis cipher suite question

From: jouni korhonen <[email-masked]>
Date: Thu, 21 Jun 2012 14:17:36 +0300

Folks,

In Section 13.1 we have the following text:

   Diameter nodes MUST be able to negotiate the following TLS/TCP and
   DTLS/SCTP cipher suites:

         TLS_RSA_WITH_RC4_128_MD5
         TLS_RSA_WITH_RC4_128_SHA
         TLS_RSA_WITH_3DES_EDE_CBC_SHA

   Diameter nodes SHOULD be able to negotiate the following TLS/TCP and
   DTLS/SCTP cipher suite:

         TLS_RSA_WITH_AES_128_CBC_SHA

   Note that that it is quite possible that support for the
   TLS_RSA_WITH_AES_128_CBC_SHA ciphersuite will be REQUIRED at some
   future date.  Diameter nodes MAY negotiate other TLS/TCP and DTLS/
   SCTP cipher suites.

I know this is a bit late in the pipe but.. but RFC6347 (DTLS v1.2) has
the following statement:

   The only stream cipher described in TLS 1.2 is RC4, which cannot be
   randomly accessed.  RC4 MUST NOT be used with DTLS.

That does not go too well with the RFC3588bis MUST for RC4 stream ciphers.

Also RFC5246 states:

   In the absence of an application profile standard specifying
   otherwise, a TLS-compliant application MUST implement the cipher
   suite TLS_RSA_WITH_AES_128_CBC_SHA..

Can we understand that the current text in RFC3588bis serves as the
profile and the SHOULD there is then OK from the RFC5246 point of
view?

- Jouni