TLS cipersuites for Rserpool

Although we have reached consensus on TLS for securing the Rserpool
infrastructure, we have not discussed TLS cipher suites.  TLS has a very
long and growing list of ciphersuites.  They vary in strength.  Security
experts want strong security.  Application developers worry about
interoperability.  The answer to this is for applications to mandate a
ciphersuite along with one or more shoulds for backward compatibility.

I am including the SIP RFC 3261 security section as an example.
In the SIP specification there is the following text:

The TLS_RSA_WITH_AES_128_CBC_SHA ciphersuite [6] MUST be supported at
   a minimum by implementers when TLS is used in a SIP application.  For
   purposes of backwards compatibility, proxy servers, redirect servers,
   and registrars SHOULD support TLS_RSA_WITH_3DES_EDE_CBC_SHA.
   Implementers MAY also support any other ciphersuite.

For Rserpool we need to secure the following:

PU <----> ENRP Server
PE <----> ENRP Server
ENRP server <-----> ENRP Server

I recommend Rserpool security text as follows (for ENRP and ASAP security
sections):

The TLS_RSA_WITH_AES_128_CBC_SHA ciphersuite MUST be supported at a minimum
by implementers of TLS for Rserpool.   For purposes of backwards
compatibility, ENRP SHOULD support TLS_RSA_WITH_3DES_EDE_CBC_SHA.
Implementers MAY also support any other ciphersuite.

I'll get Eric Rescorla's advice about this TLS cipher suite being the right one
to make mandatory to support and also his take on backward compatibility.  We might not need
this in ENRP assuming that everyone will write new code for Rserpool
infrastructure.

Any comments?

-- maureen