Re: [TLS] Working Group Last Call for draft-ietf-tls-downgrade-scsv-00

[Manuel Pégourié-Gonnard <[e-mail]>]

On 26/09/2014 06:00, Joseph Salowey (jsalowey) wrote:
> This is an announcement for the working group last call for
> draft-ietf-tls-downgrade-scsv-00.  Please review the document and send your
> comments to the list by Friday, October 17, 2014.
> 
Just to mention that I just implemented this. As expected (since it's one of the
design goals of the draft), it was very easy.

The only problem I ran into was an interop issue with OpenSSL, which apparently
does not like it if the SCSV appears before the actual ciphersuites in the
ciphersuite list. If the intention of the draft was that the SCSV MUST be placed
after the actual ciphersuites, it would be good to state so using normative
language, rather than the current one which doesn't look normative:

                                     (Since the cipher suite list in the
      ClientHello is ordered by preference, with the client's favorite
      choice first, signaling cipher suite values will generally appear
      after all cipher suites that the client actually intends to
      negotiate.)

Otherwise, it should probably be clarified that servers MUST recognize the SCSV
at any position in the ciphersuite list, which is my preferred option. (It can
be combined with a "clients SHOULD place it after actual ciphersuites", I have
no opinion on that one).

Manuel.