Re: [Uta] Eric Rescorla's Yes on draft-ietf-uta-email-deep-09: (with COMMENT)

[Alexey Melnikov <[e-mail]>]

Hi Keith,

One little thing about your new ABNF for DH group:

On 25/10/2017 01:31, Keith Moore wrote:

>> Line 328
>>        the TLS ciphersuite of the session in which the mail was 
>> received,
>>        in the Received field of the outgoing message.  (See Section 
>> 4.3.)
>> Do you want to also suggest that it include the name of the DH group, 
>> if any?
>
> I've attempted to add that attribute but please check the text:
>
>       The ESMTPS transmission type <xref target="RFC3848"/> provides 
> trace
>       information that can indicate TLS was used when transferring mail.
>       However, TLS usage by itself is not a guarantee of 
> confidentiality or
>       security. The TLS cipher suite provides additional information 
> about the
>       level of security made available for a connection. This defines 
> a new
>       SMTP "tls" Received header additional-registered-clause that is 
> used to
>       record the TLS cipher suite that was negotiated for the 
> connection. The
>       value included in this additional clause SHOULD be the 
> registered cipher
>       suite name (e.g., TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) 
> included in the TLS
>       cipher suite registry. In the event the implementation does not 
> know the
>       name of the cipher suite (a situation that should be remedied 
> promptly),
>       a four-digit hexadecimal cipher suite identifier MAY be used.
>       In addition, the Diffie-Hellman group name associated with the
>       ciphersuite MAY be included (when applicable and known) 
> following the
>       ciphersuite name.   The ABNF for the field follows:
>       <figure>
>         <artwork type="abnf">
> tls-cipher-clause  =  CFWS "tls" FWS tls-cipher [ "group" dh-group ]

Is lack of some kind of delimiter before and after "group" intentional? 
(FWS? Or maybe ";" before group).
>
> tls-cipher         =  tls-cipher-name / tls-cipher-hex
>
> tls-cipher-name    =  ALPHA *(ALPHA / DIGIT / "_")
> ; as registered in IANA cipher suite registry
>
> tls-cipher-hex     =  "0x" 4HEXDIG
>
> dh-group           = ALPHA *(ALPHA / DIGIT / "_")
> ; as registered in IANA TLS Supported Groups Registry
> </artwork>
>       </figure>