Re: [TLS] WGLC for draft-ietf-tls-grease

[Hubert Kario <[e-mail]>]

On Wednesday, 27 February 2019 09:54:17 CET Stephen Farrell wrote:
> Hiya,
> 
> On 27/02/2019 01:57, Sean Turner wrote:
> > This messages closes the WGLC for draft-ietf-tls-grease.  The draft
> > will progress as is because we received no WGLC comments.
> 
> Apologies for missing the WGLC. I've just read this and fully
> support it progressing. I have one question though:
> 
> The drafts says: 'A client MAY select one or more GREASE extension
> values and advertise corresponding extensions with varying length
> and contents' and 'For each of these, the "key_exchange" field MAY
> be any value.' and 'Implementations advertising GREASE values
> SHOULD select them at random.'
> 
> I was left wondering what ranges of lengths and what values are
> recommended to be sent for greasy extension bytes and key_exchange
> values.
> 
> Reason to ask is I happened to be looking at a few handshakes and
> noticed those lengths being zero in all cases IIRC. (It was only
> 3 cases being one 1 h/s from each of 3 browsers so could be I was
> just unlucky or missed a non-zero greasy length.)

I'm not sure which part for the key_share extension you mean as being empty, 
but the key_exchange in the KeyShareEntry can't be empty, per RFC 8446, 
Section 4.2.8:

      struct {
          NamedGroup group;
          opaque key_exchange<1..2^16-1>;
      } KeyShareEntry;

Only the client_shares inside the KeyShareClientHello may be empty:

      struct {
          KeyShareEntry client_shares<0..2^16-1>;
      } KeyShareClientHello;
 
> I've no strong opinion as to what'd be best to say about those
> lengths but I guess maybe we'd want to see some greasy lengths
> that are shorter than all real values, some that are longer and
> many in between, and value octets that that are random when
> lengths are non-zero.
> 
> Does that match what people do? If so, would it be worth adding
> something about that to the document?
> 
> Cheers,
> S.
> 
> PS: Since I'm late to the game I'm fine if the above's treated as
> a random last call comment.
> 
> > spt
> > 
> >> On Jan 24, 2019, at 10:50, Sean Turner <[e-mail]> wrote:
> >> 
> >> This is the working group last call for the "Applying GREASE to TLS
> >> Extensibility" draft available at
> >> https://datatracker.ietf.org/doc/draft-ietf-tls-grease/. Please
> >> review the document and send your comments to the list by 2359 UTC
> >> on 8 February 2019.
> >> 
> >> NOTE: There is one outstanding issue raised by Hubert [0].  Please
> >> chime in there or here so that we can address his comment one way
> >> or the other.
> >> 
> >> Thanks, Chris, Joe, and Sean
> >> 
> >> [0]
> >> https://mailarchive.ietf.org/arch/msg/tls/nr4dA2JqcpqAjh-oY_1z2l6ZMFo
> > 
> > _______________________________________________ TLS mailing list
> > [e-mail] https://www.ietf.org/mailman/listinfo/tls


-- 
Regards,
Hubert Kario
Senior Quality Engineer, QE BaseOS Security team
Web: www.cz.redhat.com
Red Hat Czech s.r.o., Purkyňova 115, 612 00  Brno, Czech Republic