Re: [TLS] ESNI GREASE - answer needed?

[Steven Valdez <[e-mail]>]

I don't think the server needs any special logic in the GREASE case?

If the server doesn't support ESNI, it won't respond with an ESNI extension
and the client will continue the handshake as normal.

If the server does support ESNI, it will send an esni_retry_requested with
the retry keys (since the client's record_digest is bogus) and then the
client will continue the handshake as normal.

A server that doesn't have ESNI keys configured shouldn't be responding to
ESNI and should instead just ignore the ESNI extensions (as if it didn't
know what it was).



On Mon, Jul 29, 2019 at 12:14 PM Stephen Farrell <[e-mail]>
wrote:

>
> Hiya,
>
> (Non-stylishly responding to myself, but sometimes you
> gotta...:-)
>
> I think I understand this better now and while I still
> figure a change is needed I'm not 100% sure exactly what'd
> be right.
>
> The issue I think is that draft-04 doesn't cover the case
> of a server that implements ESNI but has no ESNIKeys setup,
>
> In that case I think the right option in response to GREASE
> (or what may be a real but misguided attempt at ESNI) is to
> randomly return either a 16 octet value or a value that is
> sized to be like a fake ESNIKeys, with e.g. 70-100 octets or
> so. (That could be encoded into TLS presentation syntax in
> various ways so I'll not suggest one exact way for now.)
>
> (Before I waste time coding that up:-) Do we think the
> above is correct?
>
> Thanks,
> S.
>
>
> On 26/07/2019 18:31, Stephen Farrell wrote:
> >
> > Hiya,
> >
> > I've started coding up the GREASE stuff from draft -04.
> >
> > Aren't we missing some answering octets in EncryptedExtensions
> > to make it harder to tell if the CH had a real or GREASEd ESNI?
> >
> > Maybe something like:
> >
> >       enum {
> >           esni_accept(0),
> >           esni_retry_request(1),
> >           esni_grease(2),
> >       } ServerESNIResponseType;
> >
> >       struct {
> >           ServerESNIResponseType response_type;
> >           select (response_type) {
> >               case esni_accept:        uint8 nonce[16];
> >               case esni_retry_request: ESNIKeys retry_keys<1..2^16-1>;
> >               case esni_grease:        uint8 grease[16];
> >           }
> >       } ServerEncryptedSNI;
> >
> > Cheers,
> > S.
> >
> >
> > _______________________________________________
> > TLS mailing list
> > [e-mail]
> > https://www.ietf.org/mailman/listinfo/tls
> >
> _______________________________________________
> TLS mailing list
> [e-mail]
> https://www.ietf.org/mailman/listinfo/tls
>


-- 

Steven Valdez |  Chrome Networking |  [e-mail] |  210-692-4742