On Mon, Jul 4, 2016 at 1:46 PM, Ilari Liusvaara <[email protected]> wrote:
> On Mon, Jul 04, 2016 at 09:45:38PM +0200, Hannes Tschofenig wrote: > > Hi Ilari, > > > > thanks for your super quick response. > > > > On 07/04/2016 04:03 PM, Ilari Liusvaara wrote: > > > On Mon, Jul 04, 2016 at 12:21:22PM +0200, Hannes Tschofenig wrote: > > >> Hi all, > > >> > > >> I have made an attempt to integrate DTLS 1.3 into the TLS 1.3 document > > >> and you can find the result at > https://github.com/tlswg/tls13-spec/pull/512 > > >> > > >> I have worked on a prototype implementation of DTLS 1.3 and if someone > > >> else has something working by the time of the Hackathon in Berlin > please > > >> let me know. > > > > > > Taking a look: > > > > > > - The version field is described as identical to TLS 1.3 version field. > > > What value is there actually? FCFE (wasn't that how "DTLS 1.0" was > > > encoded on wire)? > > > > For the record layer TLS 1.3 says that the version field is deprecated > > and ignored. I guess the same approach applies to DTLS 1.3. So, it > > probably doesn't matter what is really is. In DTLS 1.2 the version value > > was 254.253. > > Oh, it was that. Then I presume DTLS 1.0 was 254,255 (yup, checked the > RFC). > > > For the client_version and server_version in the handshake I thought it > > would be fine to just re-use the TLS 1.3 version number. > > I think that is not a good idea, and one should follow the pattern (which > would give 254,252 for ClientHello/ServerHello). > > But for record version, reusing previous versions (either 254,255 or > 254,253) should be fine. > > > > - KeyUpdate does not work in DTLS. Might just use epochs for similar > > > purpose, and reserve first few epochs for special purposes. > > > > Could you explain in more detail why you think a key update does not > > work with DTLS? > > That message is not idempotent (nor has it timely ACK). > > > > - The full handshake protocol is only run once. After that, there's > > > only rekeying, new tickets and dynamic reauth. > > > > How TLS 1.3/DTLS 1.3 is used in specific environments remains to be seen. > > Well, certainly the main handshake only runs once per connection. > > > > - There's special case with cookies: DTLS 1.3 ClientHello getting > > > rejected with HelloVerifyRequest. I think the correct reaction > > > is for client to send a DTLS 1.3 ClientHello without 0-RTT data, > > > containing the cookie sent now in legacy cookie field (NOT the > > > extension). > > > - According to TLS 1.3 rules, handshakes rejected using > > > HelloRetryRequest use the Cookie extension for cookie > > > transmitback, not the legacy cookie field (the cookie might not > > > even fit into that field!) > > > > Regarding the issue of where to send the cookie in the ClientHello there > > are two options. The first option is to use the cookie extension, and > > the second option is to use the DTLS 1.2 style where the cookie is > > placed in the ClientHello directly (without using an extension). > > > > My (weak) preference is to use the cookie extension also in the > > ClientHello. My main reason was the length mismatch between the DTLS 1.2 > > cookie extension (which is now in the legacy_cookie filed) and the > > cookie extension. The cookie extension has a max length of 2^16-1 bytes > > and the legacy_cookie extension only 2^8-1 bytes long. If the design of > > the ClientHello uses the legacy_cookie extension then the server has to > > take care that the cookie size does not exceed the 2^8-1 bytes. > > I think the obvious way is: > > - Cookies from HelloVerifyRequest go to legacy cookie field. > - Cookies from HelloRetryRequest go to extension cookie field. > > If you don't do the first, you can't downnegotiate successfully. And > if you don't do the second, you would have to have special case with > cookie sizes (since HRR can transmit >255 byte cookie, which would be > too big for legacy cookie). > IMO we should just forbid HVR for DTLS 1.3. I.e., you should just send HRR. > > - The handshake retransmit scheme doesn't seem to work that > > > well with post-handshake auth, and even less well with > > > session tickets. > > Why do you think so? Of course, unreliable transports creates > > inconvenience; is it that what you are referring to? > > DTLS assumes handshake messages are reliable, and that reliability is > implemented via handshake messages ACKing one another. > > - Session tickets have no ACK at all. > DTLS 1.3 should add an ACK, IMO. > - CertificateRequest can have very slow ACK. > - KeyUpdate has no real ACK (and isn't idempotent either). > Yes, I think we should remove KeyUpdate for DTLS 1.3 and just use epoch instead. -Ekr > > -Ilari > > _______________________________________________ > TLS mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/tls >
_______________________________________________ TLS mailing list [email protected] https://www.ietf.org/mailman/listinfo/tls
