Yes, these are all reasonable points. It's purely a matter of thinking one might want to minimize the number of anomalies. But maybe that's not a useful goal.
-Ekr On Sat, Jun 4, 2016 at 11:10 AM, David Benjamin <david...@chromium.org> wrote: > Wouldn't the server be required to handle such a case anyway? If it's > doing post-handshake auth, it wants to do something reactive, such as based > on HTTP request or so. But that means I may have not hit an auth'd URL, > saved the session, resumed it, and then hit an auth'd URL. Or perhaps I > have two connections, one of which happens to hit auth'd URLs and the other > happens to hit unauth'd URLs. There's no ordering between the two sets of > sessions, so the unauth'd one may win. > > That means servers must already allow for resuming an unauth'd session, > hitting a auth'd URL, and sending a fresh post-handshake > CertificateRequest. If anything, I wouldn't want to encourage servers to > assume they can make assumptions here. (I have seen some sites make > strong assumptions of this sort, and they've been sufficiently strong that > they're unsupportable. It's basically incompatible with having any parallel > connections at all.) > > Incidentally, Chrome will never offer or store sessions on renegotiation, > the exact opposite here, and no one seems to have noticed. > > David > > > On Sat, Jun 4, 2016 at 1:16 PM Eric Rescorla <e...@rtfm.com> wrote: > >> I don't think it's principally about discarding keying material, but >> rather about allowing the server to attach state to a ticket and then have >> predictable behavior. Consider the obvious case of post-handshake client >> auth (which I know you hate) and a client which has tickets issue before >> and after the auth event. If it tries to use them both, that's going to be >> annoying (though I agree, not fatal). >> >> Anyway, I could live without doing this now (part of why I added ticket >> extensions is to let us make these decisions later), if nobody else thinks >> it's that valuable. I *do* think it's important that we make sure that >> analysis supports multiple tickets pointing to the same underlying RMS. >> >> -Ekr >> >> On Sat, Jun 4, 2016 at 10:06 AM, David Benjamin <david...@chromium.org> >> wrote: >> >>> I'm not sure I follow why the additional "generation" machinery is >>> necessary. >>> >>> What do we gain from having the server to tell us to discard a ticket >>> beyond what the ticket lifetime already gives? This doesn't seem an >>> effective way to discard key material since, unlike the ticket lifetime, we >>> need a live connection to the server at the time. Beyond that, if a client >>> uses a ticket the server no longer likes, we'll just fall back to a full >>> handshake. That seems fine. >>> >>> I would favor simply saying the client SHOULD prefer to use more recent >>> tickets over earlier ones (since that's probably a good idea) and that >>> clients which expect to open multiple concurrent connections SHOULD retain >>> a window of several one-use tickets. We can always add this generation >>> thing back in later as a TicketExtension if we change our minds. >>> >>> Am I missing something? >>> >>> David >>> >>> >>> On Sat, Jun 4, 2016 at 11:52 AM Eric Rescorla <e...@rtfm.com> wrote: >>> >>>> https://github.com/tlswg/tls13-spec/pull/493 >>>> >>>> Currently the server can send multiple tickets but we don't say >>>> anything about the semantics. >>>> So, say a server sends tickets T_1, T_2, T_3... T_n, and the client >>>> wants to initiate m < n connections, should he use: >>>> >>>> - only T_n >>>> - T_1...T_m >>>> - T_n, T_n-1, ... T_n-m+1 >>>> >>>> The intuition I have had is that we want the third option (latest wins, >>>> but allow multiples for linkability) but the spec doesn't say and there >>>> aren't any semantics that tell you, so I think we want some way for the >>>> server to say "these group of tickets are all co-valid". >>>> >>>> I've just created PR#493, which provides an explicit mechanism for >>>> this, "ticket generations". Tickets with the same generation M are co-valid >>>> and a ticket with generation N expires all tickets with generation M < N. >>>> The nice thing about this encoding is that a client can implement the old >>>> "one ticket at a time" behavior by just ignoring the generation and taking >>>> the last ticket. >>>> >>>> I wanted to call out to cryptographers/analysts that this formalizes >>>> the existing practice (going back to RFC 5077) of having multiple ticket >>>> values tied to the same basic secret (though less so with 1.3 because >>>> tickets issued on connection N+1 don't have the same RMS as those on >>>> connection N). If there is a problem with this, that would be good to know. >>>> >>>> Barring major objections, I'll merge this Thursday. >>>> >>>> >>>> -Ekr >>>> >>>> >>>> _______________________________________________ >>>> TLS mailing list >>>> TLS@ietf.org >>>> https://www.ietf.org/mailman/listinfo/tls >>>> >>> >>
_______________________________________________ TLS mailing list TLS@ietf.org https://www.ietf.org/mailman/listinfo/tls
