On Sun, Jul 02, 2017 at 12:30:09PM -0700, Eric Rescorla wrote: > On Sun, Jul 2, 2017 at 12:54 AM, Ilari Liusvaara <ilariliusva...@welho.com> > wrote: > > > Suppose that certificate is rather big (needs spliting to four parts), > > and: > > > > > > * The server preprares its flight, giving: > > > > - RSN 2:0 -> EncryptedExtensions, Certificate part 1/4 > > - RSN 2:1 -> Certificate part 2/4 > > - RSN 2:2 -> Certificate part 3/4 > > - RSN 2:3 -> Certificate part 4/4, CertificateVerify, Finished. > > > > * Now, RSNs 2:1, 2:3 disappear, 2:0 and 2:2 make it through. > > > > * Client ACKs RSNs 2:0 and 2:2. > > > > * Server sees the ACK, and re-encrypts the offending packets: > > > > - RSN 2:4 -> Certificate part 2/4 > > - RSN 2:5 -> Certificate part 4/4, CertificateVerify, Finished. > > > > * Now, RSN 2:4 disappears, 2:5 makes it through. > > > > * Client is one-message at a time. It can't ACK anything new. RSNs 2:1, > > 2:3 and 2:4 are lost. RSN 2:5 can not be ACKed, because that would > > imply the client received CV and F, which it did not. > > > > Thanks for clarifying your case. I think what you're assuming here is > that when the client receives out of order handshake messages, it discards > them rather than buffering them. Is that correct?
Yes, that is what one message at a time means. > In that case, yes, it > should pretend it didn't get the records as well, and I think the right > answer would be to not generate a new ACK and rely on the server's > retransmission timer (which needs to run anyway). One thing to note that there is no way for either side to say: "I received _something_, but nothing useful". One could presumably trigger fast retransmit on that. However, using that to trigger fast retransmits of ServerHello might be a bit dubious... There can also be interactions with giving up on fragment transmissions (in order to limit memory usage). Suppose similar case as before, but 2:1 gets lost instead of disappearing, and is found after 2:5 is received by the client. The client will then generate second ACK, which ACKs 2:1. The server then receives the ACK and has no idea what the client is talking about, since server has dropped the state. But presumably fast-retransmits 2:4 and 2:5, now as 2:6 and 2:7 (3rd transmission for both). -Ilari _______________________________________________ TLS mailing list TLS@ietf.org https://www.ietf.org/mailman/listinfo/tls
