On Sat, Jul 01, 2017 at 03:52:37PM -0700, Eric Rescorla wrote: > On Sat, Jul 1, 2017 at 2:00 PM, Ilari Liusvaara <ilariliusva...@welho.com> > wrote: > > > On Sat, Jul 01, 2017 at 10:26:17AM -0700, Eric Rescorla wrote: > > > On Sat, Jul 1, 2017 at 10:01 AM, Ilari Liusvaara < > > ilariliusva...@welho.com> > > > wrote: > > > > > Just noticed that DTLS allows packing multiple independent fragments > > into one record (and then multiple records into one packet). > > > > Which impiles that an implementation that only prcesses one message at > > a time is not guaranteed to even be able to generate a valid list of > > RSNs to ACK, in case the peer sends sufficiently twisted (but still > > seemingly in-spec) input. > > > > I'm not following how that's true. When you decrypt, you record the received > RSNs and when you send an ACK you send the entire list. Then when you > finish a flight, you reset the list. Can you maybe show me a sequence of > events that would cause an error here?
I think I figured out a case that doesn't involve peer intentionally generating very dubious input: 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. -Ilari _______________________________________________ TLS mailing list TLS@ietf.org https://www.ietf.org/mailman/listinfo/tls
