All, I asked ekr to write a brief summary of the server-side signing issue. The summary provided matches the WG consensus as judged by the chairs. Please let us know if you object to the way forward by August 3rd.
J&S Begin forwarded message: > From: Eric Rescorla <e...@rtfm.com> > Subject: Summary of today's discussion on server-side signing > Date: July 22, 2015 at 08:52:31 EDT > To: Sean Turner <turn...@ieca.com> > > Sean, > > Here's a summary of today's discussion on signing and KnownConfiguration. > > SUMMARY > The WG agreed that the server must sign whenever certificate authentication > is used (even if the KnownConfiguration is used). > > > BACKGROUND > The current draft requires the server to send a Certificate/CertificateVerify > whenever either: > > (a) The KnownConfiguration option is not in use. > (b) The server sends a ServerConfiguration > > but it does not need to sign if the KnownConfiguration option is in > use but no new ServerConfiguration is provided. Several people (most > recently Martin Thomson) have suggested that it would be simpler to > just require the server to sign any time certificate-based > authentication is in use. The penalty for this is an extra sign/verify, > as shown in the following table: > > Scenario Client Server > ------------------------------------------------------------------ > 1-RTT 1 (EC)DHE + Verify 1 (EC)DHE + Sign > > 0-RTT (current, 2 (EC)DHE 2 (EC)DHE > no new config) > > 0-RTT (current, 2 (EC)DHE + Verify 2 (EC)DHE + Sign > new config) > > 0-RTT (proposed) 2 (EC)DHE + Verify 2 (EC)DHE + Sign > > > So, the performance difference here is between line 2 and line 4, > since whenever you provide a new config (line 3) you have to sign > anyway. The benefit is that it makes the server side of the handshake > essentially identical in both 0-RTT and 1-RTT, which is nice from an > implementation and analysis perspective. > > > SUMMARY OF WG DISCUSSION > During the WG discussion today, there was rough consensus to adopt > this change (i.e., always sign). A number of arguments were advanced > in favor of this change. > > (1) It's significantly simpler for implementors and (at least informal) > analysis. A side benefit is being able to merge the extension > logic for 0-RTT and KnownConfiguration, since KnownConfiguration > is only useful with 0-RTT. > > (2) It extends the properties we were shooting for with online-only > signatures and requiring that the server always sign ServerConfiguration, > namely continuous proof of access to the signing key. > > (3) The performance cost of an extra ECDSA signature is small and > shrinking fast (per Ian Swett channelling Adam Langley), and > people who care about speed will cut over to ECDSA (certs are > readily available). > > (4) You can still do 0-RTT with PSK resumption, which is computationally > much faster. > > On balance the WG seemed to feel that these were more compelling than > the performance value of the optimization. > > There was also a recognition that signature amortization was valuable, > but the consensus was that instead of doing this here, it would be > better to adopt Hugo's suggeston from a while back to have a > certificate extension that allowed offline signatures. This allows > both amortization *and* delegation, while not constituting a threat > to existing TLS 1.2 implementations. We agreed that this could be > worked in in parallel but shouldn't hold up TLS 1.3. > > Per WG guidance, I'll be preparing a draft PR for this. > > -Ekr > > > > > > > > > > > > > > > > _______________________________________________ TLS mailing list TLS@ietf.org https://www.ietf.org/mailman/listinfo/tls
