On Fri, Jul 31, 2015 at 07:42:12PM +0300, Ilari Liusvaara wrote: > On Fri, Jun 26, 2015 at 01:41:29PM -0500, Nico Williams wrote: > > tls-unique depends on the Finished message strongly binding the entire > > transcript up to that point. I find this elegant (despite the > > resumption problem, which anyways, should be fixed by the session hash) > > and easy to understand and analyze. > > > > If the Finished message no longer has this property in 1.3 then that's a > > problem for tls-unique, and we'd have to fix one or the other. Surely > > 1.3 will have some handshake message that binds the transcript, and why > > that wouldn't be the Finished message is beyond me (but I am missing a > > lot of the 1.3 context, so please forgive and inform me). > > Also, it turns out some are assuming tls-unique is both connection nonce > and secret value. :-/
RFC5929 quite rightly says not to do that. Do you have examples of apps doing this? (The Finished message is generally sent encrypted, so that's not that terrible an assumption.) > I don't think the present construct for Finished values is appropriate > for such values, which means one would have to redefine tls-unique > so it meets the need. I'd rather avoid this unless we really need to. Examples of applications mis-using tls-unique would be nice. > (TLS-Exporter values already look to be secret and connection > nonces, and I have already seen stuff relying on both properties). A proper TLS-Exporter can be used (was intended to be used!) as secret and whatever "connection nonces" are. > Basically, the value needs to derive from both "master secret" (to make > it secret) and session hash /w configs (to make it connection > nonce). Which Finished messages do! The only problem with Finished messages as secrets is that the cipher used might not provide confidentiality protection. (Again, I'm not endorsing the use of tls-unique as a secret.) If we have no such ciphersuites left in TLS 1.3... Nico -- _______________________________________________ TLS mailing list TLS@ietf.org https://www.ietf.org/mailman/listinfo/tls
