I've read this draft before, but this is considerably different to what I read, and I haven't been following the discussion, so consider this as a review with fresh eyes.
First the high points. I think that this is useful, the right scope, and reasonably well formulated. I have a couple of minor points Figure 2 is in error: it shows CertificateRequest instead of Certificate. I'd like to see the document explicitly note that msg_type and length from the handshake message are not covered by the hash. The description of what is covered is a little too terse (and badly formatted). I'm not sure that I like the lack of both negotiation and signaling for the hashes that are used here. Though I think the chances of a collision being found, or that a collision would lead to an attack, are slim, I would rather see this use the PRF hash so we have at least that much flexibility. If the current design is retained, I would like to see a little discussion of this in the document. A little analysis of the properties we expect the hash to provide would also be good. I think that truncated hashes might be advantageous from the server side. Given that the server only uses hashes to identify which of the offered (available, known?) cached information is in use, is there any reason you can't save additional space by arbitrarily truncating the hash? In many cases I would imagine that the client would be offering only one option and even if there were a small number of options presented, a single byte would suffice to disambiguate. I'm trying to think why you might want the full-length hash on the client side, but I believe that the only problem there is that there might be a collision between the certificates that a server might offer if you truncate too aggressively. The connection still relies on the server presenting proof of knowledge of a key that the client extracts from a certificate bound to the server identity, so I believe that it would be equally secure if you removed all mention of certificates from the protocol. And that makes me nervous, because I'm fairly sure that Karthik will tell me that I'm wrong very shortly; since we've put in a lot of work to cover key fields in the handshake hash, and I'm concerned that this could be exploited somehow. The more I think about this, the more I think that we need a little more analysis on this point (i.e., what properties the hash function needs to provide and why). If it has already happened, mention of that in the security considerations is needed. (I think that truncation on the server side is safe if the client uses a strong hash function to identify the certificate, but I'm frequently wrong about these things.) On 6 August 2015 at 10:24, Joseph Salowey <j...@salowey.net> wrote: > Hi Folks, > > This is the Working Group last call for draft-ietf-tls-cached-info-19. This > document has undergone modification since last WGLC so another WGLC is > appropriate. This document is a dependency for the DICE working group > TLS/DTLS profile. Please send your comments to the TLS list by September 2, > 2015. > > Thanks, > > J&S > > _______________________________________________ > 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
