Martin's comment reminded me of the following that I've been meaning to post...
In a recent discussion among some crypto folks, the topic of what TLS 1.3 could be came up. Now by TLS 1.3 I mean TLS 1.3 as a simple upgrade path from TLS 1.2, not the TLS 2.0-called-TLS 1.3 that it currently is. The discussion centered around the fact that we already have lots of analysis done for TLS 1.x, and it's not too hard to create a TLS 1.3 that fixes the TLS < 1.3 problems while being as compatible as possible with existing infrastructure. So what this would do is take existing security analysis applied to TLS, namely: Bhargavan et al, "Proving the TLS handshake secure (as is)". Brzuska et al, "Less is more: relaxed yet compatible security notions for key exchange". Dowling et al, "Modelling ciphersuite and version negotiation in the TLS protocol". Firing, "Analysis of the Transport Layer Security protocol". Gajek et al, "Universally Composable Security Analysis of TLS". Giesen et al, "On the security of TLS renegotiation". Jager et al, "On the security of TLS-DHE in the standard model". Krawczyk et al, "On the security of the TLS protocol". (and probably several more) and use them to simplify TLS 1.2 to create an improved TLS that leverages about 15 years of analysis, rather than creating what's almost a new protocol based on bleeding-edge/experimental ideas, mechanisms, and algorithms. The discussion started out somewhat informally so by the time it got really interesting it was too late to take notes, but I thought I'd try and recreate the design points... - Drop 99% of all cipher suites, leaving one traditional one (DHE + AES-CBC + HMAC-SHA2 + RSA-SHA2/PSK for auth) and one ECC one (ECDHE + AES-GCM + HMAC- SHA2 + ECDSA-SHA2/PSK for auth) as must's (with a strong preference for OCB instead of GCM as the AEAD if it were freely available). - For the non-AEAD cipher, use EtM not MtE (so effectively making it AEAD as well). - Get rid of the IPsec cargo-cult MAC truncation. - For DHE, send the full set of parameters (X9.42), not p+g only (PKCS #3) to allow verification (for those who don't have a copy of X9.42, it requires the same verification steps as FIPS 186 does). Also, mix the hash of the DHE values into the computed premaster secret to protect against use of manipulated curves. - RSA-PSS, not PKCS #1 (with a subset arguing for PKCS #1 with the sig-check done as encode-then-compare, which fixes all known padding-manipulation issues). - No compression or rehandshake. - Replace the PRF with HKDF? (No pressing need for this, but it would be part of the general cleanup). Longer discussion points: - The DHE/ECDHE parameters were a bit contentious. For DHE the choice is between server-specified ephemeral parameters and IETF-blessed fixed ones. Arguments can be made either way, we had de facto IETF-blessed fixed DHE params in the form of the RFC 2409 ones, but that wasn't such a good idea. OTOH with ephemeral DHE params many implementations didn't check them, but then the spec never required any checking (or much of anything at all in regard to DHE use, which no doubt contributed to some of the dubious practices that have been found in the wild). The situation wasn't helped by the use of the PKCS #3 representation, which the requirement to use the X9.42 form alongside the accompanying checks attempts to address. - Similarly, for ECDHE the choice is between NIST and CFRG ones. The CFRG ones are obviously better (for various values of better, see endless debates elsewhere), but some people will insist on only using something that's come from NIST (I'll reserve my opinion on that one, and wouldn't dream of stooping to phrases like "cargo cult protocol design"...). Peter. _______________________________________________ TLS mailing list TLS@ietf.org https://www.ietf.org/mailman/listinfo/tls
