Hubert Kario <hka...@redhat.com> wrote: >> >> Thanks to Peter Gutmann for the summary: >> >> https://mailarchive.ietf.org/arch/msg/tls/g0MDCdZcHsvZefv4V8fssXMeEHs >> >> which you may have missed. > > yes, Joux paper also shows that attacking MD5||SHA1 is harder than attacking > SHA1 alone > > but that doesn't matter, what matters is _how much harder it is_ and Joux > paper says that it's less than a work factor of two, something also knows > as a "rounding error" for cryptographic attacks
collision attacks and real-time 2nd preimage attacks on randomly keyed hashes are substantially different things. simple math seems hard. TLSv1.0 + TLSv1.1 both use (rsa, MD5||SHA1) TLSv1.2 (rfc5246) permitted (rsa, MD5) and allows (rsa,SHA1) if we assumed that there *existed* (it currently doesn't, mind you) a successful preimage attack on MD5 with effort 2^20 a successful preimage attack on SHA1 with effort 2^56 then if Joux would apply not just to multicollisons, but also 2nd preimage, then the efforts would be: TLSv1.2 (rsa,MD5) 2^20 TLSv1.2 (rsa,SHA1) 2^56 TLSv1.0 (rsa, MD5||SHA1) >= 2^57 (slightly more than the stronger of the two) Comparing TLSv1.0 (rsa,MD5||SHA1) 2^57 with TLSv1.2 (rsa,MD5) 2^20 A factor 2^37 is significantly more than "marginally stronger". If you are aware of successfull 2nd preimage attacks on either MD5 or SHA1, please provide references. -Martin _______________________________________________ TLS mailing list TLS@ietf.org https://www.ietf.org/mailman/listinfo/tls
