On 07/21/2017 08:23 AM, Hubert Kario wrote: > Signature Algorithms for ECDSA now define both the curve and the hash > algorithm: > > ecdsa_secp256r1_sha256(0x0403), > ecdsa_secp384r1_sha384(0x0503), > ecdsa_secp521r1_sha512(0x0603), > > This is in contrast to the TLS 1.2 protocol, where any hash can be used with > any curve.
I assume you saw https://www.ietf.org/mail-archive/web/tls/current/msg23714.html which raised a different question in this same general area. I do not see how the response here cannot be the same as it was there: namely, that the current formulation is assumed to have WG consensus, having been through two WGLCs; there would need to be rather strong reasons to make changes at this stage. -Ben > There are good reasons for that change: > - less combinations to test > - establishes the low water mart for security > > I see few problems with that though: > 1). there are not insignificant number of clients that advertise support for > all (at least P-256 and P-384) curves, but don't advertise support for > hashes stronger than SHA-256 with ECDSA[1] > 2). This is inconsistent with RSA-PSS behaviour, where key size is completely > detached from the used hash algorithm. > 3). This is not how ECDSA signatures in X.509 work, so it doesn't actually > limit the signatures on certificates (in other words, as an implementer > you need to support all hashes with all curves either way) > > With the implementers hat on, I'd prefer to drop the curves from signature > algorithm names/specifications and return to TLS 1.2 behaviour. > With my security hat on, I'd say that we should set the minimal key sizes for > RSA-PSS signatures too, as we did with ECDSA. > > Any other ideas? > > > 1 - Nick Sullivan from Cloudflare provided me with some stats from random > 50000 client hellos from early 2017: > > Sigalgs: > ECDSA + SHA-256 = 39104 (78.2%) > ECDSA + (SHA-256 + SHA-384 + SHA-512) = 28678 (57.4%) > ECDSA + (SHA-256 + SHA-384 + !SHA-512) = 8934 (17.9%) > ECDSA + (SHA-256 + !SHA-384 + !SHA-512) = 1492 (2.98%) > > Note: many of the 1492 seem to be on iOS and only support: > [RSA-SHA-384, RSA-SHA-256, RSA-SHA1, ECDSA-SHA256, ECDSA-SHA1] > > Curves: > none = 757 (1.51%) > P-256 = 49243 (98.5%) > P-384 = 49233 (98.5%) > P-256 + P-384 = 49233 (98.5%) > P-256 + !P-384 = 10 (0.02%) > !P-256 + P-384 = 0 (0%) > > > _______________________________________________ > TLS mailing list > TLS@ietf.org > https://www.ietf.org/mailman/listinfo/tls
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