[gnutls-devel] GnuTLS | nettle: port upstream hardening of EC point multiplication [3.6.x] (!1407)

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Sun Apr 4 19:15:17 CEST 2021

Niels Möller commented:

I don't have the full context. Regarding https://git.lysator.liu.se/nettle/nettle/-/commit/5b7608fde3a6d2ab82bffb35db1e4e330927c906, that is indeed a cleanup. The bug fix changes are those that replace ecc_mod_mul, without any additional reduction logic, with calls to ecc_mod_mul_canonical.

I don't see see the fix to ecc_ecdsa_verify backported in this mr (https://git.lysator.liu.se/nettle/nettle/-/commit/2397757b3f95fcae1e2d3011bf99ca5b5438378f), that seems quite important?

For backports, I know that the GNU guix project is interested in a backport to nettle-3.5, see https://debbugs.gnu.org/cgi/bugreport.cgi?bug=47222

I might make sense to add a helper similar to the the ecc_mod_mul_canonical in nettl-3.7.2, but as you have noticed, it can't be identical due to the changed conventions for ecc_mod_mul and the underlying mod functions. But I think it should be fairly straight forward to write a variant with an interface compatible with ecc_mod_mul in older versions.

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