Remove SIMD support for BLAKE-2 and HMAC-BLAKE-2 #160333

Feature or enhancement

As announced on DPO, I will remove SIMD support for BLAKE2 and HMAC-BLAKE2. I want to reduce the API surface of BLAKE-2 to what OpenSSL provides
(digest, MAC). More precisely:

• Deprecate the tree-hashing parameters of hashlib.blake2b and hashlib.blake2s, namely fanout, depth, leaf_size, node_offset, node_depth, inner_size and last_node.
• Deprecate salt and person when key is not given. Keyed BLAKE-2 still accepts them.
• Remove SIMD support from blake2module.c and hmacmodule.c, together with the corresponding checks in configure.ac. This does not change the API, so there is no deprecation period. SIMD was only enabled on (some) x86-64 platforms and broke the build on many others. This also fixes HACL* HMAC does not properly use vectorized BLAKE-2 #138114¹

Deprecation starts in 3.16 and removal is planned for 3.21. Exposing the OpenSSL BLAKE-2 API (and handling the usedforsecurity parameter) will be done separately.

Has this already been discussed elsewhere?

I have already discussed this feature proposal on Discourse

Links to previous discussion of this feature:

https://discuss.python.org/t/remove-simd-support-for-blake2/109603/14

Linked PRs

• gh-160333: deprecate BLAKE-2 tree hashing parameters #160374 (withdrawn)
• gh-160333: deprecate BLAKE-2 salt and personalization without a key #160375 (withdrawn)
• gh-160333: remove SIMD support for HACL* BLAKE-2 #160392