Python uses valid Python identifiers for hashing algorithms while OpenSSL uses slightly different default names. For example OpenSSL uses "SHA3-256" while Python has "sha3_256". The function py_digest_by_name() in _hashopenssl.c maps from Python names to EVP_MD pointer.

It's possible to simplify the lookup by registering Python's aliases with OpenSSL, e.g. EVP_add_digest_alias(SN_sha3_512, "sha3_512").

Also see https://github.com/openssl/openssl/issues/11715

Adding aliases in openssl is presumably process global right? Is that wise
given it'd mean other openssl using c/c++ code in the process would now see
the same aliases and could behave differently when used with python vs
without?

On Sun, May 3, 2020, 3:55 AM Christian Heimes <report@bugs.python.org>
wrote:

>
> Change by Christian Heimes <lists@cheimes.de>:
>
>
> ----------
> keywords: +patch
> pull_requests: +19193
> pull_request: https://github.com/python/cpython/pull/19880
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <https://bugs.python.org/issue40482>
> _______________________________________
>

Yes, it changes the global state of libcrypto.

I consider the risk to other application slim to non-existing. Two cases are problematic:

1) an application relies on the fact that EVP_get_digestbyname("sha3_256") fails.
2) an application also uses EVP_add_digest_alias() but registers a different digest algorithm.

Both cases seem highly unlikely to me.

I decided against the approach.