hashes/sha2{24,56}: Remove static variables from sha256

[bergzand]

Contribution description

This removes the static (thread-unsafe) variables from sha256 and hmac_sha256 to remove a potential footgun. The static variable is only used when the caller does not supply a pointer to store the digest and it is returned via the (undocumented) return value.

This commit removes this option and makes the digest argument mandatory.

Testing procedure

The tests-hashes unittest should still work:

main(): This is RIOT! (Version: 2024.01-devel-240-gc98f3-pr/sha256/no_static)
Help: Press s to start test, r to print it is ready
s
START
...........................................
OK (43 tests)

Issues/PRs references

Introduced in #124

[mguetschow]

You'd need to adapt the documentation as well (in other places, too).

[bergzand]

Thanks! I just did a quick scan for a doxygen @return and nothing showed up.

[bergzand]

Adjusted the docs

[bergzand]

And removed the return argument from hmac_sha256 also

[mguetschow]

LGTM then. Since this is an API breaking change, do we need to note that somewhere for the next release notes?

[riot-ci]

Murdock results

✔️ PASSED

434e564 hashes/sha224: Remove static variables from sha224

Success	Failures	Total	Runtime
8101	0	8101	10m:57s

Artifacts

• Documentation preview

[maribu]

Please squash

[OlegHahm]

I assume you have checked that no existing code calls the functions with passing a NULL pointer for digest?

[maribu]

I assume you have checked that no existing code calls the functions with passing a NULL pointer for digest?

That code would need to make use of the return value, which by changing the signature will result in a compilation error that Murdock should catch.

[OlegHahm]

I assume you have checked that no existing code calls the functions with passing a NULL pointer for digest?

That code would need to make use of the return value, which by changing the signature will result in a compilation error that Murdock should catch.

Valid point. 😊

[mguetschow]

ping @bergzand for squashing

[bergzand]

ping @bergzand for squashing

Done, sorry for the delay!