Improve RSAPSS documentation

[ma-ilsi]

Summary of Changes

The documentation for RSAPSS receives additional clarity:

• Usage example extended to show error handling should be present to deal with failure when loading keys.
• Return value of Hacl_RSAPSS_new_rsapss_load_pkey and Hacl_RSAPSS_new_rsapss_load_skey explains that NULL is returned on failure.
• Supported hash algorithms are listed in every applicable function and rendered in proper bullet point form, now.
• Endianness/Byte-order addressed for key part parameters.
• Additionally, I decided to explicitly mention the disjoint memory pre-condition only for the sgnt parameter in applicable functions in the case a client, for some odd reason, decides to overwrite other arguments with the produced signature.

Issues Resolved

Resolves #346.

Local Testing

./mach build --test: all passed.
./mach doc: finished, RSAPSS documentation page renders correctly.

[cla-bot]

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[ma-ilsi]

@cryspen/core

[franziskuskiefer]

Hey, thanks for looking into this!

This code is all generated from F*. So we can't just change it here.
The code is coming from here and here etc.
Would you mind moving you changes over there?

[ma-ilsi]

Would you mind moving you changes over there?

No problem. Once we finish/resolve our above conversation, I'll head over there.

[cla-bot]

We require contributors to sign our Contributor License Agreement https://github.com/cryspen/hacl/blob/main/CLA.md ensuring that the contribution can be licensed under Apache 2.0 and MIT. In order for us to review and merge your code, please mention @cryspen/core in a comment below to get yourself added.

[ma-ilsi]

Here's the latest:

• Branch updated to include .cpp test update only. So you can merge for that change only.

• Original message of this PR updated to resolve Extend RSA-PSS examples. #346, only.

• hacl-star PR: Improve RSAPSS documentation hacl-star/hacl-star#858 to increase clarity, endianness, return values.

• Memory disjoint condition has been left out and can be addressed separately, later. (Verification conditions not checked on behalf of the client in the generated C code seems like a problem for this repo. You could add the memory note to the top of docs/reference/hacl/signature/rsapss.md file - anyways that's another issue).

That's about it. I think we're done here.

[franziskuskiefer]

Thanks

[franziskuskiefer]

Can you update your branch? Then I can merge it.

[ma-ilsi]

Gotcha