Problem:

A common pattern is:

GUARD(s2n_stuffer_skip_write(stuffer, bytes_to_write));
uint8_t* ptr = suffer->blob.data + stuffer->write_cursor - bytes_to_write;

which could be simplified.

Solution:

*ptr could be an *out parameter to s2n_stuffer_skip_write

• Does this change what S2N sends over the wire? No.
• Does this change any public APIs? No.

As I was running composer to install a new library into our repo, it warned me that:

Package yzalis/identicon is abandoned, you should avoid using it. No replacement was suggested.

I'm not familiar on what packagist.org's process is to declare a package abandoned. I see that the last commit in their repo is from 2019 and there are a number of unanswered issues and pull requests.

I

Identifiers starting with underscore and a capital letter, or with two underscore, are reserved everywhere in the C language. (Identifiers starting with an underscore and a lowercase letter are only reserved at file scope.) The library uses some reserved identifiers.

Here's a search that weeds out most positives:

grep -P '^(?!#| \*| *!?\(? *defined\(| *(__asm|__attribute__|__GNUC__)).*\b(

Please add provider support for the "botan encryption" command and implement the needed AES operations with PKCS#11.
I could not find any command line tool that I can use for that. OpenSSL's PKCS#11 engine does not support AES either.