refactor(core): move session keys to platform secure storage

[Grolleau-Benjamin]

Summary

Session keys are no longer kept in RAM. It is now up to the user to decide where they are stored, referencing them via a uint32_t key index.

This improves security, enables backend-agnostic key management, and allows integration with PSA and TrustZone Secure Storage.

Changes

• Add secure session key storage via stse_platform_store_session_key
• Session now tracks Host_MAC_key_idx and Host_cipher_key_idx
• Wipe plaintext session keys from RAM after storage
• Use key indices for AES ECB / CBC / CMAC operations

Security

• Session keys no longer persist in RAM
• Enables hardware-backed key protection

Note

STSELib remains backend-agnostic (no PSA assumption). The platform decides how keys are stored and used.

[TofMassilia13320]

Branch is out-of-date with the base branch.
Please rebase!
Tx for your contribution.

[Grolleau-Benjamin]

@TofMassilia13320
This should be fine, I’ve just rebased.

Maybe we should add a Discussions section to this repository, or create a Discord server to discuss this kind of change. It could also be useful to maintain a changelog. Your last change introduced a regression that could have been flagged through a proper changelog process (and I also introduced a huge regression in this PR).

[Grolleau-Benjamin]

Hi @TofMassilia13320,

I've just rebased my branch on prepare v1.1.7.

I also discovered the release notes (doc/resources/Markdown/02_RELEASE_NOTE/release_note.md) by reviewing the commit you just added. Since it currently lists the raw commit history, I was wondering if we could switch to a more user-centric format? Grouping updates by "Added", "Changed", "Fixed", and "Breaking Changes" is usually much easier for users to digest than reading through Git commit messages.

Additionally, it might make more sense to maintain a classic CHANGELOG.md directly at the root of the repository. It's the standard location most developers and users instinctively look for, making it much easier to track the project's evolution at a glance. Furthermore, this location permit to easily add the content to the release note using GitHub CI/CD.

Let me know what your thoughts are on this!

[Grolleau-Benjamin]

Looking at the commits, I also believe that @Grom- would be interested in this discussion.