feat(registry): add AES-SIV AEAD variant (RFC 5297)

[Mehrn0ush]

As discussed in ticket #763, this PR adds AES-SIV (RFC 5297) as an AEAD variant to the Cryptography Registry.

Fixes #763

Details

• Adds AES[-(128|192|256)]-SIV as an ae variant under the existing AES family.
• Adds authoritative standards reference for RFC 5297.
• Registry-only change (schema/cryptography-defs.json). No schema or specification behavior changes.

[stevespringett]

@bhess

[bhess]

LGTM

[Copilot]

Pull request overview

This PR adds AES-SIV (Synthetic Initialization Vector) as a new AEAD variant to the cryptography registry, addressing issue #763. AES-SIV is defined in RFC 5297 and provides deterministic authenticated encryption with associated data (AEAD).

Changes:

• Adds AES-SIV variant with support for 128, 192, and 256-bit key sizes
• Includes authoritative RFC 5297 standard reference with DOI URL
• Classified as an authenticated encryption (ae) primitive within the AES algorithm family

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Mehrn0ush]

Fixed — normalized to RFC5297 for consistency across the registry.

[stevespringett]

Thanks again for the PR. Once merge conflicts are resolved, I can go ahead and merge this in. Thanks again.

[Mehrn0ush]

Conflicts are now resolved and the branch has been rebased onto the latest upstream/master.

AES-SIV (RFC5297) is correctly registered under the AES AEAD family and RFC naming has been normalized for consistency. DCO sign-off is preserved.

Thanks again for the review.