Feature Request: COSE-HPKE (Hybrid Public Key Encryption)

[aidangarske]

Goal
Implement COSE-HPKE as defined in RFC 9459. HPKE is the modern standard for hybrid encryption, combining the efficiency of symmetric crypto with the security of asymmetric crypto.

Proposed Implementation

• Define HPKE suite identifiers (KEM, KDF, AEAD) in wolfcose/cose_types.h.
• Integrate with wolfSSL's HPKE module.
• Expose public API: wc_Cose_Encrypt_HPKE().
• Add unit tests in tests/ comparing output against RFC test vectors.
• Update tools/wolfcose_tool.c to support HPKE-specific flags.

Optimization Target

• Ensure HPKE context does not require permanent heap residency.
• Minimize binary size by making HPKE support a compile-time option.

References

Link to RFC: RFC 9459 - COSE HPKE

Competitor status: Not available in libcose; roadmap item for t_cose but not prioritized.