feat: JCS canonicalization + post-quantum dual-signature (Ed25519 + ML-DSA-65)

[HaraldeRoessler]

Summary

Two tightly related changes combined into one PR to avoid merge conflicts:

1. RFC 8785 JCS canonicalization — replaces json.dumps(sort_keys=True) with proper jcs.canonicalize() for deterministic VC serialization

2. Post-quantum dual-signature — every credential signed with both Ed25519 (64 bytes) and ML-DSA-65/Dilithium3 (3,309 bytes) when configured

Zero-risk deployment

If DILITHIUM_PRIVATE_KEY_HEX is not set, the system behaves exactly as before (Ed25519-only). Enable PQC by generating keys:

pip install liboqs-python
python scripts/generate_dilithium_keys.py
export DILITHIUM_PRIVATE_KEY_HEX=...
export DILITHIUM_PUBLIC_KEY_HEX=...

Credential format

Without Dilithium (backward compatible):

{"proof": {"type": "Ed25519Signature2020", "canonicalizationAlgorithm": "JCS", ...}}

With Dilithium (dual-signature):

{"proof": [
  {"type": "Ed25519Signature2020", "verificationMethod": "...#key-ed25519", ...},
  {"type": "DilithiumSignature2026", "verificationMethod": "...#key-dilithium", ...}
]}

New files

File	Purpose
app/crypto/dilithium.py	ML-DSA-65 key management, sign, verify (KMS + env fallback)
app/crypto/hybrid.py	dual_sign() and verify_proof() for all proof formats
scripts/generate_dilithium_keys.py	One-time keypair generation

Modified files

File	Change
app/credentials.py	Uses dual_sign(), verify_proof() handles legacy + dual + future formats
app/swarm/endorsement.py	Endorsement VCs use dual_sign()
app/main.py	DID document includes Dilithium key when configured, proof list handling

Locally tested

• Ed25519-only: works, all smoke tests pass
• Dual-signature: both proofs verified (Ed25519: valid, Dilithium: valid)
• DID document: 3 keys (#key-ed25519, #key-1 legacy, #key-dilithium)
• Legacy credentials still verify correctly

Supersedes PRs #5 and #6

Replaces #5 (JCS only) and #6 (PQC only) which would have caused merge conflicts.

Merge order

This PR is independent but recommended to merge after #1 (which adds jcs to requirements.txt).

Generated with Claude Code

[HaraldeRoessler]

Merge order

Recommended to merge last — biggest change, includes JCS + PQC. Independent of #2 and #4 but benefits from #1 (which adds jcs to requirements.txt).

Sequence: #1 → #3 → #2 → #4 → #7

Supersedes closed PRs #5 and #6.