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fix: use RFC 8785 JCS canonicalization for VC signing #5

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HaraldeRoessler wants to merge 1 commit into from
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fix: use RFC 8785 JCS canonicalization for VC signing #5

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14 changes: 11 additions & 3 deletions app/credentials.py
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Original file line number Diff line number Diff line change
@@ -1,5 +1,6 @@
"""MolTrust Verifiable Credentials - W3C VC Data Model"""
import os, json, datetime, hashlib
import jcs
from nacl.signing import SigningKey
from app.crypto.kms_signer import get_decrypted_signing_key_hex

Expand Down Expand Up @@ -27,14 +28,15 @@ def issue_credential(subject_did: str, credential_type: str, claims: dict) -> di
}

signing_key = get_signing_key()
payload = json.dumps(credential, sort_keys=True).encode()
payload = jcs.canonicalize(credential)
signed = signing_key.sign(payload)

credential["proof"] = {
"type": "Ed25519Signature2020",
"created": now.isoformat() + "Z",
"verificationMethod": f"{ISSUER_DID}#key-1",
"proofPurpose": "assertionMethod",
"canonicalizationAlgorithm": "JCS",
"proofValue": signed.signature.hex()
}
return credential
Expand All @@ -48,12 +50,18 @@ def verify_credential(credential: dict) -> dict:

try:
cred_copy = {k: v for k, v in credential.items() if k != "proof"}
payload = json.dumps(cred_copy, sort_keys=True).encode()
signature = bytes.fromhex(proof["proofValue"])

signing_key = get_signing_key()
verify_key = signing_key.verify_key
verify_key.verify(payload, signature)

# Try JCS first (new credentials), fall back to sort_keys (legacy)
if proof.get("canonicalizationAlgorithm") == "JCS":
payload = jcs.canonicalize(cred_copy)
verify_key.verify(payload, signature)
else:
payload = json.dumps(cred_copy, sort_keys=True).encode()
verify_key.verify(payload, signature)

exp = credential.get("expirationDate", "")
if exp:
Expand Down
5 changes: 3 additions & 2 deletions app/swarm/endorsement.py
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Original file line number Diff line number Diff line change
Expand Up @@ -153,15 +153,16 @@ async def issue_endorsement(

# 11. Ed25519 Signatur (HIGH-5: real signing, no more sandbox_unsigned)
from app.credentials import get_signing_key
import json as _json
import jcs as _jcs
signing_key = get_signing_key()
payload = _json.dumps(vc, sort_keys=True).encode()
payload = _jcs.canonicalize(vc)
signed = signing_key.sign(payload)
vc["proof"] = {
"type": "Ed25519Signature2020",
"created": now.isoformat(),
"verificationMethod": "did:web:api.moltrust.ch#key-1",
"proofPurpose": "assertionMethod",
"canonicalizationAlgorithm": "JCS",
"proofValue": signed.signature.hex()
}

Expand Down