src/pqc_mbom/signer.py
| 1 | """MBOM signing and verification using ML-DSA.""" |
| 2 | |
| 3 | from __future__ import annotations |
| 4 | |
| 5 | import hashlib |
| 6 | from dataclasses import dataclass |
| 7 | from datetime import datetime, timezone |
| 8 | |
| 9 | from quantumshield.core.algorithms import SignatureAlgorithm |
| 10 | from quantumshield.core.signatures import sign, verify |
| 11 | from quantumshield.identity.agent import AgentIdentity |
| 12 | |
| 13 | from pqc_mbom.errors import SignatureVerificationError |
| 14 | from pqc_mbom.mbom import MBOM |
| 15 | |
| 16 | |
| 17 | @dataclass(frozen=True) |
| 18 | class VerificationResult: |
| 19 | """Outcome of verifying a signed MBOM.""" |
| 20 | |
| 21 | signature_valid: bool |
| 22 | root_hash_valid: bool |
| 23 | mbom_id: str |
| 24 | signer_did: str | None |
| 25 | algorithm: str | None |
| 26 | error: str | None = None |
| 27 | |
| 28 | @property |
| 29 | def valid(self) -> bool: |
| 30 | """True iff both the ML-DSA signature and the recomputed root match.""" |
| 31 | return self.signature_valid and self.root_hash_valid |
| 32 | |
| 33 | |
| 34 | class MBOMSigner: |
| 35 | """Signs MBOM documents with a fixed AgentIdentity. |
| 36 | |
| 37 | Usage: |
| 38 | identity = AgentIdentity.create("llama-release-pipeline") |
| 39 | signer = MBOMSigner(identity) |
| 40 | signer.sign(mbom) # mutates mbom in place |
| 41 | """ |
| 42 | |
| 43 | def __init__(self, identity: AgentIdentity) -> None: |
| 44 | self.identity = identity |
| 45 | |
| 46 | def sign(self, mbom: MBOM) -> MBOM: |
| 47 | """Populate signature fields on `mbom` using ML-DSA. |
| 48 | |
| 49 | Recomputes the components_root_hash before signing so the signature |
| 50 | always commits to the current component set. |
| 51 | """ |
| 52 | mbom.recompute_root() |
| 53 | digest = hashlib.sha3_256(mbom.canonical_bytes()).digest() |
| 54 | sig = sign(digest, self.identity.signing_keypair) |
| 55 | mbom.signer_did = self.identity.did |
| 56 | mbom.algorithm = self.identity.signing_keypair.algorithm.value |
| 57 | mbom.signature = sig.hex() |
| 58 | mbom.public_key = self.identity.signing_keypair.public_key.hex() |
| 59 | mbom.signed_at = datetime.now(timezone.utc).isoformat() |
| 60 | return mbom |
| 61 | |
| 62 | |
| 63 | class MBOMVerifier: |
| 64 | """Verifies MBOM signatures and component-root integrity.""" |
| 65 | |
| 66 | @staticmethod |
| 67 | def verify(mbom: MBOM) -> VerificationResult: |
| 68 | """Check both the signature and the components_root_hash.""" |
| 69 | expected_root = MBOMVerifier._expected_root(mbom) |
| 70 | root_ok = expected_root == mbom.components_root_hash |
| 71 | |
| 72 | if not mbom.signature or not mbom.algorithm: |
| 73 | return VerificationResult( |
| 74 | signature_valid=False, |
| 75 | root_hash_valid=root_ok, |
| 76 | mbom_id=mbom.mbom_id, |
| 77 | signer_did=mbom.signer_did or None, |
| 78 | algorithm=mbom.algorithm or None, |
| 79 | error="mbom is unsigned", |
| 80 | ) |
| 81 | |
| 82 | try: |
| 83 | algorithm = SignatureAlgorithm(mbom.algorithm) |
| 84 | except ValueError: |
| 85 | return VerificationResult( |
| 86 | signature_valid=False, |
| 87 | root_hash_valid=root_ok, |
| 88 | mbom_id=mbom.mbom_id, |
| 89 | signer_did=mbom.signer_did, |
| 90 | algorithm=mbom.algorithm, |
| 91 | error=f"unknown algorithm {mbom.algorithm}", |
| 92 | ) |
| 93 | |
| 94 | digest = hashlib.sha3_256(mbom.canonical_bytes()).digest() |
| 95 | try: |
| 96 | sig_valid = verify( |
| 97 | digest, |
| 98 | bytes.fromhex(mbom.signature), |
| 99 | bytes.fromhex(mbom.public_key), |
| 100 | algorithm, |
| 101 | ) |
| 102 | except Exception as exc: |
| 103 | return VerificationResult( |
| 104 | signature_valid=False, |
| 105 | root_hash_valid=root_ok, |
| 106 | mbom_id=mbom.mbom_id, |
| 107 | signer_did=mbom.signer_did, |
| 108 | algorithm=mbom.algorithm, |
| 109 | error=f"signature verify failed: {exc}", |
| 110 | ) |
| 111 | |
| 112 | if not sig_valid: |
| 113 | return VerificationResult( |
| 114 | signature_valid=False, |
| 115 | root_hash_valid=root_ok, |
| 116 | mbom_id=mbom.mbom_id, |
| 117 | signer_did=mbom.signer_did, |
| 118 | algorithm=mbom.algorithm, |
| 119 | error="invalid ML-DSA signature", |
| 120 | ) |
| 121 | |
| 122 | if not root_ok: |
| 123 | return VerificationResult( |
| 124 | signature_valid=True, |
| 125 | root_hash_valid=False, |
| 126 | mbom_id=mbom.mbom_id, |
| 127 | signer_did=mbom.signer_did, |
| 128 | algorithm=mbom.algorithm, |
| 129 | error=( |
| 130 | f"components_root_hash mismatch (expected {expected_root[:16]}, " |
| 131 | f"got {mbom.components_root_hash[:16]})" |
| 132 | ), |
| 133 | ) |
| 134 | |
| 135 | return VerificationResult( |
| 136 | signature_valid=True, |
| 137 | root_hash_valid=True, |
| 138 | mbom_id=mbom.mbom_id, |
| 139 | signer_did=mbom.signer_did, |
| 140 | algorithm=mbom.algorithm, |
| 141 | ) |
| 142 | |
| 143 | @staticmethod |
| 144 | def verify_or_raise(mbom: MBOM) -> VerificationResult: |
| 145 | """Verify and raise SignatureVerificationError on any failure.""" |
| 146 | result = MBOMVerifier.verify(mbom) |
| 147 | if not result.valid: |
| 148 | raise SignatureVerificationError( |
| 149 | f"MBOM {mbom.mbom_id} failed verification: {result.error}" |
| 150 | ) |
| 151 | return result |
| 152 | |
| 153 | @staticmethod |
| 154 | def _expected_root(mbom: MBOM) -> str: |
| 155 | component_hashes = sorted(c.hash() for c in mbom.components) |
| 156 | concat = "|".join(component_hashes).encode("utf-8") |
| 157 | return hashlib.sha3_256(concat).hexdigest() |
| 158 | |