src/pqc_hypervisor_attestation/signer.py
| 1 | """Attester (signs reports) and AttestationVerifier (checks them).""" |
| 2 | |
| 3 | from __future__ import annotations |
| 4 | |
| 5 | import hashlib |
| 6 | from dataclasses import dataclass |
| 7 | |
| 8 | from quantumshield.core.algorithms import SignatureAlgorithm |
| 9 | from quantumshield.core.signatures import sign, verify |
| 10 | from quantumshield.identity.agent import AgentIdentity |
| 11 | |
| 12 | from pqc_hypervisor_attestation.claim import AttestationReport |
| 13 | from pqc_hypervisor_attestation.errors import ( |
| 14 | AttestationVerificationError, |
| 15 | RegionDriftError, |
| 16 | ) |
| 17 | |
| 18 | |
| 19 | @dataclass(frozen=True) |
| 20 | class VerificationResult: |
| 21 | """Outcome of verifying an AttestationReport.""" |
| 22 | |
| 23 | valid: bool |
| 24 | signature_valid: bool |
| 25 | not_expired: bool |
| 26 | drifts: list[str] # region_ids whose snapshot != expected |
| 27 | error: str | None = None |
| 28 | |
| 29 | |
| 30 | class Attester: |
| 31 | """Sign AttestationReports with an AgentIdentity.""" |
| 32 | |
| 33 | def __init__(self, identity: AgentIdentity): |
| 34 | self.identity = identity |
| 35 | |
| 36 | def sign(self, report: AttestationReport) -> AttestationReport: |
| 37 | canonical = report.canonical_bytes() |
| 38 | digest = hashlib.sha3_256(canonical).digest() |
| 39 | sig = sign(digest, self.identity.signing_keypair) |
| 40 | report.signer_did = self.identity.did |
| 41 | report.algorithm = self.identity.signing_keypair.algorithm.value |
| 42 | report.signature = sig.hex() |
| 43 | report.public_key = self.identity.signing_keypair.public_key.hex() |
| 44 | return report |
| 45 | |
| 46 | |
| 47 | class AttestationVerifier: |
| 48 | """Independently verify AttestationReports. |
| 49 | |
| 50 | Checks: |
| 51 | - ML-DSA signature over canonical bytes |
| 52 | - Report not expired |
| 53 | - Each claim's snapshot.content_hash matches its expected_hash (if set) |
| 54 | """ |
| 55 | |
| 56 | @staticmethod |
| 57 | def verify( |
| 58 | report: AttestationReport, |
| 59 | strict: bool = True, |
| 60 | ) -> VerificationResult: |
| 61 | # 1. Signature check |
| 62 | sig_ok = False |
| 63 | err: str | None = None |
| 64 | if not report.signature: |
| 65 | err = "missing signature" |
| 66 | else: |
| 67 | try: |
| 68 | algorithm = SignatureAlgorithm(report.algorithm) |
| 69 | digest = hashlib.sha3_256(report.canonical_bytes()).digest() |
| 70 | sig_ok = verify( |
| 71 | digest, |
| 72 | bytes.fromhex(report.signature), |
| 73 | bytes.fromhex(report.public_key), |
| 74 | algorithm, |
| 75 | ) |
| 76 | if not sig_ok: |
| 77 | err = "invalid ML-DSA signature" |
| 78 | except ValueError: |
| 79 | err = f"unknown algorithm {report.algorithm}" |
| 80 | except Exception as exc: # noqa: BLE001 - surface backend failures uniformly |
| 81 | err = f"signature verify failed: {exc}" |
| 82 | |
| 83 | # 2. Expiry check |
| 84 | fresh = not report.is_expired() |
| 85 | if sig_ok and not fresh: |
| 86 | err = "report expired" |
| 87 | |
| 88 | # 3. Drift check: each claim's snapshot vs expected_hash |
| 89 | drifts: list[str] = [] |
| 90 | for claim in report.claims: |
| 91 | if claim.expected_hash and claim.snapshot.content_hash != claim.expected_hash: |
| 92 | drifts.append(claim.region.region_id) |
| 93 | if sig_ok and fresh and drifts and strict: |
| 94 | err = ( |
| 95 | f"memory drift detected in {len(drifts)} region(s): " |
| 96 | f"{', '.join(drifts)}" |
| 97 | ) |
| 98 | |
| 99 | valid = sig_ok and fresh and (not drifts or not strict) |
| 100 | return VerificationResult( |
| 101 | valid=valid, |
| 102 | signature_valid=sig_ok, |
| 103 | not_expired=fresh, |
| 104 | drifts=drifts, |
| 105 | error=err, |
| 106 | ) |
| 107 | |
| 108 | @staticmethod |
| 109 | def verify_or_raise(report: AttestationReport, strict: bool = True) -> None: |
| 110 | result = AttestationVerifier.verify(report, strict=strict) |
| 111 | if not result.valid: |
| 112 | if result.drifts: |
| 113 | raise RegionDriftError(result.error or "drift detected") |
| 114 | raise AttestationVerificationError( |
| 115 | result.error or "verification failed" |
| 116 | ) |
| 117 | |