Competitor SBOM/Scan Signature Verification (CM2)

Status: Draft · Date: 2025-12-04 Scope: Specify signature and provenance verification requirements for accepting external SBOM and scan outputs, including rejection/flag policies.

Objectives

Define acceptable signature algorithms and formats.
Establish trust root management for external signers.
Specify verification workflow and failure modes.
Enable offline verification with bundled trust roots.

Acceptable Signatures

Signature Formats

Format	Algorithm	Key Type	Status
DSSE	Ed25519	Asymmetric	Preferred
DSSE	ECDSA P-256	Asymmetric	Accepted
DSSE	RSA-2048+	Asymmetric	Accepted
COSE	EdDSA	Asymmetric	Accepted
JWS	ES256	Asymmetric	Accepted
JWS	RS256	Asymmetric	Deprecated

Hash Algorithms

Algorithm	Usage	Status
SHA-256	Primary	Required
BLAKE3-256	Secondary	Preferred
SHA-384	Alternative	Accepted
SHA-512	Alternative	Accepted
SHA-1	Legacy	Rejected
MD5	Legacy	Rejected

Trust Root Management

Bundled Trust Roots

out/offline/competitor-ingest-kit-v1/trust/
├── root-ca.pem              # CA for signed SBOMs
├── keyring.json             # Known signing keys
├── cosign-keys/             # Cosign public keys
│   ├── syft-release.pub
│   ├── trivy-release.pub
│   └── clair-release.pub
└── fulcio-root.pem          # Sigstore Fulcio CA

Keyring Format

{
  "keys": [
    {
      "id": "syft-release-2025",
      "type": "ecdsa-p256",
      "publicKey": "-----BEGIN PUBLIC KEY-----\n...\n-----END PUBLIC KEY-----",
      "issuer": "https://github.com/anchore/syft",
      "validFrom": "2025-01-01T00:00:00Z",
      "validTo": "2026-01-01T00:00:00Z",
      "purposes": ["sbom-signing", "attestation-signing"]
    }
  ],
  "trustedIssuers": [
    "https://github.com/anchore/syft",
    "https://github.com/aquasecurity/trivy",
    "https://github.com/quay/clair"
  ]
}

Verification Workflow

┌─────────────┐
│  Receive    │
│   SBOM      │
└─────────────┘
       │
       ▼
┌─────────────┐     ┌─────────────┐
│ Has DSSE?   │──No─► Has JWS?    │──No─► Unsigned
└─────────────┘     └─────────────┘          │
       │                   │                 │
      Yes                 Yes                │
       │                   │                 │
       ▼                   ▼                 ▼
┌─────────────┐     ┌─────────────┐  ┌─────────────┐
│ Verify DSSE │     │ Verify JWS  │  │ Apply CM6   │
│  Signature  │     │  Signature  │  │  Fallback   │
└─────────────┘     └─────────────┘  └─────────────┘
       │                   │                 │
       ▼                   ▼                 ▼
┌─────────────┐     ┌─────────────┐  ┌─────────────┐
│   Valid?    │     │   Valid?    │  │ Provenance: │
└─────────────┘     └─────────────┘  │   unknown   │
    │     │             │     │      └─────────────┘
   Yes    No           Yes    No
    │     │             │     │
    ▼     ▼             ▼     ▼
 Accept  Reject      Accept  Reject

Verification Steps

Format Detection
- Check for DSSE envelope wrapper
- Check for detached signature file (.sig)
- Check for inline JWS header
Signature Extraction
- Parse envelope/signature structure
- Extract signer key ID and algorithm
Key Lookup
- Search bundled keyring for key ID
- Verify key is within validity period
- Check key purpose matches usage
Cryptographic Verification
- Verify signature over payload
- Verify hash matches content
- Check for signature expiry
Provenance Validation
- Extract signer identity
- Verify issuer is trusted
- Check build metadata if present

Failure Modes

Rejection Reasons

Code	Reason	Action
`sig_missing`	No signature present	Apply fallback (CM6)
`sig_invalid`	Signature verification failed	Reject
`sig_expired`	Signature validity period exceeded	Reject
`key_unknown`	Signing key not in keyring	Reject
`key_expired`	Signing key validity exceeded	Reject
`key_revoked`	Signing key has been revoked	Reject
`issuer_untrusted`	Issuer not in trusted list	Reject
`alg_unsupported`	Algorithm not acceptable	Reject
`hash_mismatch`	Content hash doesn’t match	Reject

Flag Policy

When --allow-unsigned is set:

Condition	Behavior
Signature missing	Accept with `provenance=unknown`, emit warning
Signature invalid	Reject (flag doesn’t override invalid)
Key unknown	Accept with `provenance=unverified`, emit warning

Verification API

Endpoint

POST /api/v1/ingest/verify
Content-Type: application/json

{
  "sbom": "<base64-encoded-sbom>",
  "signature": "<base64-encoded-signature>",
  "options": {
    "allowUnsigned": false,
    "requireProvenance": true
  }
}

Response

{
  "verification": {
    "status": "valid",
    "signature": {
      "format": "dsse",
      "algorithm": "ecdsa-p256",
      "keyId": "syft-release-2025",
      "signedAt": "2025-12-04T00:00:00Z"
    },
    "provenance": {
      "issuer": "https://github.com/anchore/syft",
      "buildId": "build-12345",
      "sourceRepo": "https://github.com/example/app"
    },
    "hash": {
      "algorithm": "sha256",
      "value": "..."
    }
  }
}

Offline Verification

Requirements

All trust roots bundled in offline kit
No network calls during verification
Keyring includes all expected signers
CRL/OCSP checks disabled (use bundled revocation lists)

Revocation List Format

{
  "revoked": [
    {
      "keyId": "compromised-key-2024",
      "revokedAt": "2024-12-01T00:00:00Z",
      "reason": "Key compromise"
    }
  ],
  "lastUpdated": "2025-12-04T00:00:00Z"
}

Integration with Normalization (CM1)

After successful verification:

Extract tool metadata from signature/provenance
Pass to normalization adapter
Include verification result in normalized output

{
  "source": {
    "tool": "syft",
    "version": "1.0.0",
    "hash": "sha256:..."
  },
  "verification": {
    "status": "verified",
    "keyId": "syft-release-2025",
    "signedAt": "2025-12-04T00:00:00Z"
  },
  "components": [...],
  "normalized_hash": "blake3:..."
}