# Key Rotation Service with Temporal Validity

## Module
Signer

## Status
IMPLEMENTED

## Description
Automated key rotation service with temporal key validity windows, key history tracking (key_history and key_audit_log tables), trust anchor management with PURL pattern matching, and CLI commands for key lifecycle operations. Ensures proof verification uses the correct key for the attestation timestamp.

## Implementation Details
- **KeyRotationService**: `src/Signer/__Libraries/StellaOps.Signer.KeyManagement/KeyRotationService.cs` -- implements advisory section 8.2: AddKeyAsync (validates algorithm against AllowedAlgorithms, creates KeyHistoryEntity + KeyAuditLogEntity, updates anchor AllowedKeyIds), RevokeKeyAsync (sets RevokedAt + RevokeReason, moves key from AllowedKeyIds to RevokedKeyIds), CheckKeyValidityAsync (temporal validation: NotYetValid if signedAt < AddedAt, Revoked if signedAt >= RevokedAt, Expired if signedAt >= ExpiresAt), GetRotationWarningsAsync (ExpiryApproaching within ExpiryWarningDays, LongLived exceeding MaxKeyAgeDays, AlgorithmDeprecating for deprecated algorithms), GetKeyHistoryAsync; EF Core transactions with InMemory provider detection
- **TrustAnchorManager**: `src/Signer/__Libraries/StellaOps.Signer.KeyManagement/TrustAnchorManager.cs` -- implements advisory section 8.3: GetAnchorAsync, FindAnchorForPurlAsync (glob-style PURL pattern matching with specificity scoring, most-specific-match-wins), CreateAnchorAsync (validates PURL pattern), UpdateAnchorAsync (AllowedPredicateTypes/PolicyRef/PolicyVersion), DeactivateAnchorAsync, VerifySignatureAuthorizationAsync (combines temporal key validity + predicate type authorization), GetActiveAnchorsAsync
- **PurlPatternMatcher**: `src/Signer/__Libraries/StellaOps.Signer.KeyManagement/TrustAnchorManager.cs` -- glob-to-regex pattern matching for PURLs (e.g., pkg:npm/*, pkg:maven/org.apache/*); specificity scoring (segments * 10 - wildcards * 5)
- **KeyRotationOptions**: configurable AllowedAlgorithms (ES256, ES384, ES512, RS256, EdDSA, SM2, GOST12-256, DILITHIUM3, FALCON512, etc.), ExpiryWarningDays (60), MaxKeyAgeDays (365), DeprecatedAlgorithms (RSA-2048, SHA1-RSA)
- **KeyManagementDbContext**: `src/Signer/__Libraries/StellaOps.Signer.KeyManagement/KeyManagementDbContext.cs` -- EF Core context with TrustAnchors, KeyHistory, KeyAuditLog DbSets
- **KeyEntities**: `src/Signer/__Libraries/StellaOps.Signer.KeyManagement/Entities/KeyEntities.cs` -- KeyHistoryEntity (HistoryId, AnchorId, KeyId, PublicKey, Algorithm, AddedAt, ExpiresAt, RevokedAt, RevokeReason), KeyAuditLogEntity (LogId, Operation enum: Add/Revoke/Rotate, Actor, Reason)
- **TrustAnchorEntity**: `src/Signer/__Libraries/StellaOps.Signer.KeyManagement/Entities/TrustAnchorEntity.cs` -- AnchorId, PurlPattern, AllowedKeyIds, RevokedKeyIds, AllowedPredicateTypes, PolicyRef, PolicyVersion, IsActive
- **KeyRotationEndpoints**: `src/Signer/StellaOps.Signer/StellaOps.Signer.WebService/Endpoints/KeyRotationEndpoints.cs` -- REST API at `/api/v1/anchors`: POST /{anchorId}/keys (add key), POST /{anchorId}/keys/{keyId}/revoke, GET /{anchorId}/keys/{keyId}/validity?signedAt=, GET /{anchorId}/keys/history, GET /{anchorId}/keys/warnings; all require KeyManagement authorization
- **IKeyRotationService**: `src/Signer/__Libraries/StellaOps.Signer.KeyManagement/IKeyRotationService.cs` -- interface contract
- **ITrustAnchorManager**: `src/Signer/__Libraries/StellaOps.Signer.KeyManagement/ITrustAnchorManager.cs` -- interface contract
- **Tests**: `src/Signer/StellaOps.Signer/StellaOps.Signer.Tests/KeyManagement/KeyRotationServiceTests.cs`, `TemporalKeyVerificationTests.cs`, `TrustAnchorManagerTests.cs`, `Integration/KeyRotationWorkflowIntegrationTests.cs`
- **Source**: SPRINT_0501_0008_0001_proof_chain_key_rotation.md

## E2E Test Plan
- [ ] POST /api/v1/anchors/{anchorId}/keys adds a key and returns updated AllowedKeyIds with audit log ID
- [ ] POST /{anchorId}/keys/{keyId}/revoke sets RevokedAt and moves key from allowed to revoked list
- [ ] GET /{anchorId}/keys/{keyId}/validity returns correct temporal validity (Active, NotYetValid, Revoked, Expired) for a given signedAt timestamp
- [ ] Verify temporal key validation: key added at T1 is invalid for signatures before T1, valid between T1 and revocation/expiry
- [ ] GET /{anchorId}/keys/warnings returns ExpiryApproaching, LongLived, and AlgorithmDeprecating warnings
- [ ] Verify PURL pattern matching finds most-specific anchor for a given PURL
- [ ] Verify VerifySignatureAuthorizationAsync combines key validity + predicate type check
- [ ] Verify algorithm validation rejects keys with unsupported algorithms