Add MEK rotation, per-engine DEKs, and v2 ciphertext format (audit #6, #22)

Implement a two-level key hierarchy: the MEK now wraps per-engine DEKs
stored in a new barrier_keys table, rather than encrypting all barrier
entries directly. A v2 ciphertext format (0x02) embeds the key ID so the
barrier can resolve which DEK to use on decryption. v1 ciphertext remains
supported for backward compatibility.

Key changes:
- crypto: EncryptV2/DecryptV2/ExtractKeyID for v2 ciphertext with key IDs
- barrier: key registry (CreateKey, RotateKey, ListKeys, MigrateToV2, ReWrapKeys)
- seal: RotateMEK re-wraps DEKs without re-encrypting data
- engine: Mount auto-creates per-engine DEK
- REST + gRPC: barrier/keys, barrier/rotate-mek, barrier/rotate-key, barrier/migrate
- proto: BarrierService (v1 + v2) with ListKeys, RotateMEK, RotateKey, Migrate
- db: migration v2 adds barrier_keys table

Also includes: security audit report, CSRF protection, engine design specs
(sshca, transit, user), path-bound AAD migration tool, policy engine
enhancements, and ARCHITECTURE.md updates.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/server/routes.go

@@ -11,6 +11,7 @@ import (
 
 	mcias "git.wntrmute.dev/kyle/mcias/clients/go"
 
+	"git.wntrmute.dev/kyle/metacrypt/internal/barrier"
 	"git.wntrmute.dev/kyle/metacrypt/internal/crypto"
 	"git.wntrmute.dev/kyle/metacrypt/internal/engine"
 	"git.wntrmute.dev/kyle/metacrypt/internal/engine/ca"
@@ -45,6 +46,11 @@ func (s *Server) registerRoutes(r chi.Router) {
 	r.Get("/v1/pki/{mount}/issuer/{name}", s.requireUnseal(s.handlePKIIssuer))
 	r.Get("/v1/pki/{mount}/issuer/{name}/crl", s.requireUnseal(s.handlePKICRL))
 
+	r.Get("/v1/barrier/keys", s.requireAdmin(s.handleBarrierKeys))
+	r.Post("/v1/barrier/rotate-mek", s.requireAdmin(s.handleRotateMEK))
+	r.Post("/v1/barrier/rotate-key", s.requireAdmin(s.handleRotateKey))
+	r.Post("/v1/barrier/migrate", s.requireAdmin(s.handleBarrierMigrate))
+
 	r.HandleFunc("/v1/policy/rules", s.requireAuth(s.handlePolicyRules))
 	r.HandleFunc("/v1/policy/rule", s.requireAuth(s.handlePolicyRule))
 	s.registerACMERoutes(r)
@@ -253,6 +259,31 @@ func (s *Server) handleEngineUnmount(w http.ResponseWriter, r *http.Request) {
 	writeJSON(w, http.StatusOK, map[string]interface{}{"ok": true})
 }
 
+// adminOnlyOperations lists engine operations that require admin role.
+// This enforces the same gates as the typed REST routes, ensuring the
+// generic endpoint cannot bypass admin requirements.
+var adminOnlyOperations = map[string]bool{
+	// CA engine.
+	"import-root":    true,
+	"create-issuer":  true,
+	"delete-issuer":  true,
+	"revoke-cert":    true,
+	"delete-cert":    true,
+	// Transit engine.
+	"create-key":        true,
+	"delete-key":        true,
+	"rotate-key":        true,
+	"update-key-config": true,
+	"trim-key":          true,
+	// SSH CA engine.
+	"create-profile": true,
+	"update-profile": true,
+	"delete-profile": true,
+	// User engine.
+	"provision":   true,
+	"delete-user": true,
+}
+
 func (s *Server) handleEngineRequest(w http.ResponseWriter, r *http.Request) {
 	var req struct {
 		Data      map[string]interface{} `json:"data"`
@@ -271,6 +302,12 @@ func (s *Server) handleEngineRequest(w http.ResponseWriter, r *http.Request) {
 
 	info := TokenInfoFromContext(r.Context())
 
+	// Enforce admin requirement for operations that have admin-only typed routes.
+	if adminOnlyOperations[req.Operation] && !info.IsAdmin {
+		http.Error(w, `{"error":"forbidden: admin required"}`, http.StatusForbidden)
+		return
+	}
+
 	// Evaluate policy before dispatching to the engine.
 	policyReq := &policy.Request{
 		Username: info.Username,
@@ -412,6 +449,90 @@ func (s *Server) handlePolicyRule(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+// --- Barrier Key Management Handlers ---
+
+func (s *Server) handleBarrierKeys(w http.ResponseWriter, r *http.Request) {
+	keys, err := s.seal.Barrier().ListKeys(r.Context())
+	if err != nil {
+		s.logger.Error("list barrier keys", "error", err)
+		http.Error(w, `{"error":"internal error"}`, http.StatusInternalServerError)
+		return
+	}
+	if keys == nil {
+		keys = []barrier.KeyInfo{}
+	}
+	writeJSON(w, http.StatusOK, keys)
+}
+
+func (s *Server) handleRotateMEK(w http.ResponseWriter, r *http.Request) {
+	var req struct {
+		Password string `json:"password"`
+	}
+	if err := readJSON(r, &req); err != nil {
+		http.Error(w, `{"error":"invalid request"}`, http.StatusBadRequest)
+		return
+	}
+	if req.Password == "" {
+		http.Error(w, `{"error":"password is required"}`, http.StatusBadRequest)
+		return
+	}
+
+	if err := s.seal.RotateMEK(r.Context(), []byte(req.Password)); err != nil {
+		if errors.Is(err, seal.ErrInvalidPassword) {
+			http.Error(w, `{"error":"invalid password"}`, http.StatusUnauthorized)
+			return
+		}
+		if errors.Is(err, seal.ErrSealed) {
+			http.Error(w, `{"error":"sealed"}`, http.StatusServiceUnavailable)
+			return
+		}
+		s.logger.Error("rotate MEK", "error", err)
+		http.Error(w, `{"error":"rotation failed"}`, http.StatusInternalServerError)
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]interface{}{"ok": true})
+}
+
+func (s *Server) handleRotateKey(w http.ResponseWriter, r *http.Request) {
+	var req struct {
+		KeyID string `json:"key_id"`
+	}
+	if err := readJSON(r, &req); err != nil {
+		http.Error(w, `{"error":"invalid request"}`, http.StatusBadRequest)
+		return
+	}
+	if req.KeyID == "" {
+		http.Error(w, `{"error":"key_id is required"}`, http.StatusBadRequest)
+		return
+	}
+
+	if err := s.seal.Barrier().RotateKey(r.Context(), req.KeyID); err != nil {
+		if errors.Is(err, barrier.ErrKeyNotFound) {
+			http.Error(w, `{"error":"key not found"}`, http.StatusNotFound)
+			return
+		}
+		s.logger.Error("rotate key", "key_id", req.KeyID, "error", err)
+		http.Error(w, `{"error":"rotation failed"}`, http.StatusInternalServerError)
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]interface{}{"ok": true})
+}
+
+func (s *Server) handleBarrierMigrate(w http.ResponseWriter, r *http.Request) {
+	migrated, err := s.seal.Barrier().MigrateToV2(r.Context())
+	if err != nil {
+		s.logger.Error("barrier migration", "error", err)
+		http.Error(w, `{"error":"migration failed"}`, http.StatusInternalServerError)
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]interface{}{
+		"migrated": migrated,
+	})
+}
+
 // --- CA Certificate Handlers ---
 
 func (s *Server) handleGetCert(w http.ResponseWriter, r *http.Request) {
@@ -608,13 +729,29 @@ func (s *Server) getCAEngine(mountName string) (*ca.CAEngine, error) {
 	return caEng, nil
 }
 
-// operationAction maps an engine operation name to a policy action ("read" or "write").
+// operationAction maps an engine operation name to a policy action.
 func operationAction(op string) string {
 	switch op {
-	case "list-issuers", "list-certs", "get-cert", "get-root", "get-chain", "get-issuer":
-		return "read"
+	// Read operations.
+	case "list-issuers", "list-certs", "get-cert", "get-root", "get-chain", "get-issuer",
+		"list-keys", "get-key", "get-public-key", "list-users", "get-profile", "list-profiles":
+		return policy.ActionRead
+
+	// Granular cryptographic operations (including batch variants).
+	case "encrypt", "batch-encrypt":
+		return policy.ActionEncrypt
+	case "decrypt", "batch-decrypt":
+		return policy.ActionDecrypt
+	case "sign", "sign-host", "sign-user":
+		return policy.ActionSign
+	case "verify":
+		return policy.ActionVerify
+	case "hmac":
+		return policy.ActionHMAC
+
+	// Everything else is a write.
 	default:
-		return "write"
+		return policy.ActionWrite
 	}
 }