Add optional server tag requirement for Blossom DELETE replay protection

- Add ORLY_BLOSSOM_DELETE_REQUIRE_SERVER_TAG config option (default: false)
- Add ValidateAuthEventForDelete() for optional server tag validation
- Update handleDeleteBlob to use new validation
- Prevents cross-server replay attacks when enabled

Based on discussion in hzrd149/blossom PR #87

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -281,7 +281,7 @@ The transport manager handles ordered startup (Start fails fast, rolls back) and
 
 ## Deploying to relay.orly.dev
 
-- **Architecture**: x86_64 (amd64)
+- **Architecture**: **x86_64 (amd64)** — NOT arm64, always use `GOARCH=amd64`
 - **OS**: Ubuntu 24.04 LTS
 - **SSH**: `ssh -i ~/.ssh/id_ed25519 -o IdentitiesOnly=yes root@69.164.249.71`
 - **Service**: `systemctl {start|stop|restart|status} orly`

app/blossom.go

@@ -26,6 +26,8 @@ func initializeBlossomServer(
 		RateLimitEnabled: cfg.BlossomRateLimitEnabled,
 		DailyLimitMB:     cfg.BlossomDailyLimitMB,
 		BurstLimitMB:     cfg.BlossomBurstLimitMB,
+		// Delete replay protection (proposed BUD enhancement)
+		DeleteRequireServerTag: cfg.BlossomDeleteRequireServerTag,
 	}
 
 	// Create blossom server with relay's ACL registry

app/config/config.go

@@ -82,6 +82,9 @@ type C struct {
 	BlossomDailyLimitMB     int64 `env:"ORLY_BLOSSOM_DAILY_LIMIT_MB" default:"10" usage:"daily upload limit in MB for non-followed users (EMA averaged)"`
 	BlossomBurstLimitMB     int64 `env:"ORLY_BLOSSOM_BURST_LIMIT_MB" default:"50" usage:"max burst upload in MB (bucket cap)"`
 
+	// Blossom delete replay protection (proposed BUD enhancement)
+	BlossomDeleteRequireServerTag bool `env:"ORLY_BLOSSOM_DELETE_REQUIRE_SERVER_TAG" default:"false" usage:"require server tag in delete auth events to prevent cross-server replay attacks (not yet ratified in spec)"`
+
 	// Web UI and dev mode settings
 	WebDisableEmbedded bool   `env:"ORLY_WEB_DISABLE" default:"false" usage:"disable serving the embedded web UI; useful for hot-reload during development"`
 	WebDevProxyURL     string `env:"ORLY_WEB_DEV_PROXY_URL" usage:"when ORLY_WEB_DISABLE is true, reverse-proxy non-API paths to this dev server URL (e.g. http://localhost:5173)"`

pkg/blossom/auth.go

@@ -273,6 +273,58 @@ func ValidateAuthEventForGet(
 	return
 }
 
+// ValidateAuthEventForDelete validates authorization for DELETE requests (BUD-02)
+// If requireServerTag is true, the auth event must include a 'server' tag matching the serverURL
+// This prevents cross-server replay attacks where a malicious server replays delete auth events
+func ValidateAuthEventForDelete(
+	r *http.Request, serverURL string, sha256Hash []byte, requireServerTag bool,
+) (authEv *AuthEvent, err error) {
+	// First do the standard validation
+	if authEv, err = ValidateAuthEvent(r, "delete", sha256Hash); chk.E(err) {
+		return
+	}
+
+	// If server tag is not required, we're done
+	if !requireServerTag {
+		return
+	}
+
+	// Extract event again to check server tags
+	var ev *event.E
+	if ev, err = ExtractAuthEvent(r); chk.E(err) {
+		return
+	}
+
+	// Check for server tag
+	serverTags := ev.Tags.GetAll([]byte("server"))
+	if len(serverTags) == 0 {
+		err = errorf.E(
+			"delete authorization requires 'server' tag for replay protection",
+		)
+		return
+	}
+
+	// Verify at least one server tag matches
+	found := false
+	for _, serverTag := range serverTags {
+		serverTagValue := string(serverTag.Value())
+		if strings.HasPrefix(serverURL, serverTagValue) {
+			found = true
+			break
+		}
+	}
+
+	if !found {
+		err = errorf.E(
+			"no 'server' tag matches this server URL '%s'",
+			serverURL,
+		)
+		return
+	}
+
+	return
+}
+
 // GetPubkeyFromRequest extracts pubkey from Authorization header if present
 func GetPubkeyFromRequest(r *http.Request) (pubkey []byte, err error) {
 	authHeader := r.Header.Get(AuthorizationHeader)

pkg/blossom/handlers.go

@@ -542,7 +542,10 @@ func (s *Server) handleDeleteBlob(w http.ResponseWriter, r *http.Request) {
 	}
 
 	// Authorization required for delete
-	authEv, err := ValidateAuthEvent(r, "delete", sha256Hash)
+	// Use ValidateAuthEventForDelete which optionally requires server tag for replay protection
+	authEv, err := ValidateAuthEventForDelete(
+		r, s.getBaseURL(r), sha256Hash, s.deleteRequireServerTag,
+	)
 	if err != nil {
 		s.setErrorResponse(w, http.StatusUnauthorized, err.Error())
 		return

pkg/blossom/server.go

@@ -16,9 +16,10 @@ type Server struct {
 	baseURL string
 
 	// Configuration
-	maxBlobSize      int64
-	allowedMimeTypes map[string]bool
-	requireAuth      bool
+	maxBlobSize            int64
+	allowedMimeTypes       map[string]bool
+	requireAuth            bool
+	deleteRequireServerTag bool
 
 	// Rate limiting for uploads
 	bandwidthLimiter *BandwidthLimiter
@@ -35,6 +36,10 @@ type Config struct {
 	RateLimitEnabled bool
 	DailyLimitMB     int64
 	BurstLimitMB     int64
+
+	// Delete replay protection (proposed BUD enhancement)
+	// When true, DELETE auth events must include a 'server' tag matching this server
+	DeleteRequireServerTag bool
 }
 
 // NewServer creates a new Blossom server instance
@@ -71,14 +76,15 @@ func NewServer(db database.Database, aclRegistry *acl.S, cfg *Config) *Server {
 	}
 
 	return &Server{
-		db:               db,
-		storage:          storage,
-		acl:              aclRegistry,
-		baseURL:          cfg.BaseURL,
-		maxBlobSize:      cfg.MaxBlobSize,
-		allowedMimeTypes: allowedMap,
-		requireAuth:      cfg.RequireAuth,
-		bandwidthLimiter: bwLimiter,
+		db:                     db,
+		storage:                storage,
+		acl:                    aclRegistry,
+		baseURL:                cfg.BaseURL,
+		maxBlobSize:            cfg.MaxBlobSize,
+		allowedMimeTypes:       allowedMap,
+		requireAuth:            cfg.RequireAuth,
+		deleteRequireServerTag: cfg.DeleteRequireServerTag,
+		bandwidthLimiter:       bwLimiter,
 	}
 }
 

pkg/version/version

@@ -1 +1 @@
-v0.58.9
+v0.58.10