Gate connected-link trust on a secure session; deny forged direct announces the connected shortcut

Residual gap after the rotation-heal containment (#1401): "verified
direct" announces prove the signature but not directness — TTL is
unsigned — so a malicious connected peer can replay a victim's fresh
announce with its TTL restored. When the victim has no live link, the
replayer's link rebinds to the victim's ID and reads as "connected",
and MessageRouter's connected fast-path then trusts it outright: every
DM stalls on a Noise handshake the replayer can never complete and is
silently lost while showing "sent".

Router-level trust gate (no wire change):
- Transport gains canDeliverSecurely(to:) — BLE answers with an
  established Noise session; Nostr keeps its prompt-delivery predicate;
  the protocol default forwards to canDeliverPromptly for transports
  without a forgeable link layer.
- MessageRouter.sendPrivate only trusts a connected link outright when
  it can deliver securely; otherwise it still sends (kicking the
  handshake on a genuine link) but retains a copy and hands a sealed
  copy to couriers, like the reachable path. flushOutbox gets the same
  gate so a flush over an insecure link resends instead of dropping the
  retained copy.

Presence hardening (defense in depth): a "direct" announce arriving on
a link already bound to a different peer no longer shortcuts the
claimed peer into "connected" — only real link state does. Genuine
first-contact and direct announces are unaffected; only the ambiguous
heal path loses the forgeable shortcut.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bitchat/Services/BLE/BLEAnnounceHandler.swift

@@ -20,6 +20,12 @@ struct BLEAnnounceHandlerEnvironment {
     let verifySignature: (_ packet: BitchatPacket, _ signingPublicKey: Data) -> Bool
     /// Direct link state for the peer (BLE-queue read).
     let linkState: (PeerID) -> (hasPeripheral: Bool, hasCentral: Bool)
+    /// Whether the link this packet arrived on is already bound to a
+    /// different peer ID (ingress-registry + BLE-queue read). Directness
+    /// rides on the unsigned TTL, so a replayed announce can look "direct"
+    /// on the replayer's link; that link must not shortcut an absent peer
+    /// into "connected".
+    let linkBoundToOtherPeer: (_ packet: BitchatPacket, _ peerID: PeerID) -> Bool
     /// Runs the registry mutation phase under the collections barrier.
     let withRegistryBarrier: (() -> Void) -> Void
     /// Upserts the verified announce into the peer registry.
@@ -135,6 +141,11 @@ final class BLEAnnounceHandler {
         var isReconnectedPeer = false
         let directLinkState = env.linkState(peerID)
         let isDirectAnnounce = packet.ttl == env.messageTTL
+        // A "direct" announce arriving on a link that another peer already
+        // owns is either a rotation heal or a replay with its TTL restored;
+        // both are ambiguous, so only the rebind (which containment-checks
+        // the claimed identity) may promote it — never this shortcut.
+        let linkBoundToOtherPeer = isDirectAnnounce && env.linkBoundToOtherPeer(packet, peerID)
 
         env.withRegistryBarrier {
             let hasPeripheralConnection = directLinkState.hasPeripheral
@@ -152,7 +163,7 @@ final class BLEAnnounceHandler {
             let update = env.upsertVerifiedAnnounce(
                 peerID,
                 announcement,
-                isDirectAnnounce || hasPeripheralConnection || hasCentralSubscription,
+                hasPeripheralConnection || hasCentralSubscription || (isDirectAnnounce && !linkBoundToOtherPeer),
                 now
             )
             isNewPeer = update.isNewPeer

bitchat/Services/BLE/BLEService.swift

@@ -674,6 +674,15 @@ final class BLEService: NSObject {
         }
     }
 
+    func canDeliverSecurely(to peerID: PeerID) -> Bool {
+        // A live link binding alone is forgeable: the rotation heal rebinds a
+        // link on a signature-verified "direct" announce, but directness rides
+        // on the unsigned TTL, so a replayed announce can bind an absent
+        // peer's ID to the replayer's link. An established Noise session
+        // proves the other end of the link holds the peer's private key.
+        noiseService.hasEstablishedSession(with: peerID)
+    }
+
     func peerNickname(peerID: PeerID) -> String? {
         collectionsQueue.sync {
             peerRegistry.nickname(for: peerID, connectedOnly: true)
@@ -4430,6 +4439,20 @@ extension BLEService {
             linkState: { [weak self] peerID in
                 self?.linkState(for: peerID) ?? (hasPeripheral: false, hasCentral: false)
             },
+            linkBoundToOtherPeer: { [weak self] packet, peerID in
+                guard let self else { return false }
+                guard let link = (self.collectionsQueue.sync { self.ingressLinks.link(for: packet) }) else { return false }
+                let boundPeerID: PeerID? = self.readLinkState { store in
+                    switch link {
+                    case .peripheral(let peripheralUUID):
+                        return store.peerID(forPeripheralID: peripheralUUID)
+                    case .central(let centralUUID):
+                        return store.peerID(forCentralUUID: centralUUID)
+                    }
+                }
+                guard let boundPeerID else { return false }
+                return boundPeerID != peerID
+            },
             withRegistryBarrier: { [weak self] body in
                 self?.collectionsQueue.sync(flags: .barrier) { body() }
             },

bitchat/Services/MessageRouter.swift

@@ -161,14 +161,31 @@ final class MessageRouter {
     // MARK: - Message Sending
 
     func sendPrivate(_ content: String, to peerID: PeerID, recipientNickname: String, messageID: String) {
-        if let transport = connectedTransport(for: peerID) {
-            // A live link is a strong delivery signal; trust it outright.
+        if let transport = connectedTransport(for: peerID), transport.canDeliverSecurely(to: peerID) {
+            // A live link that can complete an encrypted delivery is a
+            // strong delivery signal; trust it outright.
             SecureLogger.debug("Routing PM via \(type(of: transport)) (connected) to \(peerID.id.prefix(8))… id=\(messageID.prefix(8))…", category: .session)
             transport.sendPrivateMessage(content, to: peerID, recipientNickname: recipientNickname, messageID: messageID)
             return
         }
 
         let message = QueuedMessage(content: content, nickname: recipientNickname, messageID: messageID, timestamp: now(), sendAttempts: 1)
+        if let transport = connectedTransport(for: peerID) {
+            // "Connected" without an established secure session is forgeable:
+            // link bindings heal on signature-verified "direct" announces, but
+            // directness rides on the unsigned TTL, so a replayed announce can
+            // bind an absent peer's ID to the replayer's link — where the send
+            // stalls on a handshake the replayer can never complete. Send now
+            // (a genuine link finishes the handshake and delivers), but retain
+            // a copy and hand a sealed copy to couriers so nothing is silently
+            // lost; receivers dedup resends by message ID.
+            SecureLogger.debug("Routing PM via \(type(of: transport)) (connected, no secure session) to \(peerID.id.prefix(8))… id=\(messageID.prefix(8))…", category: .session)
+            transport.sendPrivateMessage(content, to: peerID, recipientNickname: recipientNickname, messageID: messageID)
+            enqueue(message, for: peerID)
+            attemptCourierDeposit(messageID: messageID, for: peerID)
+            return
+        }
+
         if let transport = reachableTransport(for: peerID) {
             // Reachability without a connection is a freshness heuristic (e.g.
             // the mesh retention window), so the send can silently go nowhere.
@@ -386,14 +403,16 @@ final class MessageRouter {
                 continue
             }
 
-            if let transport = connectedTransport(for: peerID) {
-                // Live link: send and stop retaining.
+            if let transport = connectedTransport(for: peerID), transport.canDeliverSecurely(to: peerID) {
+                // Live link with a secure session: send and stop retaining.
                 SecureLogger.debug("Outbox -> \(type(of: transport)) (connected) for \(peerID.id.prefix(8))… id=\(message.messageID.prefix(8))…", category: .session)
                 transport.sendPrivateMessage(message.content, to: peerID, recipientNickname: message.nickname, messageID: message.messageID)
                 metrics?.record(.outboxResent)
-            } else if let transport = reachableTransport(for: peerID) {
-                // Weak signal: send but keep retaining until an ack clears it,
-                // bounded by attempt count for peers that never ack.
+            } else if let transport = connectedTransport(for: peerID) ?? reachableTransport(for: peerID) {
+                // Weak signal (reachability heuristic, or a "connected" link
+                // without a secure session — possibly a stolen binding from a
+                // replayed announce): send but keep retaining until an ack
+                // clears it, bounded by attempt count for peers that never ack.
                 guard message.sendAttempts < Self.maxSendAttempts else {
                     SecureLogger.warning("📤 Dropping unacked PM for \(peerID.id.prefix(8))… id=\(message.messageID.prefix(8))… after \(message.sendAttempts) attempts", category: .session)
                     dropMessage(message.messageID, for: peerID)

bitchat/Services/NostrTransport.swift

@@ -230,7 +230,14 @@ final class NostrTransport: Transport, @unchecked Sendable {
         // instead of waiting for internet that may never come.
         isPeerReachable(peerID) && queue.sync { relaysConnected }
     }
-    
+
+    func canDeliverSecurely(to peerID: PeerID) -> Bool {
+        // Nostr has no link bindings to forge; a known recipient key plus a
+        // connected relay is the strongest delivery signal it has. The router
+        // already retains + couriers for Nostr sends, so keep that behavior.
+        canDeliverPromptly(to: peerID)
+    }
+
     func peerNickname(peerID: PeerID) -> String? { nil }
     func getPeerNicknames() -> [PeerID: String] { [:] }
 

bitchat/Services/Transport.swift

@@ -116,6 +116,14 @@ protocol Transport: AnyObject {
     /// npub as reachable even with no relay connection, where a send only
     /// joins a queue waiting for internet that may never come.
     func canDeliverPromptly(to peerID: PeerID) -> Bool
+    /// Whether a send to this peer can complete an end-to-end encrypted
+    /// delivery right now (e.g. an established Noise session). Distinct from
+    /// connectivity: a "connected" link binding alone is forgeable — link
+    /// bindings heal on signature-verified "direct" announces, but directness
+    /// rides on the unsigned TTL, so a replayed announce can wear an absent
+    /// peer's ID on the replayer's link. Routers must not trust a connected
+    /// link outright without this.
+    func canDeliverSecurely(to peerID: PeerID) -> Bool
     func peerNickname(peerID: PeerID) -> String?
     func getPeerNicknames() -> [PeerID: String]
 
@@ -244,6 +252,10 @@ extension Transport {
     // straight to the radio; queue-backed transports override this.
     func canDeliverPromptly(to peerID: PeerID) -> Bool { isPeerReachable(peerID) }
 
+    // Transports without a forgeable link-binding layer (everything but the
+    // BLE mesh) have no stronger delivery signal than prompt delivery.
+    func canDeliverSecurely(to peerID: PeerID) -> Bool { canDeliverPromptly(to: peerID) }
+
     // Noise identity hooks default to inert for transports that do not carry
     // Noise sessions (e.g. NostrTransport).
     func noiseSessionPublicKeyData(for peerID: PeerID) -> Data? { nil }

bitchatTests/BLEServiceCoreTests.swift

@@ -253,6 +253,57 @@ struct BLEServiceCoreTests {
         #expect(ble.currentPeerSnapshots().map(\.peerID).contains(attackerPeerID))
     }
 
+    @Test
+    func replayedDirectAnnounceForAbsentPeerDoesNotForgeConnectivity() async throws {
+        // Residual heal-path gap: the victim has NO live link, so the
+        // identity-owns-a-link containment cannot refuse the rebind. The
+        // replay may steal the link binding, but it must not mark the absent
+        // victim connected (TTL — the directness signal — is unsigned), and
+        // it can never produce a deliverable secure session.
+        let ble = makeService()
+        let attackerPeerID = PeerID(str: "1122334455667788")
+        let attackerLink = "central-attacker-absent-victim"
+        ble._test_seedConnectedPeer(attackerPeerID, nickname: "attacker")
+        ble._test_bindCentral(attackerLink, to: attackerPeerID)
+
+        // The absent victim's fresh signed announce, replayed on the
+        // attacker's bound link with its direct TTL restored.
+        let victimSigner = NoiseEncryptionService(keychain: MockKeychain())
+        let announcement = AnnouncementPacket(
+            nickname: "victim",
+            noisePublicKey: victimSigner.getStaticPublicKeyData(),
+            signingPublicKey: victimSigner.getSigningPublicKeyData(),
+            directNeighbors: nil
+        )
+        let payload = try #require(announcement.encode(), "Failed to encode announcement")
+        let victimPeerID = PeerID(publicKey: announcement.noisePublicKey)
+        let unsigned = BitchatPacket(
+            type: MessageType.announce.rawValue,
+            senderID: Data(hexString: victimPeerID.id) ?? Data(),
+            recipientID: nil,
+            timestamp: UInt64(Date().timeIntervalSince1970 * 1000),
+            payload: payload,
+            signature: nil,
+            ttl: 7
+        )
+        let packet = try #require(victimSigner.signPacket(unsigned), "Failed to sign announce packet")
+
+        #expect(ble._test_recordIngressIfNew(packet: packet, linkID: attackerLink))
+        ble._test_handlePacket(packet, fromPeerID: victimPeerID, preseedPeer: false)
+
+        // The victim becomes known (verified announce) …
+        let known = await TestHelpers.waitUntil(
+            { ble.currentPeerSnapshots().map(\.peerID).contains(victimPeerID) },
+            timeout: TestConstants.longTimeout
+        )
+        #expect(known)
+        // … but the forged direct TTL must not mark it connected, and the
+        // link can never deliver securely, so MessageRouter falls through to
+        // retain + courier instead of trusting the stolen link outright.
+        #expect(!ble.isPeerConnected(victimPeerID))
+        #expect(!ble.canDeliverSecurely(to: victimPeerID))
+    }
+
     @Test
     func ingressRejectsSelfLoopbackBeforeSpoofChecks() async throws {
         let ble = makeService()

bitchatTests/Mocks/MockTransport.swift

@@ -50,6 +50,10 @@ final class MockTransport: Transport {
 
     var connectedPeers: Set<PeerID> = []
     var reachablePeers: Set<PeerID> = []
+    /// Peers with an established secure session. `nil` mirrors the protocol
+    /// default (prompt delivery), so connected peers stay "secure" for tests
+    /// that never care about the distinction.
+    var securePeers: Set<PeerID>?
     var peerNicknames: [PeerID: String] = [:]
     var peerFingerprints: [PeerID: String] = [:]
     var peerNoiseStates: [PeerID: LazyHandshakeState] = [:]
@@ -87,6 +91,10 @@ final class MockTransport: Transport {
         reachablePeers.contains(peerID) || connectedPeers.contains(peerID)
     }
 
+    func canDeliverSecurely(to peerID: PeerID) -> Bool {
+        securePeers?.contains(peerID) ?? canDeliverPromptly(to: peerID)
+    }
+
     func peerNickname(peerID: PeerID) -> String? {
         peerNicknames[peerID]
     }

bitchatTests/ProtocolContractTests.swift

@@ -103,6 +103,9 @@ struct ProtocolContractTests {
         #expect(probe.sentMessages.count == 1)
         #expect(probe.sentMessages.first?.content == "hello")
         #expect(probe.acceptPendingFile(id: "pending") == nil)
+        // Secure delivery defaults to prompt delivery (itself defaulting to
+        // reachability) for transports without a forgeable link layer.
+        #expect(probe.canDeliverSecurely(to: peerID) == false)
     }
 
     @Test

bitchatTests/Services/BLEAnnounceHandlerTests.swift

@@ -8,6 +8,7 @@ struct BLEAnnounceHandlerTests {
         var existingNoisePublicKey: Data?
         var signatureValid = true
         var linkState: (hasPeripheral: Bool, hasCentral: Bool) = (false, false)
+        var linkBoundToOtherPeer = false
         var upsertResult = BLEPeerAnnounceUpdate(isNewPeer: false, wasDisconnected: false, previousNickname: nil)
         var dedupSeenIDs: Set<String> = []
         var shouldEmitReconnectLogResult = true
@@ -41,6 +42,7 @@ struct BLEAnnounceHandlerTests {
                 return recorder.signatureValid
             },
             linkState: { _ in recorder.linkState },
+            linkBoundToOtherPeer: { _, _ in recorder.linkBoundToOtherPeer },
             withRegistryBarrier: { body in
                 recorder.barrierCount += 1
                 body()
@@ -334,6 +336,60 @@ struct BLEAnnounceHandlerTests {
         #expect(recorder.afterglowDelays.count == 1)
     }
 
+    /// TTL is unsigned, so a replayed announce with its TTL restored looks
+    /// "direct" — but it arrives on a link another peer already owns. That
+    /// link must not shortcut the (possibly absent) claimed peer into
+    /// "connected".
+    @Test
+    func directAnnounceOnLinkBoundToAnotherPeerDoesNotMarkConnected() throws {
+        let now = Date(timeIntervalSince1970: 1_000)
+        let noiseKey = Data(repeating: 0x88, count: 32)
+        let peerID = PeerID(publicKey: noiseKey)
+        let packet = try makeAnnouncePacket(
+            noisePublicKey: noiseKey,
+            peerID: peerID,
+            timestamp: timestamp(now),
+            signature: Data(repeating: 0xEE, count: 64)
+        )
+
+        let recorder = Recorder()
+        recorder.linkBoundToOtherPeer = true
+        recorder.upsertResult = BLEPeerAnnounceUpdate(isNewPeer: true, wasDisconnected: false, previousNickname: nil)
+        let handler = makeHandler(recorder: recorder, now: now)
+
+        let result = handler.handle(packet, from: peerID)
+
+        #expect(result?.isDirectAnnounce == true)
+        #expect(result?.isVerified == true)
+        #expect(recorder.upsertCalls.count == 1)
+        #expect(recorder.upsertCalls.first?.isConnected == false)
+    }
+
+    /// A peer with its own live link stays connected even when a copy of its
+    /// announce arrives on someone else's link.
+    @Test
+    func directAnnounceOnForeignLinkKeepsPeerWithOwnLinkConnected() throws {
+        let now = Date(timeIntervalSince1970: 1_000)
+        let noiseKey = Data(repeating: 0x99, count: 32)
+        let peerID = PeerID(publicKey: noiseKey)
+        let packet = try makeAnnouncePacket(
+            noisePublicKey: noiseKey,
+            peerID: peerID,
+            timestamp: timestamp(now),
+            signature: Data(repeating: 0xEE, count: 64)
+        )
+
+        let recorder = Recorder()
+        recorder.linkBoundToOtherPeer = true
+        recorder.linkState = (hasPeripheral: false, hasCentral: true)
+        let handler = makeHandler(recorder: recorder, now: now)
+
+        handler.handle(packet, from: peerID)
+
+        #expect(recorder.upsertCalls.count == 1)
+        #expect(recorder.upsertCalls.first?.isConnected == true)
+    }
+
     @Test
     func announceBackIsSkippedWhenAlreadyMarked() throws {
         let now = Date(timeIntervalSince1970: 1_000)

bitchatTests/Services/MessageRouterTests.swift

@@ -316,6 +316,76 @@ struct MessageRouterTests {
         #expect(couriers.contains(favorite))
     }
 
+    /// Residual gap after the rotation-heal containment: a replayed "direct"
+    /// announce (TTL is unsigned) can bind an absent victim's peer ID to the
+    /// replayer's link, leaving the victim "connected" on a link whose Noise
+    /// handshake can never complete. The connected fast-path must not trust
+    /// that outright: the send still goes out (a genuine link finishes the
+    /// handshake), but a copy is retained and a sealed copy goes to couriers
+    /// so nothing is silently lost.
+    @Test @MainActor
+    func sendPrivate_connectedWithoutSecureSessionRetainsAndDepositsWithCourier() async {
+        let victim = PeerID(str: "00000000000000aa")
+        let victimKey = Data(repeating: 0xBB, count: 32)
+        let courier = PeerID(str: "00000000000000cc")
+        let courierKey = Data(repeating: 0xCC, count: 32)
+
+        let transport = MockTransport()
+        transport.connectedPeers.insert(victim)
+        transport.connectedPeers.insert(courier)
+        transport.securePeers = [] // no established Noise session with anyone
+        transport.updatePeerSnapshots([Self.snapshot(courier, key: courierKey, verified: true)])
+
+        let router = MessageRouter(
+            transports: [transport],
+            courierDirectory: Self.directory(recipient: victim, recipientKey: victimKey)
+        )
+        router.sendPrivate("Hello", to: victim, recipientNickname: "Peer", messageID: "cs1")
+
+        // The send is still attempted (it kicks the handshake on a genuine
+        // link) but not trusted outright: a courier gets a sealed copy now …
+        #expect(transport.sentPrivateMessages.map(\.messageID) == ["cs1"])
+        #expect(transport.sentCourierMessages.count == 1)
+        #expect(transport.sentCourierMessages.first?.messageID == "cs1")
+        #expect(transport.sentCourierMessages.first?.recipientNoiseKey == victimKey)
+        #expect(transport.sentCourierMessages.first?.couriers == [courier])
+
+        // … and the retained copy keeps flushing until a delivery ack — a
+        // flush over the insecure link must resend without dropping it.
+        router.flushOutbox(for: victim)
+        router.flushOutbox(for: victim)
+        #expect(transport.sentPrivateMessages.count == 3)
+        router.markDelivered("cs1")
+        router.flushOutbox(for: victim)
+        #expect(transport.sentPrivateMessages.count == 3)
+    }
+
+    /// With an established secure session the connected fast-path stays
+    /// exactly as before: trusted outright, no retained copy, no courier.
+    @Test @MainActor
+    func sendPrivate_connectedWithSecureSessionIsTrustedOutright() async {
+        let peerID = PeerID(str: "00000000000000ab")
+        let peerKey = Data(repeating: 0xAB, count: 32)
+        let courier = PeerID(str: "00000000000000cc")
+
+        let transport = MockTransport()
+        transport.connectedPeers.insert(peerID)
+        transport.connectedPeers.insert(courier)
+        transport.securePeers = [peerID]
+        transport.updatePeerSnapshots([Self.snapshot(courier, key: Data(repeating: 0xCC, count: 32), verified: true)])
+
+        let router = MessageRouter(
+            transports: [transport],
+            courierDirectory: Self.directory(recipient: peerID, recipientKey: peerKey)
+        )
+        router.sendPrivate("Hello", to: peerID, recipientNickname: "Peer", messageID: "cs2")
+
+        #expect(transport.sentPrivateMessages.map(\.messageID) == ["cs2"])
+        #expect(transport.sentCourierMessages.isEmpty)
+        router.flushOutbox(for: peerID)
+        #expect(transport.sentPrivateMessages.count == 1)
+    }
+
     @Test @MainActor
     func courierBecameAvailable_retriesDepositOnceWithoutDoubleBurn() async {
         let recipient = PeerID(str: "00000000000000aa")