Security fixes and improvements (#374)

- Fix force unwrapping in NostrIdentity bech32 functions that could crash on non-ASCII input
- Add comprehensive input validation for all protocol messages (peer IDs, nicknames, timestamps)
- Strengthen keychain security with better sandbox detection and consistent app group usage
- Implement secure memory clearing for cryptographic keys and shared secrets
- Fix panic mode not reconnecting to mesh by restarting services after emergency disconnect

Co-authored-by: jack <jackjackbits@users.noreply.github.com>

bitchat/Noise/NoiseProtocol.swift

@@ -149,6 +149,10 @@ class NoiseCipherState {
         self.useExtractedNonce = useExtractedNonce
     }
     
+    deinit {
+        clearSensitiveData()
+    }
+    
     func initializeKey(_ key: SymmetricKey) {
         self.key = key
         self.nonce = 0
@@ -357,6 +361,21 @@ class NoiseCipherState {
             throw error
         }
     }
+    
+    /// Securely clear sensitive cryptographic data from memory
+    func clearSensitiveData() {
+        // Clear the symmetric key
+        key = nil
+        
+        // Reset nonce
+        nonce = 0
+        highestReceivedNonce = 0
+        
+        // Clear replay window
+        for i in 0..<replayWindow.count {
+            replayWindow[i] = 0
+        }
+    }
 }
 
 // MARK: - Symmetric State
@@ -557,7 +576,10 @@ class NoiseHandshakeState {
                     throw NoiseError.missingKeys
                 }
                 let shared = try localEphemeral.sharedSecretFromKeyAgreement(with: remoteEphemeral)
-                symmetricState.mixKey(shared.withUnsafeBytes { Data($0) })
+                var sharedData = shared.withUnsafeBytes { Data($0) }
+                symmetricState.mixKey(sharedData)
+                // Clear sensitive shared secret
+                KeychainManager.secureClear(&sharedData)
                 
             case .es:
                 // DH(ephemeral, static) - direction depends on role
@@ -602,7 +624,10 @@ class NoiseHandshakeState {
                     throw NoiseError.missingKeys
                 }
                 let shared = try localStatic.sharedSecretFromKeyAgreement(with: remoteStatic)
-                symmetricState.mixKey(shared.withUnsafeBytes { Data($0) })
+                var sharedData = shared.withUnsafeBytes { Data($0) }
+                symmetricState.mixKey(sharedData)
+                // Clear sensitive shared secret
+                KeychainManager.secureClear(&sharedData)
             }
         }
         
@@ -687,14 +712,20 @@ class NoiseHandshakeState {
                     throw NoiseError.missingKeys
                 }
                 let shared = try localEphemeral.sharedSecretFromKeyAgreement(with: remoteStatic)
-                symmetricState.mixKey(shared.withUnsafeBytes { Data($0) })
+                var sharedData = shared.withUnsafeBytes { Data($0) }
+                symmetricState.mixKey(sharedData)
+                // Clear sensitive shared secret
+                KeychainManager.secureClear(&sharedData)
             } else {
                 guard let localStatic = localStaticPrivate,
                       let remoteEphemeral = remoteEphemeralPublic else {
                     throw NoiseError.missingKeys
                 }
                 let shared = try localStatic.sharedSecretFromKeyAgreement(with: remoteEphemeral)
-                symmetricState.mixKey(shared.withUnsafeBytes { Data($0) })
+                var sharedData = shared.withUnsafeBytes { Data($0) }
+                symmetricState.mixKey(sharedData)
+                // Clear sensitive shared secret
+                KeychainManager.secureClear(&sharedData)
             }
             
         case .se:
@@ -704,14 +735,20 @@ class NoiseHandshakeState {
                     throw NoiseError.missingKeys
                 }
                 let shared = try localStatic.sharedSecretFromKeyAgreement(with: remoteEphemeral)
-                symmetricState.mixKey(shared.withUnsafeBytes { Data($0) })
+                var sharedData = shared.withUnsafeBytes { Data($0) }
+                symmetricState.mixKey(sharedData)
+                // Clear sensitive shared secret
+                KeychainManager.secureClear(&sharedData)
             } else {
                 guard let localEphemeral = localEphemeralPrivate,
                       let remoteStatic = remoteStaticPublic else {
                     throw NoiseError.missingKeys
                 }
                 let shared = try localEphemeral.sharedSecretFromKeyAgreement(with: remoteStatic)
-                symmetricState.mixKey(shared.withUnsafeBytes { Data($0) })
+                var sharedData = shared.withUnsafeBytes { Data($0) }
+                symmetricState.mixKey(sharedData)
+                // Clear sensitive shared secret
+                KeychainManager.secureClear(&sharedData)
             }
             
         case .ss:

bitchat/Noise/NoiseSession.swift

@@ -221,9 +221,24 @@ class NoiseSession {
             let wasEstablished = state == .established
             state = .uninitialized
             handshakeState = nil
+            
+            // Clear sensitive cipher states
+            sendCipher?.clearSensitiveData()
+            receiveCipher?.clearSensitiveData()
             sendCipher = nil
             receiveCipher = nil
+            
+            // Clear sent handshake messages
+            for i in 0..<sentHandshakeMessages.count {
+                var message = sentHandshakeMessages[i]
+                KeychainManager.secureClear(&message)
+            }
             sentHandshakeMessages.removeAll()
+            
+            // Clear handshake hash
+            if var hash = handshakeHash {
+                KeychainManager.secureClear(&hash)
+            }
             handshakeHash = nil
             
             if wasEstablished {
@@ -270,8 +285,12 @@ class NoiseSessionManager {
     
     func removeSession(for peerID: String) {
         managerQueue.sync(flags: .barrier) {
-            if let session = sessions[peerID], session.isEstablished() {
-                SecureLogger.logSecurityEvent(.sessionExpired(peerID: peerID))
+            if let session = sessions[peerID] {
+                if session.isEstablished() {
+                    SecureLogger.logSecurityEvent(.sessionExpired(peerID: peerID))
+                }
+                // Clear sensitive data before removing
+                session.reset()
             }
             _ = sessions.removeValue(forKey: peerID)
         }