Add iOS client implementation with SoftEther protocol handshake support

SoftEtherVPN-iOS/SoftEtherVPN-iOS/Protocol/SoftEtherClientSignature.swift

@@ -0,0 +1,90 @@
+import Foundation
+
+/// Handles the specific client signature format that SoftEther expects
+class SoftEtherClientSignature {
+    
+    // MARK: - Constants
+    
+    private enum Constants {
+        static let clientBuildNumber: UInt32 = 5187
+        static let clientVersion: UInt32 = 5_02_0000 + clientBuildNumber
+        static let clientString = "SoftEther VPN Client"
+        static let softEtherMagic: [UInt8] = [0x5E, 0x68] // 'Se' in hex
+        
+        // Protocol identification constants from SoftEther source
+        static let cedar = "CEDAR"
+        static let sessionKey = "sessionkey"
+        static let protocol1 = "PROTOCOL"
+        static let protocol2 = "PROTOCOL2"
+    }
+    
+    // MARK: - Public Methods
+    
+    /// Generate the client signature packet that identifies this client as a legitimate SoftEther VPN client
+    /// - Returns: Data containing the formatted client signature
+    static func generateSignature() -> Data {
+        var data = Data()
+        
+        // 1. Add SoftEther magic bytes
+        data.append(contentsOf: Constants.softEtherMagic)
+        
+        // 2. Add client version in network byte order (big endian)
+        data.appendUInt32(Constants.clientVersion)
+        
+        // 3. Add client build number in network byte order
+        data.appendUInt32(Constants.clientBuildNumber)
+        
+        // 4. Add cedar protocol identifier
+        if let cedarData = Constants.cedar.data(using: .ascii) {
+            data.append(cedarData)
+            data.append(0) // null terminator
+        }
+        
+        // 5. Add client string with null terminator
+        if let clientString = (Constants.clientString + "\0").data(using: .ascii) {
+            data.append(clientString)
+        }
+        
+        // 6. Add protocol identifiers
+        if let protocolData = (Constants.protocol1 + "\0").data(using: .ascii) {
+            data.append(protocolData)
+        }
+        
+        if let protocol2Data = (Constants.protocol2 + "\0").data(using: .ascii) {
+            data.append(protocol2Data)
+        }
+        
+        // 7. Add session key marker
+        if let sessionKeyData = (Constants.sessionKey + "\0").data(using: .ascii) {
+            data.append(sessionKeyData)
+        }
+        
+        // 8. Add random data for session key (typically 20 bytes)
+        let randomSessionKey = SoftEtherCrypto.randomBytes(count: 20)
+        data.append(randomSessionKey)
+        
+        // 9. Calculate and append SHA-1 hash of the entire data for integrity verification
+        let hash = SoftEtherCrypto.sha1(data)
+        data.append(hash)
+        
+        return data
+    }
+    
+    /// Verify a server response to the client signature
+    /// - Parameter data: Response data from server
+    /// - Returns: True if valid response, false otherwise
+    static func verifyServerResponse(_ data: Data) -> Bool {
+        // Basic validation - a real implementation would parse and validate the server response format
+        // This is a minimal check to see if we have enough data and it starts with the magic bytes
+        guard data.count >= 8 else {
+            return false
+        }
+        
+        // Check if response starts with SoftEther magic bytes
+        if data[0] == Constants.softEtherMagic[0] && data[1] == Constants.softEtherMagic[1] {
+            return true
+        }
+        
+        return false
+    }
+}