bitchat/bitchat/Services/EncryptionService.swift

//
// EncryptionService.swift
// bitchat
//
// This is free and unencumbered software released into the public domain.
// For more information, see <https://unlicense.org>
//

import Foundation
import CryptoKit

class EncryptionService {
    // Key agreement keys for encryption
    private var privateKey: Curve25519.KeyAgreement.PrivateKey
    public let publicKey: Curve25519.KeyAgreement.PublicKey
    
    // Signing keys for authentication
    private var signingPrivateKey: Curve25519.Signing.PrivateKey
    public let signingPublicKey: Curve25519.Signing.PublicKey
    
    // Storage for peer keys
    private var peerPublicKeys: [String: Curve25519.KeyAgreement.PublicKey] = [:]
    private var peerSigningKeys: [String: Curve25519.Signing.PublicKey] = [:]
    private var peerIdentityKeys: [String: Curve25519.Signing.PublicKey] = [:]
    private var sharedSecrets: [String: SymmetricKey] = [:]
    
    // Persistent identity for favorites (separate from ephemeral keys)
    private let identityKey: Curve25519.Signing.PrivateKey
    public let identityPublicKey: Curve25519.Signing.PublicKey
    
    init() {
        // Generate ephemeral key pairs for this session
        self.privateKey = Curve25519.KeyAgreement.PrivateKey()
        self.publicKey = privateKey.publicKey
        
        self.signingPrivateKey = Curve25519.Signing.PrivateKey()
        self.signingPublicKey = signingPrivateKey.publicKey
        
        // Load or create persistent identity key
        if let identityData = UserDefaults.standard.data(forKey: "bitchat.identityKey"),
           let loadedKey = try? Curve25519.Signing.PrivateKey(rawRepresentation: identityData) {
            self.identityKey = loadedKey
        } else {
            // First run - create and save identity key
            self.identityKey = Curve25519.Signing.PrivateKey()
            UserDefaults.standard.set(identityKey.rawRepresentation, forKey: "bitchat.identityKey")
        }
        self.identityPublicKey = identityKey.publicKey
    }
    
    // Create combined public key data for exchange
    func getCombinedPublicKeyData() -> Data {
        var data = Data()
        data.append(publicKey.rawRepresentation)  // 32 bytes - ephemeral encryption key
        data.append(signingPublicKey.rawRepresentation)  // 32 bytes - ephemeral signing key
        data.append(identityPublicKey.rawRepresentation)  // 32 bytes - persistent identity key
        return data  // Total: 96 bytes
    }
    
    // Add peer's combined public keys
    func addPeerPublicKey(_ peerID: String, publicKeyData: Data) throws {
        // Convert to array for safe access
        let keyBytes = [UInt8](publicKeyData)
        
        guard keyBytes.count == 96 else {
            print("[CRYPTO] Invalid public key data size: \(keyBytes.count), expected 96")
            throw EncryptionError.invalidPublicKey
        }
        
        // Extract all three keys: 32 for key agreement + 32 for signing + 32 for identity
        let keyAgreementData = Data(keyBytes[0..<32])
        let signingKeyData = Data(keyBytes[32..<64])
        let identityKeyData = Data(keyBytes[64..<96])
        
        let publicKey = try Curve25519.KeyAgreement.PublicKey(rawRepresentation: keyAgreementData)
        peerPublicKeys[peerID] = publicKey
        
        let signingKey = try Curve25519.Signing.PublicKey(rawRepresentation: signingKeyData)
        peerSigningKeys[peerID] = signingKey
        
        let identityKey = try Curve25519.Signing.PublicKey(rawRepresentation: identityKeyData)
        peerIdentityKeys[peerID] = identityKey
        
        // Stored all three keys for peer
        
        // Generate shared secret for encryption
        if let publicKey = peerPublicKeys[peerID] {
            let sharedSecret = try privateKey.sharedSecretFromKeyAgreement(with: publicKey)
            let symmetricKey = sharedSecret.hkdfDerivedSymmetricKey(
                using: SHA256.self,
                salt: "bitchat-v1".data(using: .utf8)!,
                sharedInfo: Data(),
                outputByteCount: 32
            )
            sharedSecrets[peerID] = symmetricKey
        }
    }
    
    // Get peer's persistent identity key for favorites
    func getPeerIdentityKey(_ peerID: String) -> Data? {
        return peerIdentityKeys[peerID]?.rawRepresentation
    }
    
    // Clear persistent identity (for panic mode)
    func clearPersistentIdentity() {
        UserDefaults.standard.removeObject(forKey: "bitchat.identityKey")
        print("[CRYPTO] Cleared persistent identity key")
    }
    
    func encrypt(_ data: Data, for peerID: String) throws -> Data {
        guard let symmetricKey = sharedSecrets[peerID] else {
            throw EncryptionError.noSharedSecret
        }
        
        let sealedBox = try AES.GCM.seal(data, using: symmetricKey)
        return sealedBox.combined ?? Data()
    }
    
    func decrypt(_ data: Data, from peerID: String) throws -> Data {
        guard let symmetricKey = sharedSecrets[peerID] else {
            throw EncryptionError.noSharedSecret
        }
        
        let sealedBox = try AES.GCM.SealedBox(combined: data)
        return try AES.GCM.open(sealedBox, using: symmetricKey)
    }
    
    func sign(_ data: Data) throws -> Data {
        return try signingPrivateKey.signature(for: data)
    }
    
    func verify(_ signature: Data, for data: Data, from peerID: String) throws -> Bool {
        guard let verifyingKey = peerSigningKeys[peerID] else {
            throw EncryptionError.noSharedSecret
        }
        
        return verifyingKey.isValidSignature(signature, for: data)
    }
    
}

enum EncryptionError: Error {
    case noSharedSecret
    case invalidPublicKey
    case encryptionFailed
    case decryptionFailed
}