eq2go/internal/udp/middleware/encryptor.go

package middleware

import (
	"crypto/rand"
	"crypto/rc4"
	"crypto/rsa"
	"crypto/x509"
	"encoding/binary"
	"sync"
)

// EncryptorConfig holds configuration for encryption
type EncryptorConfig struct {
	RSAKeySize    int  // RSA key size in bits
	KeyExchangeOp byte // Opcode for key exchange packets
	MinSize       int  // Minimum packet size to encrypt
}

// DefaultEncryptorConfig returns default encryptor configuration
func DefaultEncryptorConfig() *EncryptorConfig {
	return &EncryptorConfig{
		RSAKeySize:    1024,
		KeyExchangeOp: 0x21, // OP_WSLoginRequestMsg equivalent
		MinSize:       8,
	}
}

// Encryptor implements RC4 + RSA encryption middleware
type Encryptor struct {
	config    *EncryptorConfig
	rsaKey    *rsa.PrivateKey
	rc4Key    []byte
	cipher    *rc4.Cipher
	cipherMux sync.RWMutex
	keySet    bool
	closeOnce sync.Once
}

// NewEncryptor creates a new encryption middleware
func NewEncryptor(config *EncryptorConfig) *Encryptor {
	if config == nil {
		config = DefaultEncryptorConfig()
	}

	// Generate RSA key pair
	rsaKey, err := rsa.GenerateKey(rand.Reader, config.RSAKeySize)
	if err != nil {
		panic(err) // Should handle this better in production
	}

	return &Encryptor{
		config: config,
		rsaKey: rsaKey,
	}
}

// ProcessOutbound implements Middleware.ProcessOutbound
func (e *Encryptor) ProcessOutbound(data []byte, next func([]byte) (int, error)) (int, error) {
	// Check if this is a key exchange request
	if len(data) > 4 && data[0] == 0 && data[1] == e.config.KeyExchangeOp {
		return e.handleKeyExchange(data, next)
	}

	// Skip encryption for small packets or if no key is set
	if len(data) < e.config.MinSize || !e.isKeySet() {
		return next(data)
	}

	encrypted, err := e.encrypt(data)
	if err != nil {
		return next(data) // Fallback to unencrypted
	}

	return next(encrypted)
}

// ProcessInbound implements Middleware.ProcessInbound
func (e *Encryptor) ProcessInbound(data []byte, next func([]byte) (int, error)) (int, error) {
	// Check for RSA encrypted key at end of packet
	if len(data) >= 8 && e.isRSAEncryptedKey(data) {
		return e.processRSAKey(data, next)
	}

	// Skip decryption if no key is set
	if !e.isKeySet() {
		return next(data)
	}

	decrypted, err := e.decrypt(data)
	if err != nil {
		return next(data) // Fallback to unencrypted
	}

	return next(decrypted)
}

func (e *Encryptor) handleKeyExchange(data []byte, next func([]byte) (int, error)) (int, error) {
	// Extract key size from packet
	if len(data) < 8 {
		return next(data)
	}

	keySize := binary.LittleEndian.Uint32(data[4:8])
	if keySize != 60 { // Expected key size
		return next(data)
	}

	// Create key exchange response with RSA public key
	response := make([]byte, len(data))
	copy(response, data)

	// Fill with dummy key data (in real implementation, would use proper key)
	for i := 8; i < len(response)-8; i++ {
		response[i] = 0xFF
	}

	// Add termination markers
	response[len(response)-5] = 1
	response[len(response)-1] = 1

	return next(response)
}

func (e *Encryptor) processRSAKey(data []byte, next func([]byte) (int, error)) (int, error) {
	// Extract and decrypt RSA key from end of packet
	encryptedKey := data[len(data)-8:]

	// In real implementation, would decrypt with RSA private key
	// For now, use a simple XOR pattern
	rc4Key := make([]byte, 8)
	for i := 0; i < 8; i++ {
		rc4Key[i] = encryptedKey[i] ^ 0x55 // Simple pattern
	}

	e.setRC4Key(rc4Key)

	// Pass the packet without the RSA key
	return next(data[:len(data)-8])
}

func (e *Encryptor) isRSAEncryptedKey(data []byte) bool {
	// Simple heuristic - check if last 8 bytes look like encrypted data
	if len(data) < 8 {
		return false
	}

	// Check for non-zero data in last 8 bytes
	lastBytes := data[len(data)-8:]
	nonZero := 0
	for _, b := range lastBytes {
		if b != 0 {
			nonZero++
		}
	}
	return nonZero > 4 // Heuristic: encrypted data should have some non-zero bytes
}

func (e *Encryptor) setRC4Key(key []byte) {
	e.cipherMux.Lock()
	defer e.cipherMux.Unlock()

	e.rc4Key = make([]byte, len(key))
	copy(e.rc4Key, key)

	cipher, err := rc4.NewCipher(key)
	if err == nil {
		e.cipher = cipher
		e.keySet = true
	}
}

func (e *Encryptor) isKeySet() bool {
	e.cipherMux.RLock()
	defer e.cipherMux.RUnlock()
	return e.keySet
}

func (e *Encryptor) encrypt(data []byte) ([]byte, error) {
	e.cipherMux.Lock()
	defer e.cipherMux.Unlock()

	if e.cipher == nil {
		return data, nil
	}

	// Create new cipher for this operation (RC4 is stateful)
	cipher, err := rc4.NewCipher(e.rc4Key)
	if err != nil {
		return nil, err
	}

	encrypted := make([]byte, len(data))
	cipher.XORKeyStream(encrypted, data)
	return encrypted, nil
}

func (e *Encryptor) decrypt(data []byte) ([]byte, error) {
	e.cipherMux.Lock()
	defer e.cipherMux.Unlock()

	if e.cipher == nil {
		return data, nil
	}

	// Create new cipher for this operation (RC4 is stateful)
	cipher, err := rc4.NewCipher(e.rc4Key)
	if err != nil {
		return nil, err
	}

	decrypted := make([]byte, len(data))
	cipher.XORKeyStream(decrypted, data)
	return decrypted, nil
}

// GetPublicKey returns the RSA public key for key exchange
func (e *Encryptor) GetPublicKey() []byte {
	pubKeyBytes, err := x509.MarshalPKIXPublicKey(&e.rsaKey.PublicKey)
	if err != nil {
		return nil
	}
	return pubKeyBytes
}

// Close implements Middleware.Close
func (e *Encryptor) Close() error {
	e.closeOnce.Do(func() {
		e.cipherMux.Lock()
		e.cipher = nil
		e.rc4Key = nil
		e.keySet = false
		e.cipherMux.Unlock()
	})
	return nil
}