AES/GCM encryption in Flutter (Dart)

Question

我正在尝试在扑动中实现AES/GCM/NoPadding加密。我已经成功地在JAVA中实现了它，但是当我试图在flutter中解密它时，我没有成功。

我试过在dart中编写解密代码，但我得到了未处理异常:SecretBox有错误的消息认证码(MAC)

My Java Code

public class GCMEncryption {
public static final int AES_KEY_SIZE = 128;
public static final int GCM_IV_LENGTH = 12;
public static final int GCM_TAG_LENGTH = 16;
public String getEncryptedText(String plainText) {
try {
byte[] IV = new byte[GCM_IV_LENGTH];
SecureRandom random = new SecureRandom();
random.nextBytes(IV);
String iv = Base64.getEncoder().encodeToString(IV);
System.out.println("IV : "+iv);

byte[] cipherText = encrypt(plainText.getBytes(), getKeySpec(), IV);
String text = Base64.getEncoder().encodeToString(cipherText);
text = iv+text; // Concating iv and encrypted text together 
return text;
} catch (Exception e) {
e.printStackTrace();
return "";
}
}
public String getDecryptedText(String cipherText) {
try {
// Splitting IV and Encrypted text
String iv = cipherText.substring(0,16);
System.out.println("IV : "+iv);
byte[] IV = Base64.getDecoder().decode(iv);
cipherText = cipherText.substring(16);


byte[] data = Base64.getDecoder().decode(cipherText);
return decrypt(data, getKeySpec(), IV);
} catch (Exception e) {
e.printStackTrace();
return "";
}
}
private SecretKeySpec getKeySpec() {
SecretKeySpec spec = null;
try {
byte[] bytes = new byte[32];
String pwd = "Test!ng012345678"; //Temporary
bytes = pwd.getBytes();
spec = new SecretKeySpec(bytes, "AES");
return spec;
} catch (Exception e) {
e.printStackTrace();
}
return spec;
}
private byte[] encrypt(byte[] plaintext, SecretKey key, byte[] IV) throws Exception {
// Get Cipher Instance
Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
// Create SecretKeySpec
SecretKeySpec keySpec = new SecretKeySpec(key.getEncoded(), "AES");
// Create GCMParameterSpec
GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(GCM_TAG_LENGTH * 8, IV);
// Initialize Cipher for ENCRYPT_MODE
cipher.init(Cipher.ENCRYPT_MODE, keySpec, gcmParameterSpec);
// Perform Encryption
byte[] cipherText = cipher.doFinal(plaintext);
return cipherText;
}
private String decrypt(byte[] cipherText, SecretKey key, byte[] IV) throws Exception {
// Get Cipher Instance
Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
// Create SecretKeySpec
SecretKeySpec keySpec = new SecretKeySpec(key.getEncoded(), "AES");
// Create GCMParameterSpec
GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(GCM_TAG_LENGTH * 8, IV);
// Initialize Cipher for DECRYPT_MODE
cipher.init(Cipher.DECRYPT_MODE, keySpec, gcmParameterSpec);
// Perform Decryption
byte[] decryptedText = cipher.doFinal(cipherText);
return new String(decryptedText);
}
}

My Dart Code

Future<String> decrypt(String textBlock) async {
Uint8List data  = base64.decode("4NA09I5VpmdD0o1k3VP8eIfyZRKDtzOwgJv5nh0nmEPZ/Q==");
Uint8List passphrase = utf8.encode('Test!ng012345678');
SecretKey secretKey = new SecretKey(passphrase);
Uint8List iv = utf8.encode('/U0OI/AdHDM4QFVC');
SecretBox secretBox = new SecretBox(data, nonce: iv);
List<int> decrypted = await AesGcm.with128bits().decrypt(secretBox, secretKey: secretKey);
String dec = utf8.decode(decrypted);
print("DATA : "+dec);
return dec;
}

对于这个，我在Flutter中得到了以下错误

未处理异常:SecretBox有错误的消息认证码(MAC)#0 DartAesGcm.decryptSync(包:cryptography/src/dart/aes_gcm.dart:112:7)#1 DartAesGcm.decrypt (package:cryptography/src/dart/aes_gcm.dart:58:12)#2 EncryptionHandler.decrypt (package:investment_app/encryption/encryption_handler.dart:45:27)

你能帮我解决这个问题吗?示例代码会有帮助。

Answer 1

Java中的SunJCE提供程序连接密文和MAC:密文|MAC。在Dart代码中，两者必须分别指定，而在发布的代码中则不会这样做。此外，IV不是Base64解码的。

下面的代码是修复错误的可能实现:

Uint8List ivCiphertextMac = base64.decode("/U0OI/AdHDM4QFVC4NA09I5VpmdD0o1k3VP8eIfyZRKDtzOwgJv5nh0nmEPZ/Q=="); // from the Java code
Uint8List iv = ivCiphertextMac.sublist(0, 12);
Uint8List ciphertext  = ivCiphertextMac.sublist(12, ivCiphertextMac.length - 16);
Uint8List mac = ivCiphertextMac.sublist(ivCiphertextMac.length - 16);
Uint8List passphrase = utf8.encode('Test!ng012345678');
SecretKey secretKey = new SecretKey(passphrase);
SecretBox secretBox = new SecretBox(ciphertext, nonce: iv, mac: new Mac(mac));
List<int> decrypted = await AesGcm.with128bits().decrypt(secretBox, secretKey: secretKey);
String dec = utf8.decode(decrypted);
print("Decrypted text : " + dec); // Decrypted text : Mayur, You got it!

解密给出:Mayur，你得到了!

实际上SecretBox提供了fromConcatenation()方法，该方法应该分离IV，密文和MAC的连接。但这种实现似乎返回一个损坏的密文，这可能是一个错误。

编辑:

关于你评论中的问题:MAC是在加密过程中自动生成的。以下代码实现加密，其中ivCiphertextMacB64包含Base64编码IV |密文| MAC:

Uint8List plaintext  = utf8.encode("Mayur, You got it!");
Uint8List iv = AesGcm.with128bits().newNonce();
Uint8List passphrase = utf8.encode('Test!ng012345678');
SecretKey secretKey = new SecretKey(passphrase);
SecretBox secretBox = await AesGcm.with128bits().encrypt(plaintext, nonce: iv, secretKey: secretKey);
String ivCiphertextMacB64 = base64.encode(secretBox.concatenation()); // Base64 encoding of: IV | ciphertext | MAC
print("ivCiphertextMacB64 : " + ivCiphertextMacB64);