Android Java AES加密密码填充和模式错误

Question

这是我昨天问题的延续：安卓Java AES加密

我目前正在安卓系统上测试AES加密。在我之前的问题中，我能够使用密码c = Cipher.getInstance("AES");对字符串进行加密和解密

回复中告诉我，我应该指定IV、加密模式和填充，以防止将来出现任何潜在问题，因为没有指定意味着程序将使用系统的默认值。所以我把代码改成了c = Cipher.getInstance("AES/CBC/PKCS5Padding");

但现在我的代码不再工作，它将返回一个NullPointerException。

我的代码：

byte[] a = encryptFIN128AES("pls");
String b = decryptFIN128AES(a);
Log.e("AES_Test", "b = " + b);
/**
* Encrypts a string with AES (128 bit key)
* @param fin
* @return the AES encrypted string
*/
private byte[] encryptFIN128AES(String fin) {
SecretKeySpec sks = null;
try {
sks = new SecretKeySpec(generateKey(PASSPHRASE, SALT.getBytes(StandardCharsets.UTF_8)).getEncoded(), "AES");
} catch (Exception e) {
Log.e("encryptFIN128AES", "AES key generation error");
}
// Encode the original data with AES
byte[] encodedBytes = null;
try {
Cipher c = Cipher.getInstance("AES/CBC/PKCS5Padding");
c.init(Cipher.ENCRYPT_MODE, sks);
encodedBytes = c.doFinal(fin.getBytes(StandardCharsets.UTF_8));
} catch (Exception e) {
Log.e("encryptFIN128AES", "AES encryption error");
}
return encodedBytes;
}

/**
* Decrypts a string with AES (128 bit key)
* @param encodedBytes
* @return the decrypted String
*/
private String decryptFIN128AES(byte[] encodedBytes) {
SecretKeySpec sks = null;
try {
sks = new SecretKeySpec(generateKey(PASSPHRASE, SALT.getBytes(StandardCharsets.UTF_8)).getEncoded(), "AES");
} catch (Exception e) {
Log.e("decryptFIN128AES", "AES key generation error");
}
// Decode the encoded data with AES
byte[] decodedBytes = null;
try {
Cipher c = Cipher.getInstance("AES/CBC/PKCS5Padding");
c.init(Cipher.DECRYPT_MODE, sks);
decodedBytes = c.doFinal(encodedBytes);
} catch (Exception e) {
Log.e("decryptFIN128AES", "AES decryption error");
}
//return Base64.encodeToString(decodedBytes, Base64.DEFAULT);
return new String(decodedBytes, StandardCharsets.UTF_8);
}

/**
* Build private key from a passpharase/PIN (incl. key derivation (Uses PBKDF2))
* @param passphraseOrPin
* @param salt
* @return The generated SecretKey (Used for AES-encryption, key size specified in outputKeyLength)
*/
public static SecretKey generateKey(char[] passphraseOrPin, byte[] salt)
throws NoSuchAlgorithmException, InvalidKeySpecException {
// Number of PBKDF2 hardening rounds to use. Larger values increase
// computation time. You should select a value that causes computation
// to take >100ms.
final int iterations = 1000;
// Generate a 256-bit key
final int outputKeyLength = 128;
SecretKeyFactory secretKeyFactory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA1");
KeySpec keySpec = new PBEKeySpec(passphraseOrPin, salt, iterations, outputKeyLength);
SecretKey secretKey = secretKeyFactory.generateSecret(keySpec);
return secretKey;
}

输出：

E/decryptFIN128AES: AES decryption error
E/AndroidRuntime: FATAL EXCEPTION: Thread-176
Process: testapp.ttyi.nfcapp, PID: 2920
java.lang.NullPointerException: Attempt to get length of null array
at java.lang.String.<init>(String.java:371)
at testapp.ttyi.nfcapp.DisplayQRActivity.decryptFIN128AES(DisplayQRActivity.java:254)
at testapp.ttyi.nfcapp.DisplayQRActivity.access$100(DisplayQRActivity.java:29)
at testapp.ttyi.nfcapp.DisplayQRActivity$1.run(DisplayQRActivity.java:77)
at java.lang.Thread.run(Thread.java:818)

testapp.ttyi.nfcapp.DisplayQRActivity.decryptFIN128AES(DisplayQRActivity.java:254)指向decryptFIN128AES的最后一行，即：return new String(decodedBytes, StandardCharsets.UTF_8);

我知道NullPointerException的发生是因为解密过程出现了问题。由于它一定进入了catch的情况，因此decodedBytes保持为NULL，因此在我想要返回decodedBytes时会导致错误。所以现在我的问题是：为什么会发生这种情况，我该如何解决？

非常感谢你的帮助。

Answer 1

非常感谢@Thomas W的帮助。我将catch更改为throw，现在我可以看到实际错误与BadPaddingException: error:06065064:digital envelope routines:EVP_DecryptFinal_ex:bad decrypt有关

经过一些谷歌搜索，我发现解决方案是在我的c.init中缺乏IV论点。以前我使用的是"AES"，其中Java默认为"AES/ECB/PKCS5Padding"，没有IV也能正常工作。(来源：安卓：用AES 256位加密iv和密钥加密字符串)

但是，一旦我更改为"AES/CBC/PKCS5Padding"，Java将在没有声明IV的情况下出现问题。因此，通过将c.init(Cipher.ENCRYPT_MODE, sks);和c.init(Cipher.DECRYPT_MODE, sks);更改为CCD_ 19和c.init(Cipher.DECRYPT_MODE, sks, new IvParameterSpec(new byte[16]));解决了这个问题。

现在我的程序可以正确加密和解密了。