wondergoat77 wondergoat77 - 4 months ago 18
Java Question

BadPadding Exception using same cipher instance

I have this encryption code which works no problem. I can decrypt the text it encrypts in another language, but I need to decrypt it in java now.

private static final String AES = "AES";
private static final String CBC_BLOCK = "CBC";
private static final String ECB_BLOCK = "ECB";
private static final String PADDING = "PKCS5Padding";
private static final String AES_CBC_PCKS5_CIPHER_CONFIG = AES + "/" + CBC_BLOCK + "/" + PADDING;
private static final String AES_ECB_PCKS5_CIPHER_CONFIG = AES + "/" + ECB_BLOCK + "/" + PADDING;

public static String encryptInAesEcbPkcs5Padding(String salt, String message) {
String encryptedMessage = "";
SecretKeySpec key = null;
try {
if (message != null && !message.equals("")) {
key = new SecretKeySpec(salt.getBytes(StandardCharsets.UTF_8), AES);
Cipher cipher = Cipher.getInstance(AES_ECB_PCKS5_CIPHER_CONFIG);
cipher.init(Cipher.ENCRYPT_MODE, key);
encryptedMessage = convertMessageToBase64(cipher.doFinal(message.getBytes(StandardCharsets.UTF_8)));
}
} catch (NoSuchAlgorithmException e) {
LOGGER.error(LogPreFix.ERROR + "No such algorithm [" + AES + "]", e);
} catch (NoSuchPaddingException e) {
LOGGER.error(LogPreFix.ERROR + "No such padding for algorithm [" + AES + "]", e);
} catch (IllegalBlockSizeException e) {
LOGGER.error(LogPreFix.ERROR + "Invalid block size for [" + AES + "/" + ECB_BLOCK + "]", e);
} catch (BadPaddingException e) {
LOGGER.error(LogPreFix.ERROR + "Invalid padding [" + PADDING + "]", e);
} catch (InvalidKeyException e) {
LOGGER.error("Invalid key [" + key + "]", e);
}
return encryptedMessage;
}


Trying to decrypt with this code. I am using the exact same salt as the encryption and passing in the string the encrypter creates as the "message"

public static String decrypt(String message, String salt) throws InvalidAlgorithmParameterException {
SecretKeySpec key = null;
String string = null;
try {
if (message != null && !message.equals("")) {
String decoded = convertBase64ToMessage(message.getBytes(StandardCharsets.UTF_8));
key = new SecretKeySpec(salt.getBytes(StandardCharsets.UTF_8), AES);
Cipher cipher = Cipher.getInstance(AES_ECB_PCKS5_CIPHER_CONFIG);
cipher.init(Cipher.DECRYPT_MODE, key);
byte[] decrypted = cipher.doFinal(decoded.getBytes(StandardCharsets.UTF_8));
string = new String(decrypted);
}
} catch (NoSuchAlgorithmException e) {
LOGGER.error(LogPreFix.ERROR + "No such algorithm [" + AES + "]", e);
} catch (NoSuchPaddingException e) {
LOGGER.error(LogPreFix.ERROR + "No such padding for algorithm [" + AES + "]", e);
} catch (IllegalBlockSizeException e) {
LOGGER.error(LogPreFix.ERROR + "Invalid block size for [" + AES + "/" + ECB_BLOCK + "]", e);
} catch (BadPaddingException e) {
LOGGER.error(LogPreFix.ERROR + "Invalid padding [" + PADDING + "]", e);
} catch (InvalidKeyException e) {
LOGGER.error("Invalid key [" + key + "]", e);
}
return string;
}


But I get this error, since i am using the same Cipher instance as i did when encrypting it, I am not sure why I cannot decrypt the message.

javax.crypto.BadPaddingException: Given final block not properly padded
at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:811)
at com.sun.crypto.provider.CipherCore.doFinal(CipherCore.java:676)
at com.sun.crypto.provider.AESCipher.engineDoFinal(AESCipher.java:313)
at javax.crypto.Cipher.doFinal(Cipher.java:2087)

Answer

convertBase64ToMessage should not return a String, but rather a byte[], because ciphertexts cannot be represented by a printable string (with a high probability).