Question

This is the PHP code I have.

function decrypt($s_input, $s_key, $s_iv) { 
   $s_decrypted = pack("H*" , $s_input); // Hex to binary
   $s_decrypted = mcrypt_decrypt (MCRYPT_3DES, $s_key, $s_decrypted, MCRYPT_MODE_CBC, $s_iv);  // 3des decryption
  return $s_decrypted; 
}
echo encrypt('c37551bb77f741d0bcdc16497b4f97b1','123456781234567812345678','12345678' );

what it basically does is to decrypt a 3des encrypted string (first it convert the hex string to binary using pack function and then does the actual decryption).

This perfectly works in PHP-4 and prints the “Hello World” message.

However, if I run the equivalent java code (jdk 1.6), it prints garbage output as – ¬ªmjV=7xl_ÓÄ^›*?.

Can someone help to troubleshoot this? Why Java is not properly decrypting the hex string.

private static String decrypt(String inputStr, String keyStr, String ivStr) throws Exception {

    IvParameterSpec iv = new IvParameterSpec(ivStr.getBytes());
    SecretKeySpec key = new SecretKeySpec(keyStr.getBytes(), "DESede");
    inputStr = hexToString(inputStr, 2);

    Cipher cipher = Cipher.getInstance("DESede/CBC/NoPadding");
    cipher.init(Cipher.DECRYPT_MODE, key, iv);
    byte[] decrypted = cipher.doFinal(inputStr.getBytes());

    return new String(decrypted);
}

private static String hexToString(String input, int groupLength) {
    StringBuilder sb = new StringBuilder(input.length() / groupLength);
    for (int i = 0; i < input.length() - groupLength + 1; i += groupLength) {
        String hex = input.substring(i, i + groupLength);
        sb.append((char) Integer.parseInt(hex, 16));
    }
    return sb.toString();
}

public static void main(String[] args) throws Exception {
    String decryptSignature = decrypt("c37551bb77f741d0bcdc16497b4f97b1", "123456781234567812345678", "12345678");
    System.out.println(decryptSignature);
}

Answer 1

There are a few things you should check. You might find Encryption using AES-128 in Java to be of some assistance. There could be issues with differences between how you are handling keys in the PHP and Java code. Calling getBytes() on a String in Java without an encoding is almost always a bad idea. Plus the padding used could be a problem. From what I’ve seen PHP pads with null characters by default, which does not correspond to NoPadding in Java. Finally, the hexToString method should return a byte[] instead of a String. Add the result of calling Integer.parseInt(hex, 16) into an array:

byte[] results = new byte[input.length() / groupLength];
...
    //inside the loop
    results[i / groupLength] = (byte) Integer.parseInt(hex, 16);
...
return results;