Java: How to decode string encrypted on php with known key?

Question

so I encrypted a string on my php server.

encrypt("http://google.com", "happy");

function encrypt($str, $key)
{
    $block = mcrypt_get_block_size('des', 'ecb');
    $pad = $block - (strlen($str) % $block);
    $str .= str_repeat(chr($pad), $pad);

    return mcrypt_encrypt(MCRYPT_DES, $key, $str, MCRYPT_MODE_ECB);
}

btw, this returns some weird string...I was expecting letters and numbers: ZöÞ ÔP»8

Back on Java, I need to decrypt this string with the key.

Answer 1

This may help for MCrypt in java:

http://www.java2s.com/Open-Source/Java-Document/EJB-Server/resin-4.0.7/com/caucho/quercus/lib/mcrypt/Mcrypt.java.htm

Another link:

http://www.kanatorn.info/2011/11/07/aes-encrypt-decrypt-between-java-php/

Answer 2

I'm not au fait with mcrypt, but running ASCII plaintext through encryption doesn't always result in an ASCII ciphertext. Chances are your generated encrypted ciphertext is going to translate into a 'weird string' when you try and interpret it as ASCII or unicode text.

Answer 3

first, make sure it isn't an one-way encryption. second, algorithm and arguments used in php and reverse engineering in java

Answer 4

I think this will be useful. Note that the charset is UTF-8.

public class Foo {

    public static void main(String[] args) {
        try {
            String cipherSpec = "DES/ECB/NoPadding";
            Cipher cipher = Cipher.getInstance(cipherSpec);
            int blockSize = cipher.getBlockSize();

            String keyText = "happy";
            Key key = new SecretKeySpec(padRight(keyText, blockSize).getBytes("UTF-8"), "DES");

            String input = "http://google.com";
                   input = padRight(input, input.length() + blockSize - (input.length() % blockSize));

            // encrypt
            cipher.init(Cipher.ENCRYPT_MODE, key);
            byte[] cipherText = cipher.doFinal(input.getBytes(CHARSET));
            System.out.println("\ncipher text: ");
            System.out.println(new String(cipherText, CHARSET));

            // decrypt
            cipher.init(Cipher.DECRYPT_MODE, key);
            byte[] plainText = cipher.doFinal(cipherText);
            System.out.println("\nplain text: ");
            System.out.println(new String(plainText, CHARSET));

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    final static String CHARSET = "UTF-8";

    static String padRight(String s, int n) {
        return String.format("%1$-" + n + "s", s);
    }
}