java hash from “PBKDF2WithHmacSHA512” is differs from python CRYPT(digest_alg='pbkdf2(1000,20,sha512)', salt=True)(password)[0])

Question

I have a database with passwords that are hashed using the following python code:

result = str(CRYPT(digest_alg='pbkdf2(1000,20,sha512)', salt=True)(password)[0])

(details can be found here )

for password='123' it generates

pbkdf2(1000,20,sha512)$b3c56f341284f4be$54297564f7a3be8c6e9c10b27821f8105e0a8120

I need to validate password using java. I use the following code:

    validatePassword("123", "pbkdf2(1000,20,sha512)$b3c56f341284f4be$54297564f7a3be8c6e9c10b27821f8105e0a8120");



    private static boolean validatePassword(String originalPassword, String storedPassword) throws NoSuchAlgorithmException, InvalidKeySpecException
    {
        String[] parts = storedPassword.split("\\$");
        byte[] salt = fromHex(parts[1]);
        byte[] hash = fromHex(parts[2]);

        PBEKeySpec spec = new PBEKeySpec(originalPassword.toCharArray(), salt, 1000, hash.length * 8);
        SecretKeyFactory skf = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA512");
        byte[] testHash = skf.generateSecret(spec).getEncoded();

        System.out.println(toHex(testHash));
        System.out.println(toHex(hash));

        return true;
    }


    private static byte[] fromHex(String hex) throws NoSuchAlgorithmException
    {
        byte[] bytes = new byte[hex.length() / 2];
        for(int i = 0; i<bytes.length ;i++)
        {
            bytes[i] = (byte)Integer.parseInt(hex.substring(2 * i, 2 * i + 2), 16);
        }
        return bytes;
    }

    private static String toHex(byte[] array)
    {
        StringBuilder sb = new StringBuilder();
        for(int i=0; i< array.length ;i++)
        {
            sb.append(Integer.toString((array[i] & 0xff) + 0x100, 16).substring(1));
        }
        return sb.toString();
    }

but result is the following:

80385948513c8d1826a3a5b8abc303870d41d794
54297564f7a3be8c6e9c10b27821f8105e0a8120

Please help what I am doing wrong?

Answer 1

There is kind of a "bug" in the code around web2py.

The hash LOOKS like a hex string, but it is sent to the hashlib.pbkdf2_hmac (a proxy to openssl's method) as just the character representation of the hex string. Meaning you should not use

byte[] salt = fromHex(parts[1]);

but

byte[] salt = parts[1].getBytes("utf-8");

In addition, you need to pass the KEYLENGTH instead of the salt length into PBEKeySpec's contructor.

The corrected part should read:

byte[] salt = parts[1].getBytes("utf-8");
byte[] hash = fromHex(parts[2]);
PBEKeySpec spec = new PBEKeySpec(originalPassword.toCharArray(), salt, 1000, 20*8);

Replace that and the code works. It took a while to find this out ;)