Question

I’m trying to get the SHA256 of a string in Android.

Here is the PHP code that I want to match:

echo bin2hex(mhash(MHASH_SHA256,"asdf"));
//outputs "f0e4c2f76c58916ec258f246851bea091d14d4247a2fc3e18694461b1816e13b"

Now, in Java, I’m trying to do the following:

            String password="asdf"
            MessageDigest digest=null;
    try {
        digest = MessageDigest.getInstance("SHA-256");
    } catch (NoSuchAlgorithmException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }
       digest.reset();
       try {
        Log.i("Eamorr",digest.digest(password.getBytes("UTF-8")).toString());
    } catch (UnsupportedEncodingException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

But this prints out: “a42yzk3axdv3k4yh98g8”

What did I do wrong here?

---

Solution thanks to erickson:

 Log.i("Eamorr",bin2hex(getHash("asdf")));

 public byte[] getHash(String password) {
       MessageDigest digest=null;
    try {
        digest = MessageDigest.getInstance("SHA-256");
    } catch (NoSuchAlgorithmException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }
       digest.reset();
       return digest.digest(password.getBytes());
 }
static String bin2hex(byte[] data) {
    return String.format("%0" + (data.length*2) + "X", new BigInteger(1, data));
}

Answer 1

The PHP function bin2hex means that it takes a string of bytes and encodes it as a hexadecimal number.

In the Java code, you are trying to take a bunch of random bytes and decode them as a string using your platform’s default character encoding. That isn’t going to work, and if it did, it wouldn’t produce the same results.

Here’s a quick-and-dirty binary-to-hex conversion for Java:

static String bin2hex(byte[] data) {
    StringBuilder hex = new StringBuilder(data.length * 2);
    for (byte b : data)
        hex.append(String.format("%02x", b & 0xFF));
    return hex.toString();
}

This is quick to write, not necessarily quick to execute. If you are doing a lot of these, you should rewrite the function with a faster implementation.