How can I calculate the SHA-256 hash of a string in Android?

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.

Answer 2

You are along the right lines, but converting the bytes is a little more complicated. This works on my device:

// utility function
    private static String bytesToHexString(byte[] bytes) {
        // http://stackoverflow.com/questions/332079
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < bytes.length; i++) {
            String hex = Integer.toHexString(0xFF & bytes[i]);
            if (hex.length() == 1) {
                sb.append('0');
            }
            sb.append(hex);
        }
        return sb.toString();
    }

// generate a hash

    String password="asdf";
    MessageDigest digest=null;
    String hash;
    try {
        digest = MessageDigest.getInstance("SHA-256");
        digest.update(password.getBytes());

        hash = bytesToHexString(digest.digest());

        Log.i("Eamorr", "result is " + hash);
    } catch (NoSuchAlgorithmException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }

Source: bytesToHexString function is from the IOSched project.

Answer 3

Complete answer with use example, thanks to erickson.

Put this into your "Utils" class.

public static String getSha256Hash(String password) {
    try {
        MessageDigest digest = null;
        try {
            digest = MessageDigest.getInstance("SHA-256");
        } catch (NoSuchAlgorithmException e1) {
            e1.printStackTrace();
        }
        digest.reset();
        return bin2hex(digest.digest(password.getBytes()));
    } catch (Exception ignored) {
        return null;
    }
}

private 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();
}

Example of use:

Toast.makeText(this, Utils.getSha256Hash("123456_MY_PASSWORD"), Toast.LENGTH_SHORT).show();

Answer 4

i know this has been answered but i found a Hashing Library at android arsenal and its very easy,simple and just one line of code. can hash MD5, SHA-1, SHA-256, SHA-384, or SHA-512.

1. first add this to your gradle and sync

   implementation 'com.github.1AboveAll:Hasher:1.2'

2. start hasing

   Hasher.Companion.hash("Hello",HashType.SHA_1);