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.