Hash String via SHA-256 in Java

Question

By looking around here as well as the internet in general, I have found Bouncy Castle. I want to use Bouncy Castle (or some other freely available utility) to generate a SHA-256 Hash of a String in Java. Looking at their documentation I can't seem to find any good examples of what I want to do. Can anybody here help me out?

Answer 1

If all you want to do is hash a string, I'd just use the built-in MessageDigest class.

MessageDigest md = MessageDigest.getInstance("SHA-256");
String text = "This is some text";

md.update(text.getBytes("UTF-8")); // Change this to "UTF-16" if needed
byte[] digest = md.digest();

Tada, digest now contains the hash of your string.

Answer 2

When using hashcodes with any jce provider you first try to get an instance of the algorithm, then update it with the data you want to be hashed and when you are finished you call digest to get the hash value.

MessageDigest sha = MessageDigest.getInstance("SHA-256");
sha.update(in.getBytes());
byte[] digest = sha.digest();

you can use the digest to get a base64 or hex encoded version according to your needs

Answer 3

This is already implemented in the runtim libs

public static String calc(InputStream is ) {
        String output;
        int read;
        byte[] buffer = new byte[8192];

        try {
            MessageDigest digest = MessageDigest.getInstance("SHA-256"); //"MD5");
            while ((read = is.read(buffer)) > 0) {
                digest.update(buffer, 0, read);
            }
            byte[] hash = digest.digest();
            BigInteger bigInt = new BigInteger(1, hash);
            output = bigInt.toString(16);

        } 
        catch (Exception e) {
            e.printStackTrace( System.err );
            return null;
        }
        return output;
    }