Salt

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * @author Ryan Greene
 *
 */
public final class Salt {

    /**
     * The message digest instance.
     */
    private final MessageDigest messageDigest;

    /**
     * The amount of iterations which the salt is applied.
     */
    private final int iterations;

    /**
     * The salt being applied.
     */
    private final byte[] salt;

    /**
     * Creates a new salt instance with the specified amount of iterations and
     * salt.
     *
     * @param iterations The amount of iterations which the salt is applied.
     * @param salt The salt being applied.
     * @return The created salt instance.
     */
    public static final Salt create(final int iterations, final byte[] salt) throws NoSuchAlgorithmException {
        return new Salt(MessageDigest.getInstance("SHA-1"), iterations, salt);
    }

    /**
     * Constructs a new salt instance with the specified message digest, amount
     * of iterations and salt.
     *
     * @param messageDigest The message digest instance.
     * @param iterations The amount of iterations which the salt is applied.
     * @param salt The salt being applied.
     */
    private Salt(final MessageDigest messageDigest, final int iterations, final byte[] salt) {
        this.messageDigest = messageDigest;
        this.iterations = iterations;
        this.salt = salt;
    }

    /**
     * Hashes and applies salt to the specified password.
     *
     * @param password The password being hashed.
     * @return The hashed and salted password.
     * @throws NoSuchAlgorithmException If an exception is thrown.
     * @throws UnsupportedEncodingException If an exception is thrown.
     */
    public final byte[] applySalt(final String password) throws NoSuchAlgorithmException, UnsupportedEncodingException {
        messageDigest.reset();
        messageDigest.update(salt);
        byte[] input = messageDigest.digest(password.getBytes("UTF-8"));
        for (int iteration = 0; iteration < iterations; iteration++) {
            messageDigest.reset();
            input = messageDigest.digest(input);
        }
        return input;
    }
}