e207. creating a keyed digest using md5.txt

这里面包含了一百多个JAVA源文件

A keyed digest is one in which a secret key is used to create a digest for a buffer of bytes. You can use different keys to create different digests for the same buffer of bytes. 
    public static byte[] getKeyedDigest(byte[] buffer, byte[] key) {
        try {
            MessageDigest md5 = MessageDigest.getInstance("MD5");
            md5.update(buffer);
            return md5.digest(key);
        } catch (NoSuchAlgorithmException e) {
        }
        return null;
    }