title: getting a negative value on md5
body: <p>Im trying to get an MD5 with java and I receive a negative value.
  Can an MD5 result in a negative value?</p>
  
  <p>This is my code:
  </p>
  
  <pre><code>        MessageDigest md5 = MessageDigest.getInstance("MD5");
          byte[] sigBytes = md5.digest((sharedSecret+"api_key"+API_KEY).getBytes());
          api_sig = new BigInteger(sigBytes).toString(16);
  </code></pre>
  
  <p>Thank You.</p>