code: final byte[] hash(final byte[] input, final int offset, final int len) {
  		mdHash.update(input, offset, len);
  		return mdHash.digest();
  	}
docs: Calculate HASH of input
  <p>
  <a href="http://en.wikipedia.org/wiki/SHA-1">SHA-1</a>
  
  @param input
  @param offset
  @param len
  @return