code: public String md5HexDigest(String signature) {
  		byte[] bytes = md5Digest(signature.getBytes());
  		return new String(Hex.encodeHex(bytes));
  	}
docs: Creates a MD5 digest of the given signature and returns the result as
  a hex-encoded string.
  
  @param signature The signature to digest
  
  @return The MD5 digest of the signature in hex format