code: public static byte[] hmacSHA1(byte[] data, byte[] key) {
          checkNotNull(data);
          checkNotNull(key);
          HMac hMac = new HMac(new SHA1Digest());
          KeyParameter keyParameter = new KeyParameter(key);
          hMac.init(keyParameter);
          hMac.update(data, 0, data.length);
          byte[] result = new byte[hMac.getMacSize()];
          hMac.doFinal(result, 0);
          return result;
      }
docs: Hash-based message authentication code with SHA1 digest as defined in:
  <a href="http://www.ietf.org/rfc/rfc2104.txt">RFC 2104</a>.
  
  @param data
  @param key
  @return