code: private byte[] verifyMagic(byte[] payload) {
          int payloadLen = payload.length-MAGIC.length;
          if (payloadLen<0)   return null;    // obviously broken
  
          for (int i=0; i<MAGIC.length; i++) {
              if (payload[payloadLen+i]!=MAGIC[i])
                  return null;    // broken
          }
          byte[] truncated = new byte[payloadLen];
          System.arraycopy(payload,0,truncated,0,truncated.length);
          return truncated;
      }
docs: Verifies that the given byte[] has the MAGIC trailer, to verify the integrity of the decryption process.