91色情片

Back in 1933 William Friedman and the US government鈥檚 National Security Agency applied for a patent on a way of generating an unbreakable code that the military could use to send messages. The patent describes and sketches a typewriter keyboard with electrical connections made through wheels. The wheels move randomly to keep altering the connection paths, so that the typed output bears no systematic relationship to the input-thwarting attempts to break the code. This system was remarkably similar to Germany鈥檚 Enigma system. After 67 years, the US government now reckons the principles behind the system are so well know that the patent can be published (USP 6 097 812).