Tijekom povijesti tajno komuniciranje većinom se odnosilo na vojne i državne sustave jer su ipak te tajne načuvanije i najvažnije za veliki broj ljudi. Informacije su se prenosile na takav način da nitko, osim pošiljatelja i namjernog primatelja, ne posumnja u postojanje poruke. Takav način tajnog komuniciranja naziva se steganograja. Paralelno s razvojem steganograje razvila se i kriptograja čiji cilj nije bio zatajiti samo postojanje poruke, već prikriti njezino značenje. Jedan od primjera prikrivanja poruke je korištenje nevidljive tinte. Od neobičnih metoda slanja poruka u ovom diplomskom radu spomenuli smo šifriranje pomoću točki i čvorova, crveno plavu šifru, šifriranje pomoću igrćih karata, šifriranje presavijanjem papira, te šifriranje pomoću plastičnog štapića. Od prvih ratnih kodova spominju se spartanski skital i Cezarova šifra s pomakom. Međutim, svakoj vrsti tajnog komuniciranja može se pronći neka mana s kojom bi se ona dešifrirala, ali isto tako može nastati novi ključ ili sama vrsta tajnog komuniciranja kako bi se razina sigurnosti vratila na odgovarajuću. Sukladno tome razvijaju se sustavi šifriranja kao što su Vigenereova tablica i Playfairova šifra. Za vrijeme 2. svjetskog rata pojavljuje se stroj zvan Enigma. U završnom dijelu rada navedeni su neki od primjera korištenja tajnih kodova u poznatim knjigama, kao što su Biblija i Kama sutra.

Through the history secret communication was related to military and state systems because those secrets were the most guarded and most important for many people. Information was transferred in a way that nobody, except sender and intentional receiver, doesn't suspect in existence of the message. This way of secret communication is called steganography. Parallel with the development of steganography there was development of cryptography whose aim was not to conceal the existence of the message but to cover up its meaning. The use of invisible ink was one of the examples of covering up the message. In this graduate thesis we mentioned some of the unusual methods of sending messages such as coding with dots and knots, red-blue code, coding with playing cards, coding by folding the paper, coding with plastic stick. First war codes which are mentioned are Spartan scytale and Cesar's code with shift. However, in every type of secret communication we can nd a aw with whom it could be decoded but also it could become a new key or type of secret communication so the level of security could go back to convenient one. Accordingly, new systems of coding, such as Vigenere's table and Playfair's code are developing. A machine called Enigma appears during the Second World War. In the last part of this work there are examples of using secret codes in famous books such as the Bible and Kama sutra.