The roots of Quantum Cryptography date back to the late 1960s, when Stephen Wiesner published his idea of so called 'Quantum Money'.
No one did show any interest in Wiesner’s idea except for Charles Bennett, who had been an undergraduate at the same university. Although Bennett anticipated the potential of Wiesner’s manuscript, he could not immediately find any practical approach to the concept. Nevertheless he did not stop to reread the paper in the following years and still fascinated with Wiesner’s outstanding idea he began to discuss the whole topic with a computer scientist from Montreal University named Gilles Brassard in the early eighties.
The crucial base of the Quantum Money was the fact that it was impossible to accurately perceive the polarization of the trapped photons without knowing which filter to use and Bennett and Brassard discovered that the same effect could be used in cryptography to transmit an enciphered message as a stream of photons.
After some years of research on the topic and thinking twice of each detail of such a secure transmission of data the whole concept seemed to be a flop but then in 1984 Bennett and Brassard were discussing the whole course of events again in a very informal atmosphere while standing at a station and waiting for the train which should take Brassard back to Montreal. In these few minutes they invented the protocol today known as ‘BB84’, which solves the problem of key exchange and provides secure communication on the basis of transmitting photons. If Brassard’s train would have arrived in time this brilliant concept maybe would not be known today.