Before approaching Claude Shannon's contribution to cryptography, it is necessary to examine his previous work particularly in the field of information theory, a field he theorized in his article 1948's A Mathematical Theory of Information. Shannon introduced many of the ideas mentioned and developed in this groundbreaking article to the scientific community in his 1945 article entitled A Mathematical Theory of Cryptography. Indeed, during World War II, Shannon decided to join Bell Labs, a research facility concentrating many eminent scientists of the time who decided to use their talents in the service of the war effort. While working at Bell Labs, the facility was responsible for many secret projects such as the development of System X. System While Shannon wasn't part of the project per se, he was asked to test the project's enrollment scheme. This enrollment scheme was based on two very important concepts, namely “sampling” and “quantization”. “The idea was to approximate a continuous signal with a series of steps – as if we overlay the continuous signal with what looks like a ladder that goes up and down following the shape of the signal.” Sampling refers to the action of choosing such steps while quantization refers to the action of defining the pitch of each step. This process allowed us to approximate continuous signals with series of discrete steps. When applied to the telephone, it allowed the high commands in both London and Washington to communicate with each other knowing that the Germans would never eavesdrop on their conversations. One of the problems, however, was that since the message was divided into steps first... in the middle of the paper... it didn't describe how to achieve this. It is the discovery we have just described that allowed Shannon to publish his article Communication Theory of Secret Systems in 1949 in which he developed the concept of cryptosystem. To understand the revolutionary nature of this publication, we will now describe what cryptography was before its publication. Polyalphabetic substitution ciphers were developed during the Renaissance period in Europe and were the dominant type of encryption for classified messages during both World Wars. The Second World War was considered particularly technological. Cryptography was very important and whoever broke the other side's code would have a huge advantage in the war. Eventually, the British with the help of Alan Turing cracked the German code “Enigma” and the Americans cracked the Japanese code “Purple.”