Before discussing Claude Shannon's contribution to cryptography, it is necessary to examine his previous work particularly in the field of information theory, a field that he theorized in his 1948 paper, A Mathematical Theory of Information. Shannon introduced many of the ideas mentioned and developed in this groundbreaking paper to the scientific community in his 1945 paper A Mathematical Theory of Cryptography. Indeed, during World War II, Shannon decided to join Bell Labs, a research center. concentrating many eminent scientists of the time who decided to put their talent at the service of the war effort. While he worked at Bell Labs, the facility was in charge of many secret projects such as the development of System X. System X referred to "an encrypted radiotelephone system to connect Washington and London." Although Shannon was not part of the project per se, she was asked to test the project's registration scheme. This registration scheme was based on two very important concepts, namely “sampling” and “quantification”. “The idea was to approach a continuous signal through a series of steps – as if we were superimposing the continuous signal with what appears to be a staircase that goes up and down following the shape of the signal.” Sampling refers to the action of choosing these steps, while quantization refers to the action of setting the pitch of each step. This process made it possible to approach continuous signals with series of discrete steps. Applied to the telephone, it allowed the high commands in London and Washington to communicate with each other in the knowledge that the Germans would never resume their conversations. However, one of the problems was that since the post was broken into steps before the middle of the article, it was impossible to describe how to achieve this result. It is the discovery that we have just described which allowed Shannon to publish in 1949 his article Communication Theory of Secrecy Systems 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 in Europe and were the dominant type of encryption for confidential messages during both world wars. World War II was considered particularly technological. Cryptography was very important and anyone who broke the other side's code would have a huge advantage in the war. Eventually, the British, with the help of Alan Turing, broke the German "Enigma" code and the Americans broke the Japanese "Purple" code »..”