Public key cryptography was proposed in the 1976 seminal article of Diffie and Hellman [6]. One year later, Rivest, Shamir and Adleman introduced the RSA cryptosystem as a first example. From an epistemological perspective, one can say that Diffie and Hellman have drawn the most extreme consequence of a principle stated by Auguste Kerckhoffs in the XIXth century: “le mecanisme de chiffrement doit pouvoir tomber sans inconvenient aux mains de l’ ennemi1”. Indeed, Diffie and Hellman understood that only the deciphering operation has to be controlled by a secret key: the enciphering method may perfectly be executed by means of a publicly available key, provided it is virtually impossible to infer the secret deciphering key from the public data.