This is the last session of the first week of this MOOC. We have already all the ingredients to talk about code-based cryptography. Recall that in 1976 Diffie and Hellman published their famous paper "New Directions in Cryptography", where they introduced public key cryptography providing a solution to the problem of key exchange. Mathematically speaking, public key cryptography considers the notion of one-way trapdoor function that is easy in one direction, hard in the reverse direction unless you have a special information called the trapdoor. The security of the most popular public key cryptosystems is based either on the hardness of factoring or the presumed intractability of the discrete log problem. Code-based cryptography is based on the following one-way trapdoor function. It is easy and fast to encode a message usin