A method of encoding a piece of information circulating in a network comprising at least one information transmitting node and one recipient node, using a public key encryption system, characterized in that it comprises at least the following steps: generating a public key by using a public key generation matrix NG consisting of u columns and u rows, an element of a column or of a row being a block formed by the code generation matrix G, and by use of a public key given by the matrix PUK=RI (matrix multiplication by block) NG (matrix multiplication) RP. The private key and the public key obtained are used to encode and decode the information transmitted in the network.