Abstract: A data transmission method uses at least two communication networks to exchange data. The data transmission method on a first medium includes an operation for opening a communication session on the first communication medium and during the session, an operation for receiving confidential information on a single address terminal on a second communication medium, and an operation or transmitting, on the first communication medium, a confidential message representing the confidential information and an operation for verifying whether the confidential message corresponds to the confidential information.

Abstract: The present invention relates to a process and device for electronic payment which comprises an operation of opening a communication session between a first user terminal and a merchant server, on a first communication support, such as the Internet.