System for exchanging data between at least one sender and one receiver

Method for exchange of encrypted data between a sender and a receiver, said method comprising:

• encrypting, in the sender, messages to be transmitted,
• sending the encrypted messages to the receiver by an Internet-type network,
• decrypting, in the receiver, the messages received, and
• sending an acknowledgement message to the sender, wherein the messages are encrypted by means of a symmetric secret key algorithm including:
• generating, in the sender and in the receiver, variable encryption/decryption keys, which are systematically modified in each encryption/decryption and which are produced by identical and synchronised encryption/decryption key generators installed in the sender and in the receiver, the variable encryption/decryption keys being generated on the basis of fixed data including secret codes specific to the sender and to the receiver and at least one data item that is systematically variable in each exchange, wherein the encryption and the decryption of the messages being performed without transmission of the variable encryption/decryption keys or data relating to the variable encryption/decryption keys between the sender and the receiver,
• wherein the acknowledgment message sent to the sender, after receiving and decryption of a message, includes an acknowledgement code, which is sent in encrypted form to the sender and which is used in the receiver, and after decryption in the sender, the acknowledgement code is used as a new data item associated with a synchronisation data item for the generation of a new variable encryption/decryption key.