Method of secured communications in a telecommunications system

A method of secured communication in a telecommunications system including at least two communication exchanges and a plurality of user equipments, wherein each user equipment is provided with a store which holds a user variable data word particular to that user;

• and, each exchange is provided with a store which holds all the user variables data words of the users connected to it, and, each exchange is provided with its own random variable data word, so that when a first user makes a secure call to a second user, the first user equipment encrypts the call using its particular user variable data word and sends the encrypted data to its own exchange, the exchange is provided with decrypting and generation equipment for decrypting the call using the particular user variable data word and generates the random variable data word that will be used for the call, and encrypts it with the particular user variable data word and returns it to the first user;
• the exchange also sends the random variable data word to the second user's exchange which encrypts it with the user variable data word particular to the second user and sends it to the second user, said decrypting and generation equipment generates a different random variable data word, during communication, to permit the user to change between telephony and data calls.