A traceable method for encrypting and/or decrypting data broadcast by at least one transmitter towards several decoders includes the steps: during encryption of broadcast data, the transmitter implements (in 86) at least one first secret function to transform an unencrypted message into an encrypted message; and during decryption of the broadcast data, all the decoders implement (in 92) at least one common second secret function, each decoder using therefor a mathematical description of the second function stored in a memory (21), the mathematical description of the second function being different from one decoder to another or from one group of decoders to another such that the mathematical description used identifies exclusively the particular decoder or group of decoders.