1. A traceable method for encrypting and/or decrypting data broadcast by at least one transmitter towards several decoders, this method enabling the identification of a traitor, amongst different lawful users of the decoders, who has communicated secret data to a non-authorized third party so that this third party is able to encrypt and/or decrypt data broadcast by the transmitter, in which: during encryption of the broadcast data, the transmitter applies at least a first secret cryptographic function, and during decryption of said broadcast data, all the decoders apply at least one same second secret cryptographic function identical to said first function or its inverse, each decoder having recourse for this purpose to a mathematical description of said second function recorded in a memory, wherein during the application of the second function the mathematical description of this second function, to which each decoder has recourse, is different from one decoder to another or from one group of decoders to another so that the mathematical description to which recourse is made exclusively identifies the particular decoder or group of decoders among all the decoders; and wherein said mathematical description (F Kj ) recorded in the memory of each decoder is formed of several elementary functions (G i,j ) which must be composed with each other in a determined order to form said second secret function.