Method for protection of the transmission, of a multimedia content or of a control word, between a security processor introduced into a receiver terminal and this receiver terminal, in which: - the security processor constructs a current session key SK c by diversification of a root key SK_root as a function of a parameter P c transmitted by the terminal, - the security processor decrypts the multimedia content or the control word then encrypts the decrypted multimedia content or the decrypted control word with the current key SK c and, finally, transmits to the terminal the multimedia content or the encrypted control word with the current session key SK c, and - the terminal decrypts the multimedia content or the encrypted control word with the constructed key SK c by means of a secret code C c -1 in order to obtain the multimedia content or the control word in unencrypted form, characterized in that the method comprises: - the recording in advance in the terminal of several secret codes C c -1, each secret code C i -1 allowing only the decryption of the multimedia content or of the encrypted control word by a respective session key SK i obtained by diversification of the key SK_root with a parameter P i, one of these parameters P i being the parameter Pc, - the reception of the parameter P c by the terminal in a message also containing a multimedia content or a control word to be decrypted by the security processor, and - in response to the reception of the parameter P c, the selection by the terminal, from amongst all of the secret codes recorded, of the secret code C c -1 to be used for decrypting the multimedia content or the encrypted control word with the key SK c, as a function of the parameter P c or of another parameter contained within the same message. - the security processor constructs a current session key SK c by diversification of a root key SK_root as a function of a parameter P c transmitted by the terminal, - the security processor decrypts the multimedia content or the control word then encrypts the decrypted multimedia content or the decrypted control word with the current key SK c and, finally, transmits to the terminal the multimedia content or the encrypted control word with the current session key SK c, and - the terminal decrypts the multimedia content or the encrypted control word with the constructed key SK c by means of a secret code C c -1 in order to obtain the multimedia content or the control word in unencrypted form, - the recording in advance in the terminal of several secret codes C c -1, each secret code C i -1 allowing only the decryption of the multimedia content or of the encrypted control word by a respective session key SK i obtained by diversification of the key SK_root with a parameter P i, one of these parameters P i being the parameter Pc, - the reception of the parameter P c by the terminal in a message also containing a multimedia content or a control word to be decrypted by the security processor, and - in response to the reception of the parameter P c, the selection by the terminal, from amongst all of the secret codes recorded, of the secret code C c -1 to be used for decrypting the multimedia content or the encrypted control word with the key SK c, as a function of the parameter P c or of another parameter contained within the same message.