1. A method for decrypting encrypted audio/video content in a decoder comprising at least a descrambler and a security module, said decryption being carried out by the descrambler using a final control word, said method comprising the steps of: receiving, by the security module, at least two control words from either of which the final control word is derivable; receiving, by the descrambler, the encrypted audio/video content; selecting, by the security module, one of the at least two control words, said selection based on a parameter allowing the security module to be uniquely identified; transferring the selected control word to the descrambler; converting, by the descrambler, the selected control word to the final control word using at least a first cryptographic function, said cryptographic function yielding the same final control word for at least two different control words; using the final control word to decrypt the encrypted audio/video content.