The present invention makes use of techniques such as those described by Boneh and Franklin to allow for the realization of a pseudo-asymmetric encryption scheme whereby one public encryption corresponds to a plurality of private decryption keys. This scheme therefore provides a solution to the problem of inefficient use of bandwidth in asymmetrical encryption schemes which inherently require that a plurality of encryptions of data be broadcast to a plurality of receivers. The invention further ensures that the advantage of traceability, typical found in asymmetric encryption schemes, is maintained due to the characteristic that each receiver uses a unique traceable decryption key. The traceability thus achieved by the present invention allows for the revocation of a security module which has been involved in the abusive use of conditional access data, particularly by means of clones of security modules whose security has been compromised.