CONDITIONAL ACCESS SYSTEM USING MESSAGE INCLUDING MULTIPLE CRYPTOGRAPHIC KEYS

摘要

PROBLEM TO BE SOLVED: To deal with infringement action at low cost by distributing access conditions for one user at least while containing a 1st item consisting of control words enciphered by the algorithm based on a key K1 and a 2nd item for enabling the confirmation and collation of contents of a message under the control of a key Q. SOLUTION: A message MEC is confirmed while using the confirmation algorithm controlled by the key Q. The key Q is contained in a circuit 23. Enciphered control words E(Cwi)Kj are deciphered while using a key Kj of encipher algorithm while the key Kj of encipher algorithm is stored in a decipher circuit 24. While the key Kj is stored in the decipher circuit 24, the decipher circuit 24 simultaneously stores an index (Kj) for recognizing the enciphered control words E(Cwi)Kj out of the set of enciphered control words included in the message MEC.