A conditional access system includes an EMM (Entitlement Management Message)
analyzer
for retrieving partial viewing authorization information. When the partial viewing
authorization information permits partial viewing, ECM (Entitlement Control Message)
is decrypted using work keys, and scrambling keys are intermittently retrieved
from the ECM. This can solve a problem of a conventional conditional access system
in that an unauthorized user's receiver cannot display pictures at all because
the receiver cannot retrieve scrambling keys, and hence the user cannot enjoy a
program even to such a degree as to perceive its feeling as in analog broadcasting
systems, and thus the user cannot decide as to whether to make contract or not
with viewing the program to some extent, which prevents the provider of the program
from offering effective invitation to the user.
