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Chapter 13 Encryption and Scrambling
Access Criteria and Access Rights
When a subscriber is only interested in particular services, i.e. sports and nature, he
only wants to pay for those services. Unpaid services must remain unintelligible.
Therefore, two parameters are defined, Access Criteria (AC) and Access Rights.
Access Criteria is vendor specified information and specifies service-related
criteria applied to a package of services or elementary streams. These
subscriptions (also called theme or product) are encapsulated into Entitlement
Control Messages (ECMs). Refer to Entitlement Control Messages (on page 173).
Access Rights are stored on the smart card of the descrambler and determines
which services the subscriber can access. These Access Rights are periodically
reconfirmed using Entitlement Management Messages (EMMs). When Access
Rights for a particular subscriber are changed, EMMs are sent to the descrambler
with the new Access Rights.
Example:
AC 1 subscription = Football ECM1
AC 2 subscription = Tennis ECM2
AC 3 subscription = Golf ECM3
A subscriber pays to view football and golf programs. His set top box receives all
ECM packets that contain the appropriate CWs. The set top box also receives EMM
packets that contain Access Rights for this box. These rights are compared with the
AC and the set top box is only allowed to decipher the ciphered CWs of the ECMs
for which the subscriber has Access Rights (ECM1 and ECM3).
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