Patent ID: 7486793

Claim:
A time accounting method of access to a stream of data encrypted by control words (CW) modified at intervals representing a crypto-period (CP), said stream being received by a user unit (UU) connected to a security module (SC) in charge of verifying the rights of a user and of decrypting messages (ECM) including the control words (CW), said accounting being based on accounting units (CT) authorising the use of the service for an assigned time (AT), said method comprising: communicating an encrypted stream constituting an access service per time unit, said stream being divided into a plurality of accounting units, each unit being paid separately; receiving of encrypted messages (ECM) by the security module (SC), the messages containing the control words (CW) and data specific to said service allowing to determine the assigned time (AT) and cost (CT) of the accounting unit; reading of a time variable (Rdate) representative of the time during which the use of said service is authorised, a value of the time variable (Rdate) being dynamically updated based on at least a time-current (TC), the time-current (TC) varying based on a time base included in each message (ECM); determining, if the time-current (TC) is placed during the authorisation time defined by the time variable (Rdate), and if this is the case, authorising the service by resending the control words (CW) to the user unit (UU); if this is not the case, ordering the debit of an accounting unit (CT) and determining if the time-current (TC) is included in an assigned time (AT) adjacent to the time interval defined by the time variable (Rdate), and if this is the case, determining the new value of the time variable(Rdate) in order to move the time variable (Rdate) from an assigned time (AT), and authorising the service by resending the control words (CW) in plaintext to the user unit; and if this is not the case, loading the time variable (Rdate) of an assigned time (AT) starting from the time-current (TC) and authorising the service by resending the control words (CW) in plaintext to the user unit.