A method for protecting the digital output signal of a security module,
comprising the steps of: receiving a scrambled digital signal from a
source external to said security module, recovering at least one
transport scramble control flag from the scrambled digital signal,
descrambling said received scrambled signal to generate a descrambled
signal, monitoring the at least one transport scramble control flag,
generating a scrambling key in response to said monitored at least one
transport scramble control flag, and scrambling said descrambled signal
using said scrambling key to generate a re-scrambled signal. The present
invention also includes a conditional access system comprising a host
device and a security device coupled to the host device, such that the
security device includes at least one transport scramble control flag
modification circuit. By monitoring the transport scramble control flag
as content passes through the security module, protection of the content
can be securely maintained.