With respect to satellite systems, programme providers need a conditional access system which only allows people who pay for programmes to watch them. These typically consist of a module (CAM - conditional access module) in the receiver and then a smart card that goes into the module. The card and module combined allow the encrypted transmissions to be decrypted and watched.
If you don't want to use the system provided by the programme provider, you have to emulate part or all of it. When you put a titanium card into an original receiver, for example, you are emulating just the smart card.
If you upload new firmware to a receiver, you can also emulate the CAM and card without having to have the originals.
Smart card emulation can also be done with a season interface, which has smart card contacts on a pcb and a serial connection to a computer. The computer (in linux or windows) then takes over the job of the smart card. Software like wce gives a lot of debug information , so you can see what is happening with the underlying protocol.
I found on the web an emu called "all7" for the comag SL55, it can be downloaded with the STB5518 program, Serial cable with pins 2-3, 3-2, 5-5.
I tried it on a friends reciever, and it worked very well - even decoded the latest TPS channels.