How does Safedisc 2 work?

[JamesM]

I have been trying to work out how exactly safedisc works. I have a CloneCD image of a safedisc 2 game. It is running in daemon-tools, with safedisc emulation switched off. My original toughts were that the safedisc code checks for corrupted sectors on the CD and only allows the game to run if the bad sectors are detected.

To test this theory, I used CDMage to regenerate the ECC fields of the 600 or so corrupted sectors. To my suprise the game still worked.

Then I created an iso image of the CCD using bin2iso. I mounted this in d-tools and the game still worked. This makes me think that safedisc is operating at the iso filesystem level.

Of course if I create a new iso using makeiso containing the files from the CD, it will not work.

Can anyone enlighten me to exactly what it does to check the CD?
Thanks