How can I make a disk copy protection scheme using DPM (Data Position Measurement)?

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C++

disk

copy-protection

Hi
I'm developing a copy protection for compact disk (CD/DVD) based on DPM. I want to know how I can get some unique features of disks which are different in each copied disks.

One method I tested is that I calculate RPM of the drive at a specific speed (48x) and then I make the drive to seek to the first sector. After that I read one sector and calculate the taken time and finally I use this formula:

sector degree relative to the first sector at the current speed: ((time / (60000 / RPM)) % 1) * 360

The degree I get from the above formula is a constant value for each drive. So the problem is that when I switch to another system with different CD/DVD drive, this degree is a far different value.


Is my method correct? Please give some suggestions.

Thanks.