Questions tagged [copy-protection]

For questions about copy protection techniques used on retro software.

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40
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3answers
4k views

How did Apple II BASIC programs protect against listing?

I seem to recall from my high-school days that certain Apple II programs protected themselves from being listed and therefore modified. If you tried to do it, the machine would simply reboot. How did ...
12
votes
2answers
1k views

How was Prince of Persia "better/faster" with RWTS18?

I was reading about Prince of Persia over at POP Code Review. In that article, the writer printed an interview with Roland Gustafsson, the inventor of RWTS18 copy protection for the Apple II series. ...
10
votes
4answers
894 views

Was the Amstrad's file protection considered secure in 1985?

I just reverse engineered the file protection on the Amstrad CPC, which uses two sequences of rotating bytes taken straight out of the AMSDOS ROM to XOR each byte of the file. If you have SEQa of 13 ...
4
votes
3answers
1k views

How can I view BASIC code hidden by SYS?

I ran a validation of an old disk, and it turns out this ruined a game (won't load) and deleted my old high score list on David's Midnight Magic. I would like to edit the code to get the high score ...