Kevin utilised rock-solid protection for his games
Kevin to run on it was a challenge. Matt says, “Timings are incredibly important for accurate emulation. Games programmers would take advantage of timing subtleties and undocumented side-effects of instructions. Anti-copy mechanisms were often the most sensitive to this. The 6502 CPU in the BBC
Micro had a number of bugs too – [some] game protection systems would use this to their advantage to try and prevent reverseengineering of their code bases. Kevin Edwards’ protection was the undisputed king – using interrupt timings, various hardware timers and even the self-modifying decryption code itself to generate the keys to decrypt the game.”
James Bonfield, renowned BBC hacker, talks about Kevin’s protection on Exile. “Kevin was the king of copyright protection and the only game author that truly defeated all my attempts. He had the bright idea of encrypting using the 1MHZ hardware timer values, the code doing the encryption, and the program counter. This means that the code cannot be modified, it cannot be moved (it is position-dependent) and it cannot be easily simulated due to the real-time nature of the hardware clocks. Truly a genius.”
The Ultimate BBC games, converted by Paul Proctor and with tape protection by Kevin.