this is the first I've heard about arcade roms being encrypted most of the time it was painstaking to decipher the bitmaps for their background screens, or sprites because the address boundaries of the bitmap images had to be extracted from the code and that's after you disassemble the machine code Dan
I think it was more of the later games that used heavy encryption. Things like the CPSII which just finally got fully reversed (there are tools to reprogram the crypto keys into the hardware now.) Other games such as Arkanoid use a one-time-programmable microcontroller that looks like an EPROM to answer some sort questions for the main CPU. All kinds of tricks. Current generation machines are being popped by using PCI-E DMA exploits to recover security keys used by the SATA controller chipsets and other crazy stuff on Linux/PC based systems. The hard drives require some sort of unlock command every so many nanoseconds or something. My go-to programmer I have here is the Needham Electronics EMP-100. Hollar if I can be of any assistance! - Ethan