Once upon a time, arcades were all the rage. You could head down to your local arcade with a pocket full of quarters and try many different games. These days, video arcades are less popular. As a result, many old arcade games are becoming increasingly difficult to find. They are almost like the artifacts of an ancient age. They are slowly left to rot and are often lost or forgotten with time. Enter, MAME.
MAME (Multiple Arcade Machine Emulator) is a software project, the goal of which is to protect gaming history by preventing these arcade machines from being lost or forgotten. The MAME emulator currently supports over 7000 titles, but there are still more out there that require preservation. The hackers who work on preserving these games are like the digital Indiana Jones of the world. They learn about lost games and seek them out for preservation. In some cases, they must circumvent security measures in order to accurately preserve content. Nothing as scary as giant rolling boulders or poison darts, but security nonetheless.
Many of the arcade cabinets produced by a publisher called NMK used a particular sound processor labeled, “NMK004”. This chip contains both a protected internal code ROM and an unprotected external ROM that controls the sound hardware. The actual music data is stored on a separate unprotected EEPROM and is different for each game. The system reads the music data from the EEPROM and then processes it using the secret data inside the NMK004.
The security in place around the internal ROM has prevented hackers from dumping its contents for all this time. The result is that NMK games using this chip have poorly emulated sound when played using MAME, since no one knows exactly how the original chip processed audio. [trap15] found it ridiculous that after 20 years, no one had attempted to circumvent the security and dump the ROM. He took matters into his own hands.
The full story is a bit long and contains several twists and turns, but its well worth the read. The condensed version is that after a lot of trial and error and after writing many custom tools, [trap15] was able to finally dump the ROM. He was able to accomplish this using a very clever trick, speculated by others but never before attempted on this hardware. [trap15] exploited a vulnerability found in the unprotected external ROM in order to trick the system into playing back the protected internal ROM as though it were the sound data stored on the EEPROM. The system would read through the internal ROM as though it were a song and play it out through the speakers. [trap15] recorded the resulting audio back into his PC as a WAV file. He then had to write a custom tool to decode the WAV file back into usable data.
[trap15] has released all of his tools with documentation so other hackers can use them for their own adventures into hardware hacking. The project was a long time in the making and it’s a great example of reverse engineering and perseverance.