FatArnold/Sega Naomi/Protection Key Chip
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The Naomi and Naomi 2 are arcade machines developed by Sega. The principal machines are ROM-chip based, but a GD-ROM extension was available, enabling it to read data from optical discs instead. However, to combat bootleggers from making simple copies of the GD-ROMs, Sega decided to encrypt the data on the discs. The games were then sold with a small dongle which contain the decryption key.
This decryption key chip is the only known copy protection employed on the Sega Naomi systems. Every game has its own key.