Abstract: The present invention relates to a data encryption and/or decryption system comprised of apparatus for storing encryption and/or decryption keys, an encryption and or decryption processor for receiving data signals, for receiving the key or keys from the storing apparatus, and for encrypting or decrypting the data signals in accordance with the key or keys, an output data bus for receiving the encrypted or decrypted signals from the processor, apparatus for plugging the system into a read-only memory (ROM) socket of a computer for access to a source of the data signals and to the output data bus, whereby the data signals are received, and encrypted data signals are passed through the ROM socket.