A digital interface device is provided for facilitating key encryption of a digital signal which is communicated from a computer system to an associated peripheral device, such as a digital display device. The digital interface device has a digital output, digital output formatting circuitry associated with the output and a non-volatile RAM for storing a basic input/output system (BIOS) for, inter alia, controlling digital output formatting. The interface device is configured such that the non-volatile RAM has a specific addressable write-protectable area allocated for storing an encryption key flag at a flag address along with encryption key data. The write-protectable area is rendered read-only when a predetermined flag value is stored at the flag address. Thus, encryption key data may be stored in the specific write-protectable area of the non-volatile RAM in connection with storing the predetermined flag at that flag address such that encryption data cannot be altered when the flash RAM is subsequently written to, such as when a BIOS stored in the non-volatile RAM is updated.