A system and method of generating an encryption key in a self-encrypting mass storage device that includes using a manual input device as input for a micro-controller that contains a cyclic counter. An input device event triggers the micro-controller to read the current state of the cyclic counter. An accumulation of cyclic counter values is used as a source of entropy to seed a deterministic random number generator. The output of the deterministic random number generator is used as an encryption key for encryption/decryption processes within the mass storage device.