A monolithic semiconductor device having an encryption engine and encryption key register to store one or more encryption keys, where the contents of the encryption key register are observable, or can be made observable, only to internal components of the device is disclosed herein. The encryption key register can be implemented as an integrated or non-integrated volatile or non-volatile memory location. The monolithic semiconductor device can also include means for temporarily externally accessing and/or defining the contents of the key register during the manufacturing process and/or for a limited number of times after the manufacture and/or testing of the monolithic semiconductor device is completed.