Retrofitting authentication onto firmware

Abstract From the Canadian patent

The present invention provides an inexpensive software-based security-, retrofit solution to verify the integrity of program code in embedded systems or accessories, without resorting to expensive hardware changes. All unused memory on an accessory that could be used to store a program code image is filled with random data. A host system also locally stores a copy of the accessory's program image containing the random data. The host system sends the accessory a list of memory addresses or memory ranges on the accessory which is always different and random in nature. The accessory will then produce a digest using values stored in the memory addresses as inputs to a secure hash …