Low cost attacks on tamper resistant devices

There has been considerable recent interest in the level of tamper resistance that can be provided by low cost devices such as smart-cards. It is known that such devices can be reverse engineered using chip testing equipment, but a state of the art semiconductor laboratory costs millions of dollars. In this paper, we describe a number of attacks that can be mounted by opponents with much shallower pockets. Three of them involve special (but low cost equipment: differential fault analysis, chip rewriting, and memory remanence. There are also attacks based on good old fashioned protocol failure which may not require any special equipment at all. We describe and give examples of each of these. Some of our attacks are significant improvements on the state of the art; others are useful cautionary tales. Together, they show that building tamper resistant devices, and using them effectively, is much harder than it looks.