Smart Cards in Hostile Environments

One often hears the claim that smart cards are the solution to a number of security problems, including those arising in point-of-sale systems. This paper argues that many proposed smart card systems still lack effective security for point-of-sale applications. We consider the point-of-sale terminal as a potentially hostile environment to the smart card. Moreover, we discuss several types of modifications that can be made to smart cards to improve their security and address this problem. We prove a set of equivalences among a number of these modifications: ffl private input = private output ffl trusted input + one-bit trusted output = trusted output + one-bit trusted input ffl secure input = secure outpu