Interleaving security and efficiency considerations in the design of inexpensive IC cards

Currently used inexpensive IC cards (e.g. payphone cards) prove their authenticity and generate digital signatures by means of a simple circuit which implements a nonlinear one-way transformation. The paper considers possible approaches for the efficient design and fabrication of such a circuit, based on the observation that the circuit does not have to serve any predefined exact process as long as its functioning falls within a wide range of possible allowed behaviours. It is shown how this tolerance in defining the circuit´s behaviour can potentially be traded for efficient design and fabrication of the circuit, without necessarily sacrificing security