I. Introduction
The anticipated large-scale applications of biometric technologies such as iris recognition are driving innovations at all levels, ranging from sensors to user interfaces, to algorithms and decision theory. At the same time as these good innovations, possibly even outpacing them, the demands on the technology are getting greater. Today, many countries are considering or have even announced procurement of biometrically enabled national identity (ID) card schemes, one of whose purposes will be to detect and prevent multiple IDs. Achieving that purpose will require, at least at the time when cards are issued and IDs are registered, an offline “each-against-all” cross-comparison. In effect then the number of biometric comparisons that must be performed scales as the square of the population. The decision confidence levels that will be required to keep the false match rate (FMR) negligible, despite such vast numbers of opportunities to make false matches, can only be described as astronomical.