Introduction

Abstract

Reliable authorization and authentication are becoming necessary for many everyday actions (or applications), be it boarding an aircraft, performing a financial transaction, or picking up a child from daycare. Authorization is almost always vested in a single individual or in a small group of individuals. Identity verification becomes a challenging task when it has to be automated with high accuracy and hence with low probability of break-ins and reliable non-repudiation. The user should not be able to deny having carried out the transaction and should be inconvenienced as little as possible, which only makes the task more difficult.