Everybody needs to authenticate himself on his computer before using it, or even before using different applications (email, e-commerce, intranet, . . . ). Most of the times, the adopted authentication procedure is the use of a classical couple of login and password. In order to be efficient and secure, the user must adopt a strict management of its credentials (regular changing of the password, use of different credentials for different services, use of a strong password containing various types of characters and no word contained in a dictionary). As these conditions are quite strict and difficult to be applied for most users, they do not not respect them. This is a big security flaw in the authentication mechanism (Conklin et al., 2004). According to the 2002 NTA Monitor Password Survey1, a study done on 500 users shows that there is approximately 21 passwords per user, 81% of them use common passwords and 30% of them write their passwords down or store them in a file. Hence, password-based solutions suffer from several security drawbacks. A solution to this problem, is the use of strong authentication....