With the rapid development of computer network
technologies, more and more computers connect together to
exchange great information and share system resources.
Security is then an important issue for computer networks.
To prevent the information from being accessed by
illegitimate or unauthorized users, remote authentication of
users is certainly one of the most important services.
Especially, the purpose of the one-time password is to
make it more difficult to gain unauthorized access to
restricted resources. Basically one-time password schemes
can be classified into the following four categories: