In many cases we use passwords toauthenticate ourselves on Web sites where we make transactions, andpasswords represent only one mechanism for authentication. Passwordsare “something we know” (and something that, hopefully, no one elseknows). However, there are other ways of authenticating ourselves. Forexample, we can use “something we are”, such as a fingerprint or otherbiometric, or even “something we have”, such as an access control card.“Two-factor authentication” refers to the concept of using twoinstances of “something we know”, “something we are”, or “something wehave”. Two-factor authentication provides much stronger guarantees whencompared to using just one of these means of authentication.
Oneof the most popular forms of two-factor authentication involves the useof a hardware token that displays a sequence of digits that changes atset intervals. To authenticate ourselves on a network using thismethod, we provide our regular password in...