This is a public key based authentication model that works by verifying whether the user is in posession of his private key. The user should have Keygloo installed in his system for authenticating himself into any Keygloo enabled web application.
During login time, the user will be thrown a challenge password encrypted using his public key. The user can decrypt the password by clicking a 'Decrypt' button which appears in his toolbar after installing Keygloo. The decrypted password is submitted to the Keygloo enabled application by clicking a 'submit' button on the page. The Keygloo enabled applcation then authenticates the user into the system by comparing the decrypted password with the original challenge password.
A demonstration of how the model works can be found at http://www.keygloo.com/Authentication/auth_kgnum.html.
Keygloo is free to download and install from http://www.keygloo.com/Downloads.htm.