SecurID is a two-factor authentication system developed by Security Dynamics (now RSA Security). It is generally used to secure either local or remote access to computer networks. Each SecurID user has a memorized PIN or password, and a hand-held token with a LCD display. The token displays a new pseudo-random value, called the tokencode, at a fixed time interval, usually one minute. The user combines the memorized factor with the tokencode, either by simple concatenation or entry on an optional keypad on the token, to create the passcode, which is then entered to gain access to the protected resource.
The SecurID token is a battery powered, hand-held device containing a dedicated microcontroller. The microcontroller stores, in RAM, the current time, and a 64-bit seed value that is unique to a particular token. At the specified interval, the seed value and the time are combined through a proprietary algorithm stored in the microcontroller's ROM, to create the tokencode value.
An authentication server verifies the passcodes. The server maintains a database which contains the seed value for each token and the PIN or password for each user. From this information, and the current time, the server generates a set of valid passcodes for the user and checks each one against the entered value. For more on SecurID, see http://www.rsasecurity.com/node.asp?id=1155.