Challenge-Response (Two-Way Communication)
The host generates and sends a random string to the card.
Taking the string as input, the card uses a cryptographic function to produce a result.
The result is then sent back to the host.
The host must also compute its result (another one).
Compare the two results from the card and host. If the two results match, the user is authenticated and allowed to log in to the host.
Note: One way = Challenge from the host,
Another way = Response from the card.