Overview
Challenge-Response Authentication is one of the authentication methods used to enhance security. In this method, authentication is performed without transmitting the user’s actual password over the network. This significantly reduces the risk of password leakage through eavesdropping.
Flow of Challenge-Response Authentication
[Client] Sending User Authentication Information: When a user enters their ID and password, the client sends only the ID to the authentication server. The password is not sent.
[Authentication Server] Generating and Sending the Challenge Code: The authentication server identifies the user corresponding to the received ID and generates a disposable random number (challenge code). This challenge code is sent to the client.
[Client] Generating and Sending the Response: The client combines the received challenge code with the password entered by the user (or a hash of the password) and generates a hash value using a hash function. This generated hash value (response) is sent to the authentication server.
[Authentication Server] Verifying the Response: The authentication server processes its own generated challenge code and the user’s password (or password hash) stored on the server side with the same hash function to generate a hash value. It then compares this generated hash value with the hash value (response) sent from the client. If both match, the user is determined to know the legitimate password, and authentication succeeds.
Advantages
- Reduced Risk of Password Eavesdropping: Since the password itself never travels over the network, the risk of password leakage through eavesdropping is low.
- Resistance to Replay Attacks: Since the challenge code is a different random number each time, even if past communications are intercepted, they cannot be reused as-is to break through authentication, preventing replay attacks.