Challenge Response Authentication

This document discusses challenge-response authentication and covers its definition, ways of authentication using symmetric-key ciphers, keyed-hash functions, asymmetric-key ciphers, and digital signatures. It provides figures to illustrate challenge-response authentication using a nonce, timestamp, keyed-hash function, asymmetric-key cipher, and digital signature. The key ways discussed are proving knowledge of a secret without revealing it directly and authenticating using a nonce, timestamp, or digital signature to preserve the integrity of challenge and response messages.