replay protection
also: anti-replay, replay attack prevention
A security mechanism that prevents attackers from capturing and reusing valid encrypted messages or authentication tokens to gain unauthorized access or perform unauthorized actions.
Replay protection works by ensuring that each message or authentication attempt is unique, even if encrypted identically multiple times. This is typically achieved through timestamps, sequence numbers, or nonces (one-time random values) embedded in the message.
For example, in network protocols like Kerberos or TLS, a nonce or timestamp is included with each request. Even if an attacker captures and replays an encrypted login packet, the system rejects it because the timestamp is stale or the nonce has already been used.
Without replay protection, an attacker could intercept a valid encrypted message (such as a payment authorization or login token) and send it again later to perform the same action, causing duplicate transactions or unauthorized access.
Common implementations include session tokens with expiration times, incrementing sequence numbers in protocol headers, and cryptographic challenge-response mechanisms that change with each authentication attempt.