Replay Attack
Definition
A replay attack is when an attacker captures valid authentication data or messages and later reuses them to impersonate a user or repeat an authorized action. Instead of breaking encryption, the attacker relies on re-sending a previously valid exchange, which succeeds when systems do not properly prevent reuse.
Examples
- An attacker captures a network login exchange and replays it to gain access because the protocol does not use nonces or timestamps correctly.
- A contactless access badge signal is recorded and replayed to unlock a door when the system does not detect duplicates.
Discover 🔎
A replay attack is like recording a valid pass at the door and playing it back later. The attacker does not need to know the password, understand the message, or break encryption. They only need a copy of something that was accepted once, and a system that will accept it again.
Replay attacks matter because many security systems focus on secrecy. Replay attacks focus on freshness. Even a secret message becomes dangerous if it can be reused.
Tip: The interactive version includes progress tracking, decks, and premium deep dives.