What are replay attacks?

A replay attack is when someone uses a message you sent to trick another person into thinking it came from you again.

Imagine you and your friend are playing a game where you whisper secrets to each other through a tunnel. One day, you say, “Meet me at the park!” Your friend hears it and goes to the park. But then, someone sneaks in behind you and repeats that same message later on, “Meet me at the park!”, and your friend goes again, not knowing it was a copy of your original message.

This is like having a copycat who listens to what you say and then says the same thing later. Your friend can’t tell the difference between your real message and the fake one. The copycat didn’t add anything new, they just reused what you already said.

Replay attacks are used in real life too, like when someone uses your password or a special code to log into your account from another place. They’re not making up new things, they're just repeating the message you sent earlier!