What Is Replay Attack and How Can You Stop It?

Replay attack is a type of network attack where a hacker intercepts a data transmission on a secure network and fraudulently delays or resends it. This allows the hacker to fool the receiver into thinking they have received a legitimate data transmission.

What makes replay attack particularly dangerous is the fact that the hacker doesn’t need the ability to decrypt the data transmission — the entire thing can simply be resent without arousing suspicions.

A real-world example

Here’s an example of how a replay attack could work in the real world:

1. Mark, an employee at a bank, sends a financial transfer request via an encrypted message to Penelope, the bank’s financial administrator.

2. A hacker intercepts the message and captures it. Because the message is a legitimate one, the hacker can resend it and it will appear no different from any other message.

3. The hacker resends the message to Penelope. She will have no reason to question its legitimacy and may end up unknowingly transferring a large amount of money to the hacker’s bank account.

How to stop replay attack

Prevention of replay attacks is all about having the right type of protection. Because the hacker doesn’t need to read or decipher the encrypted messages, they can simply resend them in their entirety. That said, there are a few methods that can be implemented to protect against replay attacks.

#1 — The timestamp method

When a timestamp is added to every message, it stops hackers from being able to resend messages within a large window of time. If the hackers have a significantly smaller window of time in which they can resend the messages, it makes it a lot more difficult for them.

#2 — The session key method

This method involves the use of completely random session keys, which are special codes that are only valid for a single transaction. Every time a user logs onto a network, a random session key is generated. When the user ends the session, the session key is no longer valid.

#3 — The password method

By requiring users to enter a one-time use password for each transaction, it guarantees that even if a hacker can eavesdrop on the network and intercept its messages, they would be unable to resend them.

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