toistohyökkäys

Toistohyökkäys, also known as replay attack in English, is a type of cyberattack where an attacker intercepts and retransmits a valid data transmission. This could be an authentication message, a command, or any other form of communication. The attacker doesn't necessarily need to understand the content of the message; they simply capture it and send it again later, often to impersonate a legitimate user or to gain unauthorized access to a system or resource.

The effectiveness of a toistohyökkäys relies on the fact that the intercepted data is valid and has not been altered. In many systems, once a message is deemed valid, it is accepted without further verification of its origin or timeliness. This can lead to scenarios where a user's login credentials, once captured, can be replayed to gain access repeatedly, or a command to transfer funds could be executed multiple times.

Countermeasures against toistohyökkäys typically involve introducing time-sensitive elements into communication protocols. This can include using timestamps within messages or employing sequence numbers. If a replayed message arrives with a timestamp that is too old or a sequence number that has already been used, the system can detect and reject it. Encryption can also play a role by making it harder for attackers to intercept and reuse messages, although it doesn't directly prevent the replay itself without additional mechanisms. Secure communication protocols often incorporate both encryption and replay protection to ensure data integrity and authenticity.