Replayhyökkäykset

Replayhyökkäykset, also known as replay attacks, are a type of cybersecurity threat where an attacker intercepts and retransmits a valid data transmission. The goal is to impersonate a legitimate user or device, often to gain unauthorized access or to disrupt a service. This can happen in various scenarios, from simple password retransmissions to more complex authentication protocols.

In a basic replay attack, an attacker captures a legitimate communication between two parties. This communication might contain a message that grants access or performs a specific action. The attacker then replays this captured message at a later time, tricking the receiving party into believing it's a new, valid request from the original sender. Without proper countermeasures, the receiving system may execute the same action multiple times or grant access repeatedly.

To defend against replay attacks, systems typically employ mechanisms that ensure the freshness of transmitted messages. These often involve timestamps, sequence numbers, or nonces (numbers used once). Each message is assigned a unique identifier or a time constraint, and the receiving system checks these to ensure that a message has not been seen before or is not too old. If a replayed message lacks a valid, fresh identifier, it is discarded. Cryptographic techniques, such as using session keys and message authentication codes (MACs), are also crucial in preventing and detecting replay attacks by ensuring both the authenticity and integrity of the communication.