replayattacker

replayattacker is an entity that performs a replay attack by capturing valid data transmissions and retransmitting them to trigger unauthorized actions. Unlike attackers who must break encryption, a replayattacker relies on the lack of freshness in messages, such as missing nonces, timestamps, or unique transaction identifiers, to reuse legitimate communications later.

In practice, a replayattacker can occur in authentication protocols, financial transactions, or wireless communications where an old message can be accepted as current. A replayattacker may eavesdrop on a session, store a login request or payment instruction, and later replay it to impersonate the legitimate user or authorize a duplicate operation. The risk is highest when sessions are long-lived, tokens are reusable, or sequence numbers are not validated.

Common targets include web sessions that rely on cookies or tokens without binding to a specific session, RFID-based access controls, and payment systems that do not enforce one-time use of card data. A replayattacker can be passive, simply listening for data, or active, injecting stored messages into a network stream.

Mitigation relies on techniques that ensure data freshness and uniqueness: nonces, timestamps, and one-time tokens; challenge–response authentication; binding tokens to a specific session; integrity protection with sequence numbers; and limiting token validity. Protocols such as TLS, IPSec, and DTLS incorporate anti-replay windows or stateful checks. Network monitoring and anomaly detection can help identify unusual reuse patterns.

See also: replay attack, anti-replay protection, nonce, timestamp, one-time password.