Antireplay

Antireplay, or anti-replay protection, refers to techniques that prevent an adversary from retransmitting valid messages or packets in order to deceive a recipient, reuse credentials, or disrupt a communication session. Replay attacks can exploit captured traffic to produce unauthorized actions or to overwhelm a system with duplicates. Antireplay mechanisms bind messages to unique, verifiable values so that each transmission can be accepted only once.

In practice, antireplay relies on a combination of nonces, timestamps, and sequence numbers, often cryptographically tied to the message. A common approach is a sliding-window scheme in which the receiver tracks a range of acceptable sequence numbers. Packets with duplicate, out-of-window, or previously seen identifiers are rejected, while new messages pass verification and advance the window. This design helps tolerate reordering and loss while preventing replays.

Different domains implement antireplay in protocol-specific ways. IPsec uses a per-connection anti-replay mechanism with a sliding window to detect and drop duplicate or late packets. TLS/DTLS employs monotonically increasing record sequence numbers bound to the message integrity checks. Wireless standards such as 802.11i include replay protection that uses per-frame counters to reject duplicates, helping secure wireless links against replay assaults.

Challenges include handling legitimate packet reordering, clock synchronization requirements, and the tradeoff between window size, memory use, and vulnerability to late arrivals. Overheads in processing and state maintenance can affect performance, especially in high-speed or lossy networks. Effective antireplay is a balance between robustness and efficiency within a given protocol or system.