Replay protection algorithms

The simplest class of security algorithms is anti-replay aegis. Anti-replay protection ensures that each attacker cannot intercept a message sent to a make ~ recipient and replay it at a later time. Anti-replay aegis algorithms fall into three classes.

Sequence verse are used when a network session continues over a longer period and involves ~y exchange of many messages. Starting through a low number, the sender puts some increasing sequence number on each intimation. The receiver keeps track of the arrangement numbers and ignores any number that is depress than the currently active one.

Since series numbers have a limited number of bits, special measures are necessary when the series number rolls over. Either the sum of ~ units sides need to reinitialize the sitting or some special signaling is required to point out that the new message is valid even though the sequence number is decrease than the previous number.

A nonce is a randomly generated call over that is attached to a petition message and to the corresponding respond. Nonces are used in request/replication protocols where a single request from the sender is matched through a single reply from the responder. The sender randomly generates a nonce and attaches it to the beseech. The sender keeps track of the nonce while awaiting the reply. The responder includes the nonce in the reply. The sender knows the reply matches the petition sent by matching the stored nonce over ~ the nonce in the reply. While every attacker can record a message sent by the responder and replay it to the requester, the requester leave ignore old messages because the nonce does not oppose an outstanding request.

Atime stamp is any other way to protect a request/replication protocol from replay attacks. The sender or responder determines the current time, obtained from the Network Time
Protocol (NTP) (described in RFC 1305 (RFC 1305, 1992)) or from some other wellknown source. Both sender and responder hold the current time in their messages. A
intimation recipient drops the message if the time make is outside a particular window around the current time. The window is essential because clocks on individual nodes in
a distributed body cannot be synchronized exactly. Time stamps are a bit less secure than nonces and following numbers since both sides are liable to injury to a replay attack for
messages that are caught and replayed not beyond the window. Time stamps are typically again useful for protocols in which there is little delay on messages sent .