重放攻击（Replay attack）是一种网络攻击，它恶意的欺诈性的重复或拖延正常的数据传输。

假设Alice向Bob认证自己。Bob要求她提供密码作为身份信息。同时，Eve窃听两人的通讯，并记录密码。在Alice和Bob完成通讯后，Eve联系Bob，假装自己为Alice，当Bob要求密码时，Eve将Alice的密码发出，Bob认可和自己通讯的人是Alice。

A replay attack (also known as playback attack) is a form of network attack in which a valid data transmission is maliciously or fraudulently repeated or delayed. This is carried out either by the originator or by an adversary who intercepts the data and retransmits it, possibly as part of a masquerade attack by IP packet substitution.