Web and XML Glossary

A Nonce is a randomly generated value used to defeat "playback" attacks in communication Protocols. One party randomly generates a nonce and sends it to the other party. The receiver encrypts it using the agreed upon secret key and returns it to the sender. Since the nonce was randomly generated by the sender, this defeats playback attacks because the replayer can not know in advance the nonce the sender will generate. The receiver denies connections that do not have the correctly encrypted nonce.