number used once (security) (nonce)

Nonce is the abbreviation for "Number Used Once" or "Used Only Once". Nonce is a random, non-repeatable sequence of digits generated by a random number generator and used in security protocols. For example, in the challenge- response process, where the nonce does not need to be repeated until the authentication keys are changed. Other examples of the use of nonces is the pre-shared key or the four-way handshake.