Definition: nonce

(Number ONCE) An arbitrary number that is generated to provide a unique identification or for security purposes such as when logging in to a network (see initialization vector). A nonce is also used in cryptography (see cryptographic hash function). Pronounced like the "nons" in "nonsense," nonce is actually an English word that means "for the present occasion or time."

The nonce is used one time and not repeated. Although random and pseudo-random numbers theoretically produce unique numbers, there is the possibility that the same number can be generated more than once. However, if a very large, true random number is used, the chances are extremely small. A perfect nonce is the time of day; for example, 12.53 seconds past 5:13pm on 1/1/2020 can only occur once.