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What is a Nonce?

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A nonce is a random number or string that is used once and only once for cryptography and information security. They are typically generated with a random number generator or algorithms that generate reproducible results based on factors such as a timestamp and a key. The following are illustrative examples.


Authentication protocols may use a nonce to prevent replay attacks. A nouce that can only be used once prevents an old message being resent to authenticate.

Cryptographic Salt

Cryptographic salt is a type of nouce that is added to a string before it is hashed to make the hash more difficult to reverse.

One-time Passwords

A nouce may be generated and then communicated to a user as a one time password. For example, a customer that calls customer support to reset their password may be given a nouce that enables them to perform the reset.
Overview: Nonce
A random number or phrase that is only used once.
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