What Is Nonce in Cryptography?

The word "nonce" in cryptography means "number only once", which is an arbitrary number (either random or sequential, or a combination of the two) that is non-repeating in the scope of a particular cryptographic communication. It is used to give "originality" to a message so that the data submitted in an older communication is not allowed to be reused or repeated (such as in a replay attack).

For example, an e-commerce site may use a nonce to prevent a malicious user from placing an order multiple times using valid data from an old order. There are, of course, many other uses for a nonce (such as in authentication, hashing, identity management, cryptocurrency, asymmetric cryptography, etc.) where preventing the same data from being reused is critical.

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