El 'number that can only be used once’, (number that can only be used once) also known as nuncio, is an arbitrary number that is used in cryptography within the so-called authentication protocols.

in a network blockchain based on Proof of Work nonce works in combination with hash as a control element to avoid manipulation of the block information.

This random number ensures that old hashes cannot be reused in what are called replay attacks.

A nonce in cryptography is:

A one-time, random number intended for data transfer authentication between two or more parties.

Normally the nonce also implements a timestamp or timestamp.

A customer could also be added nuncio o 'not', which will improve security by implementing access authentication.

It must be ensured that the nonce is used only once. Therefore, a time variant should be added to prevent repetition. To guarantee this, a sufficient number of bits can also be generated randomly to reduce this probability.

This adds security and causes any change within the block, whatever it is, to become impossible. This is because the alteration of any element within a block alters the entire hash and the entire structure of the block.

The calculation of the nonce is performed in a forced way, or what is the same: large amounts of computing resources and time are required, so achieving this value is necessary take a proof of work or PoW.

It is impossible to predict the bit combination, which is normally 32 bits and will result in a correct hash.