# Timestamping

By [Bnader](https://paragraph.com/@suliban) · 2023-01-18

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Cryptocurrencies use various timestamping schemes to "prove" the validity of transactions added to the blockchain ledger without the need for a trusted third party.

The first timestamping scheme invented was the [proof-of-work](https://en.wikipedia.org/wiki/Proof_of_work) scheme. The most widely used proof-of-work schemes are based on SHA-256 and [scrypt](https://en.wikipedia.org/wiki/Scrypt).[\[26\]](https://en.wikipedia.org/wiki/Cryptocurrency#cite_note-ars1-26)

Some other hashing algorithms that are used for proof-of-work include [CryptoNight](https://en.wikipedia.org/wiki/CryptoNote#Egalitarian_proof_of_work), [Blake](https://en.wikipedia.org/wiki/BLAKE_\(hash_function\)), [SHA-3](https://en.wikipedia.org/wiki/SHA-3), and [X11](https://en.wikipedia.org/wiki/X11_algorithm).

Another method is called the [proof-of-stake](https://en.wikipedia.org/wiki/Proof_of_stake) scheme. Proof-of-stake is a method of securing a cryptocurrency network and achieving distributed consensus through requesting users to show ownership of a certain amount of currency. It is different from proof-of-work systems that run difficult hashing algorithms to validate electronic transactions. The scheme is largely dependent on the coin, and there's currently no standard form of it. Some cryptocurrencies use a combined proof-of-work and proof-of-stake scheme.

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*Originally published on [Bnader](https://paragraph.com/@suliban/timestamping)*