Proof of Existence is a mechanism that proves whether a digital document exists at a specific time. A blockchain acts as a good substitute for a notary because it can prove the existence of a document without the need for a third party. Each document is identified by creating its digest using a hashing algorithm, such as SHA-256. The identity of the document is then stored in the blockchain by timestamping the transaction.
A blockchain implementation of Proof of Existence was created in early 2013 by developers Manuel Araoz and Esteban Ordano. It was released as an open source project. This service used Bitcoin's public network to store information about the document. The information about the document was stored in transaction metadata called OP_RETURN, which allowed the storage of arbitrary information in the transaction.
Proof of Existence...