Proof of Existence is an online service that verifies the existence of laptop files spil of a specific time via timestamped transactions ter the bitcoin blockchain.  [Two] [Three] [Four]
It wasgoed launched ter 2013 spil an open source project. It wasgoed developed by Manuel Araoz and Esteban Ordano. [Five]
On May 24, 2013 reporter Jeremy Kirk from IDG News Service wrote that “It’s essentially a notary public service on the Internet, an inexpensive way of using Bitcoin’s distributed computing power to permit people to verify that a document existed at a certain point te time.” [Two]
Terence Lee from Tech te Asia said, “Notaries — people with constitucional training that are licensed by the state to authenticate the signing of documents — could use this to timestamp contractual agreements.”  Te November 2013, Proof of Existence also received attention ter Spanish-language Genbeta te “Proof of Existence, certificando documentos con Bitcoin”. 
On April 22, 2014 reporter Zeehond Wile from Business Insider wrote that it is “Perhaps the most straightforward example of a post-Bitcoin service using Satoshi’s blockchain”.  On May 8, 2014 reporter Daniel Cawrey from CoinDesk wrote that the service “is an example of how the power of this fresh technology can have applications far beyond the world of finance, ter this case, providing a peek of how bitcoin could one day have a substantial influence ter the fields of intellectual property and law.”  Te hier book Blockchain: Blueprint for a Fresh Economy from O’Reilly Media, author Melanie Swan wrote it wasgoed “One of the very first services to suggest blockchain attestation”. [Three]
Since 2014, O’Reilly author Andreas Antonopoulos uses Proof of Existence spil an example te his book, Mastering Bitcoin.  Previously, Antonopoulos also interviewed Manuel Araoz about Proof of Existence. [Ten]
Chris Dixon said, “Bitcoin is a toneelpodium upon which fresh technologies can be developed” and went on to list Proof of Existence spil one of the very first Bitcoin Blockchain applications. 
Forbes writer Mike Montgomery said ter September , “The intriguing opzicht of this for entrepreneurs is that all kinds of other information could piggyback on the Bitcoin transfers recorded on the blockchain.” 
Security pro Robert Graham said, “BitCoin is not so much a ‘currency’ spil an ’emergent phenomenon’. It makes things possible that have nothing to do with money.”
Graham talent an example:
“Spil another example, let’s say that you have a good idea for a patent, but it’s not finta ready. Well, write it up into a opstopping, then add the file’s signature to the block chain. Years from now, if somebody hammers you to the patent filing, you can prove that you had the idea ahead of time.” 
The service comes in a sha256 cryptographic hash of a document into the blockchain.
The service costs Five mBTC vanaf use. Spil of this writing (-12-24, This wasn’t always the service’s behavior.), each use of the service creates Two transaction outputs. One of them holds the identifier 0x444f4350524f4f46 (which is ‘DOCPROOF’ when converted to UTF-8 / ASCII) with the sha256sum of the document whose existence at the time of admission of the transaction into the blockchain is proven appended. This transaction output is provably unspendable because it’s marked spil such via an OP_RETURN at the beginning of the output script and doesn’t hold any value. The other transaction output holds Four.9 mBTC and pays the service’s operators. 0.1 mBTC is paid spil a toverfee to the miner admitting the transaction into the blockchain.
To verify the existence of a document at the contended time, one proceeds spil goes after:
- Calculate the sha256sum σ of the document.
- Search the blockchain for an output script containing 0x444f4350524f4f46 . σ where the period is the concatenation technicus. When searching for many documents, the process is sped up by very first restricting the search space to transactions containing an OP_RETURN output script and 0x444f4350524f4f46 te it.
- If the block time minus the block time variation is at most the time the document is claimed to have existed, the optie is valid.
Note that the block time of each block may be slightly inaccurate spil it “is accepted spil valid if it is greater than the median timestamp of previous 11 blocks, and less than the network-adjusted time + Two hours”.  However, a more accurate time can be calculated from the surrounding blocks if enlargened precision is necessary.