Proof of Existence

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Proof of Existence
IndustryBlockchain Service
Founded2013; 6 years ago (2013) in Buenos Aires, Argentina
FounderManuel Araoz and Esteban Ordano
Area served
OwnerPoEx Co., Limited

Proof of Existence is an online service that verifies the existence of computer files as of a specific time via timestamped transactions in the bitcoin blockchain.[1][2][3][4]

It was launched in 2013 as an open source project. It was developed by Manuel Araoz and Esteban Ordano.[5]


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 allow people to verify that a document existed at a certain point in time."[2]

Terence Lee from Tech in Asia said, "Notaries — people with legal training that are licensed by the state to authenticate the signing of documents — could use this to timestamp contractual agreements."[6] In November 2013, Proof of Existence also received attention in Spanish-language Genbeta in "Proof of Existence, certificando documentos con Bitcoin".[7]

On April 22, 2014 reporter Rob Wile from Business Insider wrote that it is "Perhaps the most straightforward example of a post-Bitcoin service using Satoshi's blockchain".[8] On May 8, 2014 reporter Daniel Cawrey from CoinDesk wrote that the service "is an example of how the power of this new technology can have applications far beyond the world of finance, in this case, giving a glimpse of how bitcoin could one day have a substantial impact in the fields of intellectual property and law."[1] In her 2015 book Blockchain: Blueprint for a New Economy from O'Reilly Media, author Melanie Swan wrote it was "One of the first services to offer blockchain attestation".[3]

Since 2014, O'Reilly author Andreas Antonopoulos uses Proof of Existence as an example in his book, Mastering Bitcoin.[9] Previously, Antonopoulos also interviewed Manuel Araoz about Proof of Existence.[10]

Relationship to Bitcoin[edit]

Chris Dixon said, "Bitcoin is a platform upon which new technologies can be developed" and went on to list Proof of Existence as one of the first Bitcoin Blockchain applications.[11]

Forbes writer Mike Montgomery said in September 2015, "The intriguing aspect of this for entrepreneurs is that all kinds of other information could piggyback on the Bitcoin transfers recorded on the blockchain."[12]

Security expert Robert Graham said, "BitCoin is not so much a 'currency' as an 'emergent phenomenon'. It makes things possible that have nothing to do with money."

Graham gave an example:

"As another example, let’s say that you have a great idea for a patent, but it’s not quite ready. Well, write it up into a file, then add the file’s signature to the block chain. Years from now, if somebody beats you to the patent filing, you can prove that you had the idea ahead of time."[13]


The service enters a sha256 cryptographic hash of a document into the blockchain.

The service costs 5 mBTC per use. As of this writing (2016-12-24; This wasn't always the service's behavior.), each use of the service creates 2 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 as such via an OP_RETURN at the beginning of the output script and doesn't hold any value. The other transaction output holds 4.9 mBTC and pays the service's operators. 0.1 mBTC is paid as a fee to the miner admitting the transaction into the blockchain.

To verify the existence of a document at the contended time, one proceeds as follows:

  1. Calculate the sha256sum σ of the document.
  2. Search the blockchain for an output script containing 0x444f4350524f4f46 . σ where the period is the concatenation operator. When searching for many documents, the process is sped up by first restricting the search space to transactions containing an OP_RETURN output script and 0x444f4350524f4f46 in it.
  3. If the block time minus the block time variation is at most the time the document is claimed to have existed, the claim is valid.

Note that the block time of each block may be slightly inaccurate as it "is accepted as valid if it is greater than the median timestamp of previous 11 blocks, and less than the network-adjusted time + 2 hours".[14] However, a more accurate time can be calculated from the surrounding blocks if increased precision is necessary.


  • Digital Sign Agreement without revealing actual content.
  • Demonstrating data ownership without revealing actual data.
  • Document time stamping.
  • Proving ownership
  • Checking for document integrity


  1. ^ a b Daniel Cawrey (May 8, 2014). "Bitcoin's Technology Could Revolutionize Intellectual Property Rights". CoinDesk.
  2. ^ a b Jeremy Kirk (May 24, 2013). "Could the Bitcoin network be used as an ultrasecure notary service?". IDG News Service via Computerworld.
  3. ^ a b Melanie Swan (2015). "Blockchain: Blueprint for a New Economy". O'Reilly Media. pp. 38–39.
  4. ^ Ram (February 2, 2015). "Anonymous Proof Of Existence - Bitcoin Tech".
  5. ^
  6. ^ Lee, Terence (Nov 18, 2013). "Bitcoin will change the world, but no one knows how". Tech in Asia. Tech in Asia. Retrieved 2018-01-26.
  7. ^ JULIÁN, GUILLERMO (Nov 29, 2013). "Proof of Existence, certificando documentos con Bitcoin". Genbeta. Genbeta. Retrieved 2018-01-26.
  8. ^ Rob Wile (April 22, 2014). "SATOSHI'S REVOLUTION: How The Creator Of Bitcoin May Have Stumbled Onto Something Much, Much Bigger". Business Insider.
  9. ^ Andreas Antonopoulos (December 20, 2014). "Mastering Bitcoin". O'Reilly Media.
  10. ^ Andreas Antonopoulos (Dec 12, 2013). "Block-chain Notary Service,". Youtube. The LTB Network. Retrieved 2018-01-26.
  11. ^ Dixon, Chris (December 12, 2013). "Coinbase". Errata Security. Errata Security. Retrieved 2018-01-26.
  12. ^ Montgomery, Mike (September 15, 2015). "Bitcoin Is Only The Beginning For Blockchain Technology". Forbes. Forbes. Retrieved 2018-01-26.
  13. ^ Graham, Robert (May 30, 2013). "BitCoin is a public ledger". Errata Security. Errata Security. Retrieved 2018-01-26.
  14. ^

External links[edit]