Will stampd have any access to my documents?

No, stampd will not have access to your documents. They are not uploaded on our servers. They are locally processed in your browser to derive the appropriate cryptographic SHA256 hash imprint.

Is it possible to derive the document's contents using the cryptographic hash imprint?

It is impossible to derive the original document using the cryptographic hash imprint used by stampd. For more information about Cryptographic Hash please read this article on Wikipedia.

How do I know that bitcoin's public ledger (the blockchain) will be online forever?

Given bitcoin’s capitalization growth it seems very probable that this decentralized network is here to stay.

If I use the Stampd service for a document, will I be able to prove its ownership?

Blockchain stamping can certify the existence of an electronic documents’s content at a particular point in time.

When a user stamps a document, the document’s imprint (which is essentially the SHA256 hash of the document) is publicly linked with a certain date & time. It is noted that this link can be certified by anyone without reference to any centralized service or authority (the blockchain is maintained in a peer to peer network by an extremely large number of nodes and its data is readily available to anyone).

As the document’s imprint can be easily derived from the document itself, the user is able to prove that his/her document existed at that point in time because its imprint is publicly linked to that particular point in time. Note that the publicly announced imprint cannot be used to derive the document itself thus it depends on the user when to disclose the relation between his document and the publicly time stamped document imprint.

If the user blockchain stamps the imprint of authentic original work which includes a detailed ownership statement or signature, then this publicly time stamped statement can be used in the future by the user to justify that the content was in his possession at that particular time.

Therefore, if the blockchain stamped document is indeed original authentic non-stolen & non-copied work signed by the user and if no other previous public statement on the stamped content may be found anywhere (including mass media, public authorities, agencies, companies etc) then the user has a very strong argument to support ownership of the content. Of course, if a third party can actually prove theft of the content prior to the time of stamping, then the ownership justification collapses.

Thus, blockchain stamp certification of ownership may be justified for content which is properly signed and is the result of original authentic work not having previously existed.

As the blockchain technology concept is relatively new, there is no experience on how the above would stand in a court of law. Still we are confident that any experienced IT expert witness could testify and confirm all the above concepts against court.

What is the technical basis of stampd?

The SHA256 hash derived locally from the user’s browser for a particular document is transmitted to stampd’s servers. A bitcoin transaction including a call of the “OP_RETURN” type is carried out in order to post this hash on the blockchain. The byte equivalent of the ASCII text “STAMPD##” (equivalent to hex “5354414d50442323″) is also added at the beginning of the hash. The “OP_RETURN” type of transaction  has been provisioned by the bitcoin developers community in order to allow the possibility of posting data on the transactions included in the blockchain public ledger.

In stampd, the OP_RETURN call is carried out with a modified version of coinspark`s php-OP_RETURN code.

How much does it cost?

Stampd charges EUR 0.29 [29 cents!](convert to USD via Google) for each document digitally stamped through its service. This covers the miner fees required for the transaction to be included in the blockchain as well as the cost for maintaining our server.

How long does it take?

The document imprint calculation and paypal payment should not take more than a few minutes.

After the user has finalized this procedure, it normally takes 15 minutes to 1 hour for the blockchain posting to be confirmed (2 confirmations are considered adequate). Stampd shall email you with a pdf certificate showing all the details of the digital stamping (a sample may be seen here). Stampd ensures quick blockchain posting confirmation by adjusting the miner fees accordingly.

How can I use my document's digital stamp in the future?

The user (you) keeps the original electronic file of the document together with stampd’s provided digital stamp details included in the emailed pdf certificate. These digital stamp details may be used in the future by the user in order to locate and refer to the appropriate transaction within the publicly available blockchain public ledger.

There are currently various online services that provide easy access to the publicly available blockchain (some examples are,,,, Direct links to these currently available online services will be included within the pdf certificate emailed to the user after the digital stamping confirmation.

What does the stampd PDF certificate look like?

A sample may be seen below (click for the full pdf):


How is the blockchain stamping verified through a blockchain explorer?

The document hash is shown in the OUTPUT SCRIPTS marked with OP_RETURN.

See the following example through`s explorer: