BTProof

BTProof

Trusted timestamping on the Bitcoin blockchain

What is trusted timestamping?

Trusted timestamping allows to prove you held a document, some information or a file at some specific point in time, in a way that can't be forged. Read more at Wikipedia.

What is it good for?
  • Before signing an NDA, you can keep a trusted proof of the knowledge you had in that field prior to to signing it.
  • You can prove you developed a specific revesion of your software in a specific point in time by timestamping the hash of your revision tree. With Git, its as simple as timestamping the current commit SHA1.
  • Before sharing your ideas with third parties, you can timestamp the information you're about to share with them, as well as the fact that you're sharing it with them, to help resolve possible disputes.
  • Contracts can be timestamped (along with digital signatures of both parties) to prove when they were signed.
  • Musicians and other digital art producers can prove when they created their work.
How does timestamping on the Bitcoin network work?

Its possible to hash the data you wish to timestamp and turn it into a Bitcoin address. By making a small payment (a satoshi, or 0.00000001 BTC) to it, the payment is stored on the blockchain along with the address you paid to.

Since only the hash is stored on the Bitcoin blockchain, no one can tell what data you stored, but given the pre-hashed data you can prove the data was created prior to the block that contains the payment made to that address.

Update: Bitcoin-qt 0.8.2 doesn't relay transactions with small outputs by default. A lot of miners still accepts those transactions, so it'll work fine in the short-term (and once the transactions is accepted into a block, it'll be part the Bitcoin network forever). This method will be replaced in the future, when it becomes difficult to send those transactions.

What are the advantages of using the Bitcoin network?
  • You're not dependent on any single authority. Traditionally, trusted timestamps are issued by trusted third parties called TSAs (Time Stamping Authority), which are prone to data corruption and tampering. On the Bitcoin blockchain, your timestamp is safely stored all over the world, and is much harder to tamper with.
  • Its anonymous. No one knows who you are, what data you're timestamping, or even the fact that you're timestamping anything.
  • Its really cheap. At the current rates (~$110), including the transaction fees, it costs around 5 cents. You can make a transaction without fees, lowering the cost to $0.00000116, a fraction of a cent. However, it is highly recommended to pay the fees to support the miners who verify your timestamp with their computing resources. In addition to that, making such a tiny transaction without fees might take long to get into the blockchain, if ever.
  • Its really simple. You can create trusted timestamps using any Bitcoin client, and its easy to automate the process using bitcoin's JSON-RPC API.

IANAL, TINLA. That being said, I believe it will. From a technical point of view, its nearly impossible (much more so than with TSAs) to fake a timestamp created like that. You will probably need to bring a technical expert to testify to that.

Doesn't it destroy the Bitcoins used to pay to that address?

Yes. The coins are sent to an address that they can never be redeemed from, effectively taking them out of circulation. However, because its only a fraction of a bitcoin, the effect is minimal. To put this in perspective, creating one billion timestamps is equal to 10 BTC being lost due to someone losing his private keys (which is quite common and happens on much larger scale).

Create a trusted timestamp

Enter the text you wish to timestamp:

Select a file to timestamp:

Enter your hash:

The data (both from text and from a file) is hashed locally in your browser, and is never uploaded to the server. Still, if you're timestamping sensitive information, you're advised to hash it locally (howto: Linux, Windows, Mac) and only input the hash using the "Already have an hash?" tab.
Address:

Please read this carefully:

  • You must keep an exact copy of the pre-hashed data. If you cannot provide the original data that hashes to the address, you cannot prove anything using the hash alone.
  • Ensure the data you're hashing includes information about who you are. If you're timestamping a file hash, you can timestamp a message like "I, John Due, from ..., born ..., with the goverment issued ID ..., have a copy of the file that hashes to ...". In this case, you must keep both the file and the exact wording you used for the message. Alternatively, you can create a zip that contains the file(s) and a text file identifying you, and keep a copy of that zip.
  • The timestamp is accurate to a few hours precision. You can prove the data existed prior to the block which includes your payment. Blocks are created roughly every 10 minutes, but it might take a few until your payment is included.
  • Checking the timestamp is done using the blockchain.info api. If you require highly reliable result, you're advised to verify the timestamp with the Bitcoin network.
  • To reproduce the address yourself (important in case this website is unavailable), see the technical explaination. Its really simple - 3 lines of pseudocode.