About Gridcoin Blockchain Stamping

Proof of Existence is a method of verifying and recording that specific data existed at a certain time. Establishing proof requires a timestamp and a signature linked to the data, showing it existed at a particular point in time. A blockchain is a convenient way to do this: proof is stored on a public ledger that is transparent, unalterable, and permanent.

This service is a straightforward implementation of the Proof of Existence concept on the Gridcoin blockchain. You can securely and anonymously prove the existence of any document (images, videos, documents, binaries) in the decentralized ledger without revealing the actual content of the document.

We do not store any of your data, except for the document's hash. Your documents are not uploaded to our database or stored on the blockchain, and they never leave your device.The hash is calculated in your browser, so the file itself never leaves your device.

We don't use tracking pixels. The only exception is Plausible, a privacy-friendly alternative to Google Analytics.

The data is stamped on the Gridcoin blockchain by embedding the sha256 hash of the data in a transaction. This is achieved through the use of an OP_RETURN script opcode, which creates an unspendable output in the transaction that encodes the hash.

A typical transaction may contain one or two hashes, such as:

6a265ea1ed0000015f334f14161952476adde3fbd843f93f647d47a0d7e30eb5d1635fb7569a2503

or like that:

6a465ea1ed0000015bbbbbee48b735693478140de1b7f09fe0acddc0c7bce87f8665074efe53410f7158380aca149fa8422fb1274a69155303d4aaa76bf67defe0bb31628293afd2

The key difference between the two transactions is that the second one includes two hashes, while the first one only has one. The OP_RETURN script can accommodate two SHA-256 hashes, so more than one record can be stored in a single transaction. That saves on fees.

The transaction breaks down as:

# OP_RETURN script opcode (hex)
6a46

# "Sealed" identifier: hex word that marks stamp transactions
5ea1ed

# Protocol version (0.0.1, semantic versioning; legacy versions stay supported)
000001

# First SHA-256 hash
5bbbbbee48b735693478140de1b7f09fe0acddc0c7bce87f8665074efe53410f

# Second SHA-256 hash (optional; present only in two-hash transactions)
7158380aca149fa8422fb1274a69155303d4aaa76bf67defe0bb31628293afd2

For the full protocol reference, semantic versioning conventions are described at semver.org.

Verify a stamp yourself

None of this depends on stamp.gridcoin.club. Anyone can check a stamp against the Gridcoin chain directly:

1. Compute the SHA-256 hash of your file yourself, for example with sha256sum yourfile.pdf. This is the value that should have been stamped.
2. Open the stamping transaction on a block explorer such as gridcoinstats.eu. Search by the transaction id shown on your proof page.
3. In the transaction's OP_RETURN output, check that the data reads 5ea1ed followed by the version and your hash. If your SHA-256 is there, the file existed in that exact form when the block was mined.
4. Read the block's timestamp. That time is what the stamp proves.

A stamp transaction is cheap. It consists of a small burned amount (0.00000001 GRC, or one Halford) and a transaction fee of about 0.05 GRC. The average cost works out to around 0.06 GRC per proof.

The service is free, though that may change if demand grows. The low per-stamp cost and ongoing donations cover the running expenses, so it should stay free for a while yet.