Gridcoin Blockchain Stamp

Free, blockchain-backed document timestamping. Files never leave your browser. Only the SHA-256 hash gets written to the Gridcoin chain.

Use it | How it works | Tor mirror

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What it does

Drop a file in the browser. Your browser computes a SHA-256 hash locally, then writes that hash to the Gridcoin blockchain in an OP_RETURN transaction. You get back a permanent proof URL.

The file itself never uploads. We can't read your documents because we never see them. The only thing that hits our server is the hash, and from there it goes straight on-chain.

Running in production since October 2021.

Why use it

• Free. No signup, no fees, no API key.
• Permanent, shareable proof URLs (e.g. this one).
• No tracking pixels. The only analytics tool is Plausible, which doesn't follow you around.
• MIT-licensed, fully open source.
• Reachable over Tor.
• Anchored on the Gridcoin chain, so the timestamp survives even if we don't.

What people use it for

Proof of authorship. Show you had a file on a given date without revealing what's in it. Useful for IP, draft work, trade secrets.

Document timestamping. A drop-in alternative to a paid TSA. Same idea (hash plus signed time), except the signer is the blockchain.

Tamper detection. Flip a single bit and the hash changes. So if a file's hash still matches an old stamp, the file hasn't been touched.

Legal evidence. Decentralized timestamps don't depend on any one company sticking around to vouch for them.

Research priority. Stamp a manuscript or dataset before you submit. If a dispute comes up later, you have an on-chain record of when you had it.

How it works

For users:

1. Drop a file at stamp.gridcoin.club.
2. Your browser hashes it. The file does not upload.
3. The hash is written to the Gridcoin blockchain.
4. You get a proof URL. Bookmark it, share it, send it to a lawyer.
5. To verify later, drop the same file again. If the hash matches, the original timestamp is confirmed.

Protocol

Hashes go on-chain inside an OP_RETURN output:

6a46 5ea1ed 000001 <hash1> <hash2>

Segment	Meaning
6a46	OP_RETURN opcode (hex)
5ea1ed	Magic bytes, reads as "Sealed"
000001	Protocol version (0.0.1, semver)
<hash1>	SHA-256 hash (32 bytes)
<hash2>	Optional second SHA-256 hash

Two hashes per transaction, which halves the cost.

Cost per proof: about 0.06 GRC (a tiny burn plus the standard ~0.05 GRC fee). Future protocol versions stay backward compatible.

Repo layout

Nx monorepo:

Package	What it does	Stack
packages/grc-stamp	API, scraper, blockchain interaction	TypeScript, Express, Kysely, MariaDB
packages/grc-stamp-frontend	Web UI	Next.js, TypeScript, MUI

Other tooling: Gridcoin RPC client (gridcoin-rpc), CircleCI plus semantic-release for releases, Docker for the runtime.

Getting started

You'll need:

• Node 22+ (see .nvmrc)
• Docker
• A Gridcoin wallet node it can talk to

git clone https://github.com/gridcoin-community/stamp.gridcoin.club.git
cd stamp.gridcoin.club
npm install

Boot the dev stack:

docker-compose up

Run tests:

npm test

How it stacks up

	Gridcoin Stamp	Traditional TSA	Other blockchain services
Cost	Free	Paid	Varies
Account required	No	Yes	Often
File uploaded	No	Yes	Sometimes
Publicly verifiable	Yes	No	Varies
Open source	Yes	No	Rarely
Blockchain-anchored	Yes (Gridcoin)	No	Yes (various)
Tor accessible	Yes	No	Rarely

Contributing

PRs welcome. The repo uses Commitizen for conventional commits and semantic-release for versioning, so commit messages matter. For anything substantial, open an issue first.

Links

• Live service: stamp.gridcoin.club
• Tor mirror: u4embjw2uzwpdubgm72ywbmixte4kqgwurc4r4rp6elhlokutdfsy4id.onion
• Gridcoin: gridcoin.us
• Gridcoin RPC client: github.com/gridcat/gridcoin-rpc

License

MIT

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Made with ❤️ by @gridcat