Proof of Existence on Cardano — and the open standard behind it.
Hash any content, anchor the digest on the Cardano blockchain, and later prove that this content existed on or before a given block time — without trusting our servers, our domain, or any issuer identity.
We authored and maintain Label 309, the open standard for this, now accepted into the Cardano CIP process as CIP-0190, and publish its complete reference implementation as open source. The standard is issuer-agnostic and standalone-verifiable: any wallet can publish a proof, and anyone can verify it from just the transaction and a public block explorer — no issuer server required, ever.
Licensed Apache-2.0 (code) and CC-BY-4.0 (the specification).
The standard and its SDKs
| Project | Packages | What it is |
|---|---|---|
| label-309 | — | The standard: spec, CDDL, JSON Schemas, registries, conformance vectors |
| label-309-ts | @cardanowall/crypto-core · @cardanowall/poe-standard · @cardanowall/sdk-ts — npm |
TypeScript reference: primitives, wire format, SDK + standalone verifier |
| label-309-py | cardanowall-sdk — PyPI |
Python SDK — byte-parity twin |
| label-309-rs | cardanowall — crates.io |
Rust SDK — byte-parity twin |
| label-309-cli | cardanowall-cli — crates.io |
Command-line toolkit: publish, verify, seal, attest, and build/check Merkle proofs |
All three language SDKs are validated against the same canonical conformance vectors and produce byte-identical output.
Run it and wire it into CI
| Project | What it is |
|---|---|
| label-309-gateway | The open-source gateway: transaction build, submit, confirm, Arweave storage, on-chain index, and pricing behind one binary + Postgres (ghcr.io/cardanowall/label-309-gateway) |
| poe-attest | GitHub Action — anchor a release's files, commit range, or precomputed digests as a Proof of Existence straight from CI (uses: cardanowall/poe-attest@v1) |
| poe-attest — GitLab | The same tool as a GitLab CI/CD component (include: component: gitlab.com/cardanowall/poe-attest/attest@1) |
- 📖 The standard: label309.org
- 📜 The CIP: CIP-0190
- 🌐 Hosted service: cardanowall.com
- 📨 Contact: hello@cardanowall.com