How it works
From upload to immutable proof in under a minute.
Mathematically verifiable proof that you owned a file at a specific point in time — anchored on Bitcoin, OpenTimestamps, Rekor, or all three.
Proof methods
Four ways to certify
Maximum proof
OpenTimestamps + RFC 3161 TSA + Sigstore Rekor in one certificate.
OpenTimestamps
Bitcoin-backed calendar stamp. Upgrades to on-chain proof over time.
Sigstore Rekor
Public transparency log entry with cryptographic attestation.
Bitcoin blockchain
Permanent OP_RETURN anchor on Bitcoin mainnet. Uses plan quota.
01
Upload any file
Drag and drop any digital asset — logo, source code, contract, design. Any format up to 500 MB.
02
Hash in your browser
SHA-256 computed locally via Web Crypto API. Your file never touches our servers in hash-only mode.
03
Choose proof method
Maximum proof (OTS + TSA + Rekor), individual free proofs, or Bitcoin OP_RETURN anchoring.
04
Anchor & timestamp
Proofs created in parallel. Bitcoin transactions confirm in the next block (~10 min).
05
PDF certificate
Download a certificate with filename, owner, hash, proof details, QR code, and verify URL.
06
Verify independently
Anyone can verify using public tools — block explorers, Rekor, OpenTimestamps. No account required.
Bitcoin anchoring
Your SHA-256 hash is embedded in a Bitcoin OP_RETURN transaction via Blockstream.
Once confirmed, the block timestamp is immutable. The Bitcoin blockchain has run continuously since January 2009.
The math behind it
SHA-256 produces a unique 64-character fingerprint. Changing one bit produces a completely different hash.
OP_RETURN embeds up to 80 bytes on-chain. We store your 32-byte hash permanently.
Get started
Certify your first file today.
Maximum proof is free and instant. No credit card required.