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cronStamp
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How it works

Documents are hashed on your side and only the hash is submitted to the cronStamp Web API. Hashes are collected into a Merkle tree, and its root is written to the blockchains you choose. You get back a certificate holding everything needed to prove the document later, verified without contacting cronStamp.

Overview: today your file is hashed and only the fingerprint is sent to cronStamp, which anchors it on the blockchain and returns a certificate. Years later, the file and the certificate are checked against the blockchain locally, without cronStamp, and show whether the file is unchanged or was altered.
Today
File Your file is hashed (SHA-256) in your browser. The file itself never leaves your device. cronStamp Collects fingerprints in a Merkle tree and writes its root to the XRP Ledger and Solana. How it works → Certificate A small JSON file with the Merkle path and the blockchain transactions. Keep it next to your file.
Public blockchain root written once, can't be changed Public, permanent and independent of cronStamp: anyone can look the transaction up. What is a blockchain? →
Years later
File The same file. Change a single byte and its fingerprint no longer matches. Local verification in your browser, without cronStamp Recomputes the Merkle root from file and certificate and compares it to the blockchain. Verify by hand → Certificate The certificate you kept. Nothing else is needed, not even cronStamp.
unchanged Fingerprint, Merkle path and on-chain root match: the file existed at the stamped time and is unchanged. altered The roots differ: the file was changed or the certificate belongs to another file.

Where to start

Client library For JavaScript and TypeScript, in Node.js or the browser. Hashes locally, timestamps through the Web API and verifies certificates on your side. Quickstart Web API Two HTTP endpoints for timestamping from any language. Verification is up to you: use the client library or follow the algorithm. Web API reference How cronStamp works Salted hashes, Merkle trees and blockchain transactions: what happens between your file and its certificate. Read the details Verify by hand Check a certificate step by step without any cronStamp software, to see that the proof stands on its own. Follow the steps