Svartnod – prove a file existed, verified against my own Bitcoin node

- Svartnod is a free tool that lets you "timestamp" a file by committing its hash into the Bitcoin blockchain, creating a permanent, tamper-proof record that you possessed that data at a specific point in time. - The key distinction from other timestamping services (like OpenTimestamps or Bitcoin-based公证 services) is that Svartnod lets you verify the proof against your own full Bitcoin node, rather than trusting a third-party server or API. - This matters for legal evidence, intellectual property disputes, patent prior art, whistleblowing documentation, or any scenario where you need to cryptographically prove you had a file before a certain date — without revealing the file's contents. - To use it, you run a simple command-line tool that communicates with your local Bitcoin Core node (via its RPC interface), computes the file's SHA-256 hash, and then inscribes that hash into an OP_RETURN output of a transaction you broadcast yourself. - The project is open-source and aimed at technical users who already run a Bitcoin node; it removes reliance on centralized timestamping authorities while leveraging Bitcoin's security and immutability.