Merkle proof validation explained with working code

When you anchor a file to a blockchain, you're not storing the file itself. You're storing a hash that proves the file existed at that moment. ProofAnchor anchors SHA-256 hashes to the Polygon blockchain, with the file never leaving your machine. But how do you prove your specific file hash is actually included in that blockchain transaction? That's where Merkle proofs come in.

The Merkle tree structure

Think of a Merkle tree like a tournament bracket, but for hashes. Your file hash sits at a "leaf" position. Each level up combines pairs of hashes until you reach a single "root" hash. That root hash is what gets stored on the blockchain.

The proof gives you a path from your leaf to the root, plus the "sibling" hashes you need to reconstruct the tree.…