The Super-Tree: How One Merkle Tree Proves Another

A transparency log that lives forever will eventually contain billions of entries. A single Merkle tree with a billion leaves has a depth of 30, which means inclusion proofs are 30 hashes long and every append touches 30 nodes. That is manageable. But the tree file on disk grows without bound, proof generation requires random access across the entire structure, and rotating keys or changing operational parameters means you are stuck with decisions you made on day one. ATL Protocol splits the problem into two levels: short-lived Data Trees and an eternal Super-Tree . Each Data Tree accumulates entries for a bounded period (configurable -- say, 24 hours or 100,000 entries). When the period ends, the tree is closed, its root hash becomes a leaf in the Super-Tree, and a fresh Data Tree starts accepting new entries. The Super-Tree is itself a Merkle tree -- it grows by one leaf every time a Data Tree closes. I want to walk through why this architecture exists, how the two levels connect cry