US Patent 11569996 Anonymous rating structure for database

An example operation may include one or more of receiving, from an executing client, a blockchain transaction comprising an anonymous rating related to an authorizing client, a merkle tree root node value, a proof, and a nullifier, and in response, executing, by a smart contract, a valid historical value assert call on a lookback key storing the merkle tree root node value, verifying, through a valid historical value assert call, that the merkle tree root node value is a current or previous value of the merkle tree root node value, verifying the proof with the merkle tree root node value and the nullifier, adding the anonymous rating to a shared ledger, marking the nullifier as used, and storing the marked nullifier to the shared ledger.