Proof of Existence of a State/Data

State proof example

Below is a simple code snippet that shows how to use the ledger API to generate a state existence proof:

Please note: For presentation purposes, all results and error handling, except proofs, were eliminated. Ledger connectivity proof is eliminated here as well. For details and an example, see here and here.

    blockNum := 5
    db := "db2"
    key := "key2"
    value := "this is a second value"

    db, err := bcdb.Create(conConf)
    session, err := db.Session(&c.SessionConfig)
    ledger, err := session.Ledger()

    // Get data proof for <db, key> at block blockNum and validate it
    dataProof, err := ledger.GetDataProof(blockNum, db, key, false)
    // Calculating <db, key, value> tuple hash
    compositeKey, err := state.ConstructCompositeKey(db, key)
    kvHash, err := state.CalculateKeyValueHash(compositeKey, []byte(value))
    // Validation proof
    res, err := dataProof.Verify(kvHash, blockHeader.GetStateMerkleTreeRootHash(), false)

    if !res {
        fmt.Printf("DB-Key-Value tuple (%s, %s, %s) at time of block %d is not part of ledger\n", db, key, value, txReceipt.Header.BaseHeader.Number)
    }