Patent Explainer: Proof of Indexing Overlay State Verification (F-007)

What F-007 Does

F-007 describes a system for verifying the correctness of derived state computations performed by indexing nodes in blockchain overlay networks. In these networks, raw on-chain data (UTXOs and transaction graphs) must be transformed into aggregate derived state — token balances, eligibility tables, dividend accruals, rankings — by off-chain service providers. The problem is that no single provider can be trusted to compute that state honestly, and there has been no mechanism to detect or penalise incorrect computation.

The invention provides five interlocking components: a state commitment protocol where each node publishes a Merkle root over its derived state at deterministic intervals; a cross-node verification mechanism where independent nodes compare their commitments without a central coordinator; a Proof of Indexing attestation linking derived state back to Merkle-proven on-chain UTXO data; a binary narrowing challenge-response dispute protocol for isolating the first point of divergence between disagreeing nodes; and a competitive correctness incentive rewarding nodes that consistently match network consensus.

The result is that users no longer need to trust any single indexer. If a node computes an incorrect balance, fabricates a dividend accrual, or skips a transaction, the disagreement will be detected automatically at the next checkpoint, and the dispute protocol will pinpoint the exact event where the computation diverged.

The Problem It Solves

1. The derived state trust gap. Raw UTXO data is inherently verifiable — each output has a Merkle proof rooting to a block header. But derived state (balances, staking eligibility, dividend amounts) is computed off-chain in databases maintained by lookup service providers. Users querying a lookup service for a balance or dividend figure have no cryptographic guarantee that the provider computed it correctly from the underlying UTXO events.

2. Scalability vs verifiability trade-off. Representing every piece of derived state as an on-chain UTXO would eliminate the trust gap but creates prohibitive chain bloat. A content network processing millions of micro-sale events per day cannot mint a new UTXO for each incremental balance change. The industry standard is to compute derived state off-chain and serve it via lookup services, accepting a trust trade-off. No existing system resolves this trade-off.

3. Competing indexers without consensus. In federated overlay networks where multiple providers host the same overlay code, each independently computes derived state from its local copy of the UTXO graph. There is no consensus mechanism to detect a provider that computes incorrect state — whether through bugs, data loss, or deliberate manipulation.

4. No economic incentive for honest computation. Existing overlay hosting compensation models pay hosts for compute resources consumed (CPU, memory, network, disk) but not for computational correctness. A host is paid the same whether its derived state is accurate or fabricated.

How It Works

State Commitment Protocol

At defined checkpoint intervals (every N events, every T seconds, or every B blocks), each indexing node computes a deterministic State Commitment over its current derived state. The process is:

1. Serialise all derived state entries in a canonical ordering (lexicographic by public key, then by content identifier) using a fixed-format 85-byte binary representation.
2. Construct a Merkle tree over the serialised entries using SHA-256 with domain-separation bytes (0x00 for leaves, 0x01 for internal nodes) to prevent second-preimage attacks.
3. The Merkle root is the State Commitment for that checkpoint.

The State Commitment is paired with a Checkpoint Descriptor — a 218-byte signed binary message containing the version, checkpoint sequence number, overlay identifier, state root, last event hash, event count, timestamp, node public key, and a Schnorr signature over all preceding fields.

Cross-Node Verification

When a node receives State Commitments from peer nodes for the same checkpoint, it performs an agreement check. If commitments match, the peer is recorded as agreeing. If they differ, the dispute protocol is initiated. A State Commitment is considered verified when a configurable supermajority (e.g., 2/3 or 3/4) of active nodes produce matching commitments. Nodes that consistently agree with consensus earn Correctness Score points, influencing their eligibility for enhanced rewards and preferential service routing.

Proof of Indexing Attestation

A Proof of Indexing (PoI) Attestation is a compact cryptographic proof that a node can generate on demand, demonstrating that its derived state at a given checkpoint was computed by processing a specific, verifiable sequence of UTXO events. It contains:

• The first and last UTXO event hashes in the processing window
• A Merkle tree over all event hashes in the window, proving completeness (no events skipped or fabricated)
• Intermediate state hashes at regular sub-intervals within the window, enabling binary search for the point of divergence
• The final derived state Merkle root
• The node's cryptographic signature over all of the above

The Event Merkle Proof is anchored to the underlying UTXO Merkle proofs — each event hash incorporates the UTXO's own Merkle path to a block header. This creates a chain of provenance from block headers through UTXO events to derived state.

Challenge-Response Dispute Protocol

When two nodes disagree on a State Commitment, any participant can challenge a node's claimed derived state. The challenger requests the node's PoI Attestation, which contains intermediate state hashes at regular intervals within the checkpoint window. The challenger compares these intermediate hashes against its own computation (or another trusted node's attestation) to perform a binary search, narrowing the disagreement to the smallest possible event range. This isolates the first divergent event — the exact UTXO where the two computations produced different results — without requiring full replay of the entire event stream.

Nodes that fail challenges face economic consequences: token slashing or reputation penalties.

Competitive Correctness Incentive

Nodes that consistently produce state commitments matching the network consensus earn enhanced rewards (overlay-specific tokens or preferential service routing). This creates a direct economic incentive for honest, accurate, and timely state computation, aligning node behaviour with network integrity.

Live Implementation

This patent underpins the verification layer of the $402 overlay network. The state verification system ensures that token balances, dividend accruals, and staking eligibility computed by indexing nodes across the network are provably correct.

• $402 Protocol: path402.com

Filed at UKIPO by The Bitcoin Corporation Ltd. Patent pending. Application reference F-007.