zk-light-client-implementation

NEAR Light Client Implementation

Developed by Zpoken Cryptography Team

Overview

An implementation of a trustless NEAR Light Client (LC) aims to prove computational integrity (CI) of a chosen block, ensuring its full finality (BFT finality). The idea is to first prove the finality (BFT finality) of a chosen block by proving the finality of successive blocks. Then, if a block is final, prove the computational integrity of its data.

According to the protocol, the scheme needs at least three blocks with successive heights to achieve finality of the leading block in this triple. In other words, it needs blocks: Block_0 (block to be proven, BFT finality), Block_i+1 (Doomslug finality), Block_i+2.

The scheme takes five blocks, instead:

• Block_i (block to be proven, BFT finality);
• Block_i+1 (BFT finality);
• Block_i+2 (BFT finality);
• Block_i+3 (Doomslug finality);
• Block_i+4.

The scheme proves block finality of Block_i+2, if the heights of Block_i+2, Block_i+3 and Block_i+4 are consecutive. Block_i automatically becomes final, and its signatures can be safely extracted from Block_i+1. Then the CI of the required Block_i can then be proven.

Additionally, we provide two more blocks:

• Block_n-1, i.e. the last block of the epoch i-2, to prove epoch_id;
• Block_0, i.e. the first block of the epoch i-1, to prove the correspondence of the used list of validators for the current epoch with the field next_bp_hash if the Block_0.

Block Integrity and Finality Proof

1. Operational fields: NEAR zk-light-client operates on several critical fields in the blockchain ecosystem. These fields include the list of validators, next_bp_hash (the hash of the next block producers) from epoch i-1, the hash of the last block from epoch i-2 to confirm epoch_id, and a set of hashes and heights of five consecutive blocks including the required Block_i to prove.

2. Formation of next_bp_hash: The next_bp_hash is a crucial component in this process. It is derived from the set of validators responsible for producing the next block. This hash serves as a cryptographic representation of the validators’ identity and their role in the upcoming block production.

3. Calculation of the block hash: The block hash is calculated based on the data of the current block. This data includes the next_bp_hash. By incorporating the next_bp_hash into the block hash calculation, there is a direct cryptographic link between the validators of the next block and the current block’s integrity.

4. Core Idea: The core idea is to establish a traceable and verifiable chain of custody for block creation. By proving that the next_bp_hash (derived from the validators) is a part of the current block’s data, which in turn is used to calculate the block’s hash, a secure chain is formed. This chain ensures that each block is not only a product of its immediate data but also carries a cryptographic signature of its contextual environment, i.e. the validators for the next block.Therefore, verifying a block’s authenticity involves confirming that the set of validators is valid (thus legitimizing the next_bp_hash) and ensuring that the block hash is correctly derived from the data, including this next_bp_hash.

[!TIP] Scheme description: Scheme_overview.md

Input parameters for proof generation

1. A set of five consecutive blocks including the required Block_i to prove epoch i Example

2. Epoch blocks Block_n-1 from epoch i-2 and Block_0 from epoch i-1. Example

3. List of block producers for epoch i Example

Near State Proofs

• Proof of Inclusion for the NEAR Blockchain involves identifying a specific data slot in a smart contract and verifying its contents.
• Upon any data mutation, a Merkle tree is constructed using code from the NEAR core, ensuring the data’s integrity.
• This process confirms the accuracy of the data in the slot and checks that the corresponding Merkle root is recorded in the blockchain.
• The result of this verification is typically formatted to display key information like the data’s key, value, state root, and associated block hash.
• This ensures the data’s validity and its presence in a specific blockchain state.

[!TIP] Read the example here NEAR_STATE_PROOFS.md Getting started Getting-started.md