LandChain: Decentralized Land Certificate Management

This repository contains the Chaincode (Smart Contracts) and Express.js API Gateway for a blockchain-based land certificate system. The project focuses on securing land records using document hashing and multi-party digital signature consensus.

🏗 System Architecture

The system operates through three primary layers:

1. Chaincode (Hyperledger Fabric): Manages the immutable ledger and validates cryptographic signatures.
2. Middleware (Express.js): Acts as the gRPC bridge, handling identity management and transaction routing.
3. Client (Laravel): The user interface for uploading certificates and initiating verification (repository separate).

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🛠 Features & Logic

1. Multi-Party Signature Consensus

Unlike standard automated consensus, this system requires the agreement of all parties involved in a transaction.

• Each participant signs the transactionData using their Google Cloud KMS-managed keys.
• The chaincode's CreateAsset function verifies every signature against the provided public_key_pem before committing the data.
• If a single signature is invalid or a previous owner's ID does not match, the transaction is rejected.

2. Document Hashing & Privacy

• Sensitive land certificate data is not stored on the blockchain. Instead, a SHA-256 hash of the document is stored.
• This ensures data privacy while allowing anyone with the original document to verify its authenticity by comparing hashes.

3. Scalable Performance

• The system is optimized for high-throughput peer environments.
• Empirical results show a 0.62s performance gain when scaling from 2 to 6 peers, demonstrating the efficiency of the signature-based consensus model.

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🚀 Getting Started

Prerequisites

• Hyperledger Fabric (v2.x or later)
• Node.js (v18+)
• Docker & Docker Compose

Installation

1. Clone the repository:

git clone https://github.com/Cupcake-Legend/landchain-chaincode.git
cd landchain-chaincode

2. Install Dependencies:

npm install

Running the API Gateway

The Express.js server facilitates communication with the Fabric test-network. Ensure your network is running and the chaincode is deployed.

node server.js

The REST API will be available at http://localhost:3000.

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📡 API Endpoints

Method	Endpoint	Description
POST	/api/init	Initializes the ledger with dummy data.
GET	/api/certificates	Retrieves all certificate records from the ledger.
POST	/api/insert-certificate	Validates signatures and records a new certificate edition.
POST	/api/verify-certificate	Checks if a specific hash exists and if it is the latest edition.

Sample Payload for /api/insert-certificate

{
  "certificateHash": "hash_of_original_document",
  "certificateEditionFileHash": "hash_of_current_file_edition",
  "transactionData": "metadata_string",
  "participantKeys": "[{\"kms_key_id\": \"id1\", \"signature\": \"...\", \"public_key_pem\": \"...\", \"type\": \"buyer\"}]"
}

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🛡 Security Logic (Chaincode Snippet)

The core security is handled by the verifySignature function using the crypto module:

async verifySignature(signatureBase64, publicKeyPem, transactionData) {
    const signatureBuffer = Buffer.from(signatureBase64, 'base64');
    const verifier = crypto.createVerify('sha256');
    verifier.update(transactionData);
    verifier.end();
    return verifier.verify(publicKeyPem, signatureBuffer);
}

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