💸 $BOND

A centralized cryptocurrency for fun, experimentation, and learning. Built with Node.js, TypeScript, Express, and SQLite.

What is $BOND?

$BOND is a playful and educational blockchain implementation that simulates real-world crypto mechanics without decentralization headaches. It features a RESTful API for interacting with the blockchain, submitting transactions, mining blocks, and querying wallet balances. The project uses a centralized SQLite database to persist the blockchain. The mempool is stored in memory.

🛠 Features

• Blockchain Core: Each block includes signed transactions, a timestamp, a nonce, and a hash pointer to the previous block.
• Proof of Work: Configurable mining difficulty (default: 16 leading zero bits in binary).
• ECDSA Signatures: Transactions are signed with secp256k1. Sender addresses are SHA-256 hashes of the public key.
• In-Memory Mempool: Stores pending transactions until a block is mined.
• Genesis Block: Awards 42 $BOND to a hardcoded address on first run.
• Wallet Tools: CLI utilities to generate keys, sign txs, and mine blocks.
• REST API: Full set of endpoints for blocks, balances, and transactions.

Technical Details

Blockchain

• Each block is an instance of Block, containing:
• height, timestamp, transactions, previous_hash, nonce, and hash.
• Block hash is computed as:
• sha256(height + timestamp + JSON.stringify(transactions) + previous_hash + nonce)
• Proof of Work: The block hash must have DIFFICULTY leading zero bits (see DIFFICULTY).

Transactions

• Transactions are objects with:
• sender, recipient, amount, timestamp, message, signature, publicKey, and txid.
• The sender address is the SHA-256 hash of the public key.
• Transactions are signed using ECDSA (secp256k1). The signature covers all transaction fields except signature and txid.
• Signature verification is handled by verifySignature.

Mempool

• Pending transactions are stored in-memory in mempool.
• Transactions are added to the mempool after signature and balance checks.

Database

• SQLite is used for persistent storage.
• The blockchain is stored in a single blockchain table (see schema in src/db/index.ts).
• Genesis block is created automatically if the chain is empty.

Getting Started

1. Install dependencies:

npm install

2. Build the project

npm run build

3. Start the server

npm start

API

GET /api

Shows a welcome message

GET /api/blocks

Returns the latest block in the chain.

Response

{
  "height":  1,
  "timestamp":  "...",
  "transactions": [],
  "previous_hash":  "9df7...",
  "nonce":  4714,
  "hash":  "0000..."
}

GET /api/blocks/all

Get a list of all blocks in the chain.

POST /api/blocks

Submit a new block.

Request Body

{
  "height":  1,
  "timestamp":  "...",
  "transactions": [],
  "previous_hash":  "9df7...",
  "nonce":  4714,
  "hash":  "0000..."
}

Response

{
  "status":  "OK"
}

GET /api/transactions/:address

Get a list of confirmed transactions for a wallet address.

POST /api/transactions

Add a new transaction to mempool.

Request

{
  "sender":  "c6c81...",
  "recipient":  "...",
  "amount":  0.4,
  "timestamp":  "2025-06-17T22:43:30.036Z",
  "message":  "...",
  "signature":  "3045...",
  "publicKey":  "..."
}

GET /api/difficulty

Get the current mining difficulty (number of leading zeros).

If mined blocks do not meet this requirement, they are rejected and will not be added to the blockchain.

POST /api/balance/:address

Get the balance of a wallet.

Response

{
  "balance":  41.2
}

Security Notes

• All state is centralized in a single SQLite database.
• There is no peer-to-peer networking on consensus.