vanilla-blockchain

A distributed database that maintains a continuously growing list of ordered records.

Motivation

All the current implementations of blockchains are tightly coupled with the larger context and problems they (e.g. Bitcoin or Ethereum) are trying to solve. This makes understanding blockchains a necessarily harder task, than it must be. Especially source-code-wisely. This project is an attempt to provide as concise and simple implementation of a blockchain as possible.

If we look for the definition of blockchain in Wikipedia we will find something like:

Blockchain is a distributed database that maintains a continuously-growing list of records called blocks secured from tampering and revision.

So we will work on this concept extracting the most important points that vanilla-blockchain has to solve:

• Use HTTP interface in each node to add new blocks or find them.
• Use Websockets in order to communicate with the network of nodes.
• Find a way to add/remove nodes from the network.
• Super simple protocol in our P2P communication.
• All data will be persisted in JSON files.
• Use a basic implementation of Proof of work.

Overview

A blockchain is a public database that consists out of blocks that anyone can read. Nothing special, but they have an interesting property: they are immutable. Once a block has been added to the chain, it cannot be changed anymore without invalidating the rest of the chain.

That is the reason why cryptocurrencies are based on blockchains. You don't want people changing their transactions after they've made them!

Block structure

We will start by defining the block structure. Only the most essential properties are included at the block at this point.

• data: Any data that is included in the block.
• timestamp: A UTC timestamp using numeric format.
• nonce : A number of attempts to generate the correct hash.
• hash: A sha256 hash taken from the content of the block.
• previousHash: A reference to the hash of the previous block.

The code for the block structure looks like the following:

class Block {
  constructor({
    data = {}, previousHash, timestamp = new Date().getTime(),
  } = {}) {
    this.data = data;
    this.nonce = 0;
    this.previousHash = previousHash;
    this.timestamp = timestamp;
  }
}

Block hash

The block hash is one of the most important property of the block. The hash is calculated over all data of the block. This means that if anything in the block changes, the original hash is no longer valid. The block hash can also be thought as the unique identifier of the block.

We calculate the hash of the block using the following code:

import { SHA256 } from 'crypto-js';

export default ({
  previousHash, timestamp, data = {}, nonce = 0,
} = {}) => SHA256(previousHash + timestamp + JSON.stringify(data) + nonce).toString();

Proof of Work

It's a simple technique that prevents abuse by requiring a certain amount of computing work. That amount of work is key to prevent spam and tampering. Bitcoin implements proof-of-work by requiring that the hash of a block starts with a specific number of zero's. This is also called the difficulty.

To fix this problem, blockchains add a nonce value. This is a number that gets incremented until a good hash is found. And because you cannot predict the output of a hash function, you simply have to try a lot of combinations before you get a hash that satisfies the difficulty. Looking for a valid hash (to create a new block) is also called mining in the cryptoworld.

Adjusting the difficulty we can decide how long it would take to calculate a new block. Let's see the code of our mining function:

mine(difficulty = 0) {
  this.hash = calculateHash(this);
  while (this.hash.substring(0, difficulty) !== Array(difficulty + 1).join('0')) {
    this.nonce += 1;
    this.hash = calculateHash(this);
  }
}

Getting Started

Build your own Blockchain

The easiest way for choose your kind of instance is creating a .env file in the root of the project. You just to choose the kind of instance and its port of running.

const blockchain = new Blockchain();
const  { hash: previousHash } = blockchain.latestBlock;

const data = { hello: 'world' };
blockchain.addBlock(data, previousHash);