Understanding What a Block Chain Block Is

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Updated Version

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Understanding What a Blockchain Block Is

A block chain block contains the following:

• Transaction Data
• A cryptographic hash ( fingerprint / signature ) of it’s content
• A nonce value ( A random number used for cryptographic computation )
• The hash of the previous block
• A time stamp of a recent verified transaction

Lets look at an example. We will use the NPM Packages CryptoJS and NanoID to generate the signature and nonce.

Here’s our block:

import { SHA256 } from "crypto-js";
import { nanoid } from "nanoid";
class Block {
   constructor(
      public index: number,
      public timestamp: string,
      public data: any,
      public precedingHash: string,
      public nonce?: string) {
        this.nonce = this.nonce ? this.nonce : nanoid();
      }
      signature() {
        return SHA256(
            this.index + 
            this.precedingHash +
            this.timestamp +
            this.nonce +
            JSON.stringify(this.data)).toString();
       }
}

Lets create two blocks with the same data. They should have the same signature:

const transactionData = {
sender: "Ole Ersoy",
recipient: "Satoshi Nakamoto",
quantity: 1
};
const block1 = new Block(0, "02/02/2021", transactionData, "0", "nonce");
const block2 = new Block(0, "02/02/2021", transactionData, "0", "nonce");
console.log(`Signature of Block 1: ${block1.signature()}`);
console.log(`Signature of Block 2: ${block2.signature()}`);

So we see that a Block has a unique signature that is determined by what it contains. This makes it very difficult to tamper with a block.

Demo