Exploring the Blockchain

Joe Buza

What is a Blockchain?

Distributed database that is used to maintain a list of records, called blocks, which are linked and secured using cryptography.

What is a block?


Previous Hash




Which block is it.  Genesis block #0

When the block was added

Hash of the previous block

Information stored in the block

Number of iterations to find a valid block

Genesis Block

How is a block mined?

  1. Look at the latest block on the blockchain

  2. Get the Index and increment by 1

  3. Get the latest block's hash and store as previous hash

  4. Create data

  5. Calculate Hash

  6. Calculate Nonce


How is hash calculated?

  SHA256(index + previousHash + timestamp + data + nonce)

Proof of work

  • Not just any hash value is valid.

  • A valid hash has to pass a requirement, called Difficulty.


  • This is the minimum requirement for a valid hash.

  • A valid hash has at least four leading 0’s. (demo)

function isValidHashDifficulty(hash, difficulty) {
  for (var i = 0, b = hash.length; i < b; i ++) {
      if (hash[i] !== '0') {
  return i >= difficulty;

What is a nonce?

  • Number of iterations used to find a valid hash

  • This process is called mining

let nonce = 0;
let hash;
let input;

while(!isValidHashDifficulty(hash)) {     
  nonce = nonce + 1;
  input = index + previousHash + timestamp + data + nonce;
  hash = CryptoJS.SHA256(input)

What's the point?

  • Mining and POW keep the blockchain immutable.

  • This is what makes the blockchain hack proof.



Exploring the Blockchain

By Joe Buza

Exploring the Blockchain

We go inside the blockchain. What it's made of and how it all connects together.

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