Blocks, chains, and hashing in Blockchain / Solidity - Mini Project: Build & Apply

Blocks, chains, and hashing

📖 Scenario: You are building a simple blockchain to understand how blocks link together using hashes. Each block will store some data and the hash of the previous block, creating a secure chain.

🎯 Goal: Create a small blockchain with three blocks. Each block should contain data, the hash of the previous block, and its own hash. Finally, print the hashes of all blocks to see the chain.

📋 What You'll Learn

Create a dictionary called block1 with keys data and prev_hash and exact values 'First block' and '0'

Create a variable called hash1 that stores the SHA-256 hash of the string formed by concatenating block1['data'] and block1['prev_hash']

Create a dictionary called block2 with keys data and prev_hash and exact values 'Second block' and hash1

Create a variable called hash2 that stores the SHA-256 hash of the string formed by concatenating block2['data'] and block2['prev_hash']

Create a dictionary called block3 with keys data and prev_hash and exact values 'Third block' and hash2

Create a variable called hash3 that stores the SHA-256 hash of the string formed by concatenating block3['data'] and block3['prev_hash']

Print the three hashes hash1, hash2, and hash3 each on its own line

💡 Why This Matters

🌍 Real World

Blockchains are used to securely store data in a chain of blocks, making it hard to change past information without breaking the chain.

💼 Career

Understanding blocks, chains, and hashing is essential for jobs in blockchain development, cybersecurity, and data integrity.

1

Create the first block

Create a dictionary called block1 with keys data and prev_hash. Set data to 'First block' and prev_hash to '0'.

Blockchain / Solidity

# Create the first block dictionary
# Your code here

Need a hint?

Use curly braces {} to create a dictionary with the exact keys and values.

2

Hash the first block

Import the hashlib module. Create a variable called hash1 that stores the SHA-256 hash of the string formed by concatenating block1['data'] and block1['prev_hash']. Use .encode() before hashing and .hexdigest() to get the hash string.

Blockchain / Solidity

block1 = {'data': 'First block', 'prev_hash': '0'}
# Import hashlib and create hash1
# Your code here

Need a hint?

Use hashlib.sha256(...).hexdigest() to get the hash string.

3

Create and hash the second block

Create a dictionary called block2 with keys data and prev_hash. Set data to 'Second block' and prev_hash to hash1. Then create a variable called hash2 that stores the SHA-256 hash of the string formed by concatenating block2['data'] and block2['prev_hash'], encoded and converted to hex digest.

Blockchain / Solidity

import hashlib

block1 = {'data': 'First block', 'prev_hash': '0'}
hash1 = hashlib.sha256((block1['data'] + block1['prev_hash']).encode()).hexdigest()
# Create block2 and hash2
# Your code here

Need a hint?

Use the same hashing method as before but with block2 and hash1.

4

Create and hash the third block, then print all hashes

Create a dictionary called block3 with keys data and prev_hash. Set data to 'Third block' and prev_hash to hash2. Then create a variable called hash3 that stores the SHA-256 hash of the string formed by concatenating block3['data'] and block3['prev_hash'], encoded and converted to hex digest. Finally, print hash1, hash2, and hash3 each on its own line.

Blockchain / Solidity

import hashlib

block1 = {'data': 'First block', 'prev_hash': '0'}
hash1 = hashlib.sha256((block1['data'] + block1['prev_hash']).encode()).hexdigest()

block2 = {'data': 'Second block', 'prev_hash': hash1}
hash2 = hashlib.sha256((block2['data'] + block2['prev_hash']).encode()).hexdigest()
# Create block3, hash3, and print all hashes
# Your code here

Need a hint?

Remember to print each hash on its own line using three separate print() statements.