Proof of Work vs Proof of Stake in Blockchain / Solidity - Practice Questions

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Proof of Work simulation code?

Consider this simplified Python code simulating a Proof of Work mining attempt. What will it print?

Blockchain / Solidity

import hashlib

def proof_of_work(data, difficulty):
    nonce = 0
    prefix = '0' * difficulty
    while True:
        text = f'{data}{nonce}'
        hash_result = hashlib.sha256(text.encode()).hexdigest()
        if hash_result.startswith(prefix):
            return nonce, hash_result
        nonce += 1

nonce, hash_val = proof_of_work('block', 2)
print(nonce, hash_val[:4])

A It depends on the machine speed and may vary

B 5 00c1

C 0 00ab

D 12 00f3

💡 Hint

The nonce is found by trial and error to get a hash starting with two zeros. This depends on the hash function output and cannot be predicted exactly.

Proof of Work requires finding a nonce that makes the hash start with a certain number of zeros. This process is random and depends on the hash function output, so the nonce and hash prefix vary each run.

🧠 Conceptual

intermediate

Which statement correctly describes Proof of Stake?

Choose the correct description of how Proof of Stake (PoS) consensus works in blockchain.

A Transactions are validated by solving cryptographic puzzles faster than others.

B Blocks are created randomly without any stake or resource requirement.

C Miners solve complex puzzles to validate transactions and create blocks.

D Validators are chosen based on the amount of cryptocurrency they hold and lock up.

💡 Hint

Think about how PoS selects who creates the next block based on ownership rather than computational work.

Proof of Stake selects validators based on how much cryptocurrency they lock up (stake). This replaces the energy-intensive puzzle solving in Proof of Work.

🔧 Debug

advanced

Why does this Proof of Work code raise an error?

Identify the error in this Proof of Work Python code snippet and what error it raises.

Blockchain / Solidity

import hashlib

def pow(data, difficulty):
    nonce = 0
    prefix = '0' * difficulty
    while True:
        text = f'{data}{nonce}'
        hash_val = hashlib.sha256(text.encode()).hexdigest()
        if hash_val.startswith(prefix):
            return nonce
        nonce += 1

pow('block', 3)

A SyntaxError due to missing colon after while True

B TypeError because prefix is not a string

C NameError because hashlib is not imported

D RuntimeError due to infinite loop

💡 Hint

Check the syntax of the while loop line carefully.

The while loop line is missing a colon at the end, causing a SyntaxError.

❓ Predict Output

advanced

What is the output of this Proof of Stake validator selection code?

This Python code simulates selecting a validator based on stake weights. What does it print?

Blockchain / Solidity

import random

validators = {'Alice': 50, 'Bob': 30, 'Carol': 20}

random.seed(1)
choices = list(validators.keys())
weights = list(validators.values())
selected = random.choices(choices, weights=weights, k=1)[0]
print(selected)

A Bob

B Alice

C Carol

D Random selection with equal chance for all

💡 Hint

random.choices with weights picks based on stake amounts.

With the given seed, random.choices picks 'Alice' because she has the highest stake weight.

🧠 Conceptual

expert

Which is a key difference between Proof of Work and Proof of Stake?

Select the statement that best highlights a fundamental difference between Proof of Work (PoW) and Proof of Stake (PoS) consensus mechanisms.

A PoW is energy efficient; PoS consumes large amounts of electricity.

B PoW uses stake to select validators; PoS uses mining hardware to solve puzzles.

C PoW requires validators to solve puzzles using computational power; PoS selects validators based on their cryptocurrency holdings.

D PoW validators are chosen randomly; PoS validators compete to solve cryptographic puzzles.

💡 Hint

Think about what resource each consensus mechanism uses to secure the network.

PoW relies on computational work (energy) to validate blocks, while PoS relies on the amount of cryptocurrency staked by validators.