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⚔️ Attacking Hash Functions: Brute Force vs Birthday Attack

Understand different collision attack strategies and their computational costs

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⚔️ Collision Attack Simulation

Let's see how an attacker might attempt to find hash collisions and why strong hash functions are crucial for blockchain security!

🎯 Three Types of Hash Attacks

Attackers use different strategies depending on their goal. Each attack has different difficulty levels:

🎲Medium

Collision Attack

Find ANY two inputs with same hash

Complexity: 2^(n/2)

Generate many inputs, look for matching hashes

🎯Very Hard

Preimage Attack

Find input for a SPECIFIC hash

Complexity: 2^n

Given hash X, find input that produces X

🔄Very Hard

Second Preimage

Find different input with SAME hash as given input

Complexity: 2^n

Given input A, find input B where hash(A) = hash(B)

🎮 Interactive Attack Simulator

Watch how an attacker generates multiple inputs looking for a collision. This uses a WEAK hash for demonstration (real attacks on SHA-256 are impossible with current technology).

Attack Progress

⚡ Attack Strategy: Birthday Attack

The most efficient collision attack uses the birthday paradox principle:

1️⃣

Generate Many Inputs

Create millions of different inputs (transactions, messages, blocks, etc.)

inputs = ["msg1", "msg2", "msg3", ..., "msg_million"]

2️⃣

Hash Each Input

Compute hash for every input and store the results

hashes = [hash(input) for input in inputs]

3️⃣

Look for Matches

Compare all hashes to find any pair that matches (collision!)

if hash(inputA) == hash(inputB): COLLISION_FOUND

4️⃣

Exploit Collision

Use the collision for malicious purposes (forge signatures, create fake blocks, etc.)

🛡️ Defense: Hash Function Strength

❌

Weak Hash (MD5)

128 bits = 2^128 outputs
Collision at 2^64 ≈ 18 quintillion

Modern computers can find MD5 collisions in seconds. Completely broken for security!

✅

Strong Hash (SHA-256)

256 bits = 2^256 outputs
Collision at 2^128 ≈ 10^38

Even at 1 billion hashes/second, finding collision would take 10 trillion years!

🔍 Real Attack Examples

🚨

MD5 Collision (2004)

Researchers found MD5 collisions in just 1 hour on a standard laptop. This killed MD5 for security purposes.

Two different files with identical MD5: d131dd02c5e6eec4...

⚠️

SHA-1 Collision (2017)

Google found first SHA-1 collision after 2 years and massive computing power. SHA-1 deprecated.

Cost: ~$110,000 in computing time

🔒

SHA-256 (Still Secure)

No collision found after 20+ years. Bitcoin and modern blockchain rely on this strength.

Status: Theoretically secure until quantum computers

💡 Key Lessons

🎯

Collision Attacks Are Real

MD5 and SHA-1 have been broken. Always use modern, strong hash functions like SHA-256 or SHA-3.

⚡

Birthday Attack Efficiency

Collision attacks need only √n attempts, not n. This is why hash size matters exponentially.

🔒

Blockchain Depends on This

SHA-256's collision resistance is why Bitcoin's 21 million BTC supply is secure. Collisions would break everything.