Hash: The invisible cornerstone of Bitcoin and blockchain

Have you ever wondered how Bitcoin ensures that no one can counterfeit transactions? The answer lies in a mathematical tool called hash. It's not magic, it's pure cryptography.

What happens when you “hash” something?

Imagine that you have a text of any size: from a word to a 1GB document. The hash takes that text and converts it into a string of always the same size. For example, with SHA-256 ( that uses Bitcoin):

• Input: “Binance” → Output: f1624fcc63b615ac0e95daf9ab78434ec2e8ffe402144dc631b055f711225191
• Input: “binance” → Output: 59bba357145ca539dcd1ac957abc1ec5833319ddcae7f5e8b5da0c36624784b2

Do you see? It only changed one uppercase letter and the result is completely different. That is determinism: same input = same output, always.

The 3 properties that make the hash secure

1. Collision resistance: It is impossible to find two different inputs that generate the same hash. Although collisions technically exist, the probability is so low that it would take millions of years of computation.

2. Unidirectional function: Easy to go from input to output. Practically impossible ( to go the other way. If I give you a hash, you cannot discover what input originated it without massive brute force.

3. Resistance to second pre-image: If a known hash already exists, finding another input that generates the same hash is nearly impossible.

This is critical: banks store hashes of passwords, not real passwords. That's why if they hack the database, they don't know your credentials.

How Bitcoin uses this for mining

Miners do not search randomly. They must generate hashes that start with a certain number of zeros. If the network's hashrate increases, Bitcoin automatically adjusts the difficulty to maintain 10 minutes per block. It is an elegant balance.

There are multiple valid solutions per block—miners only need to find one. That's why it's not fraud: it's real computational work.

Why it matters

Each block is linked to the previous one through hash. If someone tries to change a past transaction, the hash of that block would change, breaking the entire chain. The security of blockchain rests on this: intertwined cryptographic hashes.