What Is Blockchain?
A blockchain is like a notebook where pages are linked together. Nobody can secretly change old pages.
Each page has:
- The data
- A fingerprint of the previous page
Why it’s secure: If someone tries to edit Page 1 → its fingerprint changes → Page 2 breaks → Page 3 breaks. Cheating becomes visible immediately.
That’s blockchain!
What Is a “Hash”?
A hash is a digital fingerprint. It’s a unique code for any piece of data.
Examples:
- “hello” → 2cf24dba5fb0a30e…
- “Hello” → 185f8db32271fe…
The magic part:
- ✔ Same input → same hash
- ❌ Tiny change → totally different hash
What Is a Block?
A block = one event in the chain.
A block contains:
- index - its position
- timestamp - when it was created
- data - the actual information
- previous_hash - fingerprint of the block before it
- hash - its own fingerprint
What Is a Blockchain?
A blockchain is a list of blocks linked together.
blockchain = [block0, block1, block2, ...]The first block is called the Genesis Block.
Every block after it links to the previous one. This creates an unbreakable chain.
Encryption vs Digital Signatures
I had confusion about this, so let me explain clearly:
Encryption and Digital Signatures are TWO DIFFERENT things:
| Purpose | Operation | Who Uses What |
|---|---|---|
| 🔒 Secrecy | Encryption | Public key to encrypt, Private key to decrypt |
| ✍️ Proof | Digital Signature | Private key to sign, Public key to verify |
How It Works
With Encryption:
- You use someone’s public key to send them a secret message
- Only they can decrypt it with their private key
With Digital Signatures:
- You sign something with your private key
- Anyone can verify it was really you using your public key
Why Blockchain Is Secure
In a blockchain:
-
Anyone can:
- Read the data
- See who did the action
- Verify the signature is real
- Verify the chain hasn’t been broken
-
No one can:
- Change old history
- Fake who did something
- Insert fake transactions
That’s why blockchain works - it’s transparent AND secure!