Cryptography Basics for Blockchain

Hash Functions

A hash function takes any input and produces a fixed-length output. Bitcoin uses SHA-256. The same input always produces the same output — but you cannot reverse it.

Public-Key Cryptography

• Private Key — Secret. Used to sign transactions. Never share.
• Public Key — Derived from private key. Used to verify identity.

Digital Signatures

When you send a transaction, you sign it with your private key. The network verifies using your public key — proving authorization without revealing the private key.