Complete Guide to Hash Functions

What is a Hash?

A hash function takes input data of any size and produces a fixed-size output (hash). The same input always produces the same hash, but even a tiny change in input produces a completely different hash.

Popular Hash Algorithms

MD5: 128-bit (32 hex chars) - Fast but not secure SHA-1: 160-bit (40 hex chars) - Deprecated for security SHA-256: 256-bit (64 hex chars) - Recommended SHA-512: 512-bit (128 hex chars) - Most secure

Properties

• Deterministic: Same input = same output • Fast to compute • Infeasible to reverse • Small change = completely different hash • Collision resistant

Example

Input: "hello"
MD5:    5d41402abc4b2a76b9719d911017c592
SHA-256: 2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824

Use Cases

• Password storage • Data integrity verification • Digital signatures • File checksums • Blockchain