Hash Functions Explained: MD5, SHA-1 & SHA-256

What is a Hash Function?

A hash function takes an input (or "message") and returns a fixed-size string of bytes. The output is typically a "digest" that is unique to each unique input. Hash functions are fundamental to modern cryptography and data integrity.

Key Properties of Hash Functions

• Deterministic: Same input always produces same output
• Fixed output length: Regardless of input size, output is fixed
• Avalanche effect: Small input change creates completely different hash
• One-way: Cannot reverse engineer original input from hash

MD5 vs SHA-1 vs SHA-256

• MD5 (128-bit): Old and broken. Not secure for passwords. Use only for checksums
• SHA-1 (160-bit): Deprecated. Vulnerable to collision attacks since 2017
• SHA-256 (256-bit): Currently secure. Used in Bitcoin, SSL certificates, password hashing