What is a Hash Function?
A cryptographic hash function takes an input and produces a fixed-size output (digest). The same input always produces the same output, but even tiny changes produce completely different hashes.
One-Way
Hashes cannot be reversed. You can't derive the original input from the hash output.
Deterministic
The same input always produces the exact same hash output, making verification reliable.
Collision Resistant
It's computationally infeasible to find two different inputs that produce the same hash.
Algorithm Comparison
| Algorithm | Output | Security | Use Case |
|---|---|---|---|
| MD5 | 128 bits | Broken | Checksums only |
| SHA-1 | 160 bits | Weak | Legacy systems |
| SHA-256 | 256 bits | Strong | General purpose |
| SHA-384 | 384 bits | Strong | High security |
| SHA-512 | 512 bits | Strong | Maximum security |
Never hash passwords directly
For password storage, use specialized algorithms like bcrypt, scrypt, or Argon2. These include salting and are intentionally slow to prevent brute-force attacks.
Common Use Cases
File integrity verification (checksums)
Digital signatures and certificates
Data deduplication
Cache keys and content addressing
Git commit identifiers
Blockchain and cryptocurrency