Hash Functions for Security: SHA-256, bcrypt, and When to Use What

Not all hash functions serve the same purpose. Using the wrong one can create security vulnerabilities even when your implementation is correct.

Fast Hashes: SHA-256, SHA-512

SHA-2 family hashes are designed to be fast. They are perfect for data integrity verification, digital signatures, file checksums, and HMAC authentication. They produce a fixed-size output from any input and are collision-resistant.

Slow Hashes: bcrypt, Argon2, scrypt

These are deliberately slow and memory-intensive. They are designed specifically for password hashing. The slowness is the feature — it makes brute-force attacks computationally expensive. bcrypt uses a configurable cost factor. Argon2id (the current recommendation) adds memory-hardness to resist GPU attacks.

Never Use for Passwords

MD5 and SHA-1 are broken for security purposes. Even SHA-256 is wrong for passwords because it is too fast — a modern GPU can compute billions of SHA-256 hashes per second, making brute-force attacks feasible. Always use a dedicated password hashing algorithm.

HMAC for Authentication

HMAC combines a hash function with a secret key to create a message authentication code. Use HMAC-SHA256 for API request signing, webhook verification, and session tokens. The key ensures that only parties who know the secret can generate valid MACs.

Choosing the Right Function

For passwords: Argon2id or bcrypt. For data integrity: SHA-256. For API authentication: HMAC-SHA256. For digital signatures: SHA-256 with RSA or ECDSA. For content addressing: SHA-256 (used by Git and Docker). Use our Hash Generator and HMAC Generator tools to experiment with these functions in your browser.