Key Derivation

Key derivation is the process of generating encryption keys from low-entropy passwords or high-entropy master keys, using KDFs (e.g., PBKDF2, scrypt, Argon2) to raise the cost of brute force.

Purpose

It turns human passwords (low entropy) into sufficiently long encryption keys while resisting dictionary and rainbow-table attacks.

Mechanism

A KDF takes a password, salt, iteration/cost parameters, and output length, and produces a pseudorandom key. Iterations multiply the per-attempt cost; salt prevents precomputed tables; memory-hard KDFs (scrypt/Argon2) additionally resist GPU/ASIC parallelism.

Use cases

Encrypted storage of user passwords
Disk-encryption master key derivation
TLS session key derivation (HKDF)
API token generation

Examples

Input

password + salt + 100000 iters

Output

256-bit key

Iterations multiply the cost

Common errors

Hashing passwords with a raw SHA (no salt, no iterations): Use PBKDF2, scrypt, or Argon2

Related terms

PBKDF2 (Password-Based Key Derivation Function 2) is the KDF standardized in PKCS#5 that derives keys from passwords via iterated HMAC, widely used for password hashing and key derivation.

scrypt is a memory-hard KDF designed by Colin Percival that resists GPU/ASIC parallel brute force through large memory requirements, used for password hashing and key derivation.

A salt is a random value added during password hashing so identical passwords produce different hashes, defeating rainbow tables and same-password detection.

Hash salting is adding a random salt to the hash input so identical inputs produce different hashes, defeating rainbow tables and collision detection.

Related tools

PBKDF2 Key Derivation

Derive a key from a password using PBKDF2 (RFC 2898) with Web Crypto API. Free, private, and 100% client-side.

scrypt Key Derivation

Derive a key from a password using scrypt (memory-hard KDF). Free, private, and 100% client-side.

Hash passwords with bcrypt or verify bcrypt hashes. Free, private, and 100% client-side.

References