PBKDF2

A key-stretching function that hashes a password many times with a salt to slow brute-force attacks.

PBKDF2 derives a cryptographic key from a password by applying a pseudorandom function thousands or more times with a unique salt, deliberately making each guess expensive for an attacker. It is a standard key-stretching choice alongside bcrypt and scrypt, though memory-hard functions like scrypt and Argon2 resist GPU and ASIC cracking better. The salt defeats precomputed rainbow tables, and a high iteration count raises the cost of brute force. On the exam, associate PBKDF2 with salting plus key stretching for safe password storage.