Glossary
PBKDF2
PBKDF2 derives a key by repeating an HMAC thousands of times with a salt, trading raw speed for resistance to brute force — the KDF behind Bitwarden, LastPass, WPA2 and more.
PBKDF2 (Password-Based Key Derivation Function 2) turns a password and a salt into a fixed-length key by running an HMAC — usually HMAC-SHA1, HMAC-SHA256 or HMAC-SHA512 — over and over, feeding each round's output back into the next. The iteration count is the tunable knob: more rounds means more work per guess, for both a legitimate login and an attacker's cracking attempt.
Unlike memory-hard functions such as Argon2 or scrypt, PBKDF2 needs almost no RAM, which makes it considerably cheaper to attack on a GPU for the same iteration count. It remains widely deployed anyway because it is simple, standardized (RFC 2898) and old enough to have hardware and library support everywhere.
PBKDF2 shows up constantly on this site: Bitwarden and LastPass vaults, 1Password's Cloud Keychain format, WPA2 handshakes, and the dedicated pbkdf2-hmac-sha1/pbkdf2-sha256 hash types all derive their key this way — see cracking password manager vaults for how the iteration count each one chooses directly sets how many guesses per second a GPU can test.