Glossary
Iteration count
The iteration count is how many times a key-derivation function repeats its internal round per guess — the PBKDF2 equivalent of bcrypt's cost factor, and the number that sets cracking speed.
The iteration count is the number of times a key-derivation function like PBKDF2 repeats its internal HMAC round before producing a final key. It plays the same role for PBKDF2-based formats that the cost factor plays for bcrypt: a direct, linear knob on how long one guess takes to verify, for an attacker and a legitimate user alike.
Modern guidance pushes this number far higher than it used to be. OWASP currently recommends at least 600,000 iterations for PBKDF2-HMAC-SHA256, where a decade ago 10,000 was considered reasonable — hardware got faster, so the count has to climb to keep pace. Bitwarden embeds its chosen iteration count directly in the exported hash, which is why you can read off a vault's exact cracking cost before running hashcat at all.
A low iteration count is a bigger problem than a weak salt: it is the parameter that most directly decides whether a stolen hash falls in hours or resists for years. See cracking password manager vaults for how this plays out across KeePass, 1Password, Bitwarden and LastPass.