When you lock your valut with a PIN, bitwarden appears to encrypt the vault key with a key derived from your PIN, and then stores the encrypted vault key on disk. (link) But I can’t find any information on how a key is derived from the PIN. Does bitwarden use the same KDF as used with the password, or does it use a different kdf algorithm? And does the PIN key KDF also apply the customized parameters that can be set for the master password KDF?
Yes, it uses the same KDF settings that are defined for the master password.