# PBKDF2 uses HMAC-SHA1 to generate keys, but what is the key for the HMAC?

I was reading up on PBKDF2 and noted the following:

DK = PBKDF2(PRF, Password, Salt, c, dkLen)


PRF is a keyed HMAC, but I can't seem to find out what they use as key for the HMAC?

• If unsure, read the specifications! – Maarten Bodewes Sep 4 '13 at 7:50