The part that I don't quite understand about bcrypt and the "scales with hardware speed" claim, is that, as I understand it, validating a password requires 3 pa

The part that I don't quite understand about bcrypt and the "scales with hardware speed" claim, is that, as I understand it, validating a password requires 3 parameters; password string, salt, and cost factor. If you start out now with some given cost factor, that is unfeasibly breakable with modern hardware, that factor will remain stored somewhere, presumably in the database. Once computing hardware speeds up to the point that your factor is now practical to break, you can increase the cost factor for new passwords, but older ones remain susceptible to cracking. The only option would be to re-encode them periodically with the new factor to keep them secure. Can anyone clarify if I've understood this correctly, or if I'm missing something fundamental about bcrypt? I've looked over the usenix paper, but I can't see anything obvious to confirm one way or the other.