Oooh! Hmac anyone??

I have a need for "One Time Passwords"... I have the code to generate the HMAC, but can I find the code to authenticate on a local embedded design................No!

Any... I mean ANY help would be gratefully received!

Forget it!!!! Senior moment again... Took a while to sink in! same code does both ends.... Its the 6 digit code is all that matters..