decripting some hash value

[Janez Kostanjšek]

Hello ppl,

aybody knows what is the procedure to decrypt fingerprint (signed hash
value - that is hash value encrypted with private key). What functions
are used for that in GPG ? 
If I rephrase: I have public-key & signed hash with private-key file of
type gpg, asc or sig & I would like to decode the file to become normal
(clear) - with my own c-application, do you have any idea what functions
from GPG do that (or what function to use)!!!


be good,
Janez