help with running popen

["ronald de la cruz" <rcdelacruz gmail com>]

hi there...im writing a pam module with encryption using gpg. 
im trying to use popen() to run external command like gpg.
FILE *fp
fp = popen("sudo gpg -ear....", "r");

the problem is, im trying to run this with the sudo command
but the pam module won't accept it,
the error is

sudo: gpg: commant not found


please help i really need to run gpg with sudo 

-- 
ronald de la cruz