sc_get_challenge - Request a challenge from a card
#include <opensc.h>
int sc_get_challenge(struct sc_card *card, unsigned char *rnd, size_t len);
This function requests a challenge (i.e. random bytes) from card. The
returned data will be stored in rnd, and will be len bytes long.
Returns 0 if successful, or a negative value in case of error.