how to open files with grub_file_open

[Rev. Mr. Gary Meerschaert]

need to modify grub for a project in my security class. I am adding a a 
check of a key stored on a usb drive. I also have the key stored in the 
/boot/grub2, /boot/grub, and /boot. I can not open any of them. My 
system dual-boots, and the fedora install is in hd0,1.

My code is shown (extra tracing statements included)

static void
grub_key_check (void)
{

grub_file_t key_disk_file;
grub_file_t key_usb_file;

char usb_key[512];
char disk_key[512];

char key_match;

int i;
const char *prefix;

prefix = grub_env_get ("prefix");
grub_printf("In key check\n");
key_match = 'f';

/* look for a key file on the disk */
grub_printf("before disk file open\n");
key_disk_file = grub_file_open("(hd0)grub/key");
grub_printf("after disk file open\n");
if ( ! key_disk_file )
{
grub_printf("No disk key file\n");
grub_printf("before return\n");
return;
}

grub_printf("After disk file open\n");
/* read in the key from the key file. Must be 512 char*/
if ( grub_file_read(key_disk_file, disk_key,512) != 512)
{
grub_printf("Disk key file wrong size\n");
sleep(30);
return;
}

grub_printf("After disk file read\n");
/* read the key file from the usb drive & compare */
while (key_match == 'f')
{

grub_printf("top of key match loop\n");
while ( (key_usb_file = grub_file_open("(hd0)key")) == (grub_file_t)0)
{
grub_printf("usb file open failed\n");
grub_printf("Insert key\n");
sleep(30);
}

grub_printf("usb file open worked\n");
if (grub_file_read (key_usb_file, usb_key, 512) != 512)
{
grub_printf("usb file read failed\n");
grub_file_close(key_usb_file);
grub_printf("Insert key\n");
sleep(30);
continue;
}
grub_printf("usb file read worked\n");

grub_printf("before key check\n");
grub_printf("usb file read worked\n");

grub_printf("before key check\n");
for (i=0; i<512; i++)
{
if (disk_key[i] != usb_key[i])
{
grub_printf("Key match failed at %d\n",i);
break;
}
}
grub_printf("Key check passed\n");
if (i == 512) key_match = 't';
}
grub_printf("Bottom of key_check\n");
}

/* The main routine. */
void
grub_main (void)
{
/* First of all, initialize the machine. */
grub_machine_init ();
/* First of all, initialize the machine. */
grub_machine_init ();
grub_printf("hello - before key_check\n");
/* check for USB drive key */
grub_key_check();
grub_printf("After key check\n");
/* Hello. */
grub_setcolorstate (GRUB_TERM_COLOR_HIGHLIGHT);
grub_printf ("Welcome to GRUB!\n\n");
grub_setcolorstate (GRUB_TERM_COLOR_STANDARD);


There are some trace satements in the file.c routine also (not shown).

The output I get is:
./grub-emu -r /boot
hello - before key_check
In key check
before disk file open
in grub_file_open, file = (hd0)grub/key
In grub_file_get_device_name, file = (hd0)grub/key
Malloc return = 0
Device name = hd0
device name = hd0
file name now = grub/key
After device_open
after disk file open
No disk key file
before return
After key check
Welcome to GRUB!

Segmentation fault

I have tried the file name as (hd0)/boot/key, (hd0)/boot/grub/key with 
the same results.

Can anyone tell me what I am doing wrong?

Thanks,
Gary