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// SPDX-License-Identifier: GPL-2.0-or-later
/*
* nec-enc.c - encode/decode nec firmware with key
*
* based on xorimage.c in OpenWrt
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <unistd.h>
#define KEY_LEN 16
#define PATTERN_LEN 251
static int
xor_pattern(uint8_t *data, size_t len, const char *key, int k_len, int k_off)
{
int offset = k_off;
while (len--) {
*data ^= key[offset];
data++;
offset = (offset + 1) % k_len;
}
return offset;
}
static void xor_data(uint8_t *data, size_t len, const uint8_t *pattern)
{
for (int i = 0; i < len; i++) {
*data ^= pattern[i];
data++;
}
}
static void __attribute__((noreturn)) usage(void)
{
fprintf(stderr, "Usage: nec-enc -i infile -o outfile -k <key>\n");
exit(EXIT_FAILURE);
}
static unsigned char buf_pattern[4096], buf[4096];
int main(int argc, char **argv)
{
int k_off = 0, ptn = 1, c, ret = EXIT_SUCCESS;
char *ifn = NULL, *ofn = NULL, *key = NULL;
size_t n, k_len;
FILE *out, *in;
while ((c = getopt(argc, argv, "i:o:k:h")) != -1) {
switch (c) {
case 'i':
ifn = optarg;
break;
case 'o':
ofn = optarg;
break;
case 'k':
key = optarg;
break;
case 'h':
default:
usage();
}
}
if (optind != argc || optind == 1) {
fprintf(stderr, "illegal arg \"%s\"\n", argv[optind]);
usage();
}
in = fopen(ifn, "r");
if (!in) {
perror("can not open input file");
usage();
}
out = fopen(ofn, "w");
if (!out) {
perror("can not open output file");
usage();
}
if (!key) {
fprintf(stderr, "key is not specified\n");
usage();
}
k_len = strnlen(key, KEY_LEN + 1);
if (k_len == 0 || k_len > KEY_LEN) {
fprintf(stderr, "key length is not in range (0,%d)\n", KEY_LEN);
usage();
}
while ((n = fread(buf, 1, sizeof(buf), in)) > 0) {
for (int i = 0; i < n; i++) {
buf_pattern[i] = ptn;
ptn++;
if (ptn > PATTERN_LEN)
ptn = 1;
}
k_off = xor_pattern(buf_pattern, n, key, k_len, k_off);
xor_data(buf, n, buf_pattern);
if (fwrite(buf, 1, n, out) != n) {
perror("failed to write");
ret = EXIT_FAILURE;
goto out;
}
}
if (ferror(in)) {
perror("failed to read");
ret = EXIT_FAILURE;
goto out;
}
out:
fclose(in);
fclose(out);
return ret;
}
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