src/nec-enc.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * nec-enc.c - encode/decode nec firmware with key
   4  *
   5  * based on xorimage.c in OpenWrt
   6  *
   7  */
   8
   9 #include <stdio.h>
  10 #include <stdlib.h>
  11 #include <string.h>
  12 #include <stdint.h>
  13 #include <unistd.h>
  14
  15 #define KEY_LEN     16
  16 #define PATTERN_LEN 251
  17
  18 static int
  19 xor_pattern(uint8_t *data, size_t len, const char *key, int k_len, int k_off)
  20 {
  21         int offset = k_off;
  22
  23         while (len--) {
  24                 *data ^= key[offset];
  25                 data++;
  26                 offset = (offset + 1) % k_len;
  27         }
  28
  29         return offset;
  30 }
  31
  32 static void xor_data(uint8_t *data, size_t len, const uint8_t *pattern)
  33 {
  34         for (int i = 0; i < len; i++) {
  35                 *data ^= pattern[i];
  36                 data++;
  37         }
  38 }
  39
  40 static void __attribute__((noreturn)) usage(void)
  41 {
  42         fprintf(stderr, "Usage: nec-enc -i infile -o outfile -k <key>\n");
  43         exit(EXIT_FAILURE);
  44 }
  45
  46 static unsigned char buf_pattern[4096], buf[4096];
  47
  48 int main(int argc, char **argv)
  49 {
  50         int k_off = 0, ptn = 1, c, ret = EXIT_SUCCESS;
  51         char *ifn = NULL, *ofn = NULL, *key = NULL;
  52         size_t n, k_len;
  53         FILE *out, *in;
  54
  55         while ((c = getopt(argc, argv, "i:o:k:h")) != -1) {
  56                 switch (c) {
  57                 case 'i':
  58                         ifn = optarg;
  59                         break;
  60                 case 'o':
  61                         ofn = optarg;
  62                         break;
  63                 case 'k':
  64                         key = optarg;
  65                         break;
  66                 case 'h':
  67                 default:
  68                         usage();
  69                 }
  70         }
  71
  72         if (optind != argc || optind == 1) {
  73                 fprintf(stderr, "illegal arg \"%s\"\n", argv[optind]);
  74                 usage();
  75         }
  76
  77         in = fopen(ifn, "r");
  78         if (!in) {
  79                 perror("can not open input file");
  80                 usage();
  81         }
  82
  83         out = fopen(ofn, "w");
  84         if (!out) {
  85                 perror("can not open output file");
  86                 usage();
  87         }
  88
  89         if (!key) {
  90                 fprintf(stderr, "key is not specified\n");
  91                 usage();
  92         }
  93
  94         k_len = strnlen(key, KEY_LEN + 1);
  95         if (k_len == 0 || k_len > KEY_LEN) {
  96                 fprintf(stderr, "key length is not in range (0,%d)\n", KEY_LEN);
  97                 usage();
  98         }
  99
 100         while ((n = fread(buf, 1, sizeof(buf), in)) > 0) {
 101                 for (int i = 0; i < n; i++) {
 102                         buf_pattern[i] = ptn;
 103                         ptn++;
 104
 105                         if (ptn > PATTERN_LEN)
 106                                 ptn = 1;
 107                 }
 108
 109                 k_off = xor_pattern(buf_pattern, n, key, k_len, k_off);
 110                 xor_data(buf, n, buf_pattern);
 111
 112                 if (fwrite(buf, 1, n, out) != n) {
 113                         perror("failed to write");
 114                         ret = EXIT_FAILURE;
 115                         goto out;
 116                 }
 117         }
 118
 119         if (ferror(in)) {
 120                 perror("failed to read");
 121                 ret = EXIT_FAILURE;
 122                 goto out;
 123         }
 124
 125 out:
 126         fclose(in);
 127         fclose(out);
 128         return ret;
 129 }