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 }
130
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Sources/firmware-utils/src/nec-enc.c
