Skip to content
Snippets Groups Projects
nec-enc.c 2.2 KiB
Newer Older
  • Learn to ignore specific revisions
  • // 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 = 0, 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 + 1;
    			ptn++;
    
    			if (ptn > 250)
    				ptn = 0;
    		}
    
    		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;
    }