+/*
+ * This program is designed to sign firmware images so they are accepted
+ * by D-Link DIR-882 R1 WebUIs.
+ *
+ * Copyright (C) 2020 Andrew Pikler
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include "md5.h"
+
+#define BUF_SIZE 4096
+#define MD5_HASH_LEN 16
+
+
+typedef struct _md5_digest_t {
+ uint8_t digest[MD5_HASH_LEN];
+} md5_digest_t;
+
+typedef struct _salt_t {
+ char* salt_ascii;
+ uint8_t* salt_bin;
+ size_t salt_bin_len;
+} salt_t;
+
+void read_file_bytes(FILE* f, MD5_CTX* md5_ctx) {
+ uint8_t buf[BUF_SIZE];
+ size_t bytes_read;
+ rewind(f);
+
+ while (0 != (bytes_read = fread(buf, sizeof(uint8_t), BUF_SIZE, f))) {
+ MD5_Update(md5_ctx, buf, bytes_read);
+ }
+
+ if (!feof(f)) {
+ printf("Error: expected to be at EOF\n");
+ exit(-1);
+ }
+}
+
+void add_magic_bytes(FILE* f) {
+ char magic_bytes[] = { 0x00, 0xc0, 0xff, 0xee };
+ size_t magic_bytes_len = 4;
+ fwrite(magic_bytes, magic_bytes_len, 1, f);
+}
+
+/**
+ * Add the signature produced by this salt to the file
+ * The signature consists by creating an MD5 digest wht the salt bytes plus
+ * all of the bytes in the firmware file, then adding the magic bytes to the
+ * file
+ */
+void add_signature(FILE* f, salt_t* salt) {
+ md5_digest_t digest;
+ MD5_CTX md5_context;
+
+ MD5_Init(&md5_context);
+ MD5_Update(&md5_context, salt->salt_bin, salt->salt_bin_len);
+ read_file_bytes(f, &md5_context);
+ MD5_Final(digest.digest, &md5_context);
+
+ fwrite(&digest.digest, sizeof(uint8_t), MD5_HASH_LEN, f);
+ add_magic_bytes(f);
+}
+
+void add_version_suffix(FILE* f) {
+ char* version_suffix = "c0ffeef0rge";
+ fseek(f, 0, SEEK_END);
+ fwrite(version_suffix, sizeof(char), strlen(version_suffix), f);
+}
+
+int asciihex_to_int(char c) {
+ if(c >= '0' && c <= 'F')
+ return c - '0';
+
+ if(c >= 'a' && c <= 'f')
+ return 10 + c - 'a';
+ return -1;
+}
+
+/**
+ * Verify this is a valid hex string to convert
+ */
+void verify_valid_hex_str(char* s) {
+ int i;
+ int s_len = strlen(s);
+ if (s_len == 0) {
+ printf("invalid empty salt: %s\n", s);
+ exit(-1);
+ }
+
+ if (s_len % 2 != 0) {
+ printf("invalid odd len salt: %s\n", s);
+ exit(-1);
+ }
+
+ for (i = 0; i < s_len; ++i) {
+ if (asciihex_to_int(s[i]) < 0) {
+ printf("invalid salt (invalid hex char): %s\n", s);
+ exit(-1);
+ }
+ }
+}
+
+/**
+ * Convert a hex ascii string to an allocated binary array. This array must be free'd
+ */
+uint8_t* convert_hex_to_bin(char * s) {
+ int i;
+ int s_len = strlen(s);
+
+ uint8_t* ret = malloc(s_len / 2);
+ for (i = 0; i < s_len; i += 2) {
+ ret[i / 2] = (asciihex_to_int(s[i]) << 4) | asciihex_to_int(s[i + 1]);
+ }
+
+ return ret;
+}
+
+void init_salt(salt_t* salt, char * salt_ascii) {
+ salt->salt_ascii = salt_ascii;
+ salt->salt_bin = convert_hex_to_bin(salt_ascii);
+ salt->salt_bin_len = strlen(salt_ascii) / 2;
+}
+
+void free_salt(salt_t* salt) {
+ free(salt->salt_bin);
+}
+
+/**
+ * Verify that the arguments are valid, or exit with failure
+ */
+void verify_args(int argc, char** argv) {
+ int i;
+
+ if (argc < 3) {
+ printf("Usage: %s <firmware file> <signing hash1> <signing hash2> ... <signing hash n>\n", argv[0]);
+ exit(1);
+ }
+
+ for (i = 2; i < argc; i++) {
+ verify_valid_hex_str(argv[i]);
+ }
+}
+
+FILE* make_out_file(char* filename) {
+ uint8_t buf[BUF_SIZE];
+ int bytes_read;
+ char* suffix = ".new";
+ int new_filename_len = strlen(filename) + strlen(suffix) + 1;
+ char* new_filename = malloc(new_filename_len);
+ strcpy(new_filename, filename);
+ strcat(new_filename, suffix);
+
+ FILE* f = fopen(filename, "r+");
+ if (!f) {
+ printf("cannot open file %s\n", filename);
+ exit(2);
+ }
+
+ FILE* out = fopen(new_filename, "w+");
+ free(new_filename);
+ if (!out) {
+ printf("cannot open file %s\n", filename);
+ exit(2);
+ }
+
+ while (0 != (bytes_read = fread(buf, sizeof(uint8_t), BUF_SIZE, f))) {
+ fwrite(buf, sizeof(uint8_t), bytes_read, out);
+ }
+ fclose(f);
+ return out;
+}
+
+/**
+ * Sign the firmware file after all of our checks have completed
+ */
+void sign_firmware(char* filename, char** salts, int num_salts) {
+ int i;
+ salt_t salt;
+ FILE* f = make_out_file(filename);
+
+ // add a version suffix string - dlink versions do something similar before the first signature
+ add_version_suffix(f);
+
+ //for each of the salts we are supplied with
+ for (i = 0; i < num_salts; i++) {
+ char* salt_str = salts[i];
+ // convert this str to binary
+ init_salt(&salt, salt_str);
+
+ // add the signature to the firmware file produced from this salt
+ add_signature(f, &salt);
+ free_salt(&salt);
+ printf("Signed with salt: %s\n", salt_str);
+ }
+
+ fclose(f);
+}
+
+
+int main(int argc, char ** argv) {
+ verify_args(argc, argv);
+ sign_firmware(argv[1], argv+2, argc-2);
+ return 0;
+}
projects / openwrt / openwrt.git / commitdiff