asus encrypt dsl-n66u

asus-encrypt.c

//encrypt_asus
//Ren.B
#define ALIGN_SIZE 1024
#define DEFAULT_HEADER "DSL-N66U"

//must be the same structure in /apps/private/cfg_manager/utility.c
typedef struct romfile_header_s
{
	char productName[16];
	char keyWord[16];  //encryptRomfile
	unsigned long fileLength;
	unsigned int rand;
}romfile_header_t;

//must be the same keyword in /apps/private/cfg_manager/utility.c
#define KEYWORD "EnCrYpTRomFIle"

/**
** src : source file path, ex: /tmp/var/romfile.cfg
** dst : destination file path, ex: /tmp/var/romfile_encrypt.cfg
** productName : the encrypted romfile header, string type.
** Encrypt the src file to the dst file, the src file will not be changed.
**/
int encryptRomfile(char *src, char *dst, char *productName)
{
	FILE *fp = NULL;
	unsigned long count, filelen, i;
	unsigned int rand = 0;
	char *buffer = NULL;
	int srcFD = -1;
	int ret = 0;
	romfile_header_t rhdr;

	unlink(dst);
	if ((fp = fopen(dst, "w")) == NULL) return -1;

	if( ( srcFD = open(src, O_RDONLY) ) < 0 )
	{
		return -2;
	}
	count = readFileSize(src);
	buffer = (char *) calloc( count, sizeof(char));
	
	ret = read(srcFD, buffer, count);
	close(srcFD);
	if( ret < 0 )
	{
		free(buffer);
		fclose(fp);
		return -3;
	}

	memset(&rhdr, 0, sizeof(rhdr));
	strcpy(rhdr.keyWord, KEYWORD);
	rand = (get_rand() % 15) + 15; //rand will be 15~29
	rhdr.rand = rand;

	//currently ROMFILE_PADDING is not needed. We keep it just in case in the future.
	#if defined(ROMFILE_PADDING)
	filelen = count + (ALIGN_SIZE - (count%ALIGN_SIZE));
	#else
	filelen = count;
	#endif
	rhdr.fileLength = filelen;
	
	if((!productName)||( strlen(productName) <= 0 ))
	{
		strncpy(rhdr.productName, DEFAULT_HEADER, sizeof(rhdr.productName) );
	}
	else
	{
		strncpy(rhdr.productName, productName, sizeof(rhdr.productName) );
		rhdr.productName[sizeof(rhdr.productName)-1] = '\0';
	}

	//write header
	fwrite(&rhdr, 1, sizeof(rhdr), fp);

	//encrypt data
	for (i = 0; i < count; i++)
	{{
		if (buffer[i] == 0x0)
			buffer[i] = 0xfd + get_rand() % 3;
		else
			buffer[i] = (0xff - buffer[i] + rand) & 0xff;
	}}

	//write data
	fwrite(buffer, 1, count, fp);

	#if defined(ROMFILE_PADDING)
	//paddings
	for (i = count; i < filelen; i++)
	{

		temp = 0xfd + get_rand() % 3;
		fwrite(&temp, 1, 1, fp);
	}
	#endif
	
	fclose(fp);
	free(buffer);
	return 0;
}