图片资源的加密和cocos2d-x中的解密
主要处理png图片，其他格式图片也是一样的原理。阅读前可以简略了解一下png格式图片的Data trunck。
首先使用python脚本去掉png的PNG SIG(8 bytes) 以及末尾的PNGIEND(12 bytes)。然后图片剩余数据的每一个字节和秘钥字符串的每一个字符做不进位加(按位异或，解密的原理就是 a ^ b ^ b = a)。通过改写cpp工程里的 Image::initWithImageData(const unsigned char * data, ssize_t dataLen)，来进行还原图片数据，也就是解密，过程就是对每一位加密后的数据按秘钥做异或运算还原数据，然后加上PNGSIG和PNGIEND。
加密脚本:(这个脚本会生成加密后的图片替换原始图片)
1 # -*- coding:UTF-8 -*- 2 #该脚本用于加密png图片 使用python3以上版本解释执行 3 __author__ = "ChenGuanzhou" 4 5 import os 6 import time 7 CUR_DIR = os.getcwd(); 8 print("cur_dir:",CUR_DIR) 9 #CUR_DIR = 'C:\\Users\\chenguanzhou\\Desktop' 10 _KEY = 'jiaozi2013' #指定加密秘钥,英文 11 _ENCRYSIG = 'jiaozhi' 12 _PNGSIG = bytes([0x89,0x50,0x4e,0x47,0x0d,0x0a,0x1a,0x0a]) 13 _PNGIEND = bytes([0x00, 0x00, 0x00, 0x00, 0x49, 0x45, 0x4E, 0x44, 0xAE, 0x42, 0x60, 0x82]) 14 #获取filesig是否是png 15 def isPNGSig(bytes_8): 16 return bytes_8 == _PNGSIG 17 18 def isPNG(absPath):#判断是否是PNG图片 19 """ 20 :param absPath: 文件的绝对路径 21 :return: {Bool} 22 """ 23 isFile = os.path.isfile(absPath) 24 hasPNGSig = False 25 fileExt = os.path.splitext(absPath)[1] 26 isPngExt = (fileExt == ".png" or fileExt == ".PNG") 27 if isFile and isPngExt: 28 with open(absPath,"rb") as file: 29 hasPNGSig = isPNGSig(file.read(8)[:8]) 30 return isFile and isPngExt and hasPNGSig 31 32 def preProcessPng(pngData):#预处理图片数据 33 """ 34 剪掉png的signature(8bytes),IEND(12Bytes) 35 :param pngData: 36 :return: 37 """ 38 assert type(pngData) == bytes 39 lostHeadData = pngData[8:] 40 iendData = lostHeadData[-12:] 41 if iendData == _PNGIEND:#防止Png已经进行过外部软件的压缩,丢掉了IEND 42 return lostHeadData[:-12] 43 else: 44 return lostHeadData 45 46 def encryption(fileData,key):#加密操作 ascii占一个字节 47 """ 48 加密png数据 49 :param fileData:{bytes}预处理后的png数据 50 :param key:{str}秘钥 51 :return:{bytes}加密后的数据 52 """ 53 assert type(key) is str 54 k = bytes(key,"utf8") 55 klen= len(k) 56 kindex = 0 57 fileData = bytearray(fileData) 58 for i,v in enumerate(fileData): 59 if kindex >= klen: 60 kindex = 0 61 fileData[i] = v ^ k[kindex]#加密 62 kindex = kindex + 1 63 return bytes(_ENCRYSIG,"utf8") + fileData 64 65 #处理图片 66 def processPNG(filePath): 67 global filenum 68 fileData = None 69 with open(filePath,'rb') as file: 70 fileData = encryption(preProcessPng(file.read()),_KEY) 71 os.remove(filePath) 72 with open(filePath,'wb') as file: #覆盖新文件 73 file.write(fileData) 74 filenum = filenum + 1 75 76 77 78 def traverseDir(absDir):#遍历当前目录以及递归的子目录，找到所有的png图片 79 """ 80 :param absDir: 要遍历的路径 81 :return: None 82 """ 83 assert (os.path.isdir(absDir) and os.path.isabs(absDir)) 84 dirName = absDir 85 for fileName in os.listdir(absDir): 86 absFileName = os.path.join(dirName,fileName) 87 if os.path.isdir(absFileName):#递归查找文件夹 88 traverseDir(absFileName) 89 elif isPNG(absFileName): 90 processPNG(absFileName) 91 else: 92 pass 93 94 95 #------------------- 主函数-------------------------# 96 start_clock = time.clock() 97 filenum = 0 98 #traverseDir(os.path.join(CUR_DIR,"png2")) 99 traverseDir(CUR_DIR) 100 end_clock = time.clock() 101 time = (end_clock - start_clock)*1000 102 print("encrypt %d Png Pictures"%filenum) 103 print("use time %fms"%time)
解密的cpp文件
1.新增图片类型
enum class Format { //! JPEG JPG, //! PNG PNG, //! ENCRYPTEDPNG ENCRYPTEDPNG, //加密后的Png图片 //! TIFF TIFF, //! WebP WEBP, //! PVR PVR, //! ETC ETC, //! S3TC S3TC, //! ATITC ATITC, //! TGA TGA, //! Raw Data RAW_DATA, //! Unknown format UNKNOWN };
2,修改检测图片类型的Image::detectFormat
1 bool Image::isEncryptedPng(const unsigned char * data, ssize_t dataLen){ 2 if (dataLen <= 7 || memcmp("jiaozhi", data, 7) != 0){ 3 return false; 4 } 5 return true; 6 }
1 mage::Format Image::detectFormat(const unsigned char * data, ssize_t dataLen) 2 { 3 if (isPng(data, dataLen)) 4 { 5 return Format::PNG; 6 } 7 else if(isEncryptedPng(data,dataLen)){ 8 return Format::ENCRYPTEDPNG; 9 } 10 else if (isJpg(data, dataLen)) 11 { 12 return Format::JPG; 13 } 14 else if (isTiff(data, dataLen)) 15 { 16 return Format::TIFF; 17 } 18 else if (isWebp(data, dataLen)) 19 { 20 return Format::WEBP; 21 } 22 else if (isPvr(data, dataLen)) 23 { 24 return Format::PVR; 25 } 26 else if (isEtc(data, dataLen)) 27 { 28 return Format::ETC; 29 } 30 else if (isS3TC(data, dataLen)) 31 { 32 return Format::S3TC; 33 } 34 else if (isATITC(data, dataLen)) 35 { 36 return Format::ATITC; 37 } 38 else 39 { 40 return Format::UNKNOWN; 41 } 42 }
3.修改Image::initWithImageData，进行解密png
1 bool Image::initWithImageData(const unsigned char * data, ssize_t dataLen) 2 { 3 bool ret = false; 4 do 5 { 6 CC_BREAK_IF(! data || dataLen <= 0); 7 8 unsigned char* unpackedData = nullptr; 9 ssize_t unpackedLen = 0; 10 11 //detect and unzip the compress file 12 if (ZipUtils::isCCZBuffer(data, dataLen)) 13 { 14 unpackedLen = ZipUtils::inflateCCZBuffer(data, dataLen, &unpackedData); 15 } 16 else if (ZipUtils::isGZipBuffer(data, dataLen)) 17 { 18 unpackedLen = ZipUtils::inflateMemory(const_cast<unsigned char*>(data), dataLen, &unpackedData); 19 } 20 else 21 { 22 unpackedData = const_cast<unsigned char*>(data); 23 unpackedLen = dataLen; 24 } 25 26 _fileType = detectFormat(unpackedData, unpackedLen); 27 28 switch (_fileType) 29 { 30 case Format::ENCRYPTEDPNG: 31 { 32 unsigned char* copyData = new unsigned char[unpackedLen+13];//8+12-7 33 memcpy(copyData + 8, unpackedData+7, unpackedLen-7); 34 deEncryptPng(©Data, "jiaozi2013", unpackedLen + 13); 35 ret = initWithPngData(copyData, unpackedLen + 13); 36 delete[] copyData; 37 38 } 39 break; 40 case Format::PNG: 41 ret = initWithPngData(unpackedData, unpackedLen); 42 break; 43 case Format::JPG: 44 ret = initWithJpgData(unpackedData, unpackedLen); 45 break; 46 case Format::TIFF: 47 ret = initWithTiffData(unpackedData, unpackedLen); 48 break; 49 case Format::WEBP: 50 ret = initWithWebpData(unpackedData, unpackedLen); 51 break; 52 case Format::PVR: 53 ret = initWithPVRData(unpackedData, unpackedLen); 54 break; 55 case Format::ETC: 56 ret = initWithETCData(unpackedData, unpackedLen); 57 break; 58 case Format::S3TC: 59 ret = initWithS3TCData(unpackedData, unpackedLen); 60 break; 61 case Format::ATITC: 62 ret = initWithATITCData(unpackedData, unpackedLen); 63 break; 64 default: 65 { 66 // load and detect image format 67 tImageTGA* tgaData = tgaLoadBuffer(unpackedData, unpackedLen); 68 69 if (tgaData != nullptr && tgaData->status == TGA_OK) 70 { 71 ret = initWithTGAData(tgaData); 72 } 73 else 74 { 75 CCLOG("cocos2d: unsupported image format!"); 76 } 77 78 free(tgaData); 79 break; 80 } 81 } 82 83 if(unpackedData != data) 84 { 85 free(unpackedData); 86 } 87 } while (0); 88 89 return ret; 90 }
4.新增Image::deEncryptPng做解密:
void Image::deEncryptPng(unsigned char** copyData, const char* key, ssize_t dataLen){ static const unsigned char PNG_SIGNATURE[] = { 0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a }; static const unsigned char PNG_IEND[] = { 0x00, 0x00, 0x00, 0x00, 0x49, 0x45, 0x4E, 0x44, 0xAE, 0x42, 0x60, 0x82 }; unsigned char* _data = *copyData; memcpy(_data, PNG_SIGNATURE, 8); memcpy(_data + (dataLen - 12), PNG_IEND, 12); unsigned char* de_start = _data + 8; unsigned char* de_end = _data + dataLen - 13; ssize_t keyLen = strlen(key); ssize_t keyIndex = 0; for (; de_start <= de_end;de_start++,keyIndex++){ if (keyIndex >= keyLen) keyIndex = 0; *de_start ^= key[keyIndex]; } }
最后加一句:python大法好。
