圖片資源的加密和cocos2d-x中的解密

主要處理png圖片，其餘格式圖片也是同樣的原理。閱讀前能夠簡略瞭解一下png格式圖片的Data trunck。

     首先使用python腳本去掉png的PNG SIG(8 bytes) 以及末尾的PNGIEND(12 bytes)。而後圖片剩餘數據的每個字節和祕鑰字符串的每個字符作不進位加(按位異或，解密的原理就是 a ^ b ^ b = a)。經過改寫cpp工程裏的 Image::initWithImageData(const unsigned char * data, ssize_t dataLen)，來進行還原圖片數據，也就是解密，過程就是對每一位加密後的數據按祕鑰作異或運算還原數據，而後加上PNGSIG和PNGIEND。

加密腳本:(這個腳本會生成加密後的圖片替換原始圖片)

  1 # -*- coding:UTF-8 -*-
  2 #該腳本用於加密png圖片 使用python3以上版本解釋執行
  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' #指定加密祕鑰,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 #獲取filesig是不是png
 15 def isPNGSig(bytes_8):
 16     return bytes_8 == _PNGSIG
 17 
 18 def isPNG(absPath):#判斷是不是PNG圖片
 19     """
 20     :param absPath: 文件的絕對路徑
 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):#預處理圖片數據
 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已經進行過外部軟件的壓縮,丟掉了IEND
 42         return lostHeadData[:-12]
 43     else:
 44         return lostHeadData
 45 
 46 def encryption(fileData,key):#加密操做 ascii佔一個字節
 47     """
 48     加密png數據
 49     :param fileData:{bytes}預處理後的png數據
 50     :param key:{str}祕鑰
 51     :return:{bytes}加密後的數據
 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 #處理圖片
 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: #覆蓋新文件
 73         file.write(fileData)
 74     filenum = filenum + 1
 75 
 76 
 77 
 78 def traverseDir(absDir):#遍歷當前目錄以及遞歸的子目錄，找到全部的png圖片
 79     """
 80     :param absDir: 要遍歷的路徑
 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):#遞歸查找文件夾
 88             traverseDir(absFileName)
 89         elif isPNG(absFileName):
 90             processPNG(absFileName)
 91         else:
 92             pass
 93 
 94 
 95 #------------------- 主函數-------------------------#
 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.新增圖片類型

 enum class Format
    {
        //! JPEG
        JPG,
        //! PNG
        PNG,
        //! ENCRYPTEDPNG
        ENCRYPTEDPNG, //加密後的Png圖片
        //! TIFF
        TIFF,
        //! WebP
        WEBP,
        //! PVR
        PVR,
        //! ETC
        ETC,
        //! S3TC
        S3TC,
        //! ATITC
        ATITC,
        //! TGA
        TGA,
        //! Raw Data
        RAW_DATA,
        //! Unknown format
        UNKNOWN
    };

2,修改檢測圖片類型的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，進行解密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(&copyData, "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作解密:

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];
    }
}

最後加一句:python大法好。