用按位异或(^)运算实现文件加密的代码，c语言写dll，vb调用dll中的函数

/* Replace "dll.h" with the name of your header */ #include "dll.h" #include <windows.h> #include <string.h> #include <stdio.h> const int keychar_size = 256, scan_size = 65536; const char* expandname[] = {".加密文件"}; //生成一个字节的密码的函数，将str指向的length字节内容逐字节按位异或运算 char getKey(const char *str, int length) { char key = 0x00;//更改这个常数可以“二重加密”，相同图片产生不同密码 while (length-- > 0) { key ^= *str++; } return key; } //将长度为strlength的字符串str，用长度为keylength的key加密 void strdenc(char *str, int strlength, const char *key, int keylength) { int i, j; if (keylength > 0) for (i = j = 0; i < strlength; i++, j++) { if (j >= keylength)j -= keylength; str[i] ^= key[j]; } } //返回keychar_size，让调用dll的外部程序获得size信息 inline DLLIMPORT int getkeycharsize() { return keychar_size; } inline int isenc(const char *filename) { for (int i = sizeof(expandname) / sizeof(const char*); i > 0; i--) { if (!stricmp(filename, expandname[i - 1]))return 1; } return 0; } //从bmp或bin读取key DLLIMPORT int KeyRead(const char *filename, char *key, int * keylength) {//bmp需要keylength，bin可以随便传值 char*file; FILE*fp = fopen(filename, "rb"); if (fp) { file = strrchr(filename, '.'); if (!stricmp(file, ".bin")) { fread(keylength, 4, 1, fp); if (*keylength > keychar_size) *keylength = ((*keylength & 0xff) << 24) + ((*keylength & 0xff00) << 8) + ((*keylength & 0xff0000) >> 8) + ((*keylength & 0xff000000) >> 24); if (*keylength > keychar_size) { MessageBox(NULL, "error: key.bin文件格式错误", "错误", MB_OK); } else if (*keylength) { fread(key, 1, *keylength, fp); } } else if (!stricmp(file, ".bmp")) { BITMAPFILEHEADER bmpheader; fread(&bmpheader, 14, 1, fp); if (bmpheader.bfType == 0x4d42) {//检查文件头 BITMAPINFOHEADER bmpinfo; fread(&bmpinfo, 40, 1, fp); //基本确认文件合法，输入密码长 if (bmpinfo.biHeight < *keylength) { MessageBox(NULL, "error: 密码字节数大于图片高度", "错误", MB_OK); } else {//执行操作 //分配生成密码的字节数（bmp图像每行按4字节对齐，对齐的字节也生成密码） int scansize = (((bmpinfo.biBitCount * bmpinfo.biWidth + 7) / 8 + 3) / 4 * 4) * (bmpinfo.biHeight / *keylength); char scanline[scansize]; //定位 fseek(fp, bmpheader.bfOffBits, SEEK_SET); //读取和生成密码 for (int i = 0; i < *keylength; i++) { fread(scanline, 1, scansize, fp); key[i] = getKey(scanline, scansize); } } } else { MessageBox(NULL, "error: 无法识别bmp文件文件头", "错误", MB_OK); } } else { MessageBox(NULL, "error: 不能识别该类型文件(只能识别bmp和bin)", "错误", MB_OK); } } else { MessageBox(NULL, "error: 文件未打开", "错误", MB_OK); } fclose(fp); return 0; } DLLIMPORT int FileDEnc(const char *filename, const char *key, int keylength) { char *file; char sfname[strlen(filename) + 64], scan[scan_size]; int num; strcpy(sfname, filename); file = strrchr(sfname, '.'); if (!file || !isenc(file)) { strcpy(sfname + strlen(sfname), ".加密文件"); } else { *file = '\0'; } FILE *ifp = fopen(filename, "rb"), *ofp = fopen(sfname, "wb"); if (ifp) { while (!feof(ifp)) { num = fread(scan, 1, scan_size, ifp); strdenc(scan, num, key, keylength); fwrite(scan, 1, num, ofp); } }else{ MessageBox(NULL, "error: 文件未打开", "错误", MB_OK); } fclose(ifp); fclose(ofp); return 0; } BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved) { switch (fdwReason) { case DLL_PROCESS_ATTACH: { break; } case DLL_PROCESS_DETACH: { break; } case DLL_THREAD_ATTACH: { break; } case DLL_THREAD_DETACH: { break; } } /* Return TRUE on success, FALSE on failure */ return TRUE; }