Seite 10: Listing 6

Inhaltsverzeichnis

Listing 6: processDecompression() dekodiert eine Datei

int processDecompression(char *fileName) {
    FILE    *ifp, *ofp;
    int        i, l, ch;
    DWORD    dwDestLen;
    uchar    hdr[MD5LEN], originalFileName[300], *outputBuffer;

    if ((ifp=fopen(fileName,"rb"))==NULL) {
        fprintf(stderr,"unable to open file \"%s\"\nfopen(): 
             %s\n", fileName, strerror(errno));
        return -1;
    }
    fread(hdr, 1, 3, ifp);
    if (memcmp(hdr, magicHdr, 3) || ((ch=fgetc(ifp))!=0x80 && ch!=0x81)) {
        fprintf(stderr,"invalid magic header - 
             probably not compressed with this program!\n");
        fclose(ifp);
        return -1;
    }
    isCrypt=(ch == 0x81);
    if (isCrypt) {
        if (!passwd) {
            fprintf(stderr,"File %s is encrypted but no password
               has been given in the command line\n", fileName);
            fclose(ifp);
            return -1;
        }
        fread(hdr, 1, MD5LEN, ifp);
        if (memcmp(hdr, getMD5Hash(passwd, strlen(passwd)), MD5LEN)) {
            fprintf(stderr,"wrong password!\n");
            fclose(ifp);
            return -1;
        }
    }
    /**
     * now create the output file
     * extract the filename for the original file ...
     */
    l=fgetc(ifp);
    for (i=0;i<l;i++) {
        originalFileName[i] = fgetc(ifp) ^ ~rand();
    }
    originalFileName[i]=0;
    if (access(originalFileName, 0)>=0 && !isForce) {
        fprintf(stderr,"File \"%s\" exists!\nUse 
            -f option to force overwrite!\n", originalFileName);
        fclose (ifp);
        return -1;
    }
    if ((ofp=fopen(originalFileName, "wb"))==NULL) {
        fprintf(stderr,"unable to open file \"%s\"\nfopen(): 
            %s\n", originalFileName, strerror(errno));
        return -1;
    }
    /**
     * now read the input BlockSize
     */
    blockSizeKB=(fgetc(ifp)|(fgetc(ifp))<<8);
    outputBuffer=malloc(blockSizeKB*1024);
    if (isDebug) fprintf(stderr,"Input Block Length = %d KB\n", blockSizeKB);
    for (;;) {
        uchar *inputBuffer;
        int blockLength=0;

        if (fread(hdr, 1, 4, ifp)<4) break;    // EOF
        if (isDebug)
            fprintf(stderr,"block length bytes: %02x %02x %02x %02x\n",
                  hdr[0], hdr[1], hdr[2], hdr[3]);
        for (i=3;i>=0;i--) {
            blockLength <<= 8;
            blockLength |= hdr[i];
        }
        if ((inputBuffer=malloc(blockLength))==NULL) {
            fprintf(stderr,"unable to allocate %d 
                  bytes for the input buffer!\nmalloc() returned %d: %s\n",
                blockLength, errno, strerror(errno));
            fclose(ifp);
            return -1;
        }
        if (fread(inputBuffer, 1, blockLength, ifp)<blockLength) 
                   { // unexp. EOF
            fprintf(stderr,"unexpected EOF reading from input file!\n");
            fclose(ifp);
            return -1;
        }
        dwDestLen=blockSizeKB*1024;
        if (isCrypt) {
            /**
             * block has to be de-crypted here ...
             */
#ifdef WIN32
            bool    bResult;
            DWORD    dwSize;
            HCRYPTPROV    hProv;
            HCRYPTHASH    hHash;
            HCRYPTKEY    hKey;

            if (!CryptAcquireContext(&hProv, NULL, MS_DEF_PROV, 
                PROV_RSA_FULL, 0)) {
                fprintf(stderr,"CryptAcquireContext() FAILED!\n");
                return -1;
            }
            if (!CryptCreateHash(hProv, CALG_MD5, 0, 0, &hHash)) {
                fprintf(stderr,"CryptCreateHash() FAILED!\n");
                return -1;
            }
            if (!CryptHashData(hHash, passwd, strlen(passwd), 0)) {
                fprintf(stderr,"CryptHashData() FAILED!\n");
                return -1;
            }
            if (!CryptDeriveKey(hProv, CALG_RC4, hHash, 
                  CRYPT_EXPORTABLE, &hKey)) {
                fprintf(stderr,"CryptDeriveKey() FAILED!\n");
                return -1;
            }
            dwSize=blockLength;
            if (!CryptDecrypt(hKey, 0, TRUE, 0, inputBuffer, &dwSize)) {
                fprintf(stderr,"CryptDecrypt(2) FAILED!\n");
                return -1;
            }
            blockLength=dwSize;
            CryptDestroyKey(hKey);
            CryptDestroyHash(hHash);
            CryptReleaseContext(hProv, 0);
#endif
        }
        if ((l=uncompress(outputBuffer, &dwDestLen, inputBuffer,
              blockLength))!=Z_OK) {
            fprintf(stderr,"uncompress() failed with %d - 
                dwDestLen=%d!\n", l, dwDestLen);
            fclose(ifp);
            return -1;
        }
        fwrite(outputBuffer, 1, dwDestLen, ofp);
        free(inputBuffer);
    }
    fclose(ifp);
    fclose(ofp);
    return 1;
}