Приведение типов!

 HCRYPTPROV hProv=0;
 HCRYPTKEY hKey=0;
 //--ïîäêëþ÷åíèå ê êðèïòîïðîâàéäåðó
 
 if(CryptAcquireContext(&hProv,NULL, NULL,PROV_RSA_FULL,0)==0)
  {
   Memo1->Lines->Add("Íå óäàëîñü ïîäêëþ÷èòüñÿ ê êðèïòîïðîâàéäåðó");
   Memo1->Lines->Add("----------------------------");
  }
 else
 {//--èìïîðò ñåêðåòíîãî êëþ÷à
   FILE *hFile=fopen("PrKey.txt","r");
   DWORD Length=NULL;
   unsigned char *buf=NULL;
   fread(&Length,sizeof(DWORD),1,hFile);
    buf=(unsigned char*)malloc(Length);
   fread(buf,Length,1,hFile);
 
 
  if(CryptImportKey(hProv,buf,Length,0,0,&hKey)==0)
  { LPVOID lpMsgBuf;
 
FormatMessage(
    FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
    NULL,
    GetLastError(),
    MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), // Default language
    (LPTSTR) &lpMsgBuf,
    0,
    NULL
);
 
// Display the string.
MessageBox( NULL,(LPCTSTR) lpMsgBuf, "GetLastError", MB_OK|MB_ICONINFORMATION );
 
// Free the buffer.
LocalFree( lpMsgBuf );
   Memo1->Lines->Add("Íå óäàëîñü èìïîðòèðîâàòü ñåêðåòíûé êëþ÷");
   Memo1->Lines->Add("----------------------------");
  }
 }

buf=(unsigned char*)malloc(Length)

buf=reinterpret_cast <unsigned char*>(malloc(sizeof(Length) ) )

buf=reinterpret_cast <unsigned char*>(malloc(sizeof(Length) ) )