How can I read 64-bit registry key from a 32-bit process?

Question

I\'ve been using the value of key MachineGuid from HKEY_LOCAL_MACHINE\\Software\\Microsoft\\Cryptography to uniquely identify hosts, but from 32-b

Answer 1

In my use of this registry key I went a step further. If the value didn't exist I created it: not in HKEY_LOCAL_MACHINE, that would require elevation, but in HKEY_CURRENT_USER. Anyone seeing the introduced key there is unlikely to realise that it's a dummy.

function GetComputerGUID: String;
var
  Reg: TRegistry;
  oGuid: TGUID;
  sGuid: String;
begin
  Result := '';
  // Attempt to retrieve the real key
  Reg := TRegistry.Create(KEY_READ OR KEY_WOW64_64KEY);
  try
    Reg.RootKey := HKEY_LOCAL_MACHINE;
    if Reg.OpenKeyReadOnly('SOFTWARE\Microsoft\Cryptography') and Reg.ValueExists('MachineGuid') then
      Result := Reg.ReadString('MachineGuid');
    Reg.CloseKey;
  finally
    Reg.Free;
  end;
  // If retrieval fails, look for the surrogate
  if Result = '' then begin
    Reg := TRegistry.Create;
    try
      Reg.RootKey := HKEY_CURRENT_USER;
      if Reg.OpenKey('SOFTWARE\Microsoft\Cryptography', True) then begin
        if Reg.ValueExists('MachineGuid') then
          Result := Reg.ReadString('MachineGuid')
        else begin
          // If the surrogate doesn't exist, create it
          if CreateGUID(oGUID) = 0 then begin
            sGuid := Lowercase(GUIDToString(oGUID));
            Reg.WriteString('MachineGuid', Copy(sGuid, 2, Length(sGUID) - 2));
            Result := Reg.ReadString('MachineGuid');
          end;
        end;
      end;
      Reg.CloseKey;
    finally
      Reg.Free;
    end;
  end;
  if Result = '' then
    raise Exception.Create('Unable to access registry value in GetComputerGUID');
end;

That's a good point from @Remy Lebeau - TeamB though; I should mod the above code appropriately.