Question

I’m trying to use an API under Delphi. Here’s the API documentation:

OKERR ENTRY SCardCLMifareStdAuthent 
    (IN SCARDHANDLE ulHandleCard,IN ULONG ulMifareBlockNr,
    IN UCHAR ucMifareAuthMode,IN UCHAR ucMifareAccessType,IN UCHAR ucMifareKeyNr,
    IN PUCHAR pucMifareKey,IN ULONG ulMifareKeyLen);

Whereas pucMifareKey:

A pointer to the six byte Mifare key.

The code I’ve been trying so far:

function Auth():Integer;
type
  TSCardCLMifareStdAuthent = function(SCARDHANDLE: cardinal; ulMifareBlockNr: ULONG;
   ucMifareAuthMode, ucMifareAccessType, ucMifareKeyNr: byte; pucMifareKey: puchar;
   ulMifareKeyLen: cardinal):LONG;
var
  SCardCLMifareStdAuthent: TSCardCLMifareStdAuthent;
  hDLL: Integer;
  CardHandle: cardinal;
  i: integer;
  Key: array of UCHAR;
begin
  Result:=1;
  //CardHandle is defined here
  SetLength(Key, 6);
  for i := low(key) to high(key) do
    Key[i] := $FF;
  hDLL := LoadLibrary('scardsyn.dll');
  @SCardCLMifareStdAuthent := GetProcAddress(hDLL, 'SCardCLMifareStdAuthent');
  if @SCardCLMifareStdAuthent <> nil then
    Result:=SCardCLMifareStdAuthent(CardHandle, $00, 96, 0, 0, ^Key, 6);
  FreeLibrary(hDLL);
end;

The error I’m getting is:

Incompatible types: ‘Byte’ and ‘Char’ at the line of
`Result:=SCardCL…. ` due ^Key pointer.

Any ideas?

Answer 1

I don’t know the DLL in question, but for a Delphi pre 2009 I would do the following:

function Auth: integer;
type
  TSCardCLMifareStdAuthent = function(SCARDHANDLE: cardinal;
    ulMifareBlockNr: ULONG; ucMifareAuthMode, ucMifareAccessType,
    ucMifareKeyNr: byte; pucMifareKey: PAnsiChar;
    ulMifareKeyLen: Cardinal): longint;
var
  SCardCLMifareStdAuthent: TSCardCLMifareStdAuthent;
  hDLL: Integer;
  CardHandle: Cardinal;
  Key: string;
begin
  Result := 1;
  //CardHandle is defined here...
  Key := StringOfChar(Chr($FF), 6);
  hDLL := LoadLibrary('scardsyn.dll');
  if hDLL <> 0 then begin
    @SCardCLMifareStdAuthent := GetProcAddress(hDLL, 'SCardCLMifareStdAuthent');
    if @SCardCLMifareStdAuthent <> nil then begin
      Result := SCardCLMifareStdAuthent(CardHandle, $00, 96, 0, 0,
        PChar(Key), Length(Key));
    end;
    FreeLibrary(hDLL);
  end;
end;

The access violation you get probably comes from the C string not being 0-terminated. Using a string and casting it to PChar will make things easier.