Monitoring the WinScard system calls and APDUs in a PC SC application in Windows

Introduction

On a Windows computer, all smart card-enabled applications communicate with smart cards via the system's PC/SC library, winscard.dll. winscard.dll internally communicates with the PC/SC service, which in turn communicates with the reader's driver, and finally the reader communicates with the card.

API Monitor is a free tool that lets you monitor and control Windows API calls made by applications and services. Using API Monitor, it is possible to view all WinSCard API function calls made by the application, including the APDUs exchanged with the card within SCardTransmit.

Installing and configuring API Monitor

1. Download and unzip the portable API Monitor ZIP file from http://www.rohitab.com/apimonitor.
2. Amend the following API metadata XML files in the extracted API folder (source: MySmartLogon) to make function call dwDisposition parameters symbolic and designate the variables that contain SCardTransmit APDU buffers' length.
   1. In scard.h.xml, add the following variable:

      <!-- [SCARD_DISPOSITION] -->
      <Variable Name="[SCARD_DISPOSITION]" Type="Alias" Base="LONG">
          <Display Name="LONG" />
          <Enum>
              <Set Name="SCARD_LEAVE_CARD"   Value="0" />
              <Set Name="SCARD_RESET_CARD"   Value="1" />
              <Set Name="SCARD_UNPOWER_CARD" Value="2" />
              <Set Name="SCARD_EJECT_CARD"   Value="3" />
          </Enum>
      </Variable>

   2. In winscard.xml, amend the following three functions:

      <Api Name="SCardDisconnect">
          <Param Type="SCARDHANDLE" Name="hCard" />
          <Param Type="[SCARD_DISPOSITION]" Name="dwDisposition" /> <!-- replace type -->
          <Return Type="[SCARD_ERROR]" />
      </Api>
      <Api Name="SCardEndTransaction">
          <Param Type="SCARDHANDLE" Name="hCard" />
          <Param Type="[SCARD_DISPOSITION]" Name="dwDisposition" /> <!-- replace type -->
          <Return Type="[SCARD_ERROR]" />
      </Api>
      
      <Api Name="SCardTransmit">
          <Param Type="SCARDHANDLE" Name="hCard" />
          <Param Type="LPCSCARD_IO_REQUEST" Name="pioSendPci"/>
          <Param Type="LPCBYTE" Name="pbSendBuffer" Count="cbSendLength" /> <!-- add count -->
          <Param Type="DWORD" Name="cbSendLength" />
          <Param Type="LPSCARD_IO_REQUEST" Name="pioRecvPci" />
          <Param Type="LPBYTE" Name="pbRecvBuffer" PostCount="pcbRecvLength" /> <!-- add post count -->
          <Param Type="LPDWORD" Name="pcbRecvLength" />
          <Return Type="[SCARD_ERROR]" />
      </Api>