Basic Smart Card testing in Windows - c++

Question

I am attempting to simply test for the presence of a Smart Card in Windows. The goal is to have a "daemon" running that will perform an action whenever (and for the duration) a card is inserted.
I have zero experience with things of this nature. I have read the documentation for SCardStatus and such, but I don't understand how the whole API works so I'm a bit lost.
What would be most helpful for me is if someone has a very simple example of a complete program that simply tests for the presence of a card (preferably in C++ but I'll take what I can get!). I would be most appreciative. I don't need any card status other than it exists. Thanks!

Answer 1

if you work on windows you need to use WinSCard API, if you use unix, then use PCSC. These two APIs are very similar, because of standards, but WinSCard API is much bigger and gives much more functions to use. These two APIs are implemented with C language, but you can wrap them in C++ pretty easy. I just whant to point out if you gonna wrap those two APIs in to C++ to use it ever on windows AND on unix take a look at smart card protocols numerical values, those are different on these platforms.
Basics:
You need to establish context (its like creating smart card manager)
SCardEstablishContext
It takes 4 parameters but, for basic using, you need only 2, scope and pointer to context handle.
LPSCARDCONTEXT hSCardContext = NULL;
int ret = SCardEstablishContext(SCARD_SCOPE_USER, NULL, NULL, &hSCardContext);
if (ret != ERROR_SUCCES) ... // handle error
Smart card are grouped in different groups. So there is functions to work with groups, to create it and so on.
To get readers list (for basic applications you actually dont really need groups)
SCardListReaders
It takes 4 parameters, context, pointer to group, pointer to readers and pointer to reader count
you can use it lise this
char *szGroups = NULL;
long readers = 0;
int res = SCardListReaders(hSCardContext, szGroups, NULL, &readers);
// handle errors
you get readers count first. now you can allocate memory for actual readers.
szReaders = (char *) malloc(sizeof(char) * readers);
int res = SCardListReaders(hSCardContext, szGroups, szReaders , &readers);
Now you have list of readers connected.
You can connect to a reader like so
LPSCARDHANDLE hSCard = NULL;
long activeProtocols = 0;
int ret = SCardConnect(hSCardContext, myReader, SCARD_SHARE_EXCLUSIVE, SCARD_PROTOCOL_TX, &hSCard, &activeProtocols);
// .. handle errors
specify protocols, share mode, use SCARD_SHARE_EXCLUSIVE for share mode if youre working with sensitive stuff witch needs protection that OS wont interact with transactions.
Once again if you are wrapping for windows and unix ( unix does not have SCARD_PROTOCOL_TX protocol) but it is a representation of these two SCARD_PROTOCOL_T0 | SCARD_PROTOCOL_T1.
myReader is the name of connected reader. Like (LPCTSTR)"Dermalog LF10"
you get those reader names from SCardListReaders function.
now you are connected with a card. with SCARD_SHARE_EXCLUSIVE sharing dont forget to release the smart card context, because it will deadlock.
use SCardDisconnect to disconnect, it takes 2 parameters, SmartCard handle, and disposition, for basic application SCARD_LEAVE_CARD disposition should be ok. It specifies that you dont want to do anything special to the card, you dont want to eject or whatever.
Transactions are more complex, because you need to know SCard standards and what not. But i covered the basics.
Keep in mind that this code might not compile, you need to improve types, for windows you need to cast those types in WinAPI types, like LPCTSTR, that it wont complain and unix dont have such types so you need to work around these problems too.

Answer 2

This sample code assumes card readers are plugged in at the start, it does not handle a changing number of card readers.
Other than that, it simply spams the console with inserted / not inserted status of cards.
Please do not use this as-is in production code, most error checking is omitted and some shortcuts are taken to keep the code short(ish).
#pragma comment(lib, "winscard.lib")
#include <vector>
bool test()
{
DWORD dwReaders;
LPSTR szReaders = NULL;
SCARDCONTEXT hContext;
bool bRunning = true;
std::vector<const char*> cards;
LONG status = SCardEstablishContext(SCARD_SCOPE_USER, NULL, NULL, &hContext);
if( status != SCARD_S_SUCCESS ) {
return false;
}
dwReaders = SCARD_AUTOALLOCATE;
if( SCardListReadersA(hContext, NULL, (LPSTR)&szReaders, &dwReaders) == SCARD_S_SUCCESS ) {
LPSTR reader = szReaders;
while (reader != NULL && *reader != '\0') {
std::cout << "Reader name: '" << reader << "'" << std::endl;
cards.push_back( reader );
reader += strlen(reader)+1;
}
LPSCARD_READERSTATEA lpState = new SCARD_READERSTATEA[cards.size()];
for( size_t n = 0; n < cards.size(); ++n ) {
memset( lpState + n, 0, sizeof(SCARD_READERSTATEA) );
lpState[n].szReader = cards[n];
}
do {
status = SCardGetStatusChangeA( hContext, 500, lpState, cards.size() );
switch( status )
{
case SCARD_S_SUCCESS:
case SCARD_E_TIMEOUT:
for( size_t n = 0; n < cards.size(); ++n ) {
if( lpState[n].dwEventState & SCARD_STATE_PRESENT) {
std::cout << "'" << lpState[n].szReader << "' present" << std::endl;
} else {
std::cout << "'" << lpState[n].szReader << "' not present" << std::endl;
}
}
break;
default:
std::cout << "Other result: " << status << std::endl;
break;
}
Sleep( 1000 ); // do not spam too bad
} while( bRunning );
// only do this after being done with the strings, or handle the names another way!
SCardFreeMemory( hContext, szReaders );
}
SCardReleaseContext( hContext );
return true;
}