Smart cards - basic principles
a. ISO norms - ISO7816-X
ISO7816-1 specifies the physical characteristics of integrated circuit like the limits to X-rays, UV, electromagnetic field, ambient temperature etc. Additionally, properties of smart card in flexion and robustness of contacts are specified. Important mainly for card manufactures.
ISO 7816-2 defines size, location and function of the card contacts. Vcc - power supply, RST - card reset, CLK - external clock signal, GND - ground, Vpp -programming power supply for older types of EEPROM (not used now), I/O - data communication, 2 contacts reserved for future use.
ISO7816-3 specifies communication protocol between smart card and reader on the level of the electrical signals.
• Protocol T=0 - byte-oriented protocol. Older than T1, designed for maximal simplicity and minimal memory requirements. Error detection only on parit bits level. Used in GSM cards.
• Protocol T=1 - asynchronous, half-duplex, block-oriented. Support layers separation (transport layer in OSI model).
ISO7816-4 specifies:
• Content of messages, commands and responses as are transported to card and back.
• Structure and content of historical bytes send as response after RESET command (ATR).
• Methods for accessing files and data on the card and algorithms offered by card.
• Methods for the secure messaging.
b. APDU (Application Protocol Data Unit)
APDU is basic logical communication datagram, which allows to carry up to ~260 bytes of data and contains header with possibility to specify target application on smart card which should process given APDU.
CLA	INS	PI	P2			
						
CLA	INS	PI	F2	La		
						
CLA	INS	P1	P2	Lc	Dote	
						
CLA	INS	PI	P2	Lc	Data	Le
figure 1 - APDU types
CLA - instruction class, INS - instruction number, PI, P2 - optional data, Lc - length of incoming data, Le - length of the expected output data.
Communication with smart cards
a. PC/SC for Windows, PC/SC-Lite for Linux
The PC/SC Specification builds upon existing industry smart card standards - ISO 7816 and EMV - and compliments them by defining low-level device interfaces and device-independent application APIs as well as resource management, to allow multiple applications to share smart card devices attached to a system. See picture figure 2 for overview.
figure 2 - Windows PC/SC architecture overview
Sending and receiving APDU commands in Windows
There is the Win32 API for communicating with smart cards within Windows platform in form SCardXXX. Similar implementation for Linux is developed under Muscle project as PC/SC Lite API. We will work within Windows platform. Following functions will be used:
• SCardEstablishContext
• SCardListReaders
• SCardConnect
• SCardReconnect
• SCardDisconnect
• SCardReleaseContext
• SCardTransmit
void CardConnect(APDU apdu) {
SCARDCONTEXT cardContext = NULL;
SCARDHANDLE  hCard; // OPENED SESSION HANDLE
DWORD scProtocol; char* readers = NULL;
// ESTABLISHING CONTEXT OF CARD DATABASE TO BE SEARCHED WITHIN SCardEstablishContext(SCARD_SCOPE_USER,0,0,&cardContext);
// LIST AVAILABLE READERS (readers NULL SEPARATED ARRAY) SCardListReaders(cardContext, NULL, (char *) &readers, &len));
// ... PARSE AND SELECT ONE READER INTO targetCard
// CONNECT TO CARD WITH NAME targetCard
SCardConnect(m_cardContext, targetCard, SCARD_SHARE_EXCLUSIVE, SCARD_PROTOCOL_T0 | SCARD_PROTOCOL_T1, &hCard, &scProtocol));
// ... WORK WITH CARD
// RESET CARD (POWER IS TURNED OFF AND THEN ON) // CARD IS IN DEFAULT STATE (NO SELECTED APPLETS...)
SCardReconnect(m_hCard, SCARD_SHARE_EXCLUSIVE, SCARD_PROTOCOL_T0 |
SCARD_PROTOCOL_T1, SCARD_UNPOWER_CARD, &m_scProtocol)); // DISCONNECT FROM CARD AND RELEASE CONTEXT
SCardDisconnect(m_hCard, SCARD_LEAVE_CARD); SCardReleaseContext(cardContext);
}
Function CardConnect() establish context, list all available readers, connect to selected smart card, reconnect and finally release connection to smart card.
High level function ExchangeAPDU() send APDU to smart card and handle situation when some output data are prepared on smart card and should be received. Specific APDU with CLA=0x00 and INS=0xC0 is used to obtain response data. Internally, TransmitAPDU() function is called to directly exchange one single apdu command.
void ExchangeAPDU(APDl) pAPDU) {
// CLEAR SOFTWARE RETURN STATUS pAPDU->sw = SW_NO_ERROR;
// SEND APDU
if ((status = TransmitAPDU(pAPDU)) == STAT_OK) { // CHECK FOR SOFTWARE ERROR if (pAPDU->sw == SW_NO_ERROR) {
// NO SOFWARE ERROR
}
else {
// CHECK FOR 'RESPONSE DATA AVAILABLE' STATUS if ((pAPDU->sw & 0xFF00) == SW_BYTES_REMAINING_00) { if (pAPDU->lc == 0x00) {
// SYSTEM CALL TYPE TO OBTAIN RESPONSE OUTPUT DATA)
// INSUFFICIENT OUTPUT DATA LENGTH
BYTE realLen = LOWBYTE(pAPDU->sw);
pAPDU->le = realLen;
// NEW APDU WITH REQUIRED OUTPUT DATA LENGTH
status = ExchangeAPDU(pAPDU);
}
else {
// USER CALL TYPE, OBTAIN RESPONSE DATA
BYTE     realLen = LOWBYTE(pAPDU->sw); CARDAPDU apdu;
// PREPARE SYSTEM APDU FOR RECIEVE RESPONSE OUTPUT DATA
apdu.cla = 0x00;
apdu.ins = 0xC0;
apdu.pl = 0x00;
apdu.p2 = 0x00;
apdu.lc = 0x00;
apdu.le = realLen;
if ((status = ExchangeAPDU(&apdu)) == STAT_OK) { // COPY RECIEVED APDU
memcpy(pAPDU->DataOut, apdu.DataOut, apdu.le); pAPDU->le = apdu.le;
}
}
}
else {
// CHECK FOR 'CORRECT DATA LENGTH' STATUS
if ((pAPDU->sw & 0xFF00) == SW_CORRECT_LENGTH_00) {
pAPDU->le = LOWBYTE(pAPDU->sw);
}
else {
// SOFTWARE ERROR OCCURED
status = TranslateISO7816Error(pAPDU->sw);
}
}
}
}
}
void TransmitAPDU(APDU pAPDU) { DWORD outLen = pAPDU->le;
BYTE sendData[260]; BYTE responseData[260];
// CLEAR SEND AND RESPONSE STRUCTURES pAPDU->le = 0;
memset(sendData, 0, sizeof(sendData)); memset(responseData, 0, sizeof(responseData));
// TRANSFORM APDU STRUCTURE INTO ARRAY
sendData[0] = pAPDU->cla;
sendData[l] = pAPDU->ins;
sendData[2] = pAPDU->p1;
sendData[3] = pAPDU->p2;
sendData[4] = pAPDU->lc;
memcpy(sendData + 5, pAPDU->DataIn, pAPDU->lc); outLen = 4;
// SEND APDU USING SCardTransmit FUNCTION ACCORDING TO TRANSMISSION PROTOCOL switch (m_scProtocol) {
case SCARD_PROTOCOL_T0: SCardTransmit(m_hCard, SCARD_PCI_T0, sendData, sendData[4] + 5,
NULL, responseData, &outLen)); break; case SCARD_PROTOCOL_T1: SCardTransmit(m_hCard, CARD_PCI_T1,
sendData, sendData[4] + 5, NULL, responseData, &outLen)); break;
}
// COPY SOFTWARE STATUS
((BYTE*) &(pAPDU->sw))[0] = responseData[1];
((BYTE*) &(pAPDU->sw))[1] = responseData[0];
// RECEIVE RESPONSE DATA, IF ANY
if (((pAPDU->sw & 0xFF00) == SW_BYTES_REMAINING_00) || ((pAPDU->sw & 0xFF00) == SW_CORRECT_LENGTH_00)) { // GET DATA APDU (FORM SPECIAL APDU FOR RECEIVING DATA)
sendData[0] = 0xC0; sendData[1] = 0xC0; sendData[2] = 0x00; sendData[3] = 0x00; sendData[4] = LOWBYTE(pAPDU->sw);
outLen = sendData[4] + 2; // DATA OUT + STATUS // ... SEND APDU (SEE ABOVE)
// COPY RECEIVED DATA
memcpy(pAPDU->DataOut, responseData, outLen - 2); pAPDU->le = outLen - 2;
((BYTE*) &(pAPDU->sw))[0] = responseData[outLen - 1]; // LAST BYTE ((BYTE*) &(pAPDU->sw))[1] = responseData[outLen - 2]; // PRE LAST BYTE
}
}
References
[JC221] Java Card specification 2.2.1 http://j ava.sun.com/products/j avacard/ [JPCSC]       JPC/SC API
http://www.linuxnet.c0m/middleware/files/jpcsc-O.8.O-src.zip