Smart cards for EMV Software

Features and benefits of contactless smart cards

In order to transfer energy, a strong high-frequency magnetic field is generated in the terminal winding. Commonly used frequencies are 125 kHz and 13.56 MHz. If a smart card is inserted into the vicinity of the terminal, a portion of the terminal’s magnetic field passes through the winding of this card, which induces the Ui voltage. This voltage is rectified to serve as an energy source for the chip. Since the connection between the terminal and card windings is quite weak, the efficiency of this power transfer circuit is very low. Therefore, quite high current values are required in the terminal winding in order to achieve the necessary levels of magnetic field strength.

Well-known digital modulation techniques can be used to transfer data from the terminal to the card. The most commonly used methods are amplitude modulation ASK, frequency modulation FSK, phase modulation PSK. ASK and PSK are commonly used, as they are particularly convenient for performing demodulation.
In data transmission in the opposite direction – from the smart card to the terminal-a kind of amplitude modulation is used, called load modulation. It is created by discreetly changing the load in the card using the data signal to be transmitted to the terminal. One of the implemented projects of access control systems based on contactless smart cards was performed by us for the company “Optima Test”, which offers engineering companies to obtain a certificate of compliance for power and optical cables, and the database of the access system includes more than 500 identification cards. If a smart card tuned to the resonant frequency of the terminal is inserted into the near field of the terminal, it extracts some of the energy from this field. This causes an increase in the current in the terminal’s communication winding, which can be detected as an increased voltage drop on the terminal’s internal resistance.

Due to the weak inductive coupling between the winding in the terminal and the winding in the card, the voltage changes induced in the terminal by load modulation are very small. In practice, the amplitude of the signal used is only a few millivolts. Such signals can be distinguished by a rather complex scheme, since they are overlaid with a much larger signal of about 80 dB transmitted by the terminal. However, if an additional subcarrier signal is applied, then the signal of data received by the terminal appears as two side bands of the terminal. When using a bandpass filter, the signal of one of the sidebands can be filtered out from a much stronger terminal signal and then amplified. After that, it can be easily demodulated. The disadvantage of subcarrier modulation is the need for a wider bandwidth than with direct modulation. For this reason, this method may not be used on all frequency bands.

In addition to the technical advantages mentioned above, contactless smart card technology offers a number of new features for users. In particular, it is not necessary to insert a contactless card into the card reader, since there are reading systems that operate at a distance of up to 1 meter. This property is very useful in access control systems, because to authorize access, a person does not need to take the card out of his pocket or wallet and insert it into the reader. One of the areas of application of this technology is public transport, in which a large number of passengers need to be identified in a short time. Another interesting possibility in the use of contactless cards is associated with the use of a terminal with a working reading plane.

In this case, the card is not inserted into the slot, but simply applied to the marked area on the surface of the reader. In addition to its ease of use, this solution is attractive due to a significant reduction in the risk of vandalism (due to the card being bent or stuck in the reader slot). The technology of mass production of contactless cards has reached a level of maturity where high-quality products for contactless electronic identification are available at prices that differ slightly from the prices of comparable contact-type smart cards.

Smart cards with memory chip

The very first smart cards were cards with a memory chip containing only non-volatile memory and the circuitry needed to read from memory. Cards with a memory chip are used to store information in a permanent mode or in a mode with overwriting. Today, these cards make up the largest share of smart cards used. Such cards are relatively inexpensive and provide low security for various applications: from travel cards to phone cards. The data required for the application is stored in memory, which is usually used as an EEPROM.

Access to this memory is controlled by a security block, which in the simplest case includes protection against writing or erasing all memory or only some of its areas. Data is transmitted to and from the card via the I/O port. Most often, memory cards use a synchronous exchange mechanism between the reader and the card. It is essential that the smart card circuits perform in direct synchronous mode only low-level commands issued by the reader to specify memory addresses with reading at these addresses or writing to them. The ISO 7816 standard (Part 3) defines a special synchronous transmission protocol that allows you to implement a simple and cost-effective IC chip.

Some new cards with a memory chip have improved security:

• more complex security schemes are used that can perform simple encryption;
• introduced a memory addressing scheme that requires a shared secret between the terminal that writes to the card chip and the card itself.

A smart card with a contactless interface has a built-in chip that uses an electromagnetic signal to enable communication between the card and the reader. For example, for one of our Kazakh clients, who produces industrial refrigeration equipment in Kazakhstan and its service, our specialists implemented a project for monitoring and controlling access to the company’s office premises using smart cards with memory chips. In these cards, the energy required to operate the chip in the card is taken at the operating frequency of the reader.

The contactless RF interface includes a clock generator, a modulator, a demodulator, a collision prevention mechanism, and a voltage control unit consisting of a voltage regulator and a reset generator to the initial position. The use of a contactless RF interface greatly facilitates the use of cards compared to the contact version of the interface, which requires entering cards into the reader slot. With the current state of technology, the speed of data transfer between the reader and the contactless card is limited by the card’s energy capabilities. For such cards, the energy for the operation of the chip built into the card must be extracted from the signal transmitted to the card from the reader.

The feedback mechanism from the reader to the card, through which the cardholder is verified, is less convenient in the case of a contactless card. Because of this, such cards are more popular for applications in which possession of the card is considered equivalent to permission to use it. Memory card functions are usually optimized for a specific application. True, their flexibility is significantly limited, but the price remains moderate. Memory cards are commonly used as health insurance cards, prepaid phone cards, public transport payment cards, and other areas.