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Issue #211 February 2008
RFID Payment Terminal
by Carlos Cossio
Start | System Overview | Energy Transmission | 100% Amplitude Modulation | Load Modulation | MIFARE Card | MIFARE and ISO 14443 | Pay as You Go | Hardware Design | Antenna Design Rules | Antenna Size | Directly Matched Antenna | Firmware Design | Catch the Wave! | Sources & PDF
MIFARE CARD
MIFARE technology describes an ISO 14443 Type-A-compliant RF interface for communication between a reader and a contactless card at 13.56 MHz. The MIFARE card is connected to a coil with a few turns and then embedded in plastic to form the passive contactless smart card. No battery is needed. When the card is in the proximity of the RFID payment terminal antenna, the high-speed RF communication interface enables you to transmit data at 106 kbps.
An intelligent anti-collision function enables you to operate more than one card in the field simultaneously. The anti-collision algorithm selects each card individually and ensures that the execution of a transaction with a selected card is performed correctly without data corruption resulting from other cards in the field.
Special emphasis has been placed on security against fraud. Mutual challenge and response authentication, data ciphering, and message authentication checks protect the card from any kind of tampering, thus making it attractive for ticketing applications. Serial numbers, which cannot be altered, guarantee the uniqueness of each card.
The standard MIFARE card has a memory capacity of 1,024 bytes of EEPROM and is organized in 16 sectors with four blocks of 16 bytes each. The last block of each sector contains two secret keys and programmable access conditions for each block in the sector. Each sector can be seen as an application, so it is possible to support multiple applications with key hierarchy. Other members of the MIFARE family support memories ranging from 512 bytes to 4 KB.
After the power-on reset (PoR) of a MIFARE card, it can answer to a request command—sent by the RFID payment terminal to all cards in the antenna field—by sending the answer to request code (ATQA according to ISO 14443A).
In the anti-collision loop, the serial number of a card is read. If there are several cards in the operating range of the RFID payment terminal, they can be distinguished by their unique serial numbers. One can be selected (select card) for further transactions. The unselected cards return to the standby mode and wait for a new request command.
With the Select Card command, the RFID payment terminal selects one card for authentication and memory-related operations. The card returns the answer to select (ATS), which determines the type of selected card.
After a card is selected, the RFID payment terminal specifies the memory location of the following memory access and uses the corresponding key for the three-pass authentication procedure. After a successful authentication, all memory operations are encrypted.
After authentication, any of the following operations may be performed: read a block, write a block, decrement the contents of a block into a temporary register, increment the contents of a block into a temporary register, transfer the contents of the temporary register into a block, and restore the contents of a block into a temporary register. The commands are the basis for the electronic purse application I implemented in the RFID payment terminal.
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