Cryptography Reference
In-Depth Information
2 Hardware Setup
In the following, we give a brief introduction to the physical characteristics of
the RFID technology employed in contactless smartcards. Then, our freely pro-
grammable emulator for contactless smartcards is presented.
2.1 RFID Technology
In a typical setup for contactless smartcards, a reading device generates a strong
Electro-Magnetic (EM) field at a frequency of 13.56 MHz for supplying the card
with energy for its operation. The readeractsasmaster,whilethecardserves
as slave, thus only the reader can start a communication and issue commands to
the card. The ISO 14443 standard specifies the physical characteristics, the data
modulation and other characteristics of contactless smartcards. For data trans-
mission, the reader encodes the bits using a pulsed Miller code and transmits it
by switching off the EM field for short periods of time. The data to be sent by
the card is encoded using a Manchester-code and is afterwards transmitted via
the EM field using load-modulation with a 847.5 kHz sub-carrier.
2.2 Our Emulator
For the security analyses in this paper, we developed a custom, freely pro-
grammable device termed “Chameleon”, which can emulate contactless smart-
cards compliant to the ISO 14443 standard in a stand-alone manner. Our em-
ulation device consists of off-the-shelf hardware and can be built for less than
$25. It is based on an Atmel ATxmega192A3 microcontroller [2,3] which provides
192 kB of program memory, 16 kB SRAM and 4 kB EEPROM memory. Using
an FTDI FT245RL chip [9], the ATxmega is able to communicate with a PC
via the Universal Serial Bus (USB). This communication link can be used for
debugging purposes and data manipulation at runtime. Figure 1 shows the first
version of our RFID emulation device.
We chose the ATxmega because it features a hardware acceleration of both
DES and AES-128. After loading the key and the data to the corresponding
registers, the ATxmega is able to perform a DES en- or decryption in 16 clock
Fig. 1.
Our stand-alone RFID emulation device
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