The Architecture of Electronic Data Carriers - RFID: Fundamentals and Applications in Contactless Smart Cards and Identification - page 286

of data. The resulting necessity of being able to quickly and simply calculate complex
cryptographic algorithms led to the development of powerful cryptographic coproces-
sors on the card chips.
Contactless smart cards, on the other hand, are traditionally used in applications that
require a combination of user-friendliness (access control) and short transaction times
(ticketing). The trend towards combining payment applications with typical contactless
applications (cash card with ticketing function) finally led to the development of the
dual interface card , in which both a contact and a contactless interface are available
on one chip. A dual interface card can thus be addressed either via the contactless or
the contact interface.
The philosophy underlying the dual interface card is that the smart card interface is
completely independent of the smart card logic or smart card software. The interface,
whether contact or contactless, is completely transparent to the transmitted application
data so that, from the point of view of the application software, the interface used
is unimportant. The interface is thus exchangeable at will, and interface and logic
components can be combined as desired. The greatest advantage of the dual inter-
face card for the user and system operator is the option of being able to draw upon
existing infrastructure (generally contact readers) when introducing new applications.
Also, from the point of view of the security requirements of a smart card, there is no
difference between a contact and a contactless smart card. Due to the transparency of
the interface, the replay and fraud of security-related data that has been transmitted is
effectively ruled out by the methods defined in ISO/IEC 7816 (e.g. 'secure messaging'),
regardless of the interface used. See Figures 10.26 and 10.27.
The greatest difference between a contactless and a contact smart card is the power
available. A contactless smart card in accordance with ISO 14443 has only around
5mW available for operation at the maximum distance from the reader ( H min =
1 . 5A/m)(Muhlbauer, 2001). A contact smart card, on the other hand, may have 7.2mW
(GSM 11.13), 50mW (GSM 11.11) or even up to 300mW (ISO 7816-3 Class A: 5 V,

Combi-card in
Planar Embedded Coil Technology
Reinforcement and contact ring

Chip module with
contact surface

Interconnection of
ring with module

Interconnection of
ring with module

Upper cover sheet

Inlet sheet

Lower cover sheet

Coil wire end
connected to ring

Embedded coil Coil wire end

connected to ring

AmaTech

Figure 10.26 Possible layout of a dual interface smart card. The chip module is connected
to both contact surfaces (like a telephone smart card) and a transponder coil (reproduced by
permission of Amatech GmbH & Co. KG, Pfronten)