A User Centric Security Model for Tamper-Resistant Devices

7.3 UCTD Firewall
7.3.6 Cross-Device Application Sharing
In the Cross-Device Application Sharing (CDAS) architecture, a smart card acts like a
node that is registered with a centralised system. The centralised system in our proposal
is software running on a computer, mobile phone, or tablet, which is referred as Card
Application Management Software (CAMS) [32]. For a simplistic illustration, gure 7.5
shows two possibilities for the CDAS network.
In gure 7.5a, a mobile phone has three UCTDs and all of them are connected to a CAMS
hosted on the mobile phone. The CAMS can be hosted on an insecure platform and
it provides discoverability and interconnectivity to an individual UCTD connected to the
CAMS. By discoverability, we mean that a platform registers itself with the CAMS and thus
it becomes discoverable to all other platforms in the network. The interconnectivity deals
with the communication channel established between two (or more) UCTDs. Therefore,
gure 7.5a depicts a scenario in which multiple UCTDs are connected to a mobile phone,
and their interconnectivity and discoverability is handled by the CAMS installed on it.
Computer
CAMS
UCTDs
Cell Phone
CAMS
Cell Phone
Tablet
(a) Cell Phone with Multiple UCTDs
(b) UCTDs attached to different Platforms
Figure 7.5: Cross-Device Application Sharing network
On the other hand, gure 7.5b shows a situation in which dierent computing devices
(e.g. computers, mobile phones, and tablets) are connected with each other through their
CAMS. Each individual device may have multiple UCTDs that are registered to their
respective CAMS. Although gure 7.5b depicts the situation as if there is a single centralised
CAMS, this is incorrect, as each host device has its own CAMS and there are no
centralised CAMS. Therefore, if a particular device is not available, other devices can still
communicate with each other. In this scenario, a host device will discover and register
other computing devices. There are two possible situations. In the rst, each individual
host device advertises the connected smart cards to the entire network. In second case,
each host device only provides the details of its CAMS and not the smart cards registered
with it. For our proposed CDAM, we prefer the second arrangement as it provides better
privacy for individual smart cards.
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