Spatial Authentication Using Cell Phones

Introduction

Cellular phones are becoming ubiquitous telecommunication devices. These are portable wireless devices and connect to the network through RF communication. Due to their low cost and multitude of features, these phones have been transformed from expensive equipment used for business to a low cost personal item. It is estimated that there are over two billion cell phones worldwide (Cellularonline, 2007). These phones typically have low power transceivers which typically transmit data and voice up to a few miles where the mobile tower (base station) is located. This base station connects the cellular phone to the backbone telephone network. The mobile phones cannot communicate when they are unable to connect to the base station.

The capabilities of these phones have also increased dramatically over the last few years. In addition to the standard telephone features, the phones also Instant Messaging, MMS, Internet access, and so on. More advanced features like music and video streaming, digital camera, and document scanner are being bundled with the cell phone. These features have transformed the cell phone from a simple phone to a digital Swiss army knife.

More advanced features like Bluetooth, IR have been added to allow the cell phone to connect with other devices. Avaya, Motorola, and Proxim are planning to introduce a new class of mobile phones called dual phones (Brewin, 2004; Hochmuth, 2004). These phones will be able to make voice calls over the cellular network and the 802.11a WLAN networks. The advantage of using this phone is that the user can make calls through the WLAN infrastructure when he is able to connect to the WLAN. This would save money because the cell phone user would be able to use the WLAN minutes for free. The companies have also developed the technology to “hand off” calls between the WLAN and cellular network. Cell phones can be developed which are able to connect to both the cellular network and the wireless devices. Such ability could enable them to be used in many applications.

There are many applications in wireless networks where access is granted to a user only when the user is located in certain predefined locations (Hansen & Oleshchuk, 2003; Mavridis, Georgiadis, & Pangalos, 2002; Toye, Sharp, Madhavapeddy, & Scott, 2005). For example, a doctor should be able to access the medical records only when he is located inside the hospital and not in cafeteria. In this scenario the doctor has access to the medical records only when he is located in a safe place like his office and not in a public place like the cafeteria. The server can be certain about the users’ location by using a trusted hardware sensor, which is able to determine if the cell phone is in its communication range. Another approach to be certain of the location of the phone is to have a tamper proof GPS module on the SIM card.

In this chapter we assume the cellular infrastructure to be secure. While we believe that security is always in relative terms and a work in progress, cellular networks are much more secure than the other networks like the internet. Vulnerabilities like GSM cloning are being addressed and the GSM are moving away from security by obscurity. 3GPP, which is the next generation of GSM will be using cryptographic primitives which are based out the existing research literature and open to public scrutiny (GSM cloning, 2007). Besides, we believe that cell phones being a multi-billion dollar industry have the resources to provide stronger guarantees for authentication, confidentiality and privacy if such applications are developed.