1. Secure Space: Location-based Secure Wireless Group Communication Arunesh Mishra, Suman Banerjee Department of Computer Science, University of Maryland, College Park, MD 20742, USA

2. Introduction(1/1) We define “Secure Space” as an enclosed area within which wireless devices can participate in secure group communication. There are two important problem for this discussion --- (a) determining and authenticating the location of a wireless device at the granularity of a secure space, and (b) defining scalable mechanisms to (re)- distribute a common group key among the device inside the secure space, as new devices enter and existing devices leave the space.

3. Location Determination and Authentication System (LDAS)(1/2) We define a LDAS using RF signal-strength based techniques. Our scheme requires the use of one or more trusted wireless device in the infrastructure. The trusted devices transmit beacon frames on the wireless channel and the untrusted devices are authenticated if they can prove to the LDAS that they “correctly” received these frames. We create a radio map of the space. The untrusted device must present a signal strength tuple back to the LDAS, where the tuple consists.

4. Location Determination and Authentication System (LDAS)(2/2) The LDAS checks if the received signal strength value matches the corresponding value in the radio map, for each of the beacons, in which case the location is identified and considered authenticated, else the authentication is failure. The power is picked randomly based upon the anonymity of the beacon source, as well as the use of random power value with which the beacon is transmitted. Without this information it is not possible for untrusted devices that are external to the LDAS to infer the correct signal-strength tuple for any other location.

5. LDAS example(1/1) Consider the two trusted devices T 1 and T 2 that broadcast two beacon frames b 1 and b 2. There are two untrusted devices, U 0 and U 1, are waiting for being authenticated. Step1 : b 1 and b 2 randomly choose two power value, say 100mW and 10mW. Step2 : U 0 receives the signal which is powered 60mW from b 1 and 2mw from b 2, and U 1 receives the signal which is powered 20mW from b 1 and 6mW from b 2. Step3 : If U 0 and U 1 returns the signal strength tuples as {, } and {, } Then they are authenticated with respect to the radio map available at LDAS, and their location are correctly determined.

6. Simplified example of the LDAS in one dimension

7. Secure Wireless Group Communication(1/1) Single group key Group re-keying