The Effect of Eavesdropper's Statistics in Experimental Wireless Secret-Key Generation

This paper investigates the role of the eavesdropper's statistics in the implementation of a practical secret-key generation system. We carefully conduct the information-theoretic analysis of a secret-key generation system from wireless channel gains measured with software-defined radios. In particular, we show that it is inaccurate to assume that the eavesdropper gets no information because of decorrelation with distance. We also provide a bound for the achievable secret-key rate in the finite key-length regime that takes into account the presence of correlated eavesdropper's observations. We evaluate this bound with our experimental gain measurements to show that operating with a finite number of samples incurs a loss in secret-key rate on the order of 20%.Comment: Submitted to the IEEE Transactions on Information Forensics and Securit

A Survey on Secret Key Extraction Using Received Signal Strength in Wireless Networks

Secure wireless communications typically rely on secret keys, which are difficult to establish in an ad hoc network without a key management infrastructure. The channel reciprocity and spatial decorrelation properties can be used to extract secret key, especially in a Rayleigh fading channel. But the intervention of intermediate objects between the communication nodes reduces the strength of the secret key generated through such methods. Furthermore, the impact of small fluctuations also reduces the bit matching rate of such key agreement methods. This paper is based on the survey conducted on secret key generation from Received Signal Strength (RSS). By consider ing uniqueness property of RSS as base, various authors have proposed different methods for secret key extraction. Due to use of RSS for key extraction the existing systems suffer from predictable filter response at random period. The existing system also faces signal fading and drop in RSS because of intermediate object. By this survey we specify that even after generating high entropy bits for key extraction, there are considerable drawbacks in extracted key du e to intervention of intermediate objects and remarkable fading and drop in RSS

Analysis of Secret Key Randomness Exploiting the Radio Channel Variability

A few years ago, physical layer based techniques have started to be considered as a way to improve security in wireless communications. A well known problem is the management of ciphering keys, both regarding the generation and distribution of these keys. A way to alleviate such difficulties is to use a common source of randomness for the legitimate terminals, not accessible to an eavesdropper. This is the case of the fading propagation channel, when exact or approximate reciprocity applies. Although this principle has been known for long, not so many works have evaluated the effect of radio channel properties in practical environments on the degree of randomness of the generated keys. To this end, we here investigate indoor radio channel measurements in different environments and settings at either 2.4625 GHz or 5.4 GHz band, of particular interest for WIFI related standards. Key bits are extracted by quantizing the complex channel coefficients and their randomness is evaluated using the NIST test suite. We then look at the impact of the carrier frequency, the channel variability in the space, time, and frequency degrees of freedom used to construct a long secret key, in relation to the nature of the radio environment such as the LOS/NLOS character

Doctor of Philosophy

dissertationA fundamental characteristic of wireless communications is in their broadcast nature, which allows accessibility of information without placing restrictions on a user’s location. However, the ease of accessibility also makes it vulnerable to eavesdropping. This dissertation considers the security issues of spread spectrum systems and in this context, a secure information transmission system compromised of two main parts is presented. The first component makes use of the principle of reciprocity in frequency-selective wireless channels to derive a pair of keys for two legitimate parties. The proposed key generation algorithm allows for two asynchronous transceivers to derive a pair of similar keys. Moreover, a unique augmentation - called strongest path cancellation (SPC) - is applied to the keys and has been validated through simulation and real-world measurements to significantly boost the security level of the design. In the second part of the secure information transmission system, the concept of artificial noise is introduced to multicarrier spread spectrum systems. The keys generated in the first part of the protocol are used as spreading code sequences for the spread spectrum system. Artificial noise is added to further enhance the security of the communication setup. Two different attacks on the proposed security system are evaluated. First, a passive adversary following the same steps as the legitimate users to detect confidential information is considered. The second attack studies a more sophisticated adversary with significant blind detection capabilities