Physical Layer Key Generation in Resource Constrained Wireless Communication Networks

Secure wireless communication between resource constrained devices in dynamic deployment scenarios poses a significant challenge to cryptography. This is primarily due to the fact that the dynamic nature of the device deployment environment calls for sophisticated key management strategies which usually require a trusted third party along with either a highly complex symmetric key management scheme or a public-key scheme. This places a significant burden on the computational resources of a node. Physical layer security (or Information theoretic security) aims to reduce this efficiency burden on devices and add an additional layer of location-based security. Physical layer key generation and refreshment is concerned with techniques for establishing and refreshing cryptographic keys using wireless communication channel measurements between legitimate nodes. Computational security-based public-key schemes usually derive their security on the basis of the difficulty of solving some mathematical problem such as prime number factorisation, discrete logarithm computation and the like. Practical physical layer-based schemes often derive their security on the difficulty of estimating particular wireless channel parameters with the exact same accuracy that a localised node can estimate them when you are not localised. In this thesis, the issue of Physical Layer Secure Key Generation (PLSKG) is dis- cussed and a novel pairwise PLSKG scheme and a novel Group Physical Layer Secure Key Generation (GPLSKG) scheme for resource constrained devices are proposed. The PLSKG scheme improves on the state of the art by proposing a key generation methodology that avoids the use of iterative quantisation for the purposes of key reconciliation, which reduces the loss of key entropy during the key reconciliation process. The proposed GPLSKG scheme improves on the state of the art by i) generating keys in a way that provides a means of evaluating and bounding the entropy of the generated key with respect to an adversary and ii) reducing the number of probes that need to be used for key reconciliation in certain deployment scenarios. The proposed schemes are then implemented on off-the-shelf devices and the performance of the schemes evaluated and compared to current state-of-the-art schemes. The schemes are shown to improve the performance of existing state-of-the-art PLSKG schemes and achieve near 100% success rates at short distances. The thesis also presents results on the error bounding in PLSKG schemes and presents results showing how these bounds can be used to make the key generation process more secure. Moreover, the thesis also discusses practical considerations in the design of PLSKG schemes, focusing on areas that have only received cursory treatment in current literature