Authentication protocols in pervasive computing

Long Hoang Nguyen

abstract

The popularity of personal computing devices (e.g. smart cards) exposes users to risks, notably identity theft, and creates new requirements for secure communication. A new approach to creating secure communication is to use human trust and human interactions. Thus they potentially eliminate the need for passwords as in Bluetooth, shared secrets or trusted parties, which are too complex and expensive to use in portable devices. In the new technology, handheld devices exchange data (e.g. payment, heart rates or public keys) over some medium (e.g. WiFi) and then display a short digest of the protocol's run that the devices' human owners manually compare to ensure they agree on the data, i.e. the latter uses human interactions to prevent identity theft. In this thesis, we present several new protocols of the type to optimise the work required of humans to achieve a given level of security. We discover that the design of these protocols is influenced by several principles, including the ideas of commitment without knowledge and separation of security concerns where random and cryptographic attacks should be tackled separately. Underpinning the technology is a new cryptographic function, termed keyed digest, which produces a short number for humans to compare. This is similar to universal hashes, but its output length is shorter (e.g. 16 bits). Hence, it should be faster to compute. We propose several digest constructions using Toeplitz matrices, integer multiplication and random numbers. The application of digests leads us to develop more efficient alternatives to standard digital signatures. Our protocol security analysis leads to a new bound on the key length for universal hashes, derived by combinatorial analysis. In comparing this with other well-studied bounds, we discover a crucial value of a security parameter which represents an important threshold in the behaviour of the bounds, i.e. quantifying the Wegman-Carter effect.

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