UCLA

Highly concurrent environments, like the Internet, present new challenges towards design of

secure cryptographic protocols. Indeed, it is known that protocols proved secure in the so

called `stand-alone' model, where a protocol is assumed to execute in isolation, are no longer

secure in a concurrent environment. In fact, the case of arbitrary composition is so severe

that no security can be achieved without an external secure set-up. Numerous such set-ups

have been proposed in the literature, each with its own advantages and disadvantages. In this

thesis, we study two new set-ups motivated by recent advances in secure hardware design:

tamper-proof tokens, and physically uncloneable functions. For both set-ups, we provide

universally composable protocols for general cryptographic tasks. Additionally, our protocols

using tamper-proof tokens are information-theoretically secure, and non-interactive.