Privacy Enhancing Protocols using Pairing Based Cryptography

Abstract

This thesis presents privacy enhanced cryptographic constructions, consisting of formal definitions, algorithms and motivating applications. The contributions are a step towards the development of cryptosystems which, from the design phase, incorporate privacy as a primary goal. Privacy offers a form of protection over personal and other sensitive data to individuals, and has been the subject of much study in recent years. Our constructions are based on a special type of algebraic group called bilinear groups. We present existing cryptographic constructions which use bilinear pairings, namely Identity-Based Encryption (IBE). We define a desirable property of digital signatures, blindness, and present new IBE constructions which incorporate this property. Blindness is a desirable feature from a privacy perspective as it allows an individual to obscure elements such as personal details in the data it presents to a third party. In IBE, blinding focuses on obscuring elements of the identity string which an individual presents to the key generation centre. This protects an individual's privacy in a direct manner by allowing her to blind sensitive elements of the identity string and also prevents a key generation centre from subsequently producing decryption keys using her full identity string. Using blinding techniques, the key generation centre does not learn the full identity string. In this thesis, we study selected provably-secure cryptographic constructions. Our contribution is to reconsider the design of such constructions with a view to incorporating privacy. We present the new, privacy-enhanced cryptographic protocols using these constructions as primitives. We refine useful existing security notions and present feasible security definitions and proofs for these constructions