Structure-Preserving Pairing-Based Cryptography

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Pairing-based cryptography has boomed over the last decade since it provides secure solutions to problems where traditional cryptographic methods do not suffice or are less efficient. Boneh and Franklin in a seminal paper showed how to construct identity-based encryption using pairing-based techniques. This makes it possible to encrypt a message under somebody's identity, for instance their e-mail address, eliminating the need to obtain or manage a public key for each user. In large organizations this simplifies key management and identity-based key-management solutions are now used in several Fortune 500 companies. Another example arises in the context of pervasive computing systems such as intelligent cars that communicate with each other. In an intelligent car processing hundreds of messages from surrounding vehicles in every 300ms interval it is essential to minimize communication and optimise efficiency. Pairing-based digital signatures can be useful in this scenario because they are smaller than traditional digital signatures and at the same time allow for fast verification of a large batch of signatures at once. Other proposed applications of pairing-based cryptography include e-cash, searchable encrypted data, broadcast encryption and traitor tracing, delegatable anonymous credentials, and verifying the presence of data stored in a cloud computing facility. Security is essential in all of these tasks. As our society has become increasingly digitized and networked so have criminals, hackers, industrial spies, enemy states, etc. It is therefore necessary to design secure cryptographic schemes that can be used to build a digital society that is resilient in the presence of malicious adversaries.Designing cryptographic protocols for complex tasks requires significant effort and expertise since even a small mistake may render the entire system insecure. It is therefore natural to build cryptographic protocols in a modular fashion. This is what structure-preserving pairing-based cryptography allows. The term structure-preservation refers to pairing-based schemes that preserve their underlying mathematical structure. This structure-preserving property makes it easy to compose them with other pairing-based schemes and enables modular design.We will design structure-preserving pairing-based cryptographic schemes, study the efficiency limits of structure-preserving pairing-based cryptographic schemes and evaluate the security of pairing-based cryptographic schemes.By designing structure-preserving pairing-based schemes we develop new building blocks for the digital society. Moreover, the techniques we develop for the design of structure-preserving schemes may make it possible to build pairing-based schemes for significantly more complex tasks than is currently possible.Very recent work has shown that there are limits to how efficient structure-preserving digital signatures can be. It is usually very difficult to find efficiency limitations, researchers just tend to get stuck at some point without knowing why, but because of their unique nature structure-preserving protocols lend themselves to exact efficiency analysis. By finding efficiency limits for structure-preserving pairing-based schemes, we can get an accurate picture of the exact efficiency for a variety of cryptographic tasks.Security is essential when designing cryptographic protocols. The security of cryptographic schemes relies on hardness assumptions; for instance that it is computationally infeasible to factor large integers in a short amount of time. Unfortunately, pairing-based cryptographic schemes have been based on a large variety of assumptions making it hard to assess how secure they are. We will map out the landscape of assumptions that are used in pairing-based cryptography and make it easier to assess the security of pairing-based cryptographic schemes.