Be More and be Merry: Enhancing Data and User Authentication in Collaborative Settings

Sammanfattning: Cryptography is the science and art of keeping information secret to un-intended parties. But, how can we determine who is an intended party and who is not? Authentication is the branch of cryptography that aims at confirming the source of data or at proving the identity of a person. This Ph.D. thesis is a study of different ways to perform cryptographic authentication of data and users. The main contributions are contained in the six papers included in this thesis and cover the following research areas: (i) homomorphic authentication; (ii) server-aided verification of signatures; (iii) distance-bounding authentication; and (iv) biometric authentication. The investigation flow is towards collaborative settings, that is, application scenarios where different and mutually distrustful entities work jointly for a common goal. The results presented in this thesis allow for secure and efficient authentication when more entities are involved, thus the title “be more and be merry”. Concretely, the first two papers in the collection are on homomorphic authenticators and provide an in-depth study on how to enhance existing primitives with multi- key functionalities. In particular, the papers extend homomorphic signatures and homomorphic message authentication codes to support computations on data authenticated using different secret keys. The third paper explores signer anonymity in the area of server-aided verification and provides new secure constructions. The fourth paper is in the area of distance-bounding authentication and describes a generic method to make existing protocols not only authenticate direct-neighbors, but also entities located two-hop away. The last two papers investigate the leakage of information that affects a special family of biometric authentication systems and how to combine verifiable computation techniques with biometric authentication in order to mitigate known attacks.