International Association for Cryptologic Research

Ph.D. Database

The aim of the IACR Ph.D. database is twofold. On the first hand, we want to offer an overview of Ph.D. already completed in the domain of cryptology. Where possible, this should also include a subject classification, an abstract, and access to the full text. On the second hand, it deals with Ph.D. subjects currently under investigation. This way, we provide a timely map of contemporary research in cryptology. All entries or changes need to be approved by an editor. You can contact them via phds (at)


David Pointcheval (#311)
Name David Pointcheval
Personal Homepage
Topic of his/her doctorate. Proofs of Knowledge and Security Proofs (Les Preuves de Connaissance et leurs Preuves de Sécurité)
Category public-key cryptography
Keywords identification protocols, digital signatures
Ph.D. Supervisor(s) Jacques Stern, Brigitte Vallée
Year of completion 1996
Abstract The aim of cryptography is to protect communications, using encryption and authentication protocols. But what is the real security of proposed schemes against clever attackers? In this dissertation, we present provably secure cryptographic schemes in the random oracle model. This model, formalized in 1993 by Bellare and Rogaway, opens a way towards formal security proofs for schemes using one-way or hash functions, which satisfy only computational properties. First, we present a new identification scheme, provably robust against active attacks, based on a combinatorial NP-complete problem, the Permuted Perceptrons Problem. Then, we focus on digital signatures and blind signatures. Here, we derive a generic lemma, the ``forking lemma''. It allows us to prove that any signature scheme derivated from a fair verifier zero-knowledge identification protocol is existentially unforgeable against adaptively chosen messages attacks. An improvement of this ``forking lemma'' allows its application for the more complex concept of blind signatures. It then provides the proof that a large number of blind signature schemes derivated from witness indistinguishable identification protocols cannot admit the so-called ``one-more forgery'', even under parallel attacks. Finally, we apply the results about blind signatures to electronic cash. We present an ``off-line'' electronic payment system protecting privacy and we give formal proofs of its security for the bank and the users.
Last Change 2011-04-16 15:17:38
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David Pointcheval's Students

Gaëtan Leurent - Design and Analysis of Hash Functions (secret-key cryptography)
Mark Manulis - Provably Secure Group Key Exchange (cryptographic protocols)
Phan Duong Hieu - Sécurité et efficacité de schémas cryptographiques (public-key cryptography)
Fabrice Benhamouda - Diverse modules and zero-knowledge (public-key cryptography)

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