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)


Côme Berbain (#799)
Name Côme Berbain
Topic of his/her doctorate. Analyse et conception d'algorithmes de chiffrement à flot
Category secret-key cryptography
Keywords Stream Cipher, Cryptanalysis, Provable Security, Efficient Implementation
Ph.D. Supervisor(s) Jacques Stern, Henri Gilbert
Year of completion 2007

The primary goal of cryptography is to protect the confidentiality of data and communications. Stream ciphers is one of the two most popular families of symmetric encryption algorithms that allow to guaranty confidentiality and to achieve high performances.

In the first part of this thesis, we present different cryptanalysis techniques against stream ciphers: correlation attack against the stream cipher GRAIN, guess and determine attack against the BSG mechanism, algebraic attack against special kinds of non-linear feedback shift registers, and chosen IV attack against a reduced version of the stream cipher SALSA.

In a second part, we focus on proofs of security for stream ciphers: we introduce the new algorithm QUAD and give some provable security arguments in order to link its security to the conjectured intractability of Multivariate Quadratic problem. We also try to extend the security requirements of stream ciphers to the case where initialisation values (IV) are used: we present a construction which allows us to build a secure IV dependent stream cipher from a number generator and apply it to QUAD, which becomes the first IV dependent stream cipher with provable security arguments. We also present the algorithms DECIM and SOSEMANUK, to which we made design contributions.

Finally in a third part, we present efficient software and hardware implementations of the QUAD algorithm.

Your Ph.D. thesis as fulltext 97_CmeBerbain_Analyseetconceptiondalgorithm.pdf
Last Change 2012-05-17 12:10:46
To provide an update on this entry, please click .

Contact: phds (at)

[ IACR home page ] [ IACR PhDs page ] © IACR