Serge Vaudenay

Bio: Serge Vaudenay is an academic researcher from École Polytechnique Fédérale de Lausanne. The author has contributed to research in topics: Block cipher & Cryptography. The author has an hindex of 49, co-authored 297 publications receiving 9488 citations. Previous affiliations of Serge Vaudenay include Digital Management, Inc. & Centre national de la recherche scientifique.

Advances in Cryptology - Eurocrypt 2006

Abstract: Let g be an element of prime order p in an abelian group and α ∈ Zp. We show that if g, g, and gαd are given for a positive divisor d of p − 1, we can compute the secret α in O(log p · ( p/d + √d)) group operations using O(max{ p/d, √d}) memory. If gαi (i = 0, 1, 2, . . . , d) are provided for a positive divisor d of p + 1, α can be computed in O(log p · ( p/d + d)) group operations using O(max{ p/d, √d}) memory. This implies that the strong Diffie-Hellman problem and its related problems have computational complexity reduced by O( √ d) from that of the discrete logarithm problem for such primes. Further we apply this algorithm to the schemes based on the DiffieHellman problem on an abelian group of prime order p. As a result, we reduce the complexity of recovering the secret key from O( √ p) to O( p/d) for Boldyreva’s blind signature and the original ElGamal scheme when p − 1 (resp. p + 1) has a divisor d ≤ p (resp. d ≤ p) and d signature or decryption queries are allowed.

On privacy models for RFID

Abstract: We provide a formal model for identification schemes. Under this model, we give strong definitions for security and privacy. Our model captures the notion of a powerful adversary who can monitor all communications, trace tags within a limited period of time, corrupt tags, and get side channel information on the reader output. Adversaries who do not have access to this side channel are called narrow adversaries. Depending on restrictions on corruption, adversaries are called strong, destructive, forward, or weak adversaries. We derive some separation results: strong privacy is impossible. Narrow-strong privacy implies key agreement. We also prove some constructions: narrow-strong and forward privacy based on a public-key cryptosystem, narrow-destructive privacy based on a random oracle, and weak privacy based on a pseudorandom function.

Links between differential and linear cryptanalysis

Abstract: Linear cryptanalysis, introduced last year by Matsui, will most certainly open-up the way to new attack methods which may be made more efficient when compared or combined with differential cryptanalysis.

Security flaws induced by CBC padding -applications to SSL, IPSEC, WTLS …

Abstract: In many standards, e.g. SSL/TLS, IPSEC, WTLS, messages are first pre-formatted, then encrypted in CBC mode with a block cipher. Decryption needs to check if the format is valid. Validity of the format is easily leaked from communication protocols in a chosen ciphertext attack since the receiver usually sends an acknowledgment or an error message. This is a side channel. In this paper we show various ways to perform an efficient side channel attack. We discuss potential applications, extensions to other padding schemes and various ways to fix the problem.

Secure communications over insecure channels based on short authenticated strings

Abstract: We propose a way to establish peer-to-peer authenticated communications over an insecure channel by using an extra channel which can authenticate very short strings, e.g. 15 bits.We call this SAS-based authentication as for authentication based on Short Authenticated Strings. The extra channel uses a weak notion of authentication in which strings cannot be forged nor modified, but whose delivery can be maliciously stalled, canceled, or replayed. Our protocol is optimal and relies on an extractable or equivocable commitment scheme. This approach offers an alternative (or complement) to public-key infrastructures, since we no longer need any central authority, and to password-based authenticated key exchange, since we no longer need to establish a confidential password. It can be used to establish secure associations in ad-hoc networks. Applications could be the authentication of a public key (e.g. for SSH or PGP) by users over the telephone, the user-aided pairing of wireless (e.g. Bluetooth) devices, or the restore of secure associations in a disaster case, namely when one remote peer had his long-term keys corrupted.

Handbook of Applied Cryptography

Abstract: From the Publisher: A valuable reference for the novice as well as for the expert who needs a wider scope of coverage within the area of cryptography, this book provides easy and rapid access of information and includes more than 200 algorithms and protocols; more than 200 tables and figures; more than 1,000 numbered definitions, facts, examples, notes, and remarks; and over 1,250 significant references, including brief comments on each paper.

Public-key cryptosystems based on composite degree residuosity classes

Abstract: This paper investigates a novel computational problem, namely the Composite Residuosity Class Problem, and its applications to public-key cryptography. We propose a new trapdoor mechanism and derive from this technique three encryption schemes : a trapdoor permutation and two homomorphic probabilistic encryption schemes computationally comparable to RSA. Our cryptosystems, based on usual modular arithmetics, are provably secure under appropriate assumptions in the standard model.

Differential Power Analysis

Abstract: Cryptosystem designers frequently assume that secrets will be manipulated in closed, reliable computing environments. Unfortunately, actual computers and microchips leak information about the operations they process. This paper examines specific methods for analyzing power consumption measurements to find secret keys from tamper resistant devices. We also discuss approaches for building cryptosystems that can operate securely in existing hardware that leaks information.

The Design of Rijndael: AES - The Advanced Encryption Standard

Abstract: 1. The Advanced Encryption Standard Process.- 2. Preliminaries.- 3. Specification of Rijndael.- 4. Implementation Aspects.- 5. Design Philosophy.- 6. The Data Encryption Standard.- 7. Correlation Matrices.- 8. Difference Propagation.- 9. The Wide Trail Strategy.- 10. Cryptanalysis.- 11. Related Block Ciphers.- Appendices.- A. Propagation Analysis in Galois Fields.- A.1.1 Difference Propagation.- A.l.2 Correlation.- A. 1.4 Functions that are Linear over GF(2).- A.2.1 Difference Propagation.- A.2.2 Correlation.- A.2.4 Functions that are Linear over GF(2).- A.3.3 Dual Bases.- A.4.2 Relationship Between Trace Patterns and Selection Patterns.- A.4.4 Illustration.- A.5 Rijndael-GF.- B. Trail Clustering.- B.1 Transformations with Maximum Branch Number.- B.2 Bounds for Two Rounds.- B.2.1 Difference Propagation.- B.2.2 Correlation.- B.3 Bounds for Four Rounds.- B.4 Two Case Studies.- B.4.1 Differential Trails.- B.4.2 Linear Trails.- C. Substitution Tables.- C.1 SRD.- C.2 Other Tables.- C.2.1 xtime.- C.2.2 Round Constants.- D. Test Vectors.- D.1 KeyExpansion.- D.2 Rijndael(128,128).- D.3 Other Block Lengths and Key Lengths.- E. Reference Code.

Differential privacy: a survey of results

Abstract: Over the past five years a new approach to privacy-preserving data analysis has born fruit [13, 18, 7, 19, 5, 37, 35, 8, 32]. This approach differs from much (but not all!) of the related literature in the statistics, databases, theory, and cryptography communities, in that a formal and ad omnia privacy guarantee is defined, and the data analysis techniques presented are rigorously proved to satisfy the guarantee. The key privacy guarantee that has emerged is differential privacy. Roughly speaking, this ensures that (almost, and quantifiably) no risk is incurred by joining a statistical database. In this survey, we recall the definition of differential privacy and two basic techniques for achieving it. We then show some interesting applications of these techniques, presenting algorithms for three specific tasks and three general results on differentially private learning.