Searching for authors named "Nicolas Courtois" – sorted by Relevance.

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36 documents found, showing 1 through 10. Next 10 →

The Best Differential Characteristics and Subtleties of the Biham-Shamir Attacks on DES
by Nicolas Courtois — 2005 — on DES, On eprint.iacr.org/2005/202. Nicolas T. Courtois and Gregory V
…In about every book about cryptography, we learn that the plaintext complexity of differential cryptanalysis on DES is 2^47, as reported by Biham and Shamir in [2]. Yet few people realise that in a typical setting this estimation is not exact and too optimistic. In this note we show...…
Cited by 1 (1 self) – Add To MetaCart

The security of Hidden Field Equations (HFE
by Nicolas T. Courtois — 2001 — In The Cryptographer’s Track at RSA Conference 2001, volume 2020 of Lecture Notes in Computer Science
…Abstract. We consider the basic version of the asymmetric cryptosystem HFE from Eurocrypt 96. We propose a notion of non-trivial equations as a tentative to account for a large class of attacks on one-way functions. We found equations that give experimental evidence that basic HFE can be broken in e…
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Feistel Schemes and Bi-Linear Cryptanalysis
by Nicolas T. Courtois — 2005 — in Crypto 2004, LNCS 3152
…In this paper we introduce the method of bi-linear cryptanalysis (BLC), designed specifically to attack Feistel ciphers. It allows to construct periodic biased characteristics that combine for an arbitrary number of rounds. In particular, we present a practical attack on DES based on a 1-round i…
Cited by 4 (3 self) – Add To MetaCart

How Fast can be Algebraic Attacks on Block Ciphers
by Nicolas T. Courtois — 2007 — In online proceedings of Dagstuhl Seminar 07021, Symmetric Cryptography
…Abstract. In this paper we give a specification of a new block cipher that can be called the Courtois Toy Cipher (CTC). It is quite simple, and yet very much like any other known block cipher. If the parameters are large enough, it should evidently be secure against all known attack methods.However,…
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Higher Order Correlation Attacks, XL algorithm and Cryptanalysis of Toyocrypt
by Nicolas T. Courtois — 2002
…Abstract. A popular technique to construct stream ciphers is to use a linear sequence generator with a very large period and good statistical properties and a non-linear filter. There is abundant literature on how to use linear approximations of this non-linear function to attack the cipher, which i…
Cited by 36 (6 self) – Add To MetaCart

Algebraic Attacks on Combiners with Memory and Several Outputs
by Nicolas T. Courtois — 2004 — Proc. of ICISC’04
…Abstract. Algebraic attacks on stream ciphers [9] recover the key by solving an overdefined system of multivariate equations. Such attacks can break several interesting cases of LFSR-based stream ciphers, when the output is obtained by a Boolean function, see [9– 11]. Recently this approach has been…
Cited by 17 (2 self) – Add To MetaCart

Cryptanalysis of Sfinks
by Nicolas T. Courtois — 2005 — Proceedings of ICISC ’05, Springer-Verlag Lecture Notes in Computer Science
…Abstract. Sfinks is an LFSR-based stream cipher submitted to ECRYPT call for stream ciphers by Braeken, Lano, Preneel et al. The designers of Sfinks do not include any real protection against algebraic attacks other than the so called “Algebraic Immunity”, that relates to the complexity of a simple …
Cited by 3 (0 self) – Add To MetaCart

The Inverse S-box, Non-linear Polynomial Relations and Cryptanalysis of Block Ciphers
by Nicolas T. Courtois — 2005 — in AES 4 Conference, Bonn May 10-12 2004, LNCS 3373
…Abstract. This paper is motivated by the design of AES. We consider a broader question of cryptanalysis of block ciphers having very good non-linearity and diffusion. Can we expect anyway, to attacks such ciphers, clearly designed to render hopeless the main classical attacks? Recently a lot of atte…
Cited by 4 (3 self) – Add To MetaCart

General Principles of Algebraic Attacks and New Design Criteria for Components of Symmetric Ciphers
by Nicolas T. Courtois — 2005 — in AES 4 Conference, Bonn May 10-12 2004, LNCS 3373
…Abstract. This paper is about the design of multivariate public key schemes, as well as block and stream ciphers, in relation to recent attacks that exploit various types of multivariate algebraic relations. We survey these attacks focusing on their common fundamental principles and on how to avoid …
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Short Signatures, Provable Security and Generic Attacks for Multivariate Polynomial Schemes such as HFE, Quartz and Sflash
by Nicolas T. Courtois — 2004 — Polynomial Schemes such as HFE, Quartz and Sflash.” IACR E-print
…The object of this paper is the concrete security of recent multivariate signature schemes. A major challenge is to reconcile some "tricky" ad-hoc constructions that allow to make short signatures, with regular provable security. The paper is composed of two parts.…
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