Data Encryption Standard

Le Data Encryption Standard (DES, prononcer //) est un algorithme de chiffrement symétrique (chiffrement par bloc) utilisant des clés de 56 bits. Son emploi n'est plus recommandé aujourd'hui, du fait de sa lenteur à l'exécution et de son espace de clés trop petit permettant une attaque systématique en un temps raisonnable. Quand il est encore utilisé c'est généralement en Triple DES, ce qui ne fait rien pour améliorer ses performances. DES a notamment été utilisé dans le système de mots de passe UNIX. Le premier standard DES est publié par FIPS le sous le nom FIPS PUB 46. La dernière version avant l'obsolescence date du . Histoire En , le National Bureau of Standards américain demande la création d'un algorithme de chiffrement utilisable par les entreprises. À cette époque, IBM dispose déjà d'un algorithme appelé Lucifer, conçu en 1971 par Horst Feistel. En bonne logique, cet algorithme aurait dû être sélectionné par le NBS. En pratique, ce fut presque le cas : la NS

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Chiffrement par bloc

vignette|un schéma de chiffrement par bloc Le chiffrement par bloc (en anglais block cipher) est une des deux grandes catégories de chiffrements modernes en cryptographie symétrique, l'autre étant le

Cryptographie

thumb|La machine de Lorenz utilisée par les nazis durant la Seconde Guerre mondiale pour chiffrer les communications militaires de haut niveau entre Berlin et les quartiers-généraux des différentes ar

Cryptanalyse

La cryptanalyse est la technique qui consiste à déduire un texte en clair d’un texte chiffré sans posséder la clé de chiffrement. Le processus par lequel on tente de comprendre un message en particuli

DES S-box generator

Lauren De Meyer, Serge Vaudenay

The Data Encryption Standard (DES) is a cryptographic algorithm, designed by IBM, that was selected to be the national standard in 1977 by the National Bureau of Standards. The algorithm itself was entirely published but the design criteria were kept secret until 1994 when Coppersmith, one of the designers of DES, published them. He states that the IBM team already knew about the attack called Differential cryptanalysis during the design of the algorithm and that it had an effect on choosing the S-boxes. To be more specific, he mentions eight design criteria that all the S-boxes of DES are based on. How the S-boxes were generated is a mystery, as the legend says this was outsourced to the NSA. Indeed, building a set of S-boxes respecting these criteria is a non-trivial task. In this paper we present an efficient S-box generator respecting all criteria and even more. Coppersmith's design criteria served as a basis but were strengthened for better resistance to Linear Cryptanalysis. While other researchers have already proposed S-box generators for DES satisfying either non-linearity or good diffusion, our generator offers both. Moreover, apart from suggesting a new set of 8 S-boxes, it can also very quickly produce a large pool of S-boxes to be used in further research.

Taylor & Francis Inc2016

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Heading Off Correlated Failures through Independence-as-a-Service

Bryan Alexander Ford, Ennan Zhai

Today's systems pervasively rely on redundancy to ensure reliability. In complex multi-layered hardware/software stacks, however – especially in the clouds where many independent businesses deploy interacting services on common infrastructure – seemingly independent systems may share deep, hidden dependencies, undermining redundancy efforts and introducing unanticipated correlated failures. Complementing existing post-failure forensics, we propose Independence-as-a-Service (or INDaaS), an architecture to audit the independence of redundant systems proactively, thus avoiding correlated failures. INDaaS first utilizes pluggable dependency acquisition modules to collect the structural dependency information (including network, hardware, and software dependencies) from a variety of sources. With this information, INDaaS then quantifies the independence of systems of interest using pluggable auditing modules, offering various performance, precision, and data secrecy tradeoffs. While the most general and efficient auditing modules assume the auditor is able to obtain all required information, INDaaS can employ private set intersection cardinality protocols to quantify the independence even across businesses unwilling to share their full structural information with anyone. We evaluate the practicality of INDaaS with three case studies via auditing realistic network, hardware, and software dependency structures.

2014

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Cryptanalysis of the full MMB Block Cipher

Jorge Nakahara, Yue Sun

The block cipher MMB was designed by Daemen, Govaerts and Vandewalle, in 1993, as an alternative to the IDEA block cipher. We exploit and describe unusual properties of the modular multiplication in ZZ232 −1 , which lead to a diﬀerential attack on the full 6-round MMB cipher (both versions 1.0 and 2.0). Further contributions of this paper include detailed square and linear cryptanalysis of MMB. Concerning diﬀerential cryptanalysis (DC), we can break the full MMB with 2118 chosen plaintexts, 295.91 6-round MMB encryptions and 264 counters, eﬀectively bypassing the cipher’s countermeasures against DC. For the square attack, we can recover the 128-bit user key for 4-round MMB with 234 chosen plaintexts, 2126.32 4-round encryptions and 264 mem- ory blocks. Concerning linear cryptanalysis, we present a key-recovery attack on 3-round MMB requiring 2114.56 known-plaintexts and 2126 en- cryptions. Moreover, we detail a ciphertext-only attack on 2-round MMB using 293.6 ciphertexts and 293.6 parity computations. These attacks do not depend on weak-key or weak-subkey assumptions, and are thus in- dependent of the key schedule algorithm.

Springer2009

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COM-401: Cryptography and security

This course introduces the basics of cryptography. We review several types of cryptographic primitives, when it is safe to use them and how to select the appropriate security parameters. We detail how they work and sketch how they can be implemented.

EE-552: Media security

This course provides attendees with theoretical and practical issues in media security. In addition to lectures by the professor, the course includes laboratory sessions, a mini-project, and a mid-term exam.

COM-501: Advanced cryptography

This course reviews some failure cases in public-key cryptography. It introduces some cryptanalysis techniques. It also presents fundamentals in cryptography such as interactive proofs. Finally, it presents some techniques to validate the security of cryptographic primitives.