Pitfalls in public key cryptosystems based on free partially commutative monoids and groups

At INDOCRYPT 2003 Abisha, Thomas, and Subramanian proposed two public key schemes based on word problems in free partially commutative monoids and groups. We show that both proposals are vulnerable to chosen ciphertext attacks, and thus in the present form must be considered as insecure.This work has been partially supported by the German Academic Exchange Service DAAD and the Spanish M.E.C. as part of the BaSe CoAT project within the Acciones Integradas Hispano-Alemanas

Attacking a public key cryptosystem based on tree replacement

We point out several security flaws in the cryptosystem based on tree replacement systems proposed by Samuel, Thomas, Abisha and Subramanian at INDOCRYPT 2002. Due to the success of (among others) very simple ciphertext-only attacks, we evidence that this system does not, in its present form, offer acceptable security guarantees for cryptographic applications.Work partially supported by projects BFM2001-3239-C03-01 and BFM2001-1284

Analytic surveillance: Big data business models in the time of privacy awareness

 Massive data collection and analysis is at the heart of many business models today. New technologies allow for fine-grained recommendation systems that help companies make accurate market predictions while also providing clients with highly personalized services. Because of this, extreme care must be taken when it comes to storing and managing personal (often highly sensitive) information. In this paper we focus on the influence of big data management in media business content platforms, mainly in well-known OTT (Over the Top) services. In addition, we comment on the implications of data management in social networks. We discuss the privacy and security risks associated with this novel scenario, and briefly comment on tools that aid in securing the privacy of business intelligence within this context

Combined schemes for signature and encryption: The public-key and the identity-based setting

Consider a scenario in which parties use a public-key encryption scheme and a signature scheme with a single public key/private key pair-so the private key sk is used for both signing and decrypting. Such a simultaneous use of a key is in general considered poor cryptographic practice, but from an efficiency point of view looks attractive. We offer security notions to analyze such violations of key separation. For both the identity-and the non-identity-based setting, we show that-although being insecure in general-for schemes of interest the resulting combined scheme can offer strong security guarantees.First and last author were supported by the Spanish Ministerio de Economía y Competitividad through the project grant MTM-2012-15167

"Crypto Go": criptografía simétrica en tapete verde

IV Jornadas Nacionales de Investigación en Ciberseguridad (JNIC 2018), Donostia-San Sebastián, 13, 14 y 15 de junio de 2018, pp. 53-55En este documento describimos el diseño preliminar de un juego de mesa, “Crypto Go” cuyo planteamiento mimetiza el del conocido juego de cartas “Sushi Go”. El fin de nuestra propuesta es familiarizar al alumno de una manera lúdica con las principales herramientas de clave simétrica. Así, el objetivo de cada partida es llegar a construcciones robustas para conseguir los objetivos de confidencialidad, integridad y autenticación en la transmisión de mensajes. En esta aproximación inicial obviamos numerosos aspectos que pueden incorporarse para completar nuestra propuesta, como la consideración de tamaños de clave o la generación pseudoaleatoria de calidad. Nuestro diseño inicial, sin embargo, es suficiente para conseguir que el alumno afiance los conceptos básicos más relevantes adquiridos en un curso elemental de criptografía simétrica, conozca un gran número de herramientas de amplio uso en la actualidad y sepa identificar errores de planteamiento en construcciones reales

Shuffle, cut, and learn: Crypto Go, a card game for teaching cryptography

This article belongs to the Special Issue Mathematical Modeling and Simulation in Science and Engineering Education II.Cryptography is the mathematical core of information security. It serves both as a source of hard computational problems and as precise language allowing for the formalization of sound security models. While dealing with the mathematical foundations of cybersecurity is only possible in specialized courses (tertiary level and beyond), it is essential to promote the role of mathematics in this field at early educational stages. With this in mind, we introduce Crypto Go, a physical card game that may be used both as a dissemination and as an educational tool. The game is carefully devised in order to entertain and stimulate players, while boosting their understanding on how basic cryptographic tools work and interplay. To get a preliminary assessment of our design, we collected data from a series of test workshops, which engaged over two hundred players from different ages and educational backgrounds. This basic evaluation indeed confirms that Crypto Go significantly improves students' motivation and has a positive impact in their perception and understanding of the field.The printouts of Crypto Go decks, and some of the experimental workshops described in this paper have been financially supported by several institutions: Instituto Nacional de Ciberseguridad (INCIBE; contract 2018/00520/001), Fundación Madri+d (Science Week), and Universidad Carlos III de Madrid (Technological Fridays). M.I.G.V.'s work is funded by the NATO Science for Peace and Security Programme, grant number G5448 and by MINECO under Grant MTM2016-77213-R

Choosing a leader on a complex network

In many real life applications a group of people interact through a communication network, mathematically modelled as a connected graph linking each element of the group. These participants may have diverse objectives and play very different roles depending on their knowledge and privileges. We focus on a particular scenario, in which a certain node is absolutely essential for completing the intended task. Moreover, if a technical failure results in disconnection of a participant to this leader node, this participant can no longer take part in the group's performance. In this setting a sound choice of the underlying network topology could minimize the damage caused by random or provoked technical failures. We study different criteria for choosing suitable communication networks, from the point of view of both efficiency and robustness.Partially supported by PPR-2004-16 from Universidad Rey Juan Carlo

(Password) authenticated key establishment: From 2-party to group

Proceedings of: TCC 2007: Fourth IACR Theory of Cryptography Conference, 21-24 February 2007, Amsterdam, The Netherlands.A protocol compiler is described, that transforms any provably secure authenticated 2-party key establishment into a provably secure authenticated group key establishment with 2 more rounds of communication. The compiler introduces neither idealizing assumptions nor high-entropy secrets, e.g., for signing. In particular, applying the compiler to a password-authenticated 2-party key establishment without random oracle assumption, yields a password-authenticated group key establishment without random oracle assumption. Our main technical tools are non-interactive and non-malleable commitment schemes that can be implemented in the common reference string (CRS) model.The first author was supported in part by the European Commission through the IST Program under Contract IST-2002-507932 ECRYPT and by France Telecom R&D as part of the contract CIDRE, between France Telecom R&D and École normale supérieure

A new cramer-shoup like methodology for group based provably secure encryption schemes

Proceedings of: TCC 2005: Theory of Cryptography Conference, 10-12 February 2005, Cambridge, MA, USA.A theoretical framework for the design of - in the sense of IND-CCA - provably secure public key cryptosystems taking non-abelian groups as a base is given. Our construction is inspired by Cramer and Shoup's general framework for developing secure encryption schemes from certain language membership problems; thus all our proofs are in the standard model, without any idealization assumptions. The skeleton we present is conceived as a guiding tool towards the construction of secure concrete schemes from finite non-abelian groups (although it is possible to use it also in conjunction with finite abelian groups)

Attacking a Public Key Cryptosystem Based on Tree Replacement

We point out several security flaws in the cryptosystem based on tree replacement systems proposed by Samuel, Thomas, Abisha and Subramanian at INDOCRYPT 2002. Due to the success of (among others) very simple ciphertext-only attacks, we evidence that this system does not, in its present form, offer acceptable security guarantees for cryptographic applications