A Survey of Symbolic Methods in Computational Analysis of Cryptographic Systems

Since the 1980s, two approaches have been developed for analyzing security protocols. One of the approaches relies on a computational model that considers issues of complexity and probability. This approach captures a strong notion of security, guaranteed against all probabilistic polynomial-time attacks. The other approach relies on a symbolic model of protocol executions in which cryptographic primitives are treated as black boxes. Since the seminal work of Dolev and Yao, it has been realized that this latter approach enables significantly simpler and often automated proofs. However, the guarantees that it offers have been quite unclear. For more than twenty years the two approaches have coexisted but evolved mostly independently. Recently, significant research efforts attempt to develop paradigms for cryptographic systems analysis that combines the best of both worlds. There are two broad directions that have been followed. {\em Computational soundness} aims to establish sufficient conditions under which results obtained using symbolic models imply security under computational models. The {\em direct approach} aims to apply the principles and the techniques developed in the context of symbolic models directly to computational ones. In this paper we survey existing results along both of these directions. Our goal is to provide a rather complete summary that could act as a quick reference for researchers who want to contribute to the field, want to make use of existing results, or just want to get a better picture of what results already exist

Implementation of Symmetric Encryption Algorithms

Cryptography considered being the most vital component in information security because it is responsible for securing all information passed through networked computers.  The discussions in this paper include an overview of cryptography and symmetric encryption. This paper also discusses some of the algorithms used in our research. This paper aims to design an application that consist of some symmetric encryption algorithms which allow users to encrypt and decrypt different size of files, also the application can be used as a test field to compare between different symmetric algorithms. Keywords: Cryptography, symmetric, encryptio

Privacy-Preserving Electronic Ticket Scheme with Attribute-based Credentials

Electronic tickets (e-tickets) are electronic versions of paper tickets, which enable users to access intended services and improve services' efficiency. However, privacy may be a concern of e-ticket users. In this paper, a privacy-preserving electronic ticket scheme with attribute-based credentials is proposed to protect users' privacy and facilitate ticketing based on a user's attributes. Our proposed scheme makes the following contributions: (1) users can buy different tickets from ticket sellers without releasing their exact attributes; (2) two tickets of the same user cannot be linked; (3) a ticket cannot be transferred to another user; (4) a ticket cannot be double spent; (5) the security of the proposed scheme is formally proven and reduced to well known (q-strong Diffie-Hellman) complexity assumption; (6) the scheme has been implemented and its performance empirically evaluated. To the best of our knowledge, our privacy-preserving attribute-based e-ticket scheme is the first one providing these five features. Application areas of our scheme include event or transport tickets where users must convince ticket sellers that their attributes (e.g. age, profession, location) satisfy the ticket price policies to buy discounted tickets. More generally, our scheme can be used in any system where access to services is only dependent on a user's attributes (or entitlements) but not their identities.Comment: 18pages, 6 figures, 2 table

Actively Secure Two-Party Computation: Efficient Beaver Triple Generation

Töö kombineerib erinevaid ideid, et saavutada aktiivses mudelis turvalist kahe osapoolega ühisarvutust. Töö käigus defineerime Sharemindi raamistikku kaks uut turvaala. Kasutame aditiivset ühissalastust, sõnumiautentimisskeeme, aditiivselt homomorfset krüptosüsteemi ning nullteadmustõestusi. Protokollistikud jagame kahte osasse, vastavalt ettearvutamise ja töö faas. Ettearvutamise ajal valmistatakse ette juhuslikke väärtusi, mis võimaldavad töö faasis arvutusi kiirendada. Eelkõige keskendume korrutamise jaoks vajalike Beaveri kolmikute genereerimisele.This thesis combines currently popular ideas in actively secure multi-party computation to define two actively secure two-party protocol sets for Sharemind secure multi-party computation framework. This includes additive secret sharing, dividing work as online and precomputation phase, using Beaver triples for multiplication and using message authentication codes for integrity checks. Our protocols use additively homomorphic Paillier cryptosystem, especially in the precomputation phase. The thesis includes two different setups for secure two-party computation which are also implemented and compared to each other. In addition, we propose new ideas to use additively homomorphic cryptosystem to generate Beaver triples for any chosen modulus. The important aspects of Beaver triple generation are maximising the amount of useful bits we get from one generation and assuring that these triples are correct

How to prove security of communication protocols? A discussion on the soundness of formal models w.r.t. computational ones.

Security protocols are short programs that aim at securing communication over a public network. Their design is known to be error-prone with flaws found years later. That is why they deserve a careful security analysis, with rigorous proofs. Two main lines of research have been (independently) developed to analyse the security of protocols. On the one hand, formal methods provide with symbolic models and often automatic proofs. On the other hand, cryptographic models propose a tighter modeling but proofs are more difficult to write and to check. An approach developed during the last decade consists in bridging the two approaches, showing that symbolic models are sound w.r.t. symbolic ones, yielding strong security guarantees using automatic tools. These results have been developed for several cryptographic primitives (e.g. symmetric and asymmetric encryption, signatures, hash) and security properties. While proving soundness of symbolic models is a very promising approach, several technical details are often not satisfactory. Focusing on symmetric encryption, we describe the difficulties and limitations of the available results

Computationally Sound Mechanized Proofs for Basic and Public-key Kerberos

We present a computationally sound mechanized analysis of Kerberos 5, both with and without its public-key extension PKINIT. We prove authentication and key secrecy properties using the prover CryptoVerif, which works directly in the computational model; these are the first mechanical proofs of a full industrial protocol at the computational level. We also generalize the notion of key usability and use CryptoVerif to prove that this definition is satisfied by keys in Kerberos

Modular code-based cryptographic verification

International audienceType systems are effective tools for verifying the security of cryptographic programs. They provide automation, modularity and scalability, and have been applied to large security protocols. However, they traditionally rely on abstract assumptions on the underlying cryptographic primitives, expressed in symbolic models. Cryptographers usually reason on security assumptions using lower level, computational models that precisely account for the complexity and success probability of attacks. These models are more realistic, but they are harder to formalize and automate. We present the first modular automated program verification method based on standard cryptographic assumptions. We show how to verify ideal functionalities and protocols written in ML by typing them against new cryptographic interfaces using F7, a refinement type checker coupled with an SMT-solver. We develop a probabilistic core calculus for F7 and formalize its type safety in Coq. We build typed module and interfaces for MACs, signatures, and encryptions, and establish their authenticity and secrecy properties. We relate their ideal functionalities and concrete implementations, using game-based program transformations behind typed interfaces. We illustrate our method on a series of protocol implementations

Flexible Long-Term Secure Archiving

Privacy and data protection have always been basic human needs in any society that makes use of written language. From simple personal correspondence over military communication to trade secrets or medical information, confidentiality has been of utmost importance. The implications of a leak of such sensitive information may prove devastating, as the previous examples illustrate perfectly. Furthermore reliability, that is, integrity and authenticitiy of information, is critical with risks reaching from annoying to lethal as can again be seen in the previous examples. This need for data protection has carried over from the analogue to the digital age seamlessly with the amount of data being generated, transmitted and stored increasing steadily and containing more and more personal details. And in regard of the developments in computational technology that recent years have seen, such as the ongoing improvements with respect to quantum computing as well as cryptoanalytical advances, the capabilities of attackers on the security of private information have never been more distinct. Thus the need for privacy and data protection has rarely been more dire