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.

/pdf/public-key-cryptosystems-based-on-composite-degree-1zopwb21ba.pdf

Public-key cryptosystems based on composite degree residuosity classes

All our former experience with application of quantum theory seems to say:
{\it what is predicted by quantum formalism must occur in laboratory} But the
essence of quantum formalism - entanglement, recognized by Einstein, Podolsky,
Rosen and Schr\"odinger - waited over 70 years to enter to laboratories as a
new resource as real as energy This holistic property of compound quantum systems, which involves
nonclassical correlations between subsystems, is a potential for many quantum
processes, including ``canonical'' ones: quantum cryptography, quantum
teleportation and dense coding However, it appeared that this new resource is
very complex and difficult to detect Being usually fragile to environment, it
is robust against conceptual and mathematical tools, the task of which is to
decipher its rich structure This article reviews basic aspects of entanglement including its
characterization, detection, distillation and quantifying In particular, the
authors discuss various manifestations of entanglement via Bell inequalities,
entropic inequalities, entanglement witnesses, quantum cryptography and point
out some interrelations They also discuss a basic role of entanglement in
quantum communication within distant labs paradigm and stress some
peculiarities such as irreversibility of entanglement manipulations including
its extremal form - bound entanglement phenomenon A basic role of entanglement
witnesses in detection of entanglement is emphasized

Quantum entanglement

Quantum cryptography could well be the first application of quantum mechanics at the individual quanta level. The very fast progress in both theory and experiments over the recent years are reviewed, with emphasis on open questions and technological issues.

Quantum Cryptography

Quantum key distribution (QKD) is the first quantum information task to reach the level of mature technology, already fit for commercialization. It aims at the creation of a secret key between authorized partners connected by a quantum channel and a classical authenticated channel. The security of the key can in principle be guaranteed without putting any restriction on an eavesdropper's power. This article provides a concise up-to-date review of QKD, biased toward the practical side. Essential theoretical tools that have been developed to assess the security of the main experimental platforms are presented (discrete-variable, continuous-variable, and distributed-phase-reference protocols).

/pdf/the-security-of-practical-quantum-key-distribution-1qnjoq3c7p.pdf

The security of practical quantum key distribution

After two decades of research and development, elliptic curve cryptography now has widespread exposure and acceptance. Industry, banking, and government standards are in place to facilitate extensive deployment of this efficient public-key mechanism. Anchored by a comprehensive treatment of the practical aspects of elliptic curve cryptography (ECC), this guide explains the basic mathematics, describes state-of-the-art implementation methods, and presents standardized protocols for public-key encryption, digital signatures, and key establishment. In addition, the book addresses some issues that arise in software and hardware implementation, as well as side-channel attacks and countermeasures. Readers receive the theoretical fundamentals as an underpinning for a wealth of practical and accessible knowledge about efficient application. Features & Benefits: * Breadth of coverage and unified, integrated approach to elliptic curve cryptosystems * Describes important industry and government protocols, such as the FIPS 186-2 standard from the U.S. National Institute for Standards and Technology * Provides full exposition on techniques for efficiently implementing finite-field and elliptic curve arithmetic* Distills complex mathematics and algorithms for easy understanding* Includes useful literature references, a list of algorithms, and appendices on sample parameters, ECC standards, and software toolsThis comprehensive, highly focused reference is a useful and indispensable resource for practitioners, professionals, or researchers in computer science, computer engineering, network design, and network data security.

https://cdn.preterhuman.net/texts/cryptography/Hankerson,%20Menezes,%20Vanstone.%20Guide%20to%20elliptic%20curve%20cryptography%20(Springer,%202004)(ISBN%20038795273X)(332s)_CsCr_.pdf

Guide to Elliptic Curve Cryptography

One of the basic problems in cryptography is the generation of a common secret key between two parties, for instance in order to communicate privately. In this paper we consider information-theoretically secure key agreement. Wyner and subsequently Csiszar and Korner described and analyzed settings for secret-key agreement based on noisy communication channels. Maurer as well as Ahlswede and Csiszar generalized these models to a scenario based on correlated randomness and public discussion. In all these settings, the secrecy capacity and the secret-key rate, respectively, have been defined as the maximal achievable rates at which a highly-secret key can be generated by the legitimate partners. However, the privacy requirements were too weak in all these definitions, requiring only the ratio between the adversary's information and the length of the key to be negligible, but hence tolerating her to obtain a possibly substantial amount of information about the resulting key in an absolute sense. We give natural stronger definitions of secrecy capacity and secret-key rate, requiring that the adversary obtains virtually no information about the entire key. We show that not only secret-key agreement satisfying the strong secrecy condition is possible, but even that the achievable key-generation rates are equal to the previous weak notions of secrecy capacity and secret-key rate. Hence the unsatisfactory old definitions can be completely replaced by the new ones. We prove these results by a generic reduction of strong to weak key agreement. The reduction makes use of extractors, which allow to keep the required amount of communication negligible as compared to the length of the resulting key.

/pdf/information-theoretic-key-agreement-from-weak-to-strong-vwx51hoyb4.pdf

Information-theoretic key agreement: from weak to strong secrecy for free

Shannon entropy is a useful and important measure in information processing, for instance, data compression or randomness extraction, under the assumption—which can typically safely be made in communication theory—that a certain random experiment is independently repeated many times. In cryptography, however, where a system’s working has to be proven with respect to a malicious adversary, this assumption usually translates to a restriction on the latter’s knowledge or behavior and is generally not satisfied. An example is quantum key agreement, where the adversary can attack each particle sent through the quantum channel differently or even carry out coherent attacks, combining a number of particles together. In information-theoretic key agreement, the central functionalities of information reconciliation and privacy amplification have, therefore, been extensively studied in the scenario of general distributions: Partial solutions have been given, but the obtained bounds are arbitrarily far from tight, and a full analysis appeared to be rather involved to do. We show that, actually, the general case is not more difficult than the scenario of independent repetitions—in fact, given our new point of view, even simpler. When one analyzes the possible efficiency of data compression and randomness extraction in the case of independent repetitions, then Shannon entropy H is the answer. We show that H can, in these two contexts, be generalized to two very simple quantities—$H_0^\epsilon$ and $H_\infty^\epsilon$, called smooth Renyi entropies—which are tight bounds for data compression (hence, information reconciliation) and randomness extraction (privacy amplification), respectively. It is shown that the two new quantities, and related notions, do not only extend Shannon entropy in the described contexts, but they also share central properties of the latter such as the chain rule as well as sub-additivity and monotonicity.

/pdf/simple-and-tight-bounds-for-information-reconciliation-and-2tna040r3r.pdf

Simple and tight bounds for information reconciliation and privacy amplification

This paper is concerned with secret-key agreement by public discussion. Assume that two parties Alice and Bob and an adversary Eve have access to independent realizations of random variables X, Y, and Z, respectively, with joint distribution P/sub XYZ/. The secret-key rate S(X;Y/spl par/Z) has been defined as the maximal rate at which Alice and Bob can generate a secret key by communication over an insecure, but authenticated channel such that Eve's information about this key is arbitrarily small. We define a new conditional mutual information measure, the intrinsic conditional mutual information between S and Y when given Z, denoted by I(X;Y/spl darr/Z), which is an upper bound on S(X;Y/spl par/Z). The special scenarios are analyzed where X, Y, and Z are generated by sending a binary random variable R, for example a signal broadcast by a satellite, over independent channels, or two scenarios in which Z is generated by sending X and Y over erasure channels. In the first two scenarios it can be shown that the secret-key rate is strictly positive if and only if I(X;Y/spl darr/Z) is strictly positive. For the third scenario, a new protocol is presented which allows secret-key agreement even when all the previously known protocols fail.

/pdf/unconditionally-secure-key-agreement-and-the-intrinsic-2j12td4osa.pdf

Unconditionally secure key agreement and the intrinsic conditional information

We introduce a new entropy measure, called smooth Renyi entropy. The measure characterizes fundamental properties of a random variable Z, such as the amount of uniform randomness that can be extracted from Z or the minimum length of an encoding of Z.

Smooth Renyi entropy and applications

Shannon entropy is a useful and important measure in information processing, for instance, data compression or randomness extraction, under the assumption-which can typically safely be made in communication theory-that a certain random experiment is independently repeated many times. In cryptography, however, where a system's working has to be proven with respect to a malicious adversary, this assumption usually translates to a restriction on the latter's knowledge or behavior and is generally not satisfied. An example is quantum key agreement, where the adversary can attack each particle sent through the quantum channel differently or even carry out coherent attacks, combining a number of particles together. In information-theoretic key agreement, the central functionalities of information reconciliation and privacy amplification have, therefore, been extensively studied in the scenario of general distributions: Partial solutions have been given, but the obtained bounds are arbitrarily far from tight, and a full analysis appeared to be rather involved to do. We show that, actually, the general case is not more difficult than the scenario of independent repetitions-in fact, given our new point of view, even simpler. When one analyzes the possible efficiency of data compression and randomness extraction in the case of independent repetitions, then Shannon entropy H is the answer. We show that H can, in these two contexts, be generalized to two very simple quantitiesH e 0 and H e ∞, called smooth Renyi entropies-which are tight bounds for data compression (hence, information reconciliation) and randomness extraction (privacy amplification), respectively. It is shown that the two new quantities, and related notions, do not only extend Shannon entropy in the described contexts, but they also share central properties of the latter such as the chain rule as well as sub-additivity and monotonicity.

Stefan Wolf

Papers

Information-theoretic key agreement: from weak to strong secrecy for free

Simple and tight bounds for information reconciliation and privacy amplification

Unconditionally secure key agreement and the intrinsic conditional information

Smooth Renyi entropy and applications

Simple and tight bounds for information reconciliation and privacy amplification