28 research outputs found

    Strong Leakage Resilient Encryption: Enhancing Data Confidentiality by Hiding Partial Ciphertext

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    Leakage-resilient encryption is a powerful tool to protect data confidentiality against side channel attacks. In this work, we introduce a new and strong leakage setting to counter backdoor (or Trojan horse) plus covert channel attack, by relaxing the restrictions on leakage. We allow \emph{bounded} leakage at \emph{anytime} and \emph{anywhere} and over \emph{anything}. Our leakage threshold (e.g. 10000 bits) could be much larger than typical secret key (e.g. AES key or RSA private key) size. Under such a strong leakage setting, we propose an efficient encryption scheme which is semantic secure in standard setting (i.e. without leakage) and can tolerate strong continuous leakage. We manage to construct such a secure scheme under strong leakage setting, by hiding partial (e.g. 1%1\%) ciphertext as secure as we hide the secret key using a small amount of more secure hardware resource, so that it is almost equally difficult for any adversary to steal information regarding this well-protected partial ciphertext or the secret key. We remark that, the size of such well-protected small portion of ciphertext is chosen to be much larger than the leakage threshold. We provide concrete and practical examples of such more secure hardware resource for data communication and data storage. Furthermore, we also introduce a new notion of computational entropy, as a sort of computational version of Kolmogorov complexity. Our quantitative analysis shows that, hiding partial ciphertext is a powerful countermeasure, which enables us to achieve higher security level than existing approaches in case of backdoor plus covert channel attacks. We also show the relationship between our new notion of computational entropy and existing relevant concepts, including Shannon-Entropy, Yao-Entropy, Hill-Entropy, All-or-Nothing Transform, and Exposure Resilient Function. This new computation entropy formulation may have independent interests

    Preparation for Post-Quantum era: a survey about blockchain schemes from a post-quantum perspective

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    Blockchain is a type of Distributed Ledger Technology (DLT) that has been included in various types of fields due to its numerous benefits: transparency, efficiency, reduced costs, decentralization, and distributivity realized through public-key cryptography and hash functions. At the same time, the increased progress of quantum computers and quantum-based algorithms threatens the security of the classical cryptographic algorithms, in consequence, it represents a risk for the Blockchain technology itself. This paper briefly presents the most relevant algorithms and procedures that have contributed to the progress of quantum computing and the categories of post-quantum cryptosystems. We also included a description of the current quantum capabilities because their evolution directly influences the necessity of increasing post-quantum research. Further, the paper continues as a guide to understanding the fundamentals of blockchain technology, and the primitives that are currently used to ensure security. We provide an analysis of the most important cryptocurrencies according to their ranking by market capitalization (MC) in the context of quantum threats, and we end up with a review of post-quantum blockchain (PQB) schemes proposals

    Quantum computing 40 years later

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    Forty years ago, Richard Feynman proposed harnessing quantum physics to build a more powerful kind of computer. Realizing Feynman's vision is one of the grand challenges facing 21st century science and technology. In this article, we'll recall Feynman's contribution that launched the quest for a quantum computer, and assess where the field stands 40 years later.Comment: 49 pages. To appear in Feynman Lectures on Computation, 2nd edition, published by Taylor & Francis Group, edited by Anthony J. G. Hey. (v2) typos correcte

    Efficient Statistical Zero-Knowledge Authentication Protocols for Smart Cards Secure Against Active & Concurrent Attacks

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    We construct statistical zero-knowledge authentication protocols for smart cards based on general assumptions. The main protocol is only secure against active attacks, but we present a modification based on trapdoor commitments that can resist concurrent attacks as well. Both protocols are instantiated using lattice-based primitives, which are conjectured to be secure against quantum attacks. We illustrate the practicality of our main protocol on smart cards in terms of storage, computation, communication, and round complexities. Furthermore, we compare it to other lattice-based authentication protocols, which are either zero-knowledge or have a similar structure. The comparison shows that our protocol improves the best previous protocol

    On Efficient Zero-Knowledge Arguments

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    Two results on spontaneous anonymous group signatures.

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    Chan Kwok Leong.Thesis (M.Phil.)--Chinese University of Hong Kong, 2005.Includes bibliographical references (leaves 72-78).Abstracts in English and Chinese.Chapter 1 --- Introduction --- p.1Chapter 2 --- Preliminaries --- p.4Chapter 2.1 --- Notation --- p.4Chapter 2.2 --- Cryptographic Primitives --- p.5Chapter 2.2.1 --- Symmetric Key Cryptography --- p.5Chapter 2.2.2 --- Asymmetric Key Cryptosystem --- p.6Chapter 2.2.3 --- Secure Hash Function --- p.7Chapter 2.2.4 --- Digital Signature --- p.8Chapter 2.2.5 --- Digital Certificate and Public Key Infrastructure --- p.8Chapter 2.3 --- Provable Security and Security Model --- p.9Chapter 2.3.1 --- Mathematics Background --- p.9Chapter 2.3.2 --- One-Way Function --- p.10Chapter 2.3.3 --- Candidate One-way Functions --- p.12Chapter 2.4 --- Proof Systems --- p.15Chapter 2.4.1 --- Zero-knowledge Protocol --- p.15Chapter 2.4.2 --- Proof-of-Knowledge Protocol --- p.17Chapter 2.4.3 --- Honest-Verifier Zero-Knowledge (HVZK) Proof of Knowl- edge Protocols (PoKs) --- p.18Chapter 2.5 --- Security Model --- p.19Chapter 2.5.1 --- Random Oracle Model --- p.19Chapter 2.5.2 --- Generic group model (GGM) --- p.20Chapter 3 --- Signature Scheme --- p.21Chapter 3.1 --- Introduction --- p.21Chapter 3.2 --- Security Notation for Digital Signature --- p.23Chapter 3.3 --- Security Proof for Digital Signature --- p.24Chapter 3.3.1 --- Random Oracle Model for Signature Scheme --- p.24Chapter 3.3.2 --- Adaptive Chosen Message Attack --- p.24Chapter 3.4 --- Schnorr Identification and Schnorr Signature --- p.25Chapter 3.4.1 --- Schnorr's ROS assumption --- p.26Chapter 3.5 --- Blind Signature --- p.27Chapter 4 --- Spontaneous Anonymous Group (SAG) Signature --- p.30Chapter 4.1 --- Introduction --- p.30Chapter 4.2 --- Background --- p.30Chapter 4.2.1 --- Group Signature --- p.30Chapter 4.2.2 --- Threshold Signature --- p.31Chapter 4.3 --- SAG signatures --- p.33Chapter 4.4 --- Formal Definitions and Constructions --- p.35Chapter 4.4.1 --- Ring-type construction --- p.36Chapter 4.4.2 --- CDS-type construction --- p.36Chapter 4.5 --- Discussion --- p.37Chapter 5 --- Blind Spontaneous Anonymous Signature --- p.39Chapter 5.1 --- Introduction --- p.39Chapter 5.2 --- Definition --- p.40Chapter 5.2.1 --- Security Model --- p.41Chapter 5.2.2 --- Definitions of security notions --- p.41Chapter 5.3 --- Constructing blind SAG signatures --- p.43Chapter 5.3.1 --- Blind SAG signature: CDS-type [1] --- p.43Chapter 5.3.2 --- "Blind SAG signature: ring-type [2, 3]" --- p.44Chapter 5.4 --- Security Analysis --- p.44Chapter 5.4.1 --- Multi-key parallel one-more unforgeability of blind signature --- p.45Chapter 5.4.2 --- Security of our blind SAG signatures --- p.47Chapter 5.5 --- Discussion --- p.49Chapter 6 --- Linkable Spontaneous Anonymous Group Signature --- p.51Chapter 6.1 --- introduction --- p.51Chapter 6.2 --- Related work --- p.51Chapter 6.3 --- Basic Building Blocks --- p.52Chapter 6.3.1 --- Proving the Knowledge of Several Discrete Logarithms --- p.53Chapter 6.3.2 --- Proving the Knowledge of d Out of n Equalities of Discrete Logarithms --- p.55Chapter 6.4 --- Security Model --- p.57Chapter 6.4.1 --- Syntax --- p.57Chapter 6.4.2 --- Notions of Security --- p.59Chapter 6.5 --- Our Construction --- p.63Chapter 6.5.1 --- An Linkable Threshold SAG Signature Scheme --- p.63Chapter 6.5.2 --- Security --- p.65Chapter 6.5.3 --- Discussions --- p.67Chapter 7 --- Conclusion --- p.70Bibliography --- p.7

    Studies in program obfuscation

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 159-164).Program obfuscation is the software analog to the problem of tamper-proofing hardware. The goal of program obfuscation is to construct a compiler, called an "obfuscator," that garbles the code of a computer program while maintaining its functionality. Commercial products exist to perform this procedure, but they do not provide a rigorous security guarantee. Over the past decade, program obfuscation has been studied by the theoretical cryptography community, where rigorous definitions of security have been proposed and obfuscators have been constructed for some families of programs. This thesis presents three contributions based on the virtual black-box security definition of Barak et al [10]. First, we show tight connections between obfuscation and symmetric-key encryption. Specifically, obfuscation can be used to construct an encryption scheme with strong leakage resilience and key-dependent message security. The converse is also true, and these connections scale with the level of security desired. As a result, the known constructions and impossibility results for each primitive carry over to the other. Second, we present two new security definitions that augment the virtual black-box property to incorporate non-malleability. The virtual black-box definition does not prevent an adversary from modifying an obfuscated program intelligently. By contrast, our new definitions provide software with the same security guarantees as tamper-proof and tamper-evident hardware, respectively. The first definition prohibits tampering, and the second definition requires that tampering is detectable after the fact. We construct non-malleable obfuscators of both favors for some program families of interest. Third, we present an obfuscator for programs that test for membership in a hyperplane. This generalizes prior works that obfuscate equality testing. We prove the security of the obfuscator under a new strong variant of the Decisional Diffie-Hellman assumption that holds in the generic group model. Additionally, we show a cryptographic application of the new obfuscator to leak-ageresilient one-time digital signatures. The thesis also includes a survey of the prior results in the field.by Mayank Varia.Ph.D

    Quantum algorithms for algebraic problems

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    Quantum computers can execute algorithms that dramatically outperform classical computation. As the best-known example, Shor discovered an efficient quantum algorithm for factoring integers, whereas factoring appears to be difficult for classical computers. Understanding what other computational problems can be solved significantly faster using quantum algorithms is one of the major challenges in the theory of quantum computation, and such algorithms motivate the formidable task of building a large-scale quantum computer. This article reviews the current state of quantum algorithms, focusing on algorithms with superpolynomial speedup over classical computation, and in particular, on problems with an algebraic flavor.Comment: 52 pages, 3 figures, to appear in Reviews of Modern Physic
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