The Experts below are selected from a list of 7671 Experts worldwide ranked by ideXlab platform
Dennis Hofheinz - One of the best experts on this subject based on the ideXlab platform.
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GNUC: A New Universal Composability Framework
Journal of Cryptology, 2015Co-Authors: Dennis Hofheinz, Victor ShoupAbstract:We put forward a framework for the modular design and analysis of multi-party protocols. Our framework is called “GNUC” (with the recursive meaning “GNUC’s Not UC”), already alluding to the similarity to Canetti’s Universal Composability (UC) framework. In particular, like UC, we offer a universal Composition Theorem, as well as a Theorem for composing protocols with joint state. We deviate from UC in several important aspects. Specifically, we have a rather different view than UC on the structuring of protocols, on the notion of polynomial-time protocols and attacks, and on corruptions. We will motivate our definitional choices by explaining why the definitions in the UC framework are problematic, and how we overcome these problems. Our goal is to offer a framework that is largely compatible with UC, such that previous results formulated in UC carry over to GNUC with minimal changes. We exemplify this by giving explicit formulations for several important protocol tasks, including authenticated and secure communication, as well as commitment and secure function evaluation.
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Polynomial Runtime and Composability
Journal of Cryptology, 2013Co-Authors: Dennis Hofheinz, Dominique Unruh, Jörn Müller-quadeAbstract:We devise a notion of polynomial runtime suitable for the simulation-based security analysis of multi-party cryptographic protocols. Somewhat surprisingly, straightforward notions of polynomial runtime lack expressivity for reactive tasks and/or lead to an unnatural simulation-based security notion. Indeed, the problem has been recognized in previous works, and several notions of polynomial runtime have already been proposed. However, our new notion, dubbed reactive polynomial time , is the first to combine the following properties: it is simple enough to support simple security/runtime analyses, it is intuitive in the sense that all intuitively feasible protocols and attacks (and only those) are considered polynomial-time, it supports secure Composition of protocols in the sense of a universal Composition Theorem. We work in the Universal Composability (UC) protocol framework. We remark that while the UC framework already features a universal Composition Theorem, we develop new techniques to prove secure Composition in the case of reactively polynomial-time protocols and attacks.
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Some (in)sufficient conditions for secure hybrid encryption
Information and Computation, 2010Co-Authors: Javier Herranz, Dennis Hofheinz, Eike KiltzAbstract:AbstractIn hybrid public key encryption (PKE), first a key encapsulation mechanism (KEM) is used to fix a random session key that is then fed into a highly efficient data encapsulation mechanism (DEM) to encrypt the actual message. A well-known Composition Theorem states that if both the KEM and the DEM have a high enough level of security (i.e., security against chosen-ciphertext attacks), then so does the hybrid PKE scheme. It is not known if these strong security requirements on the KEM and DEM are also necessary, nor if such general Composition Theorems exist for weaker levels of security.Using six different security notions for KEMs, 10 for DEMs, and six for PKE schemes, we completely characterize in this work which combinations lead to a secure hybrid PKE scheme (by proving a Composition Theorem) and which do not (by providing counterexamples). Furthermore, as an independent result, we revisit and extend prior work on the relations among security notions for KEMs and DEMs
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ISC - On the notion of statistical security in simulatability definitions
Lecture Notes in Computer Science, 2005Co-Authors: Dennis Hofheinz, Dominique UnruhAbstract:We investigate the definition of statistical security (i.e., security against unbounded adversaries) in the framework of reactive simulatability. This framework allows to formulate and analyze multi-party protocols modularly by providing a Composition Theorem for protocols. However, we show that the notion of statistical security, as defined by Backes, Pfitzmann and Waidner for the reactive simulatability framework, does not allow for secure Composition of protocols. This in particular invalidates the proof of the Composition Theorem. We give evidence that the reason for the non-composability of statistical security is no artifact of the framework itself, but of the particular formulation of statistical security. Therefore, we give a modified notion of statistical security in the reactive simulatability framework. We prove that this notion allows for secure Composition of protocols. As to the best of our knowledge, no formal definition of statistical security has been fixed for Canetti's universal composability framework, we believe that our observations and results can also help to avoid potential pitfalls there.
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CSFW - Polynomial runtime in simulatability definitions
18th IEEE Computer Security Foundations Workshop (CSFW'05), 1Co-Authors: Dennis Hofheinz, Jörn Müller-quade, Dominique UnruhAbstract:We elaborate on the problem of polynomial runtime in simulatability definitions for multiparty computation. First, the need for a new definition is demonstrated by showing which problems occur with common definitions of polynomial runtime. Then, we give a definition which captures in an intuitive manner what it means for a protocol or an adversary to have polynomial runtime. We show that this notion is suitable for simulatability definitions for multiparty computation. In particular, a Composition Theorem is shown for this notion.
Zhihan Zhao - One of the best experts on this subject based on the ideXlab platform.
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a new Composition Theorem for square mean almost automorphic functions and applications to stochastic differential equations
Nonlinear Analysis-theory Methods & Applications, 2011Co-Authors: Zhihan Zhao, Yongkui Chang, Gaston M NguerekataAbstract:Abstract In this paper, we establish a new Composition Theorem for square-mean almost automorphic functions under conditions which are different from Lipschitz conditions in the literature. We apply this new Composition Theorem together with Schauder’s fixed point Theorem to investigate the existence of square-mean almost automorphic mild solutions for a stochastic differential equation in a real separable Hilbert space. Finally, an interesting corollary is also given for the sub-linear growth cases.
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a new Composition Theorem for s p weighted pseudo almost periodic functions and applications to semilinear differential equations
Opuscula Mathematica, 2011Co-Authors: Zhihan Zhao, Yongkui Chang, Gaston M NguerekataAbstract:In this paper, we establish a new Composition Theorem for \(S^p\)-weighted pseudo almost periodic functions under weaker conditions than the Lipschitz ones currently encountered in the literatures. We apply this new Composition Theorem along with the Schauder's fixed point Theorem to obtain new existence Theorems for weighted pseudo almost periodic mild solutions to a semilinear differential equation in a Banach space.
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A new Composition Theorem for S^{p}-weighted pseudo almost periodic functions and applications to semilinear differential equations
Opuscula Mathematica, 2011Co-Authors: Zhihan Zhao, Yongkui Chang, Gaston M. N’guérékataAbstract:Tyt. z nagłówka.Bibliogr. s. 472-474.Dostępny również w formie drukowanej.ABSTRACT: In this paper, we establish a new Composition Theorem for Sp-weighted pseudo almost periodic functions under weaker conditions than the Lipschitz ones currently encountered in the literatures. We apply this new Composition Theorem along with the Schauder's fixed point Theorem to obtain new existence Theorems for weighted pseudo almost periodic mild solutions to a semilinear differential equation in a Banach space. KEYWORDS: Sp-weighted pseudo almost periodic, weighted pseudo almost periodicity, semilinear differential equations
Gaston M Nguerekata - One of the best experts on this subject based on the ideXlab platform.
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a new Composition Theorem for square mean almost automorphic functions and applications to stochastic differential equations
Nonlinear Analysis-theory Methods & Applications, 2011Co-Authors: Zhihan Zhao, Yongkui Chang, Gaston M NguerekataAbstract:Abstract In this paper, we establish a new Composition Theorem for square-mean almost automorphic functions under conditions which are different from Lipschitz conditions in the literature. We apply this new Composition Theorem together with Schauder’s fixed point Theorem to investigate the existence of square-mean almost automorphic mild solutions for a stochastic differential equation in a real separable Hilbert space. Finally, an interesting corollary is also given for the sub-linear growth cases.
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a new Composition Theorem for s p weighted pseudo almost periodic functions and applications to semilinear differential equations
Opuscula Mathematica, 2011Co-Authors: Zhihan Zhao, Yongkui Chang, Gaston M NguerekataAbstract:In this paper, we establish a new Composition Theorem for \(S^p\)-weighted pseudo almost periodic functions under weaker conditions than the Lipschitz ones currently encountered in the literatures. We apply this new Composition Theorem along with the Schauder's fixed point Theorem to obtain new existence Theorems for weighted pseudo almost periodic mild solutions to a semilinear differential equation in a Banach space.
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a Composition Theorem for weighted pseudo almost automorphic functions and applications
Nonlinear Analysis-theory Methods & Applications, 2010Co-Authors: Huisheng Ding, Wei Long, Gaston M NguerekataAbstract:Abstract In this paper, we establish a Composition Theorem for weighted pseudo-almost automorphic functions under a weaker Lipschitz condition. Our Composition Theorem generalizes some known results. Moreover, the existence and uniqueness of pseudo-almost automorphic solutions for abstract semilinear evolution equations are studied.
Yongkui Chang - One of the best experts on this subject based on the ideXlab platform.
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Stepanov type weighted pseudo almost automorphic sequences and their applications to difference equations
Nonlinear Studies, 2014Co-Authors: Syed Abbas, Yongkui Chang, Mokhtar HafayedAbstract:In this paper, we shall define the concept of Stepanov type weighted pseudo almost automorphic sequence and prove some basic results like Composition Theorem. Further, we investigate the existence, uniqueness of Stepanov type weighted pseudo almost automorphic sequence solutions to a difference equation as an application. The result obtained extends the theory of pseudo and weighted pseudo almost automorphic sequences to more general class of Stepanov type weighted pseudo almost automorphic sequence.
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Existence of μ-pseudo almost automorphic solutions to a neutral differential equation by interpolation theory
Filomat, 2014Co-Authors: Yongkui Chang, Xiao-xia LuoAbstract:In this paper, we shall deal with ?-pseudo almost automorphic solutions to a neutral differential equation. To achieve this goal, we first prove a Composition Theorem for ?-pseudo almost automorphic functions under suitable conditions, and then apply it to investigate some existence results by the interpolation theory and fixed point methods.
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a new Composition Theorem for square mean almost automorphic functions and applications to stochastic differential equations
Nonlinear Analysis-theory Methods & Applications, 2011Co-Authors: Zhihan Zhao, Yongkui Chang, Gaston M NguerekataAbstract:Abstract In this paper, we establish a new Composition Theorem for square-mean almost automorphic functions under conditions which are different from Lipschitz conditions in the literature. We apply this new Composition Theorem together with Schauder’s fixed point Theorem to investigate the existence of square-mean almost automorphic mild solutions for a stochastic differential equation in a real separable Hilbert space. Finally, an interesting corollary is also given for the sub-linear growth cases.
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a new Composition Theorem for s p weighted pseudo almost periodic functions and applications to semilinear differential equations
Opuscula Mathematica, 2011Co-Authors: Zhihan Zhao, Yongkui Chang, Gaston M NguerekataAbstract:In this paper, we establish a new Composition Theorem for \(S^p\)-weighted pseudo almost periodic functions under weaker conditions than the Lipschitz ones currently encountered in the literatures. We apply this new Composition Theorem along with the Schauder's fixed point Theorem to obtain new existence Theorems for weighted pseudo almost periodic mild solutions to a semilinear differential equation in a Banach space.
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A new Composition Theorem for S^{p}-weighted pseudo almost periodic functions and applications to semilinear differential equations
Opuscula Mathematica, 2011Co-Authors: Zhihan Zhao, Yongkui Chang, Gaston M. N’guérékataAbstract:Tyt. z nagłówka.Bibliogr. s. 472-474.Dostępny również w formie drukowanej.ABSTRACT: In this paper, we establish a new Composition Theorem for Sp-weighted pseudo almost periodic functions under weaker conditions than the Lipschitz ones currently encountered in the literatures. We apply this new Composition Theorem along with the Schauder's fixed point Theorem to obtain new existence Theorems for weighted pseudo almost periodic mild solutions to a semilinear differential equation in a Banach space. KEYWORDS: Sp-weighted pseudo almost periodic, weighted pseudo almost periodicity, semilinear differential equations
Victor Shoup - One of the best experts on this subject based on the ideXlab platform.
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GNUC: A New Universal Composability Framework
Journal of Cryptology, 2015Co-Authors: Dennis Hofheinz, Victor ShoupAbstract:We put forward a framework for the modular design and analysis of multi-party protocols. Our framework is called “GNUC” (with the recursive meaning “GNUC’s Not UC”), already alluding to the similarity to Canetti’s Universal Composability (UC) framework. In particular, like UC, we offer a universal Composition Theorem, as well as a Theorem for composing protocols with joint state. We deviate from UC in several important aspects. Specifically, we have a rather different view than UC on the structuring of protocols, on the notion of polynomial-time protocols and attacks, and on corruptions. We will motivate our definitional choices by explaining why the definitions in the UC framework are problematic, and how we overcome these problems. Our goal is to offer a framework that is largely compatible with UC, such that previous results formulated in UC carry over to GNUC with minimal changes. We exemplify this by giving explicit formulations for several important protocol tasks, including authenticated and secure communication, as well as commitment and secure function evaluation.
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a Composition Theorem for universal one way hash functions
Theory and Application of Cryptographic Techniques, 2000Co-Authors: Victor ShoupAbstract:In this paper we present a new scheme for constructing universal one-way hash functions that hash arbitrarily long messages out of universal one-way hash functions that hash fixed-length messages. The new construction is extremely simple and is also very efficient, yielding shorter keys than previously proposed Composition constructions.