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Journal of Sichuan University

A Trust Model of UC Secure Computation

Jie Hu, Pla Inf

Published Jan 1, 2012• 0 citations
OpenAlex

Abstract

By the analysis of the reason of using a trust model in UC(Universally Composable) secure computation,overseas existing trust models were researched and their merits and demerits were indicated.Then based on Divided Bi-Trapdoor,a trust model named DBT that has the flavor of a public-key infrastructure was proposed,and as an experiment,a UC secure commitment protocol was implemented in this model.The DBT model has the complementary benefits of the existing models,and especially supports the full-simulation of protocols.

Related papers

Universally Composable Secure Commitment Protocol Based on Tamper-proof Hardware Model

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Beginning with the research of the basic concepts of Universally Composable(UC) framework,the requirement of UC security on commitment protocols is analyzed in this paper,and the reason of the problem that all UC commitment protocols do not exist in the plain model is pointed out that the security requirement of commitment protocol and the requirement of UC security are contradictory.On the basis of this,a UC secure commitment protocol UCCOM using tamper-proof hardware is proposed.Analysis result shows that UCCOM does not depend on any trusted third-party and uses fewer cryptographic operations compared with the related works,so it has higer efficiency.

•Jan 1, 2013•0 citations

Obtaining Universally Composable Security: Towards the Bare Bones of Trust.

Ran Canetti

A desirable goal for cryptographic protocols is to guarantee security when the protocol is composed with other protocol instances. Universally Composable (UC) security provides this guarantee in a strong sense: A UC-secure protocol maintains its security properties even when composed concurrently with an unbounded number of instances of arbitrary protocols. However, many interesting cryptographic tasks are provably impossible to realize with UC security in the standard, “plain” model of computation. Impossibility holds even if ideally authenticated communication channels are provided. In contrast, it has been demonstrated that general secure computation can be obtained in a number of idealized models. Each one of these models represents a form of trust that is put in some of the system’s components. This survey examines and compares some of these trust models, both from the point of view of their sufficiency for building UC secure protocols, and from the point of view of their practical realizability. We start with the common reference string (CRS) model, and then describe several relaxations and alternatives including the Defective CRS model, the key registration models, the hardware token model, the global and augmented CRS models, and a timing assumption. Finally, we briefly touch upon trust models for obtaining authenticated communication.

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Universally Composable Protocols with Relaxed Set-Up Assumptions

Boaz Barak, Ran Canetti, Jesper Buus Nielsen +1 more

A desirable goal for cryptographic protocols is to guarantee security when the protocol is composed with other protocol instances. Universally composable (UC) protocols provide this guarantee in a strong sense: A protocol remains secure even when composed concurrently with an unbounded number of instances of arbitrary protocols. However, UC protocols for carrying out general tasks are known to exist only if a majority of the participants are honest, or in the common reference string (CRS) model where all parties are assumed to have access to a common string that is drawn from some pre-defined distribution. Furthermore, carrying out many interesting tasks in a UC manner and without honest majority or set-up assumptions is impossible, even if ideally authenticated communication is provided. A natural question is thus whether there exist more relaxed set-up assumptions than the CRS model that still allow for UC protocols. We answer this question in the affirmative: we propose alternative and relaxed set-up assumptions and show that they suffice for reproducing the general feasibility results for UC protocols in the CRS model. These alternative assumptions have the flavor of a "public-key infrastructure": parties have registered public keys, no single registration authority needs to be fully trusted, and no single piece of information has to be globally trusted and available. In addition, unlike known protocols in the CRS model, the proposed protocols guarantee some basic level of security even if the set-up assumption is violated.

Annual Symposium on Foundations of Computer Science•Dec 23, 2004•228 citations

Enhanced security models for network protocols

Yevgeniy Dodis, Shabsi Walfish

Modeling security for protocols running in the complex network environment of the Internet can be a daunting task. Ideally, a security model for the Internet should provide the following guarantee: a protocol that implements a particular task specification will retain all the same security properties as the specification itself, even when an arbitrary set of protocols runs concurrently on the same network. This guarantee must hold even when other protocols are maliciously designed to interact badly with the analyzed protocol, and even when the analyzed protocol is composed with other protocols. The popular Universal Composability (UC) security framework aims to provide this guarantee. Unfortunately, such strong security guarantees come with a price: they are impossible to achieve without the use of some trusted setup. Typically, this trusted setup is global in nature, and takes the form of a Public Key Infrastructure (PKI) and/or a Common Reference String (CRS). However, the current approach to modeling security in the presence of such setups falls short of providing expected security guarantees. A quintessential example of this phenomenon is the deniability concern: there exist natural protocols that meet the strongest known security notions (including UC) while failing to provide the same deniability guarantees that their task specifications imply they should provide. We introduce the Generalized Universal Composability (GUC) framework to extend the UC security notion and enable the re-establishment of its original intuitive security guarantees even for protocols that use global trusted setups. In particular, GUC enables us to guarantee that secure protocols will provide the same level of deniability as the task specification they implement. To demonstrate the usefulness of the GUC framework, we first apply it to the analysis and construction of deniable authentication protocols. Building upon such deniable authentication protocols, we then prove a general feasibility result showing how to construct protocols satisfying our security notion for a large class of two-party and multi-party tasks (assuming the availability of some reasonable trusted setup). Finally, we highlight the practical applicability of GUC by constructing efficient protocols that securely instantiate two common cryptographic tasks: commitments and zero-knowledge proofs.

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On the Necessary and Sufficient Assumptions for UC Computation.

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Abstract. We study the necessary and sufficient assumptions for universally composable (UC) computation, both in terms of setup and computational assumptions. We look at the common reference string model, the uniform random string model and the key-registration authority model (KRA), and provide new results for all of them. Perhaps most interestingly we show that: – For even the minimal meaningful KRA, where we only assume that the secret key is a value which is hard to compute from the public key, one can UC securely compute any poly-time functionality if there exists a passive secure oblivious-transfer protocol for the stand-alone model. Since a KRA where the secret keys can be computed from the public keys is useless, and some setup assumption is needed for UC secure computation, this establishes the best we could hope for the KRA model: any non-trivial KRA is sufficient for UC computation. – We show that in the KRA model one-way functions are sufficient for UC commitment and UC zero-knowledge. These are the first examples of UC secure protocols for non-trivial tasks which do not assume the existence of public-key primitives. In particular, the protocols show that non-trivial UC computation is possible in Minicrypt. 1

•Jan 1, 2009•2 citations

UC-Secure Non-interactive Public-Key Encryption

Jan L. Camenisch, Anja Lehmann, Gregory Neven +1 more

The universal composability (UC) framework enables the modular design of cryptographic protocols by allowing arbitrary compositions of lower-level building blocks. Public-key encryption is unarguably a very important such building block. However, so far no UC-functionality exists that offers non-interactive encryption necessary for modular protocol construction. We provide an ideal functionality for non-committing encryption (i.e., public-key encryption secure against adaptive corruptions) with locally generated, and therefore non-interactive, ciphertexts. As a sanity check, we also provide a property-based security notion that we prove to be equivalent to the UC notion. We then show that the encryption scheme of Camenisch et al. (SCN '16) based on trapdoor permutations securely implements our notion in the random-oracle model without assuming secure erasures. This is the best one can hope to achieve as standard-model constructions do not exist due to the uninstantiability of round-optimal adaptively secure message transfer in the standard model (Nielsen, Crypto '02). We illustrate the modular reusability of our functionality by constructing the first non-interactive signcryption scheme secure against adaptive corruptions without secure erasures in the UC framework.

IEEE Computer Security Foundations Workshop (CSFW)•Aug 1, 2017•7 citations
By the analysis of the reason of using a trust model in UC(Universally Composable) secure computation,overseas existing trust models were researched and their merits and demerits were indicated.Then based on Divided Bi-Trapdoor,a trust model named DBT that has the flavor of a public-key infrastructure was proposed,and as an experiment,a UC secure commitment protocol was implemented in this model.The DBT model has the complementary benefits of the existing models,and especially supports the full-simulation of protocols.
Beginning with the research of the basic concepts of Universally Composable(UC) framework,the requirement of UC security on commitment protocols is analyzed in this paper,and the reason of the problem that all UC commitment protocols do not exist in the plain model is pointed out that the security requirement of commitment protocol and the requirement of UC security are contradictory.On the basis of this,a UC secure commitment protocol UCCOM using tamper-proof hardware is proposed.Analysis result shows that UCCOM does not depend on any trusted third-party and uses fewer cryptographic operations compared with the related works,so it has higer efficiency.
A desirable goal for cryptographic protocols is to guarantee security when the protocol is composed with other protocol instances. Universally Composable (UC) security provides this guarantee in a strong sense: A UC-secure protocol maintains its security properties even when composed concurrently with an unbounded number of instances of arbitrary protocols. However, many interesting cryptographic tasks are provably impossible to realize with UC security in the standard, “plain” model of computation. Impossibility holds even if ideally authenticated communication channels are provided. In contrast, it has been demonstrated that general secure computation can be obtained in a number of idealized models. Each one of these models represents a form of trust that is put in some of the system’s components. This survey examines and compares some of these trust models, both from the point of view of their sufficiency for building UC secure protocols, and from the point of view of their practical realizability. We start with the common reference string (CRS) model, and then describe several relaxations and alternatives including the Defective CRS model, the key registration models, the hardware token model, the global and augmented CRS models, and a timing assumption. Finally, we briefly touch upon trust models for obtaining authenticated communication.
A desirable goal for cryptographic protocols is to guarantee security when the protocol is composed with other protocol instances. Universally composable (UC) protocols provide this guarantee in a strong sense: A protocol remains secure even when composed concurrently with an unbounded number of instances of arbitrary protocols. However, UC protocols for carrying out general tasks are known to exist only if a majority of the participants are honest, or in the common reference string (CRS) model where all parties are assumed to have access to a common string that is drawn from some pre-defined distribution. Furthermore, carrying out many interesting tasks in a UC manner and without honest majority or set-up assumptions is impossible, even if ideally authenticated communication is provided. A natural question is thus whether there exist more relaxed set-up assumptions than the CRS model that still allow for UC protocols. We answer this question in the affirmative: we propose alternative and relaxed set-up assumptions and show that they suffice for reproducing the general feasibility results for UC protocols in the CRS model. These alternative assumptions have the flavor of a "public-key infrastructure": parties have registered public keys, no single registration authority needs to be fully trusted, and no single piece of information has to be globally trusted and available. In addition, unlike known protocols in the CRS model, the proposed protocols guarantee some basic level of security even if the set-up assumption is violated.
Modeling security for protocols running in the complex network environment of the Internet can be a daunting task. Ideally, a security model for the Internet should provide the following guarantee: a protocol that implements a particular task specification will retain all the same security properties as the specification itself, even when an arbitrary set of protocols runs concurrently on the same network. This guarantee must hold even when other protocols are maliciously designed to interact badly with the analyzed protocol, and even when the analyzed protocol is composed with other protocols. The popular Universal Composability (UC) security framework aims to provide this guarantee. Unfortunately, such strong security guarantees come with a price: they are impossible to achieve without the use of some trusted setup. Typically, this trusted setup is global in nature, and takes the form of a Public Key Infrastructure (PKI) and/or a Common Reference String (CRS). However, the current approach to modeling security in the presence of such setups falls short of providing expected security guarantees. A quintessential example of this phenomenon is the deniability concern: there exist natural protocols that meet the strongest known security notions (including UC) while failing to provide the same deniability guarantees that their task specifications imply they should provide. We introduce the Generalized Universal Composability (GUC) framework to extend the UC security notion and enable the re-establishment of its original intuitive security guarantees even for protocols that use global trusted setups. In particular, GUC enables us to guarantee that secure protocols will provide the same level of deniability as the task specification they implement. To demonstrate the usefulness of the GUC framework, we first apply it to the analysis and construction of deniable authentication protocols. Building upon such deniable authentication protocols, we then prove a general feasibility result showing how to construct protocols satisfying our security notion for a large class of two-party and multi-party tasks (assuming the availability of some reasonable trusted setup). Finally, we highlight the practical applicability of GUC by constructing efficient protocols that securely instantiate two common cryptographic tasks: commitments and zero-knowledge proofs.
Abstract. We study the necessary and sufficient assumptions for universally composable (UC) computation, both in terms of setup and computational assumptions. We look at the common reference string model, the uniform random string model and the key-registration authority model (KRA), and provide new results for all of them. Perhaps most interestingly we show that: – For even the minimal meaningful KRA, where we only assume that the secret key is a value which is hard to compute from the public key, one can UC securely compute any poly-time functionality if there exists a passive secure oblivious-transfer protocol for the stand-alone model. Since a KRA where the secret keys can be computed from the public keys is useless, and some setup assumption is needed for UC secure computation, this establishes the best we could hope for the KRA model: any non-trivial KRA is sufficient for UC computation. – We show that in the KRA model one-way functions are sufficient for UC commitment and UC zero-knowledge. These are the first examples of UC secure protocols for non-trivial tasks which do not assume the existence of public-key primitives. In particular, the protocols show that non-trivial UC computation is possible in Minicrypt. 1
The universal composability (UC) framework enables the modular design of cryptographic protocols by allowing arbitrary compositions of lower-level building blocks. Public-key encryption is unarguably a very important such building block. However, so far no UC-functionality exists that offers non-interactive encryption necessary for modular protocol construction. We provide an ideal functionality for non-committing encryption (i.e., public-key encryption secure against adaptive corruptions) with locally generated, and therefore non-interactive, ciphertexts. As a sanity check, we also provide a property-based security notion that we prove to be equivalent to the UC notion. We then show that the encryption scheme of Camenisch et al. (SCN '16) based on trapdoor permutations securely implements our notion in the random-oracle model without assuming secure erasures. This is the best one can hope to achieve as standard-model constructions do not exist due to the uninstantiability of round-optimal adaptively secure message transfer in the standard model (Nielsen, Crypto '02). We illustrate the modular reusability of our functionality by constructing the first non-interactive signcryption scheme secure against adaptive corruptions without secure erasures in the UC framework.