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.
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.
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.
The Universal Composability framework was introduced by Canetti to study the security of protocols which are concurrently executed with other protocols in a network environment. Unfortunately it was shown that in the so called plain model, a large class of functionalities cannot be securely realized. These severe impossibility results motivated the study of other models involving some sort of setup assumptions, where general positive results can be obtained. Until recently, all the setup assumptions which were proposed required some trusted third party (or parties). Katz recently proposed using a physical setup to avoid such trusted setup assumptions. In his model, the physical setup phase includes the parties exchanging tamper proof hardware tokens implementing some functionality. The tamper proof hardware is modeled so as to assume that the receiver of the token can do nothing more than observe its input/output characteristics. It is further assumed that the sender knows the program code of the hardware token which it distributed. Based on the DDH assumption, Katz gave general positive results for universally composable multi-party computation tolerating any number of dishonest
The difficulty of every security proof of cryptographic protocols in UC framework(universally composable security analysis framework) is to construct a simulator correctly.However,there is no generally effective method used to construct a simulator.A desired method is proposed.Firstly,the building principle of UC framework is researched,and the essential requirement of UC security is analyzed.Secondly,the existence condition and simulation content of a simulator are given.Finally,an effective and universal solution to prove the security of cryptographic protocols in UC framework is formulated.The method is helpful understanding UC framework in-depth and in analyzing cryptographic protocols accurately using the framework.
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.
Designing secure protocols in the Universal Composability (UC) framework confers many advantages. In particular, it allows the protocols to be securely used as building blocks in more complex protocols, and assists in understanding their security properties. Unfortunately, most existing models in which universally composable computation is possible (for useful functionalities) require a trusted setup stage. Recently, Katz [Eurocrypt ’07] proposed an alternative to the trusted setup assumption: tamper-proof hardware. Instead of trusting a third party to correctly generate the setup information, each party can create its own hardware tokens, which it sends to the other parties. Each party is only required to trust that its own tokens are tamper-proof. Katz designed a UC commitment protocol that requires both parties to generate hardware tokens. In addition, his protocol relies on a specific number-theoretic assumption. In this paper, we construct UC commitment protocols for “David ” and “Goliath”: we only require a single party (Goliath) to be capable of generating tokens. We construct a version of the protocol that is secure for computationally unbounded parties, and a more efficient version that makes computational assumptions only about David (we require only the existence of a one-way function). Our protocols are simple enough to be performed by hand on David’s side. These properties may allow such protocols to be used in situations which are inherently asymmetric in real-life, especially those involving individuals versus large organizations. Classic examples include voting protocols (voters versus “the government”) and protocols involving private medical data (patients versus insurance-agencies or hospitals).
Abstract. We propose a new security measure for commitment pro-tocols, called Universally Composable (UC) Commitment. The measure guarantees that commitment protocols behave like an \\ideal commitment service, " even when concurrently composed with an arbitrary set of pro-tocols. This is a strong guarantee: it implies that security is maintained even when an unbounded number of copies of the scheme are running concurrently, it implies non-malleability (not only with respect to other copies of the same protocol but even with respect to other protocols), it provides resilience to selective decommitment, and more. Unfortunately, two-party uc commitment protocols do not exist in the plain model. However, we construct two-party uc commitment proto-cols, based on general complexity assumptions, in the common reference string model where all parties have access to a common string taken from a predetermined distribution. The protocols are non-interactive, in the sense that both the commitment and the opening phases consist of a single message from the committer to the receiver.