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Universally composable security: A new paradigm for cryptographic protocols
, 2013
"... We present a general framework for representing cryptographic protocols and analyzing their security. The framework allows specifying the security requirements of practically any cryptographic task in a unified and systematic way. Furthermore, in this framework the security of protocols is preserved ..."
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Cited by 833 (37 self)
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We present a general framework for representing cryptographic protocols and analyzing their security. The framework allows specifying the security requirements of practically any cryptographic task in a unified and systematic way. Furthermore, in this framework the security of protocols is preserved under a general protocol composition operation, called universal composition. The proposed framework with its securitypreserving composition operation allows for modular design and analysis of complex cryptographic protocols from relatively simple building blocks. Moreover, within this framework, protocols are guaranteed to maintain their security in any context, even in the presence of an unbounded number of arbitrary protocol instances that run concurrently in an adversarially controlled manner. This is a useful guarantee, that allows arguing about the security of cryptographic protocols in complex and unpredictable environments such as modern communication networks.
An efficient system for nontransferable anonymous credentials with optional anonymity revocation
, 2001
"... A credential system is a system in which users can obtain credentials from organizations and demonstrate possession of these credentials. Such a system is anonymous when transactions carried out by the same user cannot be linked. An anonymous credential system is of significant practical relevance ..."
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Cited by 308 (13 self)
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A credential system is a system in which users can obtain credentials from organizations and demonstrate possession of these credentials. Such a system is anonymous when transactions carried out by the same user cannot be linked. An anonymous credential system is of significant practical relevance because it is the best means of providing privacy for users. In this paper we propose a practical anonymous credential system that is based on the strong RSA assumption and the decisional DiffieHellman assumption modulo a safe prime product and is considerably superior to existing ones: (1) We give the first practical solution that allows a user to unlinkably demonstrate possession of a credential as many times as necessary without involving the issuing organization. (2) To prevent misuse of anonymity, our scheme is the first to offer optional anonymity revocation for particular transactions. (3) Our scheme offers separability: all organizations can choose their cryptographic keys independently of each other. Moreover, we suggest more effective means of preventing users from sharing their credentials, by introducing allornothing sharing: a user who allows a friend to use one of her credentials once, gives him the ability to use all of her credentials, i.e., taking over her identity. This is implemented by a new primitive, called circular encryption, which is of independent interest, and can be realized from any semantically secure cryptosystem in the random oracle model.
Direct Anonymous Attestation
, 2004
"... This paper describes the direct anonymous attestation scheme (DAA). This scheme was adopted by the Trusted Computing Group as the method for remote authentication of a hardware module, called trusted platform module (TPM), while preserving the privacy of the user of the platform that contains the ..."
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Cited by 215 (24 self)
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This paper describes the direct anonymous attestation scheme (DAA). This scheme was adopted by the Trusted Computing Group as the method for remote authentication of a hardware module, called trusted platform module (TPM), while preserving the privacy of the user of the platform that contains the module. Direct anonymous attestation can be seen as a group signature without the feature that a signature can be opened, i.e., the anonymity is not revocable. Moreover, DAA allows for pseudonyms, i.e., for each signature a user (in agreement with the recipient of the signature) can decide whether or not the signature should be linkable to another signature. DAA furthermore allows for detection of "known" keys: if the DAA secret keys are extracted from a TPM and published, a verifier can detect that a signature was produced using these secret keys. The scheme is provably secure in the random oracle model under the strong RSA and the decisional DiffieHellman assumption.
Dynamic accumulators and application to efficient revocation of anonymous credentials
, 2002
"... We introduce the notion of a dynamic accumulator. Anaccumulator scheme allows one to hash a large set of inputs into one short value, such that there is a short proof that a given input was incorporated into this value. A dynamic accumulator allows one to dynamically add and delete a value, such th ..."
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Cited by 213 (11 self)
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We introduce the notion of a dynamic accumulator. Anaccumulator scheme allows one to hash a large set of inputs into one short value, such that there is a short proof that a given input was incorporated into this value. A dynamic accumulator allows one to dynamically add and delete a value, such that the cost of an add or delete is independent of the number of accumulated values. We provide a construction of a dynamic accumulator and an efficient zeroknowledge proof of knowledge of an accumulated value. We prove their security under the strong RSA assumption. We then show that our construction of dynamic accumulators enables efficient revocation of anonymous credentials, and membership revocation for recent group signature and identity escrow schemes.
A Model for Asynchronous Reactive Systems and its Application to Secure Message Transmission
, 2000
"... We present the first rigorous model for secure reactive systems in asynchronous networks with a sound cryptographic semantics, supporting abstract specifications and the composition of secure systems. This enables modular proofs of security, which is essential in bridging the gap between the rigorou ..."
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Cited by 176 (20 self)
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We present the first rigorous model for secure reactive systems in asynchronous networks with a sound cryptographic semantics, supporting abstract specifications and the composition of secure systems. This enables modular proofs of security, which is essential in bridging the gap between the rigorous proof techniques of cryptography and toolsupported formal proof techniques. The model follows the general simulatability approach of modern cryptography. A variety of network structures and trust models can be described, such as static and adaptive adversaries. As an example of our specification methodology we provide the first abstract and complete specification for Secure Message Transmission, improving on recent results by Lynch, and verify one concrete implementation. Our proof is based on a general theorem on the security of encryption in a reactive multiuser setting, generalizing a recent result by Bellare et al.
Universally Composable TwoParty and MultiParty Secure Computation
, 2002
"... We show how to securely realize any twoparty and multiparty functionality in a universally composable way, regardless of the number of corrupted participants. That is, we consider an asynchronous multiparty network with open communication and an adversary that can adaptively corrupt as many pa ..."
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Cited by 151 (34 self)
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We show how to securely realize any twoparty and multiparty functionality in a universally composable way, regardless of the number of corrupted participants. That is, we consider an asynchronous multiparty network with open communication and an adversary that can adaptively corrupt as many parties as it wishes. In this setting, our protocols allow any subset of the parties (with pairs of parties being a special case) to securely realize any desired functionality of their local inputs, and be guaranteed that security is preserved regardless of the activity in the rest of the network. This implies that security is preserved under concurrent composition of an unbounded number of protocol executions, it implies nonmalleability with respect to arbitrary protocols, and more. Our constructions are in the common reference string model and rely on standard intractability assumptions.
Indifferentiability, impossibility results on reductions, and applications to the random oracle methodology
 Theory of Cryptography  TCC 2004, Lecture Notes in Computer Science
, 2004
"... Abstract. The goals of this paper are threefold. First we introduce and motivate a generalization of the fundamental concept of the indistinguishability of two systems, called indifferentiability. This immediately leads to a generalization of the related notion of reducibility of one system to anot ..."
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Cited by 96 (2 self)
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Abstract. The goals of this paper are threefold. First we introduce and motivate a generalization of the fundamental concept of the indistinguishability of two systems, called indifferentiability. This immediately leads to a generalization of the related notion of reducibility of one system to another. Second, we prove that indifferentiability is the necessary and sufficient condition on two systems S and T such that the security of any cryptosystem using T as a component is not affected when T is substituted by S. In contrast to indistinguishability, indifferentiability is applicable in settings where a possible adversary is assumed to have access to additional information about the internal state of the involved systems, for instance the public parameter selecting a member from a family of hash functions. Third, we state an easily verifiable criterion for a system U not to be reducible (according to our generalized definition) to another system V and, as an application, prove that a random oracle is not reducible to a weaker primitive, called asynchronous beacon, and also that an asynchronous beacon is not reducible to a finitelength random string. Each of these irreducibility results alone implies the main theorem of Canetti, Goldreich and Halevi stating that there exist cryptosystems that are secure in the random oracle model but for which replacing the random oracle by any implementation leads to an insecure cryptosystem. Key words. Indistinguishability, reductions, indifferentiability, security proofs, random oracle methodology, hash functions.
A General Composition Theorem for Secure Reactive Systems
 In TCC 2004
, 2004
"... We consider compositional properties of reactive systems that are secure in a cryptographic sense. We follow the wellknown simulatability approach of modern cryptography, i.e., the specification is an ideal system and a real system should in some sense simulate this ideal one. We show that if a ..."
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Cited by 75 (8 self)
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We consider compositional properties of reactive systems that are secure in a cryptographic sense. We follow the wellknown simulatability approach of modern cryptography, i.e., the specification is an ideal system and a real system should in some sense simulate this ideal one. We show that if a system consists of a polynomial number of arbitrary ideal subsystems such that each of them has a secure implementation in the sense of blackbox simulatability, then one can securely replace all ideal subsystems with their respective secure counterparts without destroying the blackbox simulatability relation. We further prove our theorem for universal simulatability by showing that blackbox simulatability implies universal simulatability under reasonable assumptions. We show all our results with concrete security.
Universally Composable Privacy Amplification against Quantum Adversaries
, 2004
"... Privacy amplification is the art of shrinking a partially secret string Z to a highly secret key S. We introduce a universally composable security definition for secret keys in a context where an adversary holds quantum information and show that privacy amplification by twouniversal hashing is secu ..."
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Cited by 71 (12 self)
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Privacy amplification is the art of shrinking a partially secret string Z to a highly secret key S. We introduce a universally composable security definition for secret keys in a context where an adversary holds quantum information and show that privacy amplification by twouniversal hashing is secure with respect to this definition. Additionally, we give an asymptotically optimal lower bound on the length of the extractable key S in terms of the adversary's (quantum) knowledge about Z.