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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 128 (32 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.
General Secure MultiParty Computation from any Linear SecretSharing Scheme
, 2000
"... Abstract. We show that verifiable secret sharing (VSS) and secure multiparty computation (MPC) among a set of n players can efficiently be based on any linear secret sharing scheme (LSSS) for the players, provided that the access structure of the LSSS allows MPC or VSS at all. Because an LSSS neith ..."
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Cited by 122 (20 self)
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Abstract. We show that verifiable secret sharing (VSS) and secure multiparty computation (MPC) among a set of n players can efficiently be based on any linear secret sharing scheme (LSSS) for the players, provided that the access structure of the LSSS allows MPC or VSS at all. Because an LSSS neither guarantees reconstructability when some shares are false, nor verifiability of a shared value, nor allows for the multiplication of shared values, an LSSS is an apparently much weaker primitive than VSS or MPC. Our approach to secure MPC is generic and applies to both the informationtheoretic and the cryptographic setting. The construction is based on 1) a formalization of the special multiplicative property of an LSSS that is needed to perform a multiplication on shared values, 2) an efficient generic construction to obtain from any LSSS a multiplicative LSSS for the same access structure, and 3) an efficient generic construction to build verifiability into every LSSS (always assuming that the adversary structure allows for MPC or VSS at all). The protocols are efficient. In contrast to all previous informationtheoretically secure protocols, the field size is not restricted (e.g, to be greater than n). Moreover, we exhibit adversary structures for which our protocols are polynomial in n while all previous approaches to MPC for nonthreshold adversaries provably have superpolynomial complexity. 1
On the Limitations of Universally Composable TwoParty Computation without Setup Assumptions
 Journal of Cryptology
, 2003
"... Abstract. The recently proposed universally composable (UC) security framework, for analyzing security of cryptographic protocols, provides very strong security guarantees. In particular, a protocol proven secure in this framework is guaranteed to maintain its security even when deployed in arbitrar ..."
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Cited by 84 (17 self)
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Abstract. The recently proposed universally composable (UC) security framework, for analyzing security of cryptographic protocols, provides very strong security guarantees. In particular, a protocol proven secure in this framework is guaranteed to maintain its security even when deployed in arbitrary multiparty, multiprotocol, multiexecution environments. Protocols for securely carrying out essentially any cryptographic task in a universally composable way exist, both in the case of an honest majority (in the plain model, i.e., without setup assumptions) and in the case of no honest majority (in the common reference string model). However, in the plain model, little was known for the case of no honest majority and, in particular, for the important special case of twoparty protocols. We study the feasibility of universally composable twoparty function evaluation in the plain model. Our results show that very few functions can be computed in this model so as to provide the UC security guarantees. Specifically, for the case of deterministic functions, we provide a full characterization of the functions computable in this model. (Essentially, these are the functions that depend on at most one of the parties’ inputs, and furthermore are “efficiently invertible ” in a sense defined within.) For the case of probabilistic functions, we show that the only functions computable in this model are those where one of the parties can essentially uniquely determine the joint output. 1
Simplified VSS and Fasttrack Multiparty Computations with Applications to Threshold Cryptography
, 1998
"... The goal of this paper is to introduce a simple verifiable secret sharing scheme, to improve the efficiency of known secure multiparty protocols and, by employing these techniques, to improve the efficiency of applications which use these protocols. First we present a very simple Verifiable Secret ..."
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Cited by 84 (5 self)
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The goal of this paper is to introduce a simple verifiable secret sharing scheme, to improve the efficiency of known secure multiparty protocols and, by employing these techniques, to improve the efficiency of applications which use these protocols. First we present a very simple Verifiable Secret Sharing protocol which is based on fast cryptographic primitives and avoids altogether the need for expensive zeroknowledge proofs. This is followed by a highly simplified protocol to compute multiplications over shared secrets. This is a major component in secure multiparty computation protocols and accounts for much of the complexity of proposed solutions. Using our protocol as a plugin unit in known protocols reduces their complexity. We show how to achieve efficient multiparty computations in the computational model, through the application of homomorphic commitments. Finally, we present fasttrack multiparty computation protocols. In a model in which malicious faults are rare we s...
An Uninstantiable RandomOracleModel Scheme for a HybridEncryption Problem,” Full version of this paper. Available at http://wwwcse.ucsd.edu/users/mihir
"... Abstract. We present a simple, natural randomoracle (RO) model scheme, for a practical goal, that is uninstantiable, meaning is proven in the RO model to meet its goal yet admits no standardmodel instantiation that meets this goal. The goal in question is INDCCApreserving asymmetric encryption w ..."
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Cited by 80 (5 self)
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Abstract. We present a simple, natural randomoracle (RO) model scheme, for a practical goal, that is uninstantiable, meaning is proven in the RO model to meet its goal yet admits no standardmodel instantiation that meets this goal. The goal in question is INDCCApreserving asymmetric encryption which formally captures security of the most common practical usage of asymmetric encryption, namely to transport a symmetric key in such a way that symmetric encryption under the latter remains secure. The scheme is an ElGamal variant, called Hash ElGamal, that resembles numerous existing ROmodel schemes, and on the surface shows no evidence of its anomalous properties. These results extend our understanding of the gap between the standard and RO models, and bring concerns raised by previous work closer to practice by indicating that the problem of ROmodel schemes admitting no secure instantiation can arise in domains where RO schemes are commonly designed. 1
Player simulation and general adversary structures in perfect multiparty computation
, 2000
"... The goal of secure multiparty computation is to transform a given protocol involving a trusted party into a protocol without need for the trusted party, by simulating the party among the players. Indeed, by the same means, one can simulate an arbitrary player in any given protocol. We formally defin ..."
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Cited by 72 (9 self)
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The goal of secure multiparty computation is to transform a given protocol involving a trusted party into a protocol without need for the trusted party, by simulating the party among the players. Indeed, by the same means, one can simulate an arbitrary player in any given protocol. We formally define what it means to simulate a player by a multiparty protocol among a set of (new) players, and we derive the resilience of the new protocol as a function of the resiliences of the original protocol and the protocol used for the simulation. In contrast to all previous protocols that specify the tolerable adversaries by the number of corruptible players (a threshold), we consider general adversaries characterized by an adversary structure, a set of subsets of the player set, where the adversary may corrupt the players of one set in the structure. Recursively applying the simulation technique to standard threshold multiparty protocols results in protocols secure against general adversaries. The classical results in unconditional multiparty computation among a set of n players state that, in the passive model, any adversary that corrupts less than n=2 players can be tolerated, and in the active model, any adversary that corrupts less than n=3 players can be tolerated. Strictly generalizing
Complete characterization of adversaries tolerable in secure multiparty computation
 Proc. 16th ACM Symposium on Principles of Distributed Computing (PODC
, 1997
"... Abstract The classical results in unconditional multiparty computation among a set of n players state that less than n=2 passive or less than n=3 active adversaries can be tolerated; assuming a broadcast channel the threshold for active adversaries is n=2. Strictly generalizing these results we spe ..."
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Cited by 64 (11 self)
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Abstract The classical results in unconditional multiparty computation among a set of n players state that less than n=2 passive or less than n=3 active adversaries can be tolerated; assuming a broadcast channel the threshold for active adversaries is n=2. Strictly generalizing these results we specify the set of potentially misbehaving players as an arbitrary set of subsets of the player set. We prove the necessary and sufficient conditions for the existence of secure multiparty protocols in terms of the potentially misbehaving player sets. For every function there exists a protocol secure against a set of potential passive collusions if and only if no two of these collusions add up to the full player set. The same condition applies for active adversaries when assuming a broadcast channel. Without broadcast channels, for every function there exists a protocol secure against a set of potential active adverse player sets if and only if no three of these sets add up to the full player set. The complexities of the protocols not using a broadcast channel are polynomial, that of the protocol with broadcast is only slightly higher.
Symmetric Encryption in a Simulatable DolevYao Style Cryptographic Library
 In Proc. 17th IEEE Computer Security Foundations Workshop (CSFW
, 2004
"... Recently we solved the longstanding open problem of justifying a DolevYao type model of cryptography as used in virtually all automated protocol provers under active attacks. The justification was done by defining an ideal system handling DolevYaostyle terms and a cryptographic realization wi ..."
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Cited by 59 (18 self)
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Recently we solved the longstanding open problem of justifying a DolevYao type model of cryptography as used in virtually all automated protocol provers under active attacks. The justification was done by defining an ideal system handling DolevYaostyle terms and a cryptographic realization with the same user interface, and by showing that the realization is as secure as the ideal system in the sense of reactive simulatability. This definition encompasses arbitrary active attacks and enjoys general composition and propertypreservation properties. Security holds in the standard model of cryptography and under standard assumptions of adaptively secure primitives.
Magic Functions
, 1999
"... We consider three apparently unrelated fundamental problems in distributed computing, cryptography and complexity theory and prove that they are essentially the same problem. ..."
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Cited by 55 (0 self)
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We consider three apparently unrelated fundamental problems in distributed computing, cryptography and complexity theory and prove that they are essentially the same problem.
PublicKey Cryptography and Password Protocols: The MultiUser Case
 In CCS ’99: Proceedings of the 6th ACM conference on Computer and communications security
, 1999
"... The problem of password authentication over an insecure network when the user holds only a humanmemorizable password has received much attention in the literature. The first rigorous treatment was provided by Halevi and Krawczyk, who studied offline password guessing attacks in the scenario in whi ..."
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Cited by 31 (0 self)
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The problem of password authentication over an insecure network when the user holds only a humanmemorizable password has received much attention in the literature. The first rigorous treatment was provided by Halevi and Krawczyk, who studied offline password guessing attacks in the scenario in which the authentication server possesses a pair of private and public keys. In this work we: ffl Show the inadequacy of both the HK formalization and protocol in the case where there is more than a single user: using a simple and realistic attack, we prove failure of the HK solution in the twouser case. ffl Propose a new definition of security for the multiuser case, expressed in terms of transcripts of the entire system, rather than individual protocol executions. ffl Suggest several ways of achieving this security against both static and dynamic adversaries. In a recent revision of their paper, Halevi and Krawczyk again attempted to handle the multiuser case. We expose a weakness in their revised definition. 1