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177
NonMalleable Cryptography
 SIAM Journal on Computing
, 2000
"... The notion of nonmalleable cryptography, an extension of semantically secure cryptography, is defined. Informally, in the context of encryption the additional requirement is that given the ciphertext it is impossible to generate a different ciphertext so that the respective plaintexts are related. ..."
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Cited by 447 (22 self)
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The notion of nonmalleable cryptography, an extension of semantically secure cryptography, is defined. Informally, in the context of encryption the additional requirement is that given the ciphertext it is impossible to generate a different ciphertext so that the respective plaintexts are related. The same concept makes sense in the contexts of string commitment and zeroknowledge proofs of possession of knowledge. Nonmalleable schemes for each of these three problems are presented. The schemes do not assume a trusted center; a user need not know anything about the number or identity of other system users. Our cryptosystem is the first proven to be secure against a strong type of chosen ciphertext attack proposed by Rackoff and Simon, in which the attacker knows the ciphertext she wishes to break and can query the decryption oracle on any ciphertext other than the target.
Universal OneWay Hash Functions and their Cryptographic Applications
, 1989
"... We define a Universal OneWay Hash Function family, a new primitive which enables the compression of elements in the function domain. The main property of this primitive is that given an element x in the domain, it is computationally hard to find a different domain element which collides with x. We ..."
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Cited by 313 (13 self)
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We define a Universal OneWay Hash Function family, a new primitive which enables the compression of elements in the function domain. The main property of this primitive is that given an element x in the domain, it is computationally hard to find a different domain element which collides with x. We prove constructively that universal oneway hash functions exist if any 11 oneway functions exist. Among the various applications of the primitive is a OneWay based Secure Digital Signature Scheme which is existentially secure against adoptive attacks. Previously, all provably secure signature schemes were based on the stronger mathematical assumption that trapdoor oneway functions exist. Key words. cryptography, randomized algorithms AMS subject classifications. 68M10, 68Q20, 68Q22, 68R05, 68R10 Part of this work was done while the authors were at the IBM Almaden Research Center. The first author was supported in part by NSF grant CCR88 13632. A preliminary version of this work app...
How to Go Beyond the BlackBox Simulation Barrier
 In 42nd FOCS
, 2001
"... The simulation paradigm is central to cryptography. A simulator is an algorithm that tries to simulate the interaction of the adversary with an honest party, without knowing the private input of this honest party. Almost all known simulators use the adversary’s algorithm as a blackbox. We present t ..."
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Cited by 214 (13 self)
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The simulation paradigm is central to cryptography. A simulator is an algorithm that tries to simulate the interaction of the adversary with an honest party, without knowing the private input of this honest party. Almost all known simulators use the adversary’s algorithm as a blackbox. We present the first constructions of nonblackbox simulators. Using these new nonblackbox techniques we obtain several results that were previously proven to be impossible to obtain using blackbox simulators. Specifically, assuming the existence of collision resistent hash functions, we construct a new zeroknowledge argument system for NP that satisfies the following properties: 1. This system has a constant number of rounds with negligible soundness error. 2. It remains zero knowledge even when composed concurrently n times, where n is the security parameter. Simultaneously obtaining 1 and 2 has been recently proven to be impossible to achieve using blackbox simulators. 3. It is an ArthurMerlin (public coins) protocol. Simultaneously obtaining 1 and 3 was known to be impossible to achieve with a blackbox simulator. 4. It has a simulator that runs in strict polynomial time, rather than in expected polynomial time. All previously known constantround, negligibleerror zeroknowledge arguments utilized expected polynomialtime simulators.
How to Construct ConstantRound ZeroKnowledge Proof Systems for NP
 Journal of Cryptology
, 1995
"... Constantround zeroknowledge proof systems for every language in NP are presented, assuming the existence of a collection of clawfree functions. In particular, it follows that such proof systems exist assuming the intractability of either the Discrete Logarithm Problem or the Factoring Problem for ..."
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Cited by 157 (8 self)
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Constantround zeroknowledge proof systems for every language in NP are presented, assuming the existence of a collection of clawfree functions. In particular, it follows that such proof systems exist assuming the intractability of either the Discrete Logarithm Problem or the Factoring Problem for Blum Integers.
Pseudonym Systems
, 1999
"... Pseudonym systems allow users to interact with multiple organizations anonymously, using pseudonyms. The pseudonyms cannot be linked, but are formed in such a way that a user can prove to one organization a statement about his relationship with another. Such statement is called a credential. Previou ..."
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Cited by 118 (11 self)
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Pseudonym systems allow users to interact with multiple organizations anonymously, using pseudonyms. The pseudonyms cannot be linked, but are formed in such a way that a user can prove to one organization a statement about his relationship with another. Such statement is called a credential. Previous work in this area did not protect the system against dishonest users who collectively use their pseudonyms and credentials, i.e. share an identity. Previous practical schemes also relied very heavily on the involvement of a trusted center. In the present paper we give a formal definition of pseudonym systems where users are motivated not to share their identity, and in which the trusted center's involvement is minimal. We give theoretical constructions for such systems based on any oneway function. We also suggest an efficient and easy to implement practical scheme. This is joint work with Ronald L. Rivest and Amit Sahai.
On the Concurrent Composition of ZeroKnowledge Proofs
 In EuroCrypt99, Springer LNCS 1592
, 1999
"... Abstract. We examine the concurrent composition of zeroknowledge proofs. By concurrent composition, we indicate a single prover that is involved in multiple, simultaneous zeroknowledge proofs with one or multiple verifiers. Under this type of composition it is believed that standard zeroknowledge ..."
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Cited by 110 (3 self)
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Abstract. We examine the concurrent composition of zeroknowledge proofs. By concurrent composition, we indicate a single prover that is involved in multiple, simultaneous zeroknowledge proofs with one or multiple verifiers. Under this type of composition it is believed that standard zeroknowledge protocols are no longer zeroknowledge. We show that, modulo certain complexity assumptions, any statement in NP has k ɛround proofs and arguments in which one can efficiently simulate any k O(1) concurrent executions of the protocol.
BlackBox Concurrent ZeroKnowledge Requires (almost) Logarithmically Many Rounds
 SIAM Journal on Computing
, 2002
"... We show that any concurrent zeroknowledge protocol for a nontrivial language (i.e., for a language outside BPP), whose security is proven via blackbox simulation, must use at least ~ \Omega\Gamma/10 n) rounds of interaction. This result achieves a substantial improvement over previous lower bound ..."
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Cited by 85 (6 self)
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We show that any concurrent zeroknowledge protocol for a nontrivial language (i.e., for a language outside BPP), whose security is proven via blackbox simulation, must use at least ~ \Omega\Gamma/10 n) rounds of interaction. This result achieves a substantial improvement over previous lower bounds, and is the first bound to rule out the possibility of constantround concurrent zeroknowledge when proven via blackbox simulation. Furthermore, the bound is polynomially related to the number of rounds in the best known concurrent zeroknowledge protocol for languages in NP (which is established via blackbox simulation).
Efficient Cryptographic Schemes Provably as Secure as Subset Sum
 Journal of Cryptology
, 1993
"... We show very efficient constructions for a pseudorandom generator and for a universal oneway hash function based on the intractability of the subset sum problem for certain dimensions. (Pseudorandom generators can be used for private key encryption and universal oneway hash functions for sign ..."
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Cited by 78 (8 self)
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We show very efficient constructions for a pseudorandom generator and for a universal oneway hash function based on the intractability of the subset sum problem for certain dimensions. (Pseudorandom generators can be used for private key encryption and universal oneway hash functions for signature schemes). The increase in efficiency in our construction is due to the fact that many bits can be generated/hashed with one application of the assumed oneway function. All our construction can be implemented in NC using an optimal number of processors. Part of this work done while both authors were at UC Berkeley and part when the second author was at the IBM Almaden Research Center. Research supported by NSF grant CCR 88  13632. A preliminary version of this paper appeared in Proc. of the 30th Symp. on Foundations of Computer Science, 1989. 1 Introduction Many cryptosystems are based on the intractability of such number theoretic problems such as factoring and discrete logarit...
An Efficient Protocol for Secure TwoParty Computation in the Presence of Malicious Adversaries
 In EUROCRYPT 2007, SpringerVerlag (LNCS 4515
, 2007
"... We show an efficient secure twoparty protocol, based on Yao’s construction, which provides security against malicious adversaries. Yao’s original protocol is only secure in the presence of semihonest adversaries, and can be transformed into a protocol that achieves security against malicious adver ..."
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Cited by 70 (10 self)
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We show an efficient secure twoparty protocol, based on Yao’s construction, which provides security against malicious adversaries. Yao’s original protocol is only secure in the presence of semihonest adversaries, and can be transformed into a protocol that achieves security against malicious adversaries by applying the compiler of Goldreich, Micali and Wigderson (the “GMW compiler”). However, this approach does not seem to be very practical as it requires using generic zeroknowledge proofs. Our construction is based on applying cutandchoose techniques to the original circuit and inputs. Security is proved according to the ideal/real simulation paradigm, and the proof is in the standard model (with no random oracle model or common reference string assumptions). The resulting protocol is computationally efficient: the only usage of asymmetric cryptography is for running O(1) oblivious transfers for each input bit (or for each bit of a statistical security parameter, whichever is larger). Our protocol combines techniques from folklore (like cutandchoose) along with new techniques for efficiently proving consistency of inputs. We remark that a naive implementation of the cutandchoose technique with Yao’s protocol does not yield a
Practical and ProvablySecure Commitment Schemes from CollisionFree Hashing
 in Advances in Cryptology  CRYPTO96, Lecture Notes in Computer Science 1109
, 1996
"... . We present a very practical stringcommitment scheme which is provably secure based solely on collisionfree hashing. Our scheme enables a computationally bounded party to commit strings to an unbounded one, and is optimal (within a small constant factor) in terms of interaction, communication, a ..."
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Cited by 64 (6 self)
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. We present a very practical stringcommitment scheme which is provably secure based solely on collisionfree hashing. Our scheme enables a computationally bounded party to commit strings to an unbounded one, and is optimal (within a small constant factor) in terms of interaction, communication, and computation. Our result also proves that constant round statistical zeroknowledge arguments and constantround computational zeroknowledge proofs for NP exist based on the existence of collisionfree hash functions. 1 Introduction String commitment is a fundamental primitive for cryptographic protocols. A commitment scheme is an electronic way to temporarily hide a value that cannot be changed. Such a scheme emulates by means of a protocol the following twostage process. In Stage 1 (the Commit stage), a party called the Sender locks a message in a box, and sends the locked box to another party called the receiver. In Stage 2 (the Decommit stage), the Sender provides the Receiver with ...