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56
Random Oracles are Practical: A Paradigm for Designing Efficient Protocols
, 1995
"... We argue that the random oracle model  where all parties have access to a public random oracle  provides a bridge between cryptographic theory and cryptographic practice. In the paradigm we suggest, a practical protocol P is produced by first devising and proving correct a protocol P R for the ..."
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Cited by 1360 (64 self)
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We argue that the random oracle model  where all parties have access to a public random oracle  provides a bridge between cryptographic theory and cryptographic practice. In the paradigm we suggest, a practical protocol P is produced by first devising and proving correct a protocol P R for the random oracle model, and then replacing oracle accesses by the computation of an "appropriately chosen" function h. This paradigm yields protocols much more efficient than standard ones while retaining many of the advantages of provable security. We illustrate these gains for problems including encryption, signatures, and zeroknowledge proofs.
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 454 (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.
Publickey Cryptosystems Provably Secure against Chosen Ciphertext Attacks
 In Proc. of the 22nd STOC
, 1995
"... We show how to construct a publickey cryptosystem (as originally defined by Diffie and Hellman) secure against chosen ciphertext attacks, given a publickey cryptosystem secure against passive eavesdropping and a noninteractive zeroknowledge proof system in the shared string model. No such secure ..."
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Cited by 258 (16 self)
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We show how to construct a publickey cryptosystem (as originally defined by Diffie and Hellman) secure against chosen ciphertext attacks, given a publickey cryptosystem secure against passive eavesdropping and a noninteractive zeroknowledge proof system in the shared string model. No such secure cryptosystems were known before. Key words. cryptography, randomized algorithms AMS subject classifications. 68M10, 68Q20, 68Q22, 68R05, 68R10 A preliminary version of this paper appeared in the Proc. of the Twenty Second ACM Symposium of Theory of Computing. y Incumbent of the Morris and Rose Goldman Career Development Chair, Dept. of Applied Mathematics and Computer Science, Weizmann Institute of Science, Rehovot 76100, Israel. Work performed while at the IBM Almaden Research Center. Research supported by an Alon Fellowship and a grant from the Israel Science Foundation administered by the Israeli Academy of Sciences. Email: naor@wisdom.weizmann.ac.il. z IBM Research Division, T.J ...
Noninteractive ZeroKnowledge
 SIAM J. COMPUTING
, 1991
"... This paper investigates the possibility of disposing of interaction between prover and verifier in a zeroknowledge proof if they share beforehand a short random string. Without any assumption, it is proven that noninteractive zeroknowledge proofs exist for some numbertheoretic languages for which ..."
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Cited by 193 (19 self)
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This paper investigates the possibility of disposing of interaction between prover and verifier in a zeroknowledge proof if they share beforehand a short random string. Without any assumption, it is proven that noninteractive zeroknowledge proofs exist for some numbertheoretic languages for which no efficient algorithm is known. If deciding quadratic residuosity (modulo composite integers whose factorization is not known) is computationally hard, it is shown that the NPcomplete language of satisfiability also possesses noninteractive zeroknowledge proofs.
The NPcompleteness column: an ongoing guide
 Journal of Algorithms
, 1985
"... This is the nineteenth edition of a (usually) quarterly column that covers new developments in the theory of NPcompleteness. The presentation is modeled on that used by M. R. Garey and myself in our book ‘‘Computers and Intractability: A Guide to the Theory of NPCompleteness,’ ’ W. H. Freeman & ..."
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Cited by 190 (0 self)
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This is the nineteenth edition of a (usually) quarterly column that covers new developments in the theory of NPcompleteness. The presentation is modeled on that used by M. R. Garey and myself in our book ‘‘Computers and Intractability: A Guide to the Theory of NPCompleteness,’ ’ W. H. Freeman & Co., New York, 1979 (hereinafter referred to as ‘‘[G&J]’’; previous columns will be referred to by their dates). A background equivalent to that provided by [G&J] is assumed, and, when appropriate, crossreferences will be given to that book and the list of problems (NPcomplete and harder) presented there. Readers who have results they would like mentioned (NPhardness, PSPACEhardness, polynomialtimesolvability, etc.) or open problems they would like publicized, should
Concurrent ZeroKnowledge
 IN 30TH STOC
, 1999
"... Concurrent executions of a zeroknowledge protocol by a single prover (with one or more verifiers) may leak information and may not be zeroknowledge in toto. In this paper, we study the problem of maintaining zeroknowledge We introduce the notion of an (; ) timing constraint: for any two proces ..."
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Cited by 162 (19 self)
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Concurrent executions of a zeroknowledge protocol by a single prover (with one or more verifiers) may leak information and may not be zeroknowledge in toto. In this paper, we study the problem of maintaining zeroknowledge We introduce the notion of an (; ) timing constraint: for any two processors P1 and P2 , if P1 measures elapsed time on its local clock and P2 measures elapsed time on its local clock, and P2 starts after P1 does, then P2 will finish after P1 does. We show that if the adversary is constrained by an (; ) assumption then there exist fourround almost concurrent zeroknowledge interactive proofs and perfect concurrent zeroknowledge arguments for every language in NP . We also address the more specific problem of Deniable Authentication, for which we propose several particularly efficient solutions. Deniable Authentication is of independent interest, even in the sequential case; our concurrent solutions yield sequential solutions without recourse to timing, i.e., in the standard model.
Foundations of Group Signatures: Formal Definitions, Simplified Requirements, and a Construction Based on General Assumptions
, 2003
"... This paper provides theoretical foundations for the group signature primitive. We introduce strong, formal definitions for the core requirements of anonymity and traceability. We then show that these imply the large set of sometimes ambiguous existing informal requirements in the literature, thereb ..."
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Cited by 130 (6 self)
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This paper provides theoretical foundations for the group signature primitive. We introduce strong, formal definitions for the core requirements of anonymity and traceability. We then show that these imply the large set of sometimes ambiguous existing informal requirements in the literature, thereby unifying and simplifying the requirements for this primitive. Finally we prove the existence of a construct meeting our definitions based only on the assumption that trapdoor permutations exist.
COMPUTATIONALLY SOUND PROOFS
, 2000
"... This paper puts forward a new notion of a proof based on computational complexity and explores its implications for computation at large. Computationally sound proofs provide, in a novel and meaningful framework, answers to old and new questions in complexity theory. In particular, given a random o ..."
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Cited by 98 (3 self)
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This paper puts forward a new notion of a proof based on computational complexity and explores its implications for computation at large. Computationally sound proofs provide, in a novel and meaningful framework, answers to old and new questions in complexity theory. In particular, given a random oracle or a new complexity assumption, they enable us to 1. prove that verifying is easier than deciding for all theorems; 2. provide a quite effective way to prove membership in computationally hard languages (such as CoNPcomplete ones); and 3. show that every computation possesses a short certificate vouching its correctness. Finally, if a special type of computationally sound proof exists, we show that Blum’s notion of program checking can be meaningfully broadened so as to prove that NPcomplete languages are checkable.
Foundations of Group Signatures: The Case of Dynamic Groups
, 2004
"... Recently, a first step toward establishing foundations for group signatures was taken [5], with a treatment of the case where the group is static. However the bulk of existing practical schemes and applications are for dynamic groups, and these involve important new elements and security issues. Thi ..."
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Cited by 88 (1 self)
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Recently, a first step toward establishing foundations for group signatures was taken [5], with a treatment of the case where the group is static. However the bulk of existing practical schemes and applications are for dynamic groups, and these involve important new elements and security issues. This paper treats this case, providing foundations for dynamic group signatures, in the form of a model, strong formal denitions of security, and a construction proven secure under general assumptions. We believe this is an important and useful step because it helps bridge the gap between [5] and the previous practical work, and delivers a basis on which existing practical schemes may in future be evaluated or proven secure.