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48
A randomized protocol for signing contracts
, 1990
"... Two parties, A and B, want to sign a contract C over a communication network. To do so, they must “simultaneously” exchange their commitments to C. Since simultaneous exchange is usually impossible in practice, protocols are needed to approximate simultaneity by exchanging partial commitments in pie ..."
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Cited by 602 (11 self)
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Two parties, A and B, want to sign a contract C over a communication network. To do so, they must “simultaneously” exchange their commitments to C. Since simultaneous exchange is usually impossible in practice, protocols are needed to approximate simultaneity by exchanging partial commitments in piece by piece manner. During such a protocol, one party or another may have a slight advantage; a “fair” protocol keeps this advantage within acceptable limits. We present a new protocol that is fair in the sense that, at any stage in its execution, the conditional probability that one party cannot commit both parties to the contract given that the other party can, is close to zero. This is true even if A and B have vastly different computing powers, and is proved under very weak cryptographic assumptions. Our protocol has the following additional properties: 4 during the procedure the parties exchange probadilistic options for committing both parties to the contract; the protocol never terminates in an asymmetric situation where party A knows that party B is committed to the contract while he is not; the protocol makes use of a weak form of a third party (judge). If both A and B are honest, the judge will never be called upon. Otherwise, the judge rules by performing a simple computation. No bookkeeping is required of the judge.
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 493 (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.
Security Arguments for Digital Signatures and Blind Signatures
 JOURNAL OF CRYPTOLOGY
, 2000
"... Since the appearance of publickey cryptography in the seminal DiffieHellman paper, many new schemes have been proposed and many have been broken. Thus, the ..."
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Cited by 374 (41 self)
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Since the appearance of publickey cryptography in the seminal DiffieHellman paper, many new schemes have been proposed and many have been broken. Thus, the
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 358 (15 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...
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 284 (20 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 ...
Untraceable Offline Cash in Wallets with Observers
, 1993
"... . Incorporating the property of untraceability of payments into offline electronic cash systems has turned out to be no easy matter. Two key concepts have been proposed in order to attain the same level of security against doublespending as can be trivially attained in systems with full traceabili ..."
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Cited by 272 (3 self)
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. Incorporating the property of untraceability of payments into offline electronic cash systems has turned out to be no easy matter. Two key concepts have been proposed in order to attain the same level of security against doublespending as can be trivially attained in systems with full traceability of payments. The first of these, oneshow blind signatures, ensures traceability of doublespenders after the fact. The realizations of this concept that have been proposed unfortunately require either a great sacrifice in efficiency or seem to have questionable security, if not both. The second concept, wallets with observers, guarantees prior restraint of doublespending, while still offering traceability of doublespenders after the fact in case tamperresistance is compromised. No realization of this concept has yet been proposed in literature, which is a serious problem. It seems that the known cash systems cannot be extended to this important setting without significantly worsening ...
Oneway functions are necessary and sufficient for secure signatures
, 1990
"... Much research in theoretical cryptography has been centered around finding the weakest possible cryptographic assumptions required to implement major primitives. Ever since Diffie and Hellman first suggested that modern ..."
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Cited by 233 (0 self)
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Much research in theoretical cryptography has been centered around finding the weakest possible cryptographic assumptions required to implement major primitives. Ever since Diffie and Hellman first suggested that modern
Foundations of Cryptography (Fragments of a Book)
, 1995
"... this paper date to early 1983. Yet, the paper, being rejected three times from major conferences, has first appeared in public only in 1985, concurrently to the paper of Babai [B85].) A restricted form of interactive proofs, known by the name Arthur Mer'lin Games, was introduced by Babai [B85]. ..."
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Cited by 146 (21 self)
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this paper date to early 1983. Yet, the paper, being rejected three times from major conferences, has first appeared in public only in 1985, concurrently to the paper of Babai [B85].) A restricted form of interactive proofs, known by the name Arthur Mer'lin Games, was introduced by Babai [B85]. (The restricted form turned out to be equivalent in power see Section [mssng(effp.sec)].) The interactive proof for Graph NonIsomorphism is due to Goldreich, Micali and Wigderson The concept of zeroknowledge has been introduced by Goldwasser, Micali and Rackoff, in the same paper quoted above [R85]. Their paper contained also a perfect zeroknowledge proof for Quadratic Non Residuousity. The perfect zeroknowledge proof system for Graph Isomorphism is due to Goldreich, Micali and Wigderson [W86]. The latter paper is also the source to the zeroknowledge proof systems for all languages in 2V72, using any (nonunifomly) oneway function. (Brassard and Crapeau have later' constructed alternative zeroknowledge proof systems for 2V72, using a stronger' intractability assumption, specifically the intractability of the Quadratic Residuousity Problem.) The cryptographic applications of zeroknowledge proofs were the very motivation for their presentation in [R85]. Zeroknowledge proofs were applied to solve cryptographic problems in [FRW85] and [CF85]. However, many more applications were possible once it was shown how to construct zeroknowledge proof systems for every language in In particular, general methodologies for the construction of cryptographic protocols have appeared in [6MW86,GW87]
OnLine/OffLine Digital Signatures
, 1994
"... A new type of signature scheme is proposed. It consists of two phases. The first phase is performed offline, before the message to be signed is even known. The second online phase is performed once the message to be signed is known, and is supposed to be very fast. A method for constructing such o ..."
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Cited by 104 (1 self)
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A new type of signature scheme is proposed. It consists of two phases. The first phase is performed offline, before the message to be signed is even known. The second online phase is performed once the message to be signed is known, and is supposed to be very fast. A method for constructing such online/offline signature schemes is presented. The method uses onetime signature schemes, which are very fast, for the online signing. An ordinary signature scheme is used for the offline stage. In a practical implementation of our scheme, we use a variant of Rabin's signature scheme (based on factoring) and DES. In the online phase, all we use is a moderate amount of DES computation and a single modular multiplication. We stress that the costly modular exponentiation operation is performed offline. This implementation is ideally suited for electronic wallets or smart cards. A preliminary version appeared in the proceedings of Crypto89. OnLine/OffLine Digital Signing has obtained p...