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Design and Analysis of Practical PublicKey Encryption Schemes Secure against Adaptive Chosen Ciphertext Attack
 SIAM Journal on Computing
, 2001
"... A new public key encryption scheme, along with several variants, is proposed and analyzed. The scheme and its variants are quite practical, and are proved secure against adaptive chosen ciphertext attack under standard intractability assumptions. These appear to be the first publickey encryption sc ..."
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Cited by 193 (11 self)
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A new public key encryption scheme, along with several variants, is proposed and analyzed. The scheme and its variants are quite practical, and are proved secure against adaptive chosen ciphertext attack under standard intractability assumptions. These appear to be the first publickey encryption schemes in the literature that are simultaneously practical and provably secure.
On the security of joint signature and encryption
, 2002
"... We formally study the notion of a joint signature and encryption in the publickey setting. We refer to this primitive as signcryption, adapting the terminology of [35]. We present two definitions for the security of signcryption depending on whether the adversary is an outsider or a legal user of t ..."
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Cited by 139 (6 self)
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We formally study the notion of a joint signature and encryption in the publickey setting. We refer to this primitive as signcryption, adapting the terminology of [35]. We present two definitions for the security of signcryption depending on whether the adversary is an outsider or a legal user of the system. We then examine generic sequential composition methods of building signcryption from a signature and encryption scheme. Contrary to what recent results in the symmetric setting [5, 22] might lead one to expect, we show that classical “encryptthensign” (EtS) and “signthenencrypt” (StE) methods are both secure composition methods in the publickey setting. We also present a new composition method which we call “committhenencryptandsign” (CtE&S). Unlike the generic sequential composition methods, CtE&S applies the expensive signature and encryption operations in parallel, which could imply a gain in efficiency over the StE and EtS schemes. We also show that the new CtE&S method elegantly combines with the recent “hashsignswitch” technique of [30], leading to efficient online/offline signcryption. Finally and of independent interest, we discuss the definitional inadequacy of the standard notion of chosen ciphertext (CCA2) security. We suggest a natural and very slight relaxation of CCA2security, which we call generalized CCA2ecurity (gCCA2). We show that gCCA2security suffices for all known uses of CCA2secure encryption, while no longer suffering from the definitional shortcomings of the latter.
Notions of Reducibility between Cryptographic Primitives
, 2004
"... Starting with the seminal paper of Impagliazzo and Rudich [18], there has been a large body of work showing that various cryptographic primitives cannot be reduced to each other via "blackbox" reductions. ..."
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Cited by 64 (7 self)
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Starting with the seminal paper of Impagliazzo and Rudich [18], there has been a large body of work showing that various cryptographic primitives cannot be reduced to each other via "blackbox" reductions.
Lower bounds on the Efficiency of Generic Cryptographic Constructions
 41ST IEEE SYMPOSIUM ON FOUNDATIONS OF COMPUTER SCIENCE (FOCS), IEEE
, 2000
"... A central focus of modern cryptography is the construction of efficient, “highlevel” cryptographic tools (e.g., encryption schemes) from weaker, “lowlevel ” cryptographic primitives (e.g., oneway functions). Of interest are both the existence of such constructions, and their efficiency. Here, we ..."
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Cited by 61 (6 self)
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A central focus of modern cryptography is the construction of efficient, “highlevel” cryptographic tools (e.g., encryption schemes) from weaker, “lowlevel ” cryptographic primitives (e.g., oneway functions). Of interest are both the existence of such constructions, and their efficiency. Here, we show essentiallytight lower bounds on the best possible efficiency of any blackbox construction of some fundamental cryptographic tools from the most basic and widelyused cryptographic primitives. Our results hold in an extension of the model introduced by Impagliazzo and Rudich, and improve and extend earlier results of Kim, Simon, and Tetali. We focus on constructions of pseudorandom generators, universal oneway hash functions, and digital signatures based on oneway permutations, as well as constructions of public and privatekey encryption schemes based on trapdoor permutations. In each case, we show that any blackbox construction beating our efficiency bound would yield the unconditional existence of a oneway function and thus, in particular, prove P != NP.
Strengthening Digital Signatures Via Randomized Hashing
 In CRYPTO
, 2006
"... Abstract. We propose randomized hashing as a mode of operation for cryptographic hash functions intended for use with standard digital signatures and without necessitating of any changes in the internals of the underlying hash function (e.g., the SHA family) or in the signature algorithms (e.g., RSA ..."
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Cited by 58 (2 self)
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Abstract. We propose randomized hashing as a mode of operation for cryptographic hash functions intended for use with standard digital signatures and without necessitating of any changes in the internals of the underlying hash function (e.g., the SHA family) or in the signature algorithms (e.g., RSA or DSA). The goal is to free practical digital signature schemes from their current reliance on strong collision resistance by basing the security of these schemes on significantly weaker properties of the underlying hash function, thus providing a safety net in case the (current or future) hash functions in use turn out to be less resilient to collision search than initially thought. We design a specific mode of operation that takes into account engineering considerations (such as simplicity, efficiency and compatibility with existing implementations) as well as analytical soundness. Specifically, the scheme consists of a regular use of the hash function with randomization applied only to the message before it is input to the hash function. We formally show the sufficiency of weaker than collisionresistance assumptions for proving the security of the scheme. 1
A composition theorem for universal oneway hash functions
 In Eurocrypt ’00
, 2000
"... Abstract. In this paper we present a new scheme for constructing universal oneway hash functions that hash arbitrarily long messages out of universal oneway hash functions that hash fixedlength messages. The new construction is extremely simple and is also very efficient, yielding shorter keys th ..."
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Cited by 45 (5 self)
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Abstract. In this paper we present a new scheme for constructing universal oneway hash functions that hash arbitrarily long messages out of universal oneway hash functions that hash fixedlength messages. The new construction is extremely simple and is also very efficient, yielding shorter keys than previously proposed composition constructions. 1
Efficient collisionresistant hashing from worstcase assumptions on cyclic lattices
 In TCC
, 2006
"... Abstract The generalized knapsack function is defined as fa(x) = Pi ai * xi, where a = (a1,..., am)consists of m elements from some ring R, and x = (x1,..., xm) consists of m coefficients froma specified subset S ` R. Micciancio (FOCS 2002) proposed a specific choice of the ring R andsubset S for w ..."
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Cited by 45 (13 self)
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Abstract The generalized knapsack function is defined as fa(x) = Pi ai * xi, where a = (a1,..., am)consists of m elements from some ring R, and x = (x1,..., xm) consists of m coefficients froma specified subset S ` R. Micciancio (FOCS 2002) proposed a specific choice of the ring R andsubset S for which inverting this function (for random a, x) is at least as hard as solving certainworstcase problems on cyclic lattices. We show that for a different choice of S ae R, the generalized knapsack function is in factcollisionresistant, assuming it is infeasible to approximate the shortest vector in ndimensionalcyclic lattices up to factors ~ O(n). For slightly larger factors, we even get collisionresistancefor any m> = 2. This yields very efficient collisionresistant hash functions having key size andtime complexity almost linear in the security parameter n. We also show that altering S isnecessary, in the sense that Micciancio's original function is not collisionresistant (nor even universal oneway).Our results exploit an intimate connection between the linear algebra of ndimensional cycliclattices and the ring Z [ ff]/(ffn 1), and crucially depend on the factorization of ffn 1 intoirreducible cyclotomic polynomials. We also establish a new bound on the discrete Gaussian distribution over general lattices, employing techniques introduced by Micciancio and Regev(FOCS 2004) and also used by Micciancio in his study of compact knapsacks. 1 Introduction A function family {fa}a2A is said to be collisionresistant if given a uniformly chosen a 2 A, it is infeasible to find elements x1 6 = x2 so that fa(x1) = fa(x2). Collisionresistant hash functions are one of the most widelyemployed cryptographic primitives. Their applications include integrity checking, user and message authentication, commitment protocols, and more. Many of the applications of collisionresistant hashing tend to invoke the hash function only a small number of times. Thus, the efficiency of the function has a direct effect on the efficiency of the application that uses it. This is in contrast to primitives such as oneway functions, which typically must be invoked many times in their applications (at least when used in a blackbox way) [9].
Separating succinct noninteractive arguments from all falsifiable assumptions
 In Proceedings of the 43rd Annual ACM Symposium on Theory of Computing, STOC ’11
, 2011
"... An argument system (computationally sound proof) for N P is succinct, if its communication complexity is polylogarithmic the instance and witness sizes. The seminal works of Kilian ’92 and Micali ’94 show that such arguments can be constructed under standard cryptographic hardness assumptions with f ..."
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Cited by 42 (1 self)
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An argument system (computationally sound proof) for N P is succinct, if its communication complexity is polylogarithmic the instance and witness sizes. The seminal works of Kilian ’92 and Micali ’94 show that such arguments can be constructed under standard cryptographic hardness assumptions with four rounds of interaction, and that they be made noninteractive in the randomoracle model. The latter construction also gives us some evidence that succinct noninteractive arguments (SNARGs) may exist in the standard model with a common reference string (CRS), by replacing the oracle with a sufficiently complicated hash function whose description goes in the CRS. However, we currently do not know of any construction of SNARGs with a proof of security under any simple cryptographic assumption. In this work, we give a broad blackbox separation result, showing that blackbox reductions cannot be used to prove the security of any SNARG construction based on any falsifiable cryptographic assumption. This includes essentially all common assumptions used in cryptography (oneway functions, trapdoor permutations, DDH, RSA, LWE etc.). More generally, we say that an assumption is falsifiable if it can be modeled as an interactive game between an adversary and an efficient challenger that can efficiently decide if the adversary won the game. This is similar, in spirit, to the notion of falsifiability of Naor ’03, and captures the fact that we can efficiently check if an adversarial strategy breaks the assumption. Our separation result also extends to designated verifier SNARGs, where the verifier needs a trapdoor associated with the CRS to verify arguments, and slightly succinct SNARGs, whose size is only required to be sublinear in the statement and witness size.
Finding collisions in interactive protocols – A tight lower bound on the round complexity of statisticallyhiding commitments
 In Proceedings of the 48th Annual IEEE Symposium on Foundations of Computer Science
, 2007
"... We study the round complexity of various cryptographic protocols. Our main result is a tight lower bound on the round complexity of any fullyblackbox construction of a statisticallyhiding commitment scheme from oneway permutations, and even from trapdoor permutations. This lower bound matches th ..."
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Cited by 33 (11 self)
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We study the round complexity of various cryptographic protocols. Our main result is a tight lower bound on the round complexity of any fullyblackbox construction of a statisticallyhiding commitment scheme from oneway permutations, and even from trapdoor permutations. This lower bound matches the round complexity of the statisticallyhiding commitment scheme due to Naor, Ostrovsky, Venkatesan and Yung (CRYPTO ’92). As a corollary, we derive similar tight lower bounds for several other cryptographic protocols, such as singleserver private information retrieval, interactive hashing, and oblivious transfer that guarantees statistical security for one of the parties. Our techniques extend the collisionfinding oracle due to Simon (EUROCRYPT ’98) to the setting of interactive protocols (our extension also implies an alternative proof for the main property of the original oracle). In addition, we substantially extend the reconstruction paradigm of Gennaro and Trevisan (FOCS ‘00). In both cases, our extensions are quite delicate and may be found useful in proving additional blackbox separation results.
Infeasibility of instance compression and succinct PCPs for NP
 Electronic Colloquium on Computational Complexity (ECCC
"... The ORSAT problem asks, given Boolean formulae φ1,..., φm each of size at most n, whether at least one of the φi’s is satisfiable. We show that there is no reduction from ORSAT to any set A where the length of the output is bounded by a polynomial in n, unless NP ⊆ coNP/poly, and the PolynomialTi ..."
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Cited by 33 (1 self)
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The ORSAT problem asks, given Boolean formulae φ1,..., φm each of size at most n, whether at least one of the φi’s is satisfiable. We show that there is no reduction from ORSAT to any set A where the length of the output is bounded by a polynomial in n, unless NP ⊆ coNP/poly, and the PolynomialTime Hierarchy collapses. This result settles an open problem proposed by Bodlaender et. al. [4] and Harnik and Naor [15] and has a number of implications. • A number of parametric NP problems, including Satisfiability, Clique, Dominating Set and Integer Programming, are not instance compressible or polynomially kernelizable unless NP ⊆ coNP/poly. • Satisfiability does not have PCPs of size polynomial in the number of variables unless NP ⊆ coNP/poly. • An approach of Harnik and Naor to constructing collisionresistant hash functions from oneway functions is unlikely to be viable in its present form. • (BuhrmanHitchcock) There are no subexponentialsize hard sets for NP unless NP is in coNP/poly. We also study probabilistic variants of compression, and show various results about and connections between these variants. To this end, we introduce a new strong derandomization hypothesis, the Oracle Derandomization Hypothesis, and discuss how it relates to traditional derandomization assumptions. Categories and Subject Descriptors