Results 1  10
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205
An InformationTheoretic Model for Steganography
, 1998
"... An informationtheoretic model for steganography with passive adversaries is proposed. The adversary's task of distinguishing between an innocentcover message C and a modified message S containing a secret part is interpreted as a hypothesis testing problem. The security of a steganographic system i ..."
Abstract

Cited by 194 (3 self)
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An informationtheoretic model for steganography with passive adversaries is proposed. The adversary's task of distinguishing between an innocentcover message C and a modified message S containing a secret part is interpreted as a hypothesis testing problem. The security of a steganographic system is quantified in terms of the relative entropy (or discrimination) between PC and PS . Several secure steganographic schemes are presented in this model; one of them is a universal information hiding scheme based on universal data compression techniques that requires no knowledge of the covertext statistics.
On the (im)possibility of obfuscating programs
 Lecture Notes in Computer Science
, 2001
"... Informally, an obfuscator O is an (efficient, probabilistic) “compiler ” that takes as input a program (or circuit) P and produces a new program O(P) that has the same functionality as P yet is “unintelligible ” in some sense. Obfuscators, if they exist, would have a wide variety of cryptographic an ..."
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Cited by 189 (10 self)
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Informally, an obfuscator O is an (efficient, probabilistic) “compiler ” that takes as input a program (or circuit) P and produces a new program O(P) that has the same functionality as P yet is “unintelligible ” in some sense. Obfuscators, if they exist, would have a wide variety of cryptographic and complexitytheoretic applications, ranging from software protection to homomorphic encryption to complexitytheoretic analogues of Rice’s theorem. Most of these applications are based on an interpretation of the “unintelligibility ” condition in obfuscation as meaning that O(P) is a “virtual black box, ” in the sense that anything one can efficiently compute given O(P), one could also efficiently compute given oracle access to P. In this work, we initiate a theoretical investigation of obfuscation. Our main result is that, even under very weak formalizations of the above intuition, obfuscation is impossible. We prove this by constructing a family of efficient programs P that are unobfuscatable in the sense that (a) given any efficient program P ′ that computes the same function as a program P ∈ P, the “source code ” P can be efficiently reconstructed, yet (b) given oracle access to a (randomly selected) program P ∈ P, no efficient algorithm can reconstruct P (or even distinguish a certain bit in the code from random) except with negligible probability. We extend our impossibility result in a number of ways, including even obfuscators that (a) are not necessarily computable in polynomial time, (b) only approximately preserve the functionality, and (c) only need to work for very restricted models of computation (TC 0). We also rule out several potential applications of obfuscators, by constructing “unobfuscatable” signature schemes, encryption schemes, and pseudorandom function families.
Sequences of Games: A Tool for Taming Complexity in Security Proofs
, 2004
"... This paper is brief tutorial on a technique for structuring security proofs as sequences games. ..."
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Cited by 114 (0 self)
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This paper is brief tutorial on a technique for structuring security proofs as sequences games.
Keyprivacy in publickey encryption
, 2001
"... We consider a novel security requirement of encryption schemes that we call “keyprivacy” or “anonymity”.It asks that an eavesdropper in possession of a ciphertext not be able to tell which specific key, out of a set of known public keys, is the one under which the ciphertext was created, meaning t ..."
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Cited by 93 (8 self)
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We consider a novel security requirement of encryption schemes that we call “keyprivacy” or “anonymity”.It asks that an eavesdropper in possession of a ciphertext not be able to tell which specific key, out of a set of known public keys, is the one under which the ciphertext was created, meaning the receiver is anonymous from the point of view of the adversary.We investigate the anonymity of known encryption schemes.We prove that the El Gamal scheme provides anonymity under chosenplaintext attack assuming the Decision DiffieHellman problem is hard and that the CramerShoup scheme provides anonymity under chosenciphertext attack under the same assumption.We also consider anonymity for trapdoor permutations.Known attacks indicate that the RSA trapdoor permutation is not anonymous and neither are the standard encryption schemes based on it.We provide a variant of RSAOAEP that provides anonymity in the random oracle model assuming RSA is oneway.We also give constructions of anonymous trapdoor permutations, assuming RSA is oneway, which yield anonymous encryption schemes in the standard model.
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).
A General Composition Theorem for Secure Reactive Systems
 In TCC 2004
, 2004
"... We consider compositional properties of reactive systems that are secure in a cryptographic sense. We follow the wellknown simulatability approach of modern cryptography, i.e., the specification is an ideal system and a real system should in some sense simulate this ideal one. We show that if a ..."
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Cited by 68 (8 self)
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We consider compositional properties of reactive systems that are secure in a cryptographic sense. We follow the wellknown simulatability approach of modern cryptography, i.e., the specification is an ideal system and a real system should in some sense simulate this ideal one. We show that if a system consists of a polynomial number of arbitrary ideal subsystems such that each of them has a secure implementation in the sense of blackbox simulatability, then one can securely replace all ideal subsystems with their respective secure counterparts without destroying the blackbox simulatability relation. We further prove our theorem for universal simulatability by showing that blackbox simulatability implies universal simulatability under reasonable assumptions. We show all our results with concrete security.
Secure and efficient asynchronous broadcast protocols (Extended Abstract)
 Advances in Cryptology: CRYPTO 2001
, 2001
"... Broadcast protocols are a fundamental building block for implementing replication in faulttolerant distributed systems. This paper addresses secure service replication in an asynchronous environment with a static set of servers, where a malicious adversary may corrupt up to a threshold of servers ..."
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Cited by 67 (19 self)
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Broadcast protocols are a fundamental building block for implementing replication in faulttolerant distributed systems. This paper addresses secure service replication in an asynchronous environment with a static set of servers, where a malicious adversary may corrupt up to a threshold of servers and controls the network. We develop a formal model using concepts from modern cryptography, give modular definitions for several broadcast problems, including reliable, atomic, and secure causal broadcast, and present protocols implementing them. Reliable broadcast is a basic primitive, also known as the Byzantine generals problem, providing agreement on a delivered message. Atomic broadcast imposes additionally a total order on all delivered messages. We present a randomized atomic broadcast protocol based on a new, efficient multivalued asynchronous Byzantine agreement primitive with an external validity condition. Apparently, no such efficient asynchronous atomic broadcast protocol maintaining liveness and safety in the Byzantine model has appeared previously in the literature. Secure causal broadcast extends atomic broadcast by encryption to guarantee a causal order among the delivered messages. Our protocols use threshold cryptography for signatures, encryption, and cointossing.
A Framework for PasswordBased Authenticated Key Exchange
 in Cryptology — Eurocrypt 2003, LNCS
, 2003
"... In this paper we present a general framework for passwordbased authenticated key exchange protocols, in the common reference string model. Our protocol is actually an abstraction of the key exchange protocol of Katz et al. and is based on the recently introduced notion of smooth projective hashi ..."
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Cited by 64 (1 self)
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In this paper we present a general framework for passwordbased authenticated key exchange protocols, in the common reference string model. Our protocol is actually an abstraction of the key exchange protocol of Katz et al. and is based on the recently introduced notion of smooth projective hashing by Cramer and Shoup. We gain a number of benefits from this abstraction. First, we obtain a modular protocol that can be described using just three highlevel cryptographic tools. This allows a simple and intuitive understanding of its security.
Privacy Preserving Keyword Searches on Remote Encrypted Data
, 2004
"... We consider the following problem: a user wants to store his files in an encrypted form on a remote file server S. ..."
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Cited by 61 (0 self)
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We consider the following problem: a user wants to store his files in an encrypted form on a remote file server S.