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A secure deniable authentication protocol based on Bilinear Diffie Hellman algorithm, Cryptology eprint Archive
, 2010
"... Abstract. This paper describes a new deniable authentication protocol whose security is based DiffeHellman (CDH) Problem of type Decisional DiffieHellman(DDH) and the Hash DiffieHellman (HDDH) problem.This protocol can be implemented in low power and small processor mobile devices such as smart c ..."
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Abstract. This paper describes a new deniable authentication protocol whose security is based DiffeHellman (CDH) Problem of type Decisional DiffieHellman(DDH) and the Hash DiffieHellman (HDDH) problem.This protocol can be implemented in low power and small processor mobile devices such as smart card, PDA etc which work in low power and small processor. A deniable authentication protocol enables a receiver to identify the true source of a given message, but not to prove the identity of the sender to a third party. This property is very useful for providing secure negotiation over the internet. Our proposed protocol will be achieving the most three security requirement like deniable authentication, Confidentialities and also it is resistant against Manin middle Attack.
Collisions and other NonRandom Properties for StepReduced SHA256. Cryptology eprint Archive, April 2008. Available at http://eprint.iacr
"... Abstract. We study the security of stepreduced but otherwise unmodified SHA256. We show the first collision attacks on SHA256 reduced to 23 and 24 steps with complexities 2 18 and 2 28.5, respectively. We give example colliding message pairs for 23step and 24step SHA256. The best previous, rec ..."
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Abstract. We study the security of stepreduced but otherwise unmodified SHA256. We show the first collision attacks on SHA256 reduced to 23 and 24 steps with complexities 2 18 and 2 28.5, respectively. We give example colliding message pairs for 23step and 24step SHA256. The best previous, recently obtained result was a collision attack for up to 22 steps. We extend our attacks to 23 and 24step reduced SHA512 with respective complexities of 2 44.9 and 2 53.0. Additionally, we show nonrandom behaviour of the SHA256 compression function in the form of freestart nearcollisions for up to 31 steps, which is 6 more steps than the recently obtained nonrandom behaviour in the form of a freestart nearcollision. Even though this represents a step forwards in terms of cryptanalytic techniques, the results do not threaten the security of applications using SHA256. Keywords: SHA256, SHA512, hash functions, collisions, semifreestart collisions, freestart collisions, freestart nearcollisions.
Security of Verifiably Encrypted Signatures and a Construction Without Random Oracles (Extended Version). Number 2009/027 in Cryptology eprint archive. eprint.iacr.org
, 2009
"... rueckert @ cdc.informatik.tudarmstadt.de schroeder @ me.com Abstract. In a verifiably encrypted signature scheme, signers encrypt their signature under the public key of a trusted third party and prove that they did so correctly. The security properties, due to Boneh et al. (Eurocrypt 2003), are un ..."
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rueckert @ cdc.informatik.tudarmstadt.de schroeder @ me.com Abstract. In a verifiably encrypted signature scheme, signers encrypt their signature under the public key of a trusted third party and prove that they did so correctly. The security properties, due to Boneh et al. (Eurocrypt 2003), are unforgeability and opacity. This paper proposes two novel fundamental requirements for verifiably encrypted signatures, called extractability and abusefreeness, and analyzes its effects on the established security model. Extractability ensures that the trusted third party is always able to extract a valid signature from a valid verifiably encrypted signature and abusefreeness guarantees that a malicious signer, who cooperates with the trusted party, is not able to forge a verifiably encrypted signature. We further show that both properties are not covered by the model of Boneh et al. The second main contribution of this paper is a verifiably encrypted signature scheme, provably secure without random oracles, that is more efficient and greatly improves the public key size of the only other construction in the standard model by Lu et al. (Eurocrypt 2006). Moreover, we present strengthened definitions for unforgeability and opacity in the spirit of strong unforgeability of digital signature schemes. 1
Assessing security of some group based cryptosystems, Contemporary Mathematics, to appear. (Cryptology Eprint Archive: Report 2003/123) David Garber, Einstein institute of Mathematics, The Hebrew University, GivatRam 91904
 Kaplan, Mina Teicher, and Uzi Vishne, Department of Mathematics and Statistics, BarIlan University, RamatGan 52900, Israel
"... Abstract. One of the possible generalizations of the discrete logarithm problem to arbitrary groups is the socalled conjugacy search problem (sometimes erroneously called just the conjugacy problem) : given two elements a, b of a group G and the information that a x = b for some x ∈ G, find at leas ..."
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Abstract. One of the possible generalizations of the discrete logarithm problem to arbitrary groups is the socalled conjugacy search problem (sometimes erroneously called just the conjugacy problem) : given two elements a, b of a group G and the information that a x = b for some x ∈ G, find at least one particular element x like that. Here a x stands for xax −1. The computational difficulty of this problem in some particular groups has been used in several group based cryptosystems. Recently, a few preprints have been in circulation that suggested various “neighbourhood search ” type heuristic attacks on the conjugacy search problem. The goal of the present survey is to stress a (probably well known) fact that these heuristic attacks alone are not a threat to the security of a cryptosystem, and, more importantly, to suggest a more credible approach to assessing security of group based cryptosystems. Such an approach should be necessarily based on the concept of the average case complexity (or expected running time) of an algorithm. These arguments support the following conclusion: although it is generally feasible to base the security of a cryptosystem on the difficulty of the conjugacy search problem, the group G itself (the “platform”) has to be chosen very carefully. In particular, experimental as well as theoretical evidence collected so far makes it appear likely that braid groups are not a good choice for the platform. We also reflect on possible replacements. 1
Fuzzy extractors: How to generate strong keys from biometrics and other noisy data. Technical Report 2003/235, Cryptology ePrint archive, http://eprint.iacr.org, 2006. Previous version appeared at EUROCRYPT 2004
 34 [DRS07] [DS05] [EHMS00] [FJ01] Yevgeniy Dodis, Leonid Reyzin, and Adam
, 2004
"... We provide formal definitions and efficient secure techniques for • turning noisy information into keys usable for any cryptographic application, and, in particular, • reliably and securely authenticating biometric data. Our techniques apply not just to biometric information, but to any keying mater ..."
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Cited by 532 (38 self)
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We provide formal definitions and efficient secure techniques for • turning noisy information into keys usable for any cryptographic application, and, in particular, • reliably and securely authenticating biometric data. Our techniques apply not just to biometric information, but to any keying material that, unlike traditional cryptographic keys, is (1) not reproducible precisely and (2) not distributed uniformly. We propose two primitives: a fuzzy extractor reliably extracts nearly uniform randomness R from its input; the extraction is errortolerant in the sense that R will be the same even if the input changes, as long as it remains reasonably close to the original. Thus, R can be used as a key in a cryptographic application. A secure sketch produces public information about its input w that does not reveal w, and yet allows exact recovery of w given another value that is close to w. Thus, it can be used to reliably reproduce errorprone biometric inputs without incurring the security risk inherent in storing them. We define the primitives to be both formally secure and versatile, generalizing much prior work. In addition, we provide nearly optimal constructions of both primitives for various measures of “closeness” of input data, such as Hamming distance, edit distance, and set difference.
New logic minimization techniques with applications to cryptology. Cryptology ePrint Archive, Report 2009/191
, 2009
"... to cryptology. ..."
Security Architecture for the Internet Protocol
 RFC 1825
, 1995
"... ContentType: text/plain ..."
Community detection in graphs
, 2009
"... The modern science of networks has brought significant advances to our understanding of complex systems. One of the most relevant features of graphs representing real systems is community structure, or clustering, i. e. the organization of vertices in clusters, with many edges joining vertices of th ..."
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Cited by 801 (1 self)
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The modern science of networks has brought significant advances to our understanding of complex systems. One of the most relevant features of graphs representing real systems is community structure, or clustering, i. e. the organization of vertices in clusters, with many edges joining vertices of the same cluster and comparatively few edges joining vertices of different clusters. Such
Short Signatures without Random Oracles
, 2004
"... We describe a short signature scheme which is existentially unforgeable under a chosen message attack without using random oracles. The security of our scheme depends on a new complexity assumption we call the Strong Di#eHellman assumption. This assumption has similar properties to the Strong RS ..."
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Cited by 387 (13 self)
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We describe a short signature scheme which is existentially unforgeable under a chosen message attack without using random oracles. The security of our scheme depends on a new complexity assumption we call the Strong Di#eHellman assumption. This assumption has similar properties to the Strong RSA assumption, hence the name. Strong RSA was previously used to construct signature schemes without random oracles. However, signatures generated by our scheme are much shorter and simpler than signatures from schemes based on Strong RSA.
Searchable encryption revisited: Consistency properties, relation to anonymous ibe, and extensions. Full version of current paper. Available at IACR Cryptology ePrint Archive, http://eprint.iacr.org
"... Abstract. We identify and fill some gaps with regard to consistency (the extent to which false positives are produced) for publickey encryption with keyword search (PEKS). We define computational and statistical relaxations of the existing notion of perfect consistency, show that the scheme of [7] ..."
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Cited by 134 (3 self)
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Abstract. We identify and fill some gaps with regard to consistency (the extent to which false positives are produced) for publickey encryption with keyword search (PEKS). We define computational and statistical relaxations of the existing notion of perfect consistency, show that the scheme of [7] is computationally consistent, and provide a new scheme that is statistically consistent. We also provide a transform of an anonymous IBE scheme to a secure PEKS scheme that, unlike the previous one, guarantees consistency. Finally we suggest three extensions of the basic notions considered here, namely anonymous HIBE, publickey encryption with temporary keyword search, and identitybased encryption
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