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122
Efficient Fully Homomorphic Encryption from (Standard) LWE
 LWE, FOCS 2011, IEEE 52ND ANNUAL SYMPOSIUM ON FOUNDATIONS OF COMPUTER SCIENCE, IEEE
, 2011
"... We present a fully homomorphic encryption scheme that is based solely on the (standard) learning with errors (LWE) assumption. Applying known results on LWE, the security of our scheme is based on the worstcase hardness of “short vector problems ” on arbitrary lattices. Our construction improves on ..."
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Cited by 117 (6 self)
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We present a fully homomorphic encryption scheme that is based solely on the (standard) learning with errors (LWE) assumption. Applying known results on LWE, the security of our scheme is based on the worstcase hardness of “short vector problems ” on arbitrary lattices. Our construction improves on previous works in two aspects: 1. We show that “somewhat homomorphic” encryption can be based on LWE, using a new relinearization technique. In contrast, all previous schemes relied on complexity assumptions related to ideals in various rings. 2. We deviate from the “squashing paradigm” used in all previous works. We introduce a new dimensionmodulus reduction technique, which shortens the ciphertexts and reduces the decryption complexity of our scheme, without introducing additional assumptions. Our scheme has very short ciphertexts and we therefore use it to construct an asymptotically efficient LWEbased singleserver private information retrieval (PIR) protocol. The communication complexity of our protocol (in the publickey model) is k · polylog(k) + log DB  bits per singlebit query (here, k is a security parameter).
Functional Encryption: Definitions and Challenges
"... We initiate the formal study of functional encryption by giving precise definitions of the concept and its security. Roughly speaking, functional encryption supports restricted secret keys that enable a key holder to learn a specific function of encrypted data, but learn nothing else about the data. ..."
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Cited by 110 (17 self)
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We initiate the formal study of functional encryption by giving precise definitions of the concept and its security. Roughly speaking, functional encryption supports restricted secret keys that enable a key holder to learn a specific function of encrypted data, but learn nothing else about the data. For example, given an encrypted program the secret key may enable the key holder to learn the output of the program on a specific input without learning anything else about the program. We show that defining security for functional encryption is nontrivial. First, we show that a natural gamebased definition is inadequate for some functionalities. We then present a natural simulationbased definition and show that it (provably) cannot be satisfied in the standard model, but can be satisfied in the random oracle model. We show how to map many existing concepts to our formalization of functional encryption and conclude with several interesting open problems in this young area.
Efficient lattice (H)IBE in the standard model
 In EUROCRYPT 2010, LNCS
, 2010
"... Abstract. We construct an efficient identity based encryption system based on the standard learning with errors (LWE) problem. Our security proof holds in the standard model. The key step in the construction is a family of lattices for which there are two distinct trapdoors for finding short vectors ..."
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Cited by 96 (15 self)
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Abstract. We construct an efficient identity based encryption system based on the standard learning with errors (LWE) problem. Our security proof holds in the standard model. The key step in the construction is a family of lattices for which there are two distinct trapdoors for finding short vectors. One trapdoor enables the real system to generate short vectors in all lattices in the family. The other trapdoor enables the simulator to generate short vectors for all lattices in the family except for one. We extend this basic technique to an adaptivelysecure IBE and a Hierarchical IBE. 1
GENERATING SHORTER BASES FOR HARD RANDOM LATTICES
, 2009
"... We revisit the problem of generating a “hard” random lattice together with a basis of relatively short vectors. This problem has gained in importance lately due to new cryptographic schemes that use such a procedure for generating public/secret key pairs. In these applications, a shorter basis dire ..."
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Cited by 69 (7 self)
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We revisit the problem of generating a “hard” random lattice together with a basis of relatively short vectors. This problem has gained in importance lately due to new cryptographic schemes that use such a procedure for generating public/secret key pairs. In these applications, a shorter basis directly corresponds to milder underlying complexity assumptions and smaller key sizes. The contributions of this work are twofold. First, using the Hermite normal form as an organizing principle, we simplify and generalize an approach due to Ajtai (ICALP 1999). Second, we improve the construction and its analysis in several ways, most notably by tightening the length of the output basis essentially to the optimum value.
Better key sizes (and attacks) for LWEbased encryption
 In CTRSA
, 2011
"... We analyze the concrete security and key sizes of theoretically sound latticebased encryption schemes based on the “learning with errors ” (LWE) problem. Our main contributions are: (1) a new lattice attack on LWE that combines basis reduction with an enumeration algorithm admitting a time/success ..."
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Cited by 68 (7 self)
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We analyze the concrete security and key sizes of theoretically sound latticebased encryption schemes based on the “learning with errors ” (LWE) problem. Our main contributions are: (1) a new lattice attack on LWE that combines basis reduction with an enumeration algorithm admitting a time/success tradeoff, which performs better than the simple distinguishing attack considered in prior analyses; (2) concrete parameters and security estimates for an LWEbased cryptosystem that is more compact and efficient than the wellknown schemes from the literature. Our new key sizes are up to 10 times smaller than prior examples, while providing even stronger concrete security levels.
Attributebased encryption for circuits from multilinear maps. Cryptology ePrint Archive, Report 2013/128, 2013. http://eprint.iacr.org/. Oded Goldreich and
"... In this work, we provide the first construction of AttributeBased Encryption (ABE) for general circuits. Our construction is based on the existence of multilinear maps. We prove selective security of our scheme in the standard model under the natural multilinear generalization of the BDDH assumptio ..."
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Cited by 54 (8 self)
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In this work, we provide the first construction of AttributeBased Encryption (ABE) for general circuits. Our construction is based on the existence of multilinear maps. We prove selective security of our scheme in the standard model under the natural multilinear generalization of the BDDH assumption. Our scheme achieves both KeyPolicy and CiphertextPolicy variants of ABE. Our scheme and its proof of security directly translate to the recent multilinear map framework of Garg, Gentry, and Halevi. This paper subsumes the manuscript of Sahai and Waters [SW12].
Lattice basis delegation in fixed dimension and shorterciphertext hierarchical IBE
 In Advances in Cryptology — CRYPTO 2010, Springer LNCS 6223
, 2010
"... Abstract. We present a technique for delegating a short lattice basis that has the advantage of keeping the lattice dimension unchanged upon delegation. Building on this result, we construct two new hierarchical identitybased encryption (HIBE) schemes, with and without random oracles. The resulting ..."
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Cited by 50 (10 self)
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Abstract. We present a technique for delegating a short lattice basis that has the advantage of keeping the lattice dimension unchanged upon delegation. Building on this result, we construct two new hierarchical identitybased encryption (HIBE) schemes, with and without random oracles. The resulting systems are very different from earlier latticebased HIBEs and in some cases result in shorter ciphertexts and private keys. We prove security from classic lattice hardness assumptions. 1
Making NTRU as secure as worstcase problems over ideal lattices
 In Proc. of EUROCRYPT, volume 6632 of LNCS
, 2011
"... Abstract. NTRUEncrypt, proposed in 1996 by Ho stein, Pipher and Silverman, is the fastest known latticebased encryption scheme. Its moderate keysizes, excellent asymptotic performance and conjectured resistance to quantum computers could make it a desirable alternative to factorisation and discret ..."
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Cited by 49 (5 self)
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Abstract. NTRUEncrypt, proposed in 1996 by Ho stein, Pipher and Silverman, is the fastest known latticebased encryption scheme. Its moderate keysizes, excellent asymptotic performance and conjectured resistance to quantum computers could make it a desirable alternative to factorisation and discretelog based encryption schemes. However, since its introduction, doubts have regularly arisen on its security. In the present work, we show how to modify NTRUEncrypt to make it provably secure in the standard model, under the assumed quantum hardness of standard worstcase lattice problems, restricted to a family of lattices related to some cyclotomic elds. Our main contribution is to show that if the secret key polynomials are selected by rejection from discrete Gaussians, then the public key, which is their ratio, is statistically indistinguishable from uniform over its domain. The security then follows from the already proven hardness of the RLWE problem.
New proof methods for attributebased encryption: Achieving full security through selective techniques
 in Proc. of CRYPTO
, 2012
"... We develop a new methodology for utilizing the prior techniques to prove selective security for functional encryption systems as a direct ingredient in devising proofs of full security. This deepens the relationship between the selective and full security models and provides a path for transferring ..."
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Cited by 47 (10 self)
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We develop a new methodology for utilizing the prior techniques to prove selective security for functional encryption systems as a direct ingredient in devising proofs of full security. This deepens the relationship between the selective and full security models and provides a path for transferring the best qualities of selectively secure systems to fully secure systems. In particular, we present a CiphertextPolicy AttributeBased Encryption scheme that is proven fully secure while matching the efficiency of the state of the art selectively secure systems. 1
Lattice Signatures Without Trapdoors
"... We provide an alternative method for constructing latticebased digital signatures which does not use the “hashandsign” methodology of Gentry, Peikert, and Vaikuntanathan (STOC 2008). Our resulting signature scheme is secure, in the random oracle model, based on the worstcase hardness of the Õ(n ..."
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Cited by 43 (9 self)
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We provide an alternative method for constructing latticebased digital signatures which does not use the “hashandsign” methodology of Gentry, Peikert, and Vaikuntanathan (STOC 2008). Our resulting signature scheme is secure, in the random oracle model, based on the worstcase hardness of the Õ(n1.5)SIVP problem in general lattices. The secret key, public key, and the signature size of our scheme are smaller than in all previous instantiations of the hashandsign signature, and our signing algorithm is also quite simple, requiring just a few matrixvector multiplications and rejection samplings. We then also show that by slightly changing the parameters, one can get even more efficient signatures that are based on the hardness of the Learning With Errors problem. Our construction naturally transfers to the ring setting, where the size of the public and secret keys can be significantly shrunk, which results in the most practical todate provably secure signature scheme based on lattices.