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71
Candidate indistinguishability obfuscation and functional encryption for all circuits
 In FOCS
, 2013
"... In this work, we study indistinguishability obfuscation and functional encryption for general circuits: Indistinguishability obfuscation requires that given any two equivalent circuits C0 and C1 of similar size, the obfuscations of C0 and C1 should be computationally indistinguishable. In functional ..."
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Cited by 169 (37 self)
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In this work, we study indistinguishability obfuscation and functional encryption for general circuits: Indistinguishability obfuscation requires that given any two equivalent circuits C0 and C1 of similar size, the obfuscations of C0 and C1 should be computationally indistinguishable. In functional encryption, ciphertexts encrypt inputs x and keys are issued for circuits C. Using the key SKC to decrypt a ciphertext CTx = Enc(x), yields the value C(x) but does not reveal anything else about x. Furthermore, no collusion of secret key holders should be able to learn anything more than the union of what they can each learn individually. We give constructions for indistinguishability obfuscation and functional encryption that supports all polynomialsize circuits. We accomplish this goal in three steps: • We describe a candidate construction for indistinguishability obfuscation for NC 1 circuits. The security of this construction is based on a new algebraic hardness assumption. The candidate and assumption use a simplified variant of multilinear maps, which we call Multilinear Jigsaw Puzzles. • We show how to use indistinguishability obfuscation for NC 1 together with Fully Homomorphic Encryption (with decryption in NC 1) to achieve indistinguishability obfuscation for all circuits.
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).
(Leveled) Fully Homomorphic Encryption without Bootstrapping
"... We present a novel approach to fully homomorphic encryption (FHE) that dramatically improves performance and bases security on weaker assumptions. A central conceptual contribution in our work is a new way of constructing leveled fully homomorphic encryption schemes (capable of evaluating arbitrary ..."
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Cited by 74 (9 self)
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We present a novel approach to fully homomorphic encryption (FHE) that dramatically improves performance and bases security on weaker assumptions. A central conceptual contribution in our work is a new way of constructing leveled fully homomorphic encryption schemes (capable of evaluating arbitrary polynomialsize circuits), without Gentry’s bootstrapping procedure. Specifically, we offer a choice of FHE schemes based on the learning with error (LWE) or Ring LWE (RLWE) problems that have 2λ security against known attacks. We construct: • A leveled FHE scheme that can evaluate depthL arithmetic circuits (composed of fanin 2 gates) using Õ(λ·L3) pergate computation. That is, the computation is quasilinear in the security parameter. Security is based on RLWE for an approximation factor exponential in L. This construction does not use the bootstrapping procedure. • A leveled FHE scheme that can evaluate depthL arithmetic circuits (composed of fanin 2 gates) using Õ(λ2) pergate computation, which is independent of L. Security is based on RLWE for quasipolynomial factors. This construction uses bootstrapping as an
Homomorphic evaluation of the AES circuit
 In CRYPTO
, 2012
"... We describe a working implementation of leveled homomorphic encryption (without bootstrapping) that can evaluate the AES128 circuit in three different ways. One variant takes under over 36 hours to evaluate an entire AES encryption operation, using NTL (over GMP) as our underlying software platform ..."
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Cited by 63 (6 self)
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We describe a working implementation of leveled homomorphic encryption (without bootstrapping) that can evaluate the AES128 circuit in three different ways. One variant takes under over 36 hours to evaluate an entire AES encryption operation, using NTL (over GMP) as our underlying software platform, and running on a largememory machine. Using SIMD techniques, we can process over 54 blocks in each evaluation, yielding an amortized rate of just under 40 minutes per block. Another implementation takes just over two and a half days to evaluate the AES operation, but can process 720 blocks in each evaluation, yielding an amortized rate of just over five minutes per block. We also detail a third implementation, which theoretically could yield even better amortized complexity, but in practice turns out to be less competitive. For our implementations we develop both AESspecific optimizations as well as several “generic” tools for FHE evaluation. These last tools include (among others) a different variant of the BrakerskiVaikuntanathan keyswitching technique that does not require reducing the norm of the ciphertext vector, and a method of implementing the BrakerskiGentryVaikuntanathan modulusswitching transformation on ciphertexts in CRT representation.
Reusable garbled circuits and succinct functional encryption
, 2013
"... Garbled circuits, introduced by Yao in the mid 80s, allow computing a function f on an input x without leaking anything about f or x besides f(x). Garbled circuits found numerous applications, but every known construction suffers from one limitation: it offers no security if used on multiple inputs ..."
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Cited by 42 (3 self)
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Garbled circuits, introduced by Yao in the mid 80s, allow computing a function f on an input x without leaking anything about f or x besides f(x). Garbled circuits found numerous applications, but every known construction suffers from one limitation: it offers no security if used on multiple inputs x. In this paper, we construct for the first time reusable garbled circuits. The key building block is a new succinct singlekey functional encryption scheme. Functional encryption is an ambitious primitive: given an encryption Enc(x) of a value x, and a secret key skf for a function f, anyone can compute f(x) without learning any other information about x. We construct, for the first time, a succinct functional encryption scheme for any polynomialtime function f where succinctness means that the ciphertext size does not grow with the size of the circuit for f, but only with its depth. The security of our construction is based on the intractability of the Learning with Errors (LWE) problem and holds as long as an adversary has access to a single key skf (or even an a priori bounded number of keys for different functions). Building on our succinct singlekey functional encryption scheme, we show several new applications in addition to reusable garbled circuits, such as a paradigm for general function obfuscation which we call tokenbased obfuscation, homomorphic encryption for a class of Turing machines where the evaluation runs in inputspecific time rather than worstcase time, and a scheme for delegating computation which is publicly verifiable and maintains the privacy of the computation.
Optimizing ORAM and Using it Efficiently for Secure Computation
, 2013
"... Oblivious RAM (ORAM) allows a client to access her data on a remote server while hiding the access pattern (which locations she is accessing) from the server. Beyond its immediate utility in allowing private computation over a client’s outsourced data, ORAM also allows mutually distrustful parties t ..."
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Cited by 38 (0 self)
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Oblivious RAM (ORAM) allows a client to access her data on a remote server while hiding the access pattern (which locations she is accessing) from the server. Beyond its immediate utility in allowing private computation over a client’s outsourced data, ORAM also allows mutually distrustful parties to run securecomputations over their joint data with sublinear online complexity. In this work we revisit the treebased ORAM of Shi et al. [20] and show how to optimize its performance as a standalone scheme, as well as its performance within higher level constructions. More specifically, we make several contributions: • We describe two optimizations to the treebased ORAM protocol of Shi et al., one reducing the storage overhead of that protocol by an O(k) multiplicative factor, and another reducing its time complexity by an O(log k) multiplicative factor, where k is the security parameter. Our scheme also enjoys a much simpler and tighter analysis than the original protocol. • We describe a protocol for binary search over this ORAM construction, where the entire binary search operation is done in the same complexity as a single ORAM access (as
Improved Security for a RingBased Fully Homomorphic Encryption Scheme
"... Abstract. In 1996, Hoffstein, Pipher and Silverman introduced an efficient lattice based encryption scheme dubbed NTRUEncrypt. Unfortunately, this scheme lacks a proof of security. However, in 2011, Stehlé and Steinfeld showed how to modify NTRUEncrypt to reduce security to standard problems in idea ..."
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Cited by 26 (6 self)
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Abstract. In 1996, Hoffstein, Pipher and Silverman introduced an efficient lattice based encryption scheme dubbed NTRUEncrypt. Unfortunately, this scheme lacks a proof of security. However, in 2011, Stehlé and Steinfeld showed how to modify NTRUEncrypt to reduce security to standard problems in ideal lattices. At STOC 2012, LópezAlt, Tromer and Vaikuntanathan proposed a fully homomorphic scheme based on this modified system. However, to allow homomorphic operations and prove security, a nonstandard assumption is required in their scheme. In this paper, we show how to remove this nonstandard assumption via techniques introduced by Brakerski at CRYPTO 2012 and construct a new fully homomorphic encryption scheme from the Stehlé and Steinfeld version based on standard lattice assumptions and a circular security assumption. The scheme is scaleinvariant and therefore avoids modulus switching, it eliminates ciphertext expansion in homomorphic multiplication, and the size of ciphertexts is one ring element. Moreover, we present a practical variant of our scheme, which is secure under stronger assumptions, along with parameter recommendations and promising implementation results. Finally, we present a novel approach for encrypting larger input sizes by applying a CRT approach on the input space.
ML Confidential: Machine Learning on Encrypted Data
"... Abstract. We demonstrate that, by using a recently proposed leveled homomorphic encryption scheme, it is possible to delegate the execution of a machine learning algorithm to a computing service while retaining confidentiality of the training and test data. Since the computational complexity of the ..."
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Cited by 17 (5 self)
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Abstract. We demonstrate that, by using a recently proposed leveled homomorphic encryption scheme, it is possible to delegate the execution of a machine learning algorithm to a computing service while retaining confidentiality of the training and test data. Since the computational complexity of the homomorphic encryption scheme depends primarily on the number of levels of multiplications to be carried out on the encrypted data, we define a new class of machine learning algorithms in which the algorithm’s predictions, viewed as functions of the input data, can be expressed as polynomials of bounded degree. We propose confidential algorithms for binary classification based on polynomial approximations to leastsquares solutions obtained by a small number of gradient descent steps. We present experimental validation of the confidential machine learning pipeline and discuss the tradeoffs regarding computational complexity, prediction accuracy and cryptographic security. 1
How to Run Turing Machines on Encrypted Data
"... Abstract. Algorithms for computing on encrypted data promise to be a fundamental building block of cryptography. The way one models such algorithms has a crucial effect on the efficiency and usefulness of the resulting cryptographic schemes. As of today, almost all known schemes for fully homomorphi ..."
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Cited by 15 (1 self)
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Abstract. Algorithms for computing on encrypted data promise to be a fundamental building block of cryptography. The way one models such algorithms has a crucial effect on the efficiency and usefulness of the resulting cryptographic schemes. As of today, almost all known schemes for fully homomorphic encryption, functional encryption, and garbling schemes work by modeling algorithms as circuits rather than as Turing machines. As a consequence of this modeling, evaluating an algorithm over encrypted data is as slow as the worstcase running time of that algorithm, a dire fact for many tasks. In addition, in settings where an evaluator needs a description of the algorithm itself in some “encoded ” form, the cost of computing and communicating such encoding is as large as the worstcase running time of this algorithm. In this work, we construct cryptographic schemes for computing Turing machines on encrypted data that avoid the worstcase problem. Specifically, we show: – An attributebased encryption scheme for any polynomialtime Turing machine and Random Access Machine (RAM).
Private database queries using somewhat homomorphic encryption
"... In a private database query system, a client issues queries to a database and obtains the results without learning anything else about the database and without the server learning the query. While previous work has yielded systems that can efficiently support disjunction queries, performing conjunct ..."
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Cited by 13 (0 self)
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In a private database query system, a client issues queries to a database and obtains the results without learning anything else about the database and without the server learning the query. While previous work has yielded systems that can efficiently support disjunction queries, performing conjunction queries privately remains an open problem. In this work, we show that using a polynomial encoding of the database enables efficient implementations of conjunction queries using somewhat homomorphic encryption. We describe a threeparty protocol that supports efficient evaluation of conjunction queries. Then, we present two implementations of our protocol using Paillier’s additively homomorphic system as well as Brakerski’s somewhat homomorphic cryptosystem. Finally, we show that the additional homomorphic properties of the Brakerski cryptosystem allow us to handle queries involving several thousand elements over a millionrecord database in just a few minutes, far outperforming the implementation using the additively homomorphic system.