Lattice-Based Cryptography
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Lectures on the NTRU Encryption Algorithm and Digital Signature Scheme: Grenoble, June 2002
Lectures on the NTRU encryption algorithm and digital signature scheme: Grenoble, June 2002 J. Pipher Brown University, Providence RI 02912 1 Lecture 1 1.1 Integer lattices Lattices have been studied by cryptographers for quite some time, in both the field of cryptanalysis (see for example [16{18]) and as a source of hard problems on which to build encryption schemes (see [1, 8, 9]). In this lecture, we describe the NTRU encryption algorithm, and the lattice problems on which this is based. We begin with some definitions and a brief overview of lattices. If a ; a ; :::; a are n independent vectors in Rm, n m, then the 1 2 n ≤ integer lattice with these vectors as basis is the set = n x a : x L f 1 i i i 2 Z . A lattice is often represented as matrix A whose rows are the basis g P vectors a1; :::; an. The elements of the lattice are simply the vectors of the form vT A, which denotes the usual matrix multiplication. We will specialize for now to the situation when the rank of the lattice and the dimension are the same (n = m). The determinant of a lattice det( ) is the volume of the fundamen- L tal parallelepiped spanned by the basis vectors. By the Gram-Schmidt process, one can obtain a basis for the vector space generated by , and L the det( ) will just be the product of these orthogonal vectors. Note that L these vectors are not a basis for as a lattice, since will not usually L L possess an orthogonal basis. -
Solving Hard Lattice Problems and the Security of Lattice-Based Cryptosystems
Solving Hard Lattice Problems and the Security of Lattice-Based Cryptosystems † Thijs Laarhoven∗ Joop van de Pol Benne de Weger∗ September 10, 2012 Abstract This paper is a tutorial introduction to the present state-of-the-art in the field of security of lattice- based cryptosystems. After a short introduction to lattices, we describe the main hard problems in lattice theory that cryptosystems base their security on, and we present the main methods of attacking these hard problems, based on lattice basis reduction. We show how to find shortest vectors in lattices, which can be used to improve basis reduction algorithms. Finally we give a framework for assessing the security of cryptosystems based on these hard problems. 1 Introduction Lattice-based cryptography is a quickly expanding field. The last two decades have seen exciting devel- opments, both in using lattices in cryptanalysis and in building public key cryptosystems on hard lattice problems. In the latter category we could mention the systems of Ajtai and Dwork [AD], Goldreich, Goldwasser and Halevi [GGH2], the NTRU cryptosystem [HPS], and systems built on Small Integer Solu- tions [MR1] problems and Learning With Errors [R1] problems. In the last few years these developments culminated in the advent of the first fully homomorphic encryption scheme by Gentry [Ge]. A major issue in this field is to base key length recommendations on a firm understanding of the hardness of the underlying lattice problems. The general feeling among the experts is that the present understanding is not yet on the same level as the understanding of, e.g., factoring or discrete logarithms. -
Universit`A Di Pisa Post Quantum Cryptography
Universit`adi Pisa Facolt`a di Scienze Matematiche, Fisiche e Naturali Corso di Laurea Magistrale in Fisica Anno Accademico 2013/2014 Elaborato Finale Post Quantum Cryptography Candidato: Relatori: Antonio Vaira Prof. Oliver Morsch Ing. Cristiano Borrelli Alla mia mamma Abstract I started my experience with cryptography within the Airbus environment working on this master thesis. I have been asked to provide a framework, or in other words, a big picture about present-day alternatives to the most used public key crypto-system, the RSA, that are supposed to be quantum resistant. The final application of my work eventually resulted in recommendations on how to handle the quantum threat in the near future. This was quite a complex task to accomplish because it involves a huge variety of topics but by physical background was really helpful in facing it. Not because of specific and previous knowledge but for the mathematical toolsacquired during the studies and especially for that attitude that belongs to out category that make us, physicist problem solver in a large variety of fields. Indeed I also tried to go a bit further with my studies. I took one of the most promising algorithm on my opinion, but not well known yet so unfeasible for a recommendation and therefore an implementation in the close future, and I tried to figure out how to enhance it from both a security and an operational point of view (how to increase the correctness ratio of the decryption and the speed of the cryptographic operations). It followed a period of time in which I improved my skills with few computing languages and in the end I decided to implement a toy model at a high level using an interface that already implements all the mathematical and algebraical structures used to build the model. -
NTRU Cryptosystem: Recent Developments and Emerging Mathematical Problems in Finite Polynomial Rings
XXXX, 1–33 © De Gruyter YYYY NTRU Cryptosystem: Recent Developments and Emerging Mathematical Problems in Finite Polynomial Rings Ron Steinfeld Abstract. The NTRU public-key cryptosystem, proposed in 1996 by Hoffstein, Pipher and Silverman, is a fast and practical alternative to classical schemes based on factorization or discrete logarithms. In contrast to the latter schemes, it offers quasi-optimal asymptotic effi- ciency and conjectured security against quantum computing attacks. The scheme is defined over finite polynomial rings, and its security analysis involves the study of natural statistical and computational problems defined over these rings. We survey several recent developments in both the security analysis and in the applica- tions of NTRU and its variants, within the broader field of lattice-based cryptography. These developments include a provable relation between the security of NTRU and the computa- tional hardness of worst-case instances of certain lattice problems, and the construction of fully homomorphic and multilinear cryptographic algorithms. In the process, we identify the underlying statistical and computational problems in finite rings. Keywords. NTRU Cryptosystem, lattice-based cryptography, fully homomorphic encryption, multilinear maps. AMS classification. 68Q17, 68Q87, 68Q12, 11T55, 11T71, 11T22. 1 Introduction The NTRU public-key cryptosystem has attracted much attention by the cryptographic community since its introduction in 1996 by Hoffstein, Pipher and Silverman [32, 33]. Unlike more classical public-key cryptosystems based on the hardness of integer factorisation or the discrete logarithm over finite fields and elliptic curves, NTRU is based on the hardness of finding ‘small’ solutions to systems of linear equations over polynomial rings, and as a consequence is closely related to geometric problems on certain classes of high-dimensional Euclidean lattices. -
On Ideal Lattices and Learning with Errors Over Rings∗
On Ideal Lattices and Learning with Errors Over Rings∗ Vadim Lyubashevskyy Chris Peikertz Oded Regevx June 25, 2013 Abstract The “learning with errors” (LWE) problem is to distinguish random linear equations, which have been perturbed by a small amount of noise, from truly uniform ones. The problem has been shown to be as hard as worst-case lattice problems, and in recent years it has served as the foundation for a plethora of cryptographic applications. Unfortunately, these applications are rather inefficient due to an inherent quadratic overhead in the use of LWE. A main open question was whether LWE and its applications could be made truly efficient by exploiting extra algebraic structure, as was done for lattice-based hash functions (and related primitives). We resolve this question in the affirmative by introducing an algebraic variant of LWE called ring- LWE, and proving that it too enjoys very strong hardness guarantees. Specifically, we show that the ring-LWE distribution is pseudorandom, assuming that worst-case problems on ideal lattices are hard for polynomial-time quantum algorithms. Applications include the first truly practical lattice-based public-key cryptosystem with an efficient security reduction; moreover, many of the other applications of LWE can be made much more efficient through the use of ring-LWE. 1 Introduction Over the last decade, lattices have emerged as a very attractive foundation for cryptography. The appeal of lattice-based primitives stems from the fact that their security can often be based on worst-case hardness assumptions, and that they appear to remain secure even against quantum computers. -
Performance Evaluation of RSA and NTRU Over GPU with Maxwell and Pascal Architecture
Performance Evaluation of RSA and NTRU over GPU with Maxwell and Pascal Architecture Xian-Fu Wong1, Bok-Min Goi1, Wai-Kong Lee2, and Raphael C.-W. Phan3 1Lee Kong Chian Faculty of and Engineering and Science, Universiti Tunku Abdul Rahman, Sungai Long, Malaysia 2Faculty of Information and Communication Technology, Universiti Tunku Abdul Rahman, Kampar, Malaysia 3Faculty of Engineering, Multimedia University, Cyberjaya, Malaysia E-mail: [email protected]; {goibm; wklee}@utar.edu.my; [email protected] Received 2 September 2017; Accepted 22 October 2017; Publication 20 November 2017 Abstract Public key cryptography important in protecting the key exchange between two parties for secure mobile and wireless communication. RSA is one of the most widely used public key cryptographic algorithms, but the Modular exponentiation involved in RSA is very time-consuming when the bit-size is large, usually in the range of 1024-bit to 4096-bit. The speed performance of RSA comes to concerns when thousands or millions of authentication requests are needed to handle by the server at a time, through a massive number of connected mobile and wireless devices. On the other hand, NTRU is another public key cryptographic algorithm that becomes popular recently due to the ability to resist attack from quantum computer. In this paper, we exploit the massively parallel architecture in GPU to perform RSA and NTRU computations. Various optimization techniques were proposed in this paper to achieve higher throughput in RSA and NTRU computation in two GPU platforms. To allow a fair comparison with existing RSA implementation techniques, we proposed to evaluate the speed performance in the best case Journal of Software Networking, 201–220. -
Private Searching on Streaming Data∗
J. Cryptology (2007) 20: 397–430 DOI: 10.1007/s00145-007-0565-3 © 2007 International Association for Cryptologic Research Private Searching on Streaming Data∗ Rafail Ostrovsky Department of Computer Science and Department of Mathematics, University of California, Los Angeles, CA 90095, U.S.A. [email protected] William E. Skeith III Department of Mathematics, University of California, Los Angeles, CA 90095, U.S.A. [email protected] Communicated by Dan Boneh Received 1 September 2005 and revised 16 July 2006 Online publication 13 July 2007 Abstract. In this paper we consider the problem of private searching on streaming data, where we can efficiently implement searching for documents that satisfy a secret criteria (such as the presence or absence of a hidden combination of hidden keywords) under various cryptographic assumptions. Our results can be viewed in a variety of ways: as a generalization of the notion of private information retrieval (to more general queries and to a streaming environment); as positive results on privacy-preserving datamining; and as a delegation of hidden program computation to other machines. Key words. Code obfuscation, Public-key program obfuscation, Program obfus- cation, Crypto-computing, Software security, Database security, Public-key encryp- tion with special properties, Private information retrieval, Privacy-preserving keyword search, Secure algorithms for streaming data, Privacy-preserving datamining, Secure delegation of computation, Searching with privacy, Mobile code. 1. Introduction 1.1. Data Filtering for the Intelligence Community As our motivating example, we examine one of the tasks of the intelligence community, which is to collect “potentially useful” information from huge streaming sources of ∗ An abridged version appeared at CRYPTO 2005. -
On Lattices, Learning with Errors, Random Linear Codes, and Cryptography
On Lattices, Learning with Errors, Random Linear Codes, and Cryptography Oded Regev ¤ May 2, 2009 Abstract Our main result is a reduction from worst-case lattice problems such as GAPSVP and SIVP to a certain learning problem. This learning problem is a natural extension of the ‘learning from parity with error’ problem to higher moduli. It can also be viewed as the problem of decoding from a random linear code. This, we believe, gives a strong indication that these problems are hard. Our reduction, however, is quantum. Hence, an efficient solution to the learning problem implies a quantum algorithm for GAPSVP and SIVP. A main open question is whether this reduction can be made classical (i.e., non-quantum). We also present a (classical) public-key cryptosystem whose security is based on the hardness of the learning problem. By the main result, its security is also based on the worst-case quantum hardness of GAPSVP and SIVP. The new cryptosystem is much more efficient than previous lattice-based cryp- tosystems: the public key is of size O~(n2) and encrypting a message increases its size by a factor of O~(n) (in previous cryptosystems these values are O~(n4) and O~(n2), respectively). In fact, under the assumption that all parties share a random bit string of length O~(n2), the size of the public key can be reduced to O~(n). 1 Introduction Main theorem. For an integer n ¸ 1 and a real number " ¸ 0, consider the ‘learning from parity with n error’ problem, defined as follows: the goal is to find an unknown s 2 Z2 given a list of ‘equations with errors’ hs; a1i ¼" b1 (mod 2) hs; a2i ¼" b2 (mod 2) . -
Making NTRU As Secure As Worst-Case Problems Over Ideal Lattices
Making NTRU as Secure as Worst-Case Problems over Ideal Lattices Damien Stehlé1 and Ron Steinfeld2 1 CNRS, Laboratoire LIP (U. Lyon, CNRS, ENS Lyon, INRIA, UCBL), 46 Allée d’Italie, 69364 Lyon Cedex 07, France. [email protected] – http://perso.ens-lyon.fr/damien.stehle 2 Centre for Advanced Computing - Algorithms and Cryptography, Department of Computing, Macquarie University, NSW 2109, Australia [email protected] – http://web.science.mq.edu.au/~rons Abstract. NTRUEncrypt, proposed in 1996 by Hoffstein, Pipher and Sil- verman, is the fastest known lattice-based encryption scheme. Its mod- erate key-sizes, excellent asymptotic performance and conjectured resis- tance to quantum computers could make it a desirable alternative to fac- torisation and discrete-log 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 worst-case lattice problems, restricted to a family of lattices related to some cyclotomic fields. Our main contribution is to show that if the se- cret 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 R-LWE problem. Keywords. Lattice-based cryptography, NTRU, provable security. 1 Introduction NTRUEncrypt, devised by Hoffstein, Pipher and Silverman, was first presented at the Crypto’96 rump session [14]. Although its description relies on arithmetic n over the polynomial ring Zq[x]=(x − 1) for n prime and q a small integer, it was quickly observed that breaking it could be expressed as a problem over Euclidean lattices [6]. -
The Cramer-Shoup Strong-RSA Signature Scheme Revisited
The Cramer-Shoup Strong-RSA Signature Scheme Revisited Marc Fischlin Johann Wolfgang Goethe-University Frankfurt am Main, Germany marc @ mi.informatik.uni-frankfurt.de http://www.mi.informatik.uni-frankfurt.de/ Abstract. We discuss a modification of the Cramer-Shoup strong-RSA signature scheme. Our proposal also presumes the strong RSA assump- tion (and a collision-intractable hash function for long messages), but |without loss in performance| the size of a signature is almost halved compared to the original scheme. We also show how to turn the signature scheme into a \lightweight" anonymous (but linkable) group identifica- tion protocol without random oracles. 1 Introduction Cramer and Shoup [CS00] have presented a signature scheme which is secure against adaptive chosen-message attacks under the strong RSA (aka. flexible RSA) assumption, and which does not rely on the random oracle model. For a 1024-bit RSA modulus and a 160-bit (hash value of a) message a signature has about 2200 bits. Cramer and Shoup also discuss a variation of their scheme which, in addition to the strong RSA assumption, requires the discrete-log as- sumption and which produces signatures of roughly half the length (about 1350 bits). Here, we show that we can achieve the same signature size under the strong RSA assumption only, even with a slightly improved performance than in the original strong-RSA-only case or the discrete-log & strong-RSA case. Our signature scheme also has the feature that for short messages, e.g., of 120 bits, a collision-intractable (or universal one-way) hash function becomes obsolete. -
Lattices That Admit Logarithmic Worst-Case to Average-Case Connection Factors
Lattices that Admit Logarithmic Worst-Case to Average-Case Connection Factors Chris Peikert∗ Alon Rosen† April 4, 2007 Abstract We demonstrate an average-case problem that is as hard as finding γ(n)-approximate√ short- est vectors in certain n-dimensional lattices in the worst case, where γ(n) = O( log n). The previously best known factor for any non-trivial class of lattices was γ(n) = O˜(n). Our results apply to families of lattices having special algebraic structure. Specifically, we consider lattices that correspond to ideals in the ring of integers of an algebraic number field. The worst-case problem we rely on is to find approximate shortest vectors in these lattices, under an appropriate form of preprocessing of the number field. For the connection factors γ(n) we achieve, the corresponding decision problems on ideal lattices are not known to be NP-hard; in fact, they are in P. However, the search approximation problems still appear to be very hard. Indeed, ideal lattices are well-studied objects in com- putational number theory, and the best known algorithms for them seem to perform no better than the best known algorithms for general lattices. To obtain the best possible connection factor, we instantiate our constructions with infinite families of number fields having constant root discriminant. Such families are known to exist and are computable, though no efficient construction is yet known. Our work motivates the search for such constructions. Even constructions of number fields having root discriminant up to O(n2/3−) would yield connection factors better than O˜(n). -
Cryptography from Ideal Lattices
Introduction Ideal lattices Ring-SIS Ring-LWE Other algebraic lattices Conclusion Ideal Lattices Damien Stehl´e ENS de Lyon Berkeley, 07/07/2015 Damien Stehl´e Ideal Lattices 07/07/2015 1/32 Introduction Ideal lattices Ring-SIS Ring-LWE Other algebraic lattices Conclusion Lattice-based cryptography: elegant but impractical Lattice-based cryptography is fascinating: simple, (presumably) post-quantum, expressive But it is very slow Recall the SIS hash function: 0, 1 m Zn { } → q x xT A 7→ · Need m = Ω(n log q) to compress O(1) m n q is n , A is uniform in Zq × O(n2) space and cost ⇒ Example parameters: n 26, m n 2e4, log q 23 ≈ ≈ · 2 ≈ Damien Stehl´e Ideal Lattices 07/07/2015 2/32 Introduction Ideal lattices Ring-SIS Ring-LWE Other algebraic lattices Conclusion Lattice-based cryptography: elegant but impractical Lattice-based cryptography is fascinating: simple, (presumably) post-quantum, expressive But it is very slow Recall the SIS hash function: 0, 1 m Zn { } → q x xT A 7→ · Need m = Ω(n log q) to compress O(1) m n q is n , A is uniform in Zq × O(n2) space and cost ⇒ Example parameters: n 26, m n 2e4, log q 23 ≈ ≈ · 2 ≈ Damien Stehl´e Ideal Lattices 07/07/2015 2/32 Introduction Ideal lattices Ring-SIS Ring-LWE Other algebraic lattices Conclusion Lattice-based cryptography: elegant but impractical Lattice-based cryptography is fascinating: simple, (presumably) post-quantum, expressive But it is very slow Recall the SIS hash function: 0, 1 m Zn { } → q x xT A 7→ · Need m = Ω(n log q) to compress O(1) m n q is n , A is uniform in Zq × O(n2)