Lectures on the NTRU Encryption Algorithm and Digital Signature Scheme: Grenoble, June 2002
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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. -
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. -
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]. -
Lower Bounds on Lattice Sieving and Information Set Decoding
Lower bounds on lattice sieving and information set decoding Elena Kirshanova1 and Thijs Laarhoven2 1Immanuel Kant Baltic Federal University, Kaliningrad, Russia [email protected] 2Eindhoven University of Technology, Eindhoven, The Netherlands [email protected] April 22, 2021 Abstract In two of the main areas of post-quantum cryptography, based on lattices and codes, nearest neighbor techniques have been used to speed up state-of-the-art cryptanalytic algorithms, and to obtain the lowest asymptotic cost estimates to date [May{Ozerov, Eurocrypt'15; Becker{Ducas{Gama{Laarhoven, SODA'16]. These upper bounds are useful for assessing the security of cryptosystems against known attacks, but to guarantee long-term security one would like to have closely matching lower bounds, showing that improvements on the algorithmic side will not drastically reduce the security in the future. As existing lower bounds from the nearest neighbor literature do not apply to the nearest neighbor problems appearing in this context, one might wonder whether further speedups to these cryptanalytic algorithms can still be found by only improving the nearest neighbor subroutines. We derive new lower bounds on the costs of solving the nearest neighbor search problems appearing in these cryptanalytic settings. For the Euclidean metric we show that for random data sets on the sphere, the locality-sensitive filtering approach of [Becker{Ducas{Gama{Laarhoven, SODA 2016] using spherical caps is optimal, and hence within a broad class of lattice sieving algorithms covering almost all approaches to date, their asymptotic time complexity of 20:292d+o(d) is optimal. Similar conditional optimality results apply to lattice sieving variants, such as the 20:265d+o(d) complexity for quantum sieving [Laarhoven, PhD thesis 2016] and previously derived complexity estimates for tuple sieving [Herold{Kirshanova{Laarhoven, PKC 2018]. -
Optimizing NTRU Using AVX2
Master Thesis Computing Science Cyber Security Specialisation Radboud University Optimizing NTRU using AVX2 Author: First supervisor/assessor: Oussama Danba dr. Peter Schwabe Second assessor: dr. Lejla Batina July, 2019 Abstract The existence of Shor's algorithm, Grover's algorithm, and others that rely on the computational possibilities of quantum computers raise problems for some computational problems modern cryptography relies on. These algo- rithms do not yet have practical implications but it is believed that they will in the near future. In response to this, NIST is attempting to standardize post-quantum cryptography algorithms. In this thesis we will look at the NTRU submission in detail and optimize it for performance using AVX2. This implementation takes about 29 microseconds to generate a keypair, about 7.4 microseconds for key encapsulation, and about 6.8 microseconds for key decapsulation. These results are achieved on a reasonably recent notebook processor showing that NTRU is fast and feasible in practice. Contents 1 Introduction3 2 Cryptographic background and related work5 2.1 Symmetric-key cryptography..................5 2.2 Public-key cryptography.....................6 2.2.1 Digital signatures.....................7 2.2.2 Key encapsulation mechanisms.............8 2.3 One-way functions........................9 2.3.1 Cryptographic hash functions..............9 2.4 Proving security......................... 10 2.5 Post-quantum cryptography................... 12 2.6 Lattice-based cryptography................... 15 2.7 Side-channel resistance...................... 16 2.8 Related work........................... 17 3 Overview of NTRU 19 3.1 Important NTRU operations................... 20 3.1.1 Sampling......................... 20 3.1.2 Polynomial addition................... 22 3.1.3 Polynomial reduction.................. 22 3.1.4 Polynomial multiplication............... -
Post-Quantum TLS Without Handshake Signatures Full Version, September 29, 2020
Post-Quantum TLS Without Handshake Signatures Full version, September 29, 2020 Peter Schwabe Douglas Stebila Thom Wiggers Max Planck Institute for Security and University of Waterloo Radboud University Privacy & Radboud University [email protected] [email protected] [email protected] ABSTRACT Client Server static (sig): pk(, sk( We present KEMTLS, an alternative to the TLS 1.3 handshake that TCP SYN uses key-encapsulation mechanisms (KEMs) instead of signatures TCP SYN-ACK for server authentication. Among existing post-quantum candidates, G $ Z @ 6G signature schemes generally have larger public key/signature sizes compared to the public key/ciphertext sizes of KEMs: by using an ~ $ Z@ ss 6G~ IND-CCA-secure KEM for server authentication in post-quantum , 0, 00, 000 KDF(ss) TLS, we obtain multiple benefits. A size-optimized post-quantum ~ 6 , AEAD (cert[pk( ]kSig(sk(, transcript)kkey confirmation) instantiation of KEMTLS requires less than half the bandwidth of a ss 6~G size-optimized post-quantum instantiation of TLS 1.3. In a speed- , 0, 00, 000 KDF(ss) optimized instantiation, KEMTLS reduces the amount of server CPU AEAD 0 (application data) cycles by almost 90% compared to TLS 1.3, while at the same time AEAD 00 (key confirmation) reducing communication size, reducing the time until the client can AEAD 000 (application data) start sending encrypted application data, and eliminating code for signatures from the server’s trusted code base. Figure 1: High-level overview of TLS 1.3, using signatures CCS CONCEPTS for server authentication. • Security and privacy ! Security protocols; Web protocol security; Public key encryption. -
Timing Attacks and the NTRU Public-Key Cryptosystem
Eindhoven University of Technology BACHELOR Timing attacks and the NTRU public-key cryptosystem Gunter, S.P. Award date: 2019 Link to publication Disclaimer This document contains a student thesis (bachelor's or master's), as authored by a student at Eindhoven University of Technology. Student theses are made available in the TU/e repository upon obtaining the required degree. The grade received is not published on the document as presented in the repository. The required complexity or quality of research of student theses may vary by program, and the required minimum study period may vary in duration. General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain Timing Attacks and the NTRU Public-Key Cryptosystem by Stijn Gunter supervised by prof.dr. Tanja Lange ir. Leon Groot Bruinderink A thesis submitted in partial fulfilment of the requirements for the degree of Bachelor of Science July 2019 Abstract As we inch ever closer to a future in which quantum computers exist and are capable of break- ing many of the cryptographic algorithms that are in use today, more and more research is being done in the field of post-quantum cryptography. -
On Adapting NTRU for Post-Quantum Public-Key Encryption
On adapting NTRU for Post-Quantum Public-Key Encryption Dutto Simone, Morgari Guglielmo, Signorini Edoardo Politecnico di Torino & Telsy S.p.A. De Cifris AugustæTaurinorum - September 30th, 2020 Dutto, Morgari, Signorini On adapting NTRU for Post-Quantum Public-Key Encryption 1 / 30 Introduction Introduction Post-QuantumCryptography (PQC) aims to find non-quantum asymmetric cryptographic schemes able to resist attacks by quantum computers [1]. The main developments in this field were obtained after the realization of the first functioning quantum computers in the 2000s. Of all the ongoing research projects, one of the most followed by the international community is the NIST PQC Standardization Process, which began in 2016 and is now in its final stages [2]. Dutto, Morgari, Signorini On adapting NTRU for Post-Quantum Public-Key Encryption 2 / 30 Introduction This public, competition-like process focuses on selecting post-quantumKey-EncapsulationMechanisms (KEMs) and Digital Signature schemes. Public-KeyEncryption (PKE) schemes won't be standardized since, in general, the submitted KEMs are obtained from PKE schemes and the inverse processes are simple. However, there are cases for which re-obtaining the PKE scheme from the KEM is not straightforward, like the NTRU submission [3]. Our work focused on solving this problem by introducing a PKE scheme obtained from the KEM proposed in the NTRU submission, while maintaining its security. Dutto, Morgari, Signorini On adapting NTRU for Post-Quantum Public-Key Encryption 3 / 30 NTRU The original PKE scheme NTRU The original PKE scheme The NTRU submission is inspired by a PKE scheme introduced by Hoffstein, Pipher, Silverman in 1998 [4]. -
Comparing Proofs of Security for Lattice-Based Encryption
Comparing proofs of security for lattice-based encryption Daniel J. Bernstein1;2 1 Department of Computer Science, University of Illinois at Chicago, Chicago, IL 60607{7045, USA 2 Horst G¨ortz Institute for IT Security, Ruhr University Bochum, Germany [email protected] Abstract. This paper describes the limits of various \security proofs", using 36 lattice-based KEMs as case studies. This description allows the limits to be systematically compared across these KEMs; shows that some previous claims are incorrect; and provides an explicit framework for thorough security reviews of these KEMs. 1 Introduction It is disastrous if a cryptosystem X is standardized, deployed, and then broken. Perhaps the break is announced publicly and users move to another cryptosystem (hopefully a secure one this time), but (1) upgrading cryptosystems incurs many costs and (2) attackers could have been exploiting X in the meantime, perhaps long before the public announcement. \Security proofs" sound like they eliminate the risk of systems being broken. If X is \provably secure" then how can it possibly be insecure? A closer look shows that, despite the name, something labeled as a \security proof" is more limited: it is a claimed proof that an attack of type T against the cryptosystem X implies an attack against some problem P . There are still ways to argue that such proofs reduce risks, but these arguments have to account for potentially devastating gaps between (1) what has been proven and (2) security. Section 2 classifies these gaps into four categories, illustrated by the following four examples of breaks of various cryptographic standards: • 2000 [37]: Successful factorization of the RSA-512 challenge.