In this work, we initially present in Chapter 1 the theoretical background of the LWE problem. Chapter 2 describes in depth the NewHope post-quantum lattice-based cryptosystem, which is based on a variant of LWE called Ring Learning With Errors (RLWE). Chapter 3 analyses two key reuse attacks on NewHope as published in literature and our implementation of them.
In this work, we initially present in Chapter 1 the theoretical background of the LWE problem. Chapter 2 describes in depth the NewHope post-quantum lattice-based cryptosystem, which is based on a variant of LWE called Ring Learning With Errors (RLWE). Chapter 3 analyses two key reuse attacks on NewHope as published in literature and our implementation of them.
Lattice-based cryptographic primitives are believed to offer resilience against attacks by quantum computers. Following increasing interest from both companies and government agencies in building quantum computers, a number of works have proposed instantiations of practical post-quantum key-exchange protocols based on hard problems in lattices, mainly based on the Ring Learning With Errors (R-LWE) problem.\nIn this work we present an analysis of Ring-LWE based key-exchange mechanisms and compare two implementations of Ring-LWE based key-exchange protocol: BCNS and NewHope. This is important as NewHope protocol implementation outperforms state-of-the art elliptic curve based Diffie-Hellman key-exchange X25519, thus showing that using quantum safe key-exchange is not only a viable option but also a faster one. Specifically, this thesis compares different reconciliation methods, parameter choices, noise sampling algorithms and performance.
This note describes a key exchange method based on the ring-LWE (RLWE)
assumption. It builds upon several results, including Regev's
landmark quantum reduction from certain worst case lattice problems
(approx. GapSVP and SIVP) to random instances of the search variant of
a particular learning problem (LWE). It also builds on the follow on
work of Lyubashevsky, Peikert and Regev on the average case hardness
of the RLWE search variant for polynomially bounded numbers of RLWE
samples, along with novel applications of automorphism groups in
number fields for a RLWE search to decision reduction (thereby
demonstrating pseudorandomness of RLWE in these number fields).
Subsequently, these results were adopted for the construction of
Diffie-Hellman like key exchange methods by Peikert, and then by
Lindner and Peikert followed by Ding and then by Ding, Xie and Lin who
proposed efficient variants of such protocols. Subsequent work by
Peikert proposed another efficient variant, phrased as a key
encapsulation method, incorporating a low bandwidth reconciliation
technique allowing two parties to exactly agree on a uniformly
distributed secret value from noisy RLWE instances. This was followed
by a concrete instantiation with parameter sets by Bos, Costello,
Naehrig, Stebila, followed by another instantiation by Alkim, Ducas,
Poppelmann and Schwabe with the same ring polynomial but a smaller
modulus and a different reconciliation method. Unlike most other
public key cryptography based key exchange methods, it is believed
that RLWE based key exchange would remain secure in the event that an
adversary is able to build a quantum computer. This document is a
product of the Crypto Forum Research Group (CFRG).
With the possibility of quantum computers making an appearance, possibly capable of breaking several well established and widespread crytposystems (especially those that implement public key cryptography), necessity has arisen to create new cryptographic algorithms which remain safe even against adversaries using quantum computers. Several algorithms based on different mathematical problems have been proposed which are considered to be hard to solve with quantum computers. In recent years, a new lattice-based mathematical problem called Learning With Errors (and its variant Ring - Learning With Errors) was introduced, and several cryptosystems based on this problem were introduced, some of which are becoming practical enough to compete with traditional schemes that have been used for decades. The primary focus in this work is the implementation of two Ring - Learning With Errors based schemes (one key exchange mechanism and one digital signature scheme) on the TLS protocol via the OpenSSL library as a way of checking their overall viability in real-world scenarios, by comparing them to classical schemes implementing the same functionalities.
There are cryptographic systems that are secure against attacks by both classical and quantum computers. One of these systems is the NewHope key encapsulation mechanism (KEM) based on the Ring-learning with error problem (Ring-LWE problem). The Ring-LWE problem is presumed to be hard to solve even on a quantum computer. A KEM scheme allows sharing of a common key between two parts (Alice & Bob). This thesis presents original contributions to the security and analysis of key mismatch and information leakage attacks on NewHope KEM and some vulnerabilities on (small)-Ring-LWE problem (a variant of Ring-LWE problem). The first contribution contains some improvements on key mismatch attacks proposed by Bauer et al. and Qin et al. (Bauer et al., 2019; Qin et al., 2019). These key mismatch attacks retrieve Alices secret key. And, we propose two new methods named Fast Qin and Double Qin. The methods Fast Qin and Double Qin require around 240k and 34k oracle queries, respectively; instead of 840k queries of the Qin et al.s method. Moreover, these two new methods are adapted to retrieve Alices secret key on NewHope-512 (a variant of NewHope). The second contribution analyzes the information leakage of Bobs secret key on NewHope when it is reused. Our result corroborates that Bobs secret key must not be reused since with two communications to Bob, his secret key is leaked. In Ring-LWE problem, a polynomial a is selected randomly and a polynomial b is calculated as b = a.s+e where s is the secret polynomial (selected randomly) and the e is a noise polynomial. Our third contribution shows that in small-Ring-LWE, a variant where polynomials s and e are small, there are values of the public parameter a that leak a large percentage of the coefficients of the secret s. And, the last contribution shows that the secret s can be retrieved successfully if at least 50% of the random known coefficients of s and e are known.
Lattice-based cryptography seems to be a good area for the researchers in cryptology because of its vulnerability against quantum computing attacks. Such resources as extensive documentation, theoretical foundations, and practical implementations are provided with respect to some key algorithms, which are Learning With Errors (LWE) and Ring-LWE, and sophisticated ones such as homomorphic encryption. This paper aims to make academic research more practical by providing tools for cryptographers and programmers to experiment with lattice-based cryptography in secure communications and data protection. Thus, we examine and implement Lizard, Ring-Lizard, Kyber, Frodo, and NewHope in JavaScript, which are current postquantum cryptography possibilities due to their applicability and efficiency. In this case quantum computational capabilities are referred to as those that may compromise security thus undermining post-quantum cryptography.
Lattice-based cryptography stands at the forefront of contemporary cryptographic research, offering robust security guarantees that withstand the challenges posed by quantum computing. This research paper undertakes a comprehensive exploration of lattice-based key exchange protocols, with a specific and meticulous focus on the Ring Learning with Errors (RLWE) problem—a cornerstone in the lattice-based paradigm. In addition, the paper delves deeply into the innovative ding reconciliation technique, strategically employed to amplify the efficiency and effectiveness of RLWE-based key exchange protocols.Within this paper's purview lies a holistic examination of key concepts, intricacies, and recent developments in the field of lattice-based cryptography. The paper rigorously analyzes the theoretical foundations that underpin the security assurances of lattice-based protocols, particularly in the context of post-quantum cryptography. The RLWE problem, as a central tenet, is dissected to unveil its significance as a building block for cryptographic constructions, especially in the realm of key exchange.The integration of the ding reconciliation technique introduces an added layer of depth to the research. By elucidating the mechanics of this method, the paper showcases its role in streamlining the error correction process inherent in RLWE-based protocols. The reconciliation technique's contribution to efficiency is examined through both theoretical analysis and empirical validation, presenting a compelling case for its adoption in practical scenarios.Moreover, this paper critically surveys the landscape of recent developments in lattice-based cryptography, elucidating novel protocol designs, algorithmic optimizations, and real-world applications. The inherent challenges, ranging from computational complexity to practical implementation considerations, are scrutinized, providing a balanced perspective on the field's ongoing evolution.As the paper concludes, it consolidates the insights garnered from its comprehensive review, offering a panoramic understanding of lattice-based cryptography's inner workings. It outlines the broader implications of these cryptographic protocols in safeguarding digital communications and securing data transmission in a quantum-advantaged era. By synthesizing a comprehensive overview, this research paper aims to provide researchers, practitioners, and enthusiasts with a nuanced understanding of lattice-based cryptography, RLWE-based key exchange protocols, and the innovative ding reconciliation technique.