Power Analysis on NTRU Prime
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The Twin Diffie-Hellman Problem and Applications
The Twin Diffie-Hellman Problem and Applications David Cash1 Eike Kiltz2 Victor Shoup3 February 10, 2009 Abstract We propose a new computational problem called the twin Diffie-Hellman problem. This problem is closely related to the usual (computational) Diffie-Hellman problem and can be used in many of the same cryptographic constructions that are based on the Diffie-Hellman problem. Moreover, the twin Diffie-Hellman problem is at least as hard as the ordinary Diffie-Hellman problem. However, we are able to show that the twin Diffie-Hellman problem remains hard, even in the presence of a decision oracle that recognizes solutions to the problem — this is a feature not enjoyed by the Diffie-Hellman problem in general. Specifically, we show how to build a certain “trapdoor test” that allows us to effectively answer decision oracle queries for the twin Diffie-Hellman problem without knowing any of the corresponding discrete logarithms. Our new techniques have many applications. As one such application, we present a new variant of ElGamal encryption with very short ciphertexts, and with a very simple and tight security proof, in the random oracle model, under the assumption that the ordinary Diffie-Hellman problem is hard. We present several other applications as well, including: a new variant of Diffie and Hellman’s non-interactive key exchange protocol; a new variant of Cramer-Shoup encryption, with a very simple proof in the standard model; a new variant of Boneh-Franklin identity-based encryption, with very short ciphertexts; a more robust version of a password-authenticated key exchange protocol of Abdalla and Pointcheval. -
Blind Schnorr Signatures in the Algebraic Group Model
An extended abstract of this work appears in EUROCRYPT’20. This is the full version. Blind Schnorr Signatures and Signed ElGamal Encryption in the Algebraic Group Model Georg Fuchsbauer1, Antoine Plouviez2, and Yannick Seurin3 1 TU Wien, Austria 2 Inria, ENS, CNRS, PSL, Paris, France 3 ANSSI, Paris, France first.last@{tuwien.ac.at,ens.fr,m4x.org} January 16, 2021 Abstract. The Schnorr blind signing protocol allows blind issuing of Schnorr signatures, one of the most widely used signatures. Despite its practical relevance, its security analysis is unsatisfactory. The only known security proof is rather informal and in the combination of the generic group model (GGM) and the random oracle model (ROM) assuming that the “ROS problem” is hard. The situation is similar for (Schnorr-)signed ElGamal encryption, a simple CCA2-secure variant of ElGamal. We analyze the security of these schemes in the algebraic group model (AGM), an idealized model closer to the standard model than the GGM. We first prove tight security of Schnorr signatures from the discrete logarithm assumption (DL) in the AGM+ROM. We then give a rigorous proof for blind Schnorr signatures in the AGM+ROM assuming hardness of the one-more discrete logarithm problem and ROS. As ROS can be solved in sub-exponential time using Wagner’s algorithm, we propose a simple modification of the signing protocol, which leaves the signatures unchanged. It is therefore compatible with systems that already use Schnorr signatures, such as blockchain protocols. We show that the security of our modified scheme relies on the hardness of a problem related to ROS that appears much harder. -
Implementation and Performance Evaluation of XTR Over Wireless Network
Implementation and Performance Evaluation of XTR over Wireless Network By Basem Shihada [email protected] Dept. of Computer Science 200 University Avenue West Waterloo, Ontario, Canada (519) 888-4567 ext. 6238 CS 887 Final Project 19th of April 2002 Implementation and Performance Evaluation of XTR over Wireless Network 1. Abstract Wireless systems require reliable data transmission, large bandwidth and maximum data security. Most current implementations of wireless security algorithms perform lots of operations on the wireless device. This result in a large number of computation overhead, thus reducing the device performance. Furthermore, many current implementations do not provide a fast level of security measures such as client authentication, authorization, data validation and data encryption. XTR is an abbreviation of Efficient and Compact Subgroup Trace Representation (ECSTR). Developed by Arjen Lenstra & Eric Verheul and considered a new public key cryptographic security system that merges high level of security GF(p6) with less number of computation GF(p2). The claim here is that XTR has less communication requirements, and significant computation advantages, which indicate that XTR is suitable for the small computing devices such as, wireless devices, wireless internet, and general wireless applications. The hoping result is a more flexible and powerful secure wireless network that can be easily used for application deployment. This project presents an implementation and performance evaluation to XTR public key cryptographic system over wireless network. The goal of this project is to develop an efficient and portable secure wireless network, which perform a variety of wireless applications in a secure manner. The project literately surveys XTR mathematical and theoretical background as well as system implementation and deployment over wireless network. -
Lecture 14: Elgamal Encryption, Hash Functions from DL, Prgs from DDH 1 Topics Covered 2 Recall 3 Key Agreement from the Diffie
CS 7880 Graduate Cryptography October 29, 2015 Lecture 14: ElGamal Encryption, Hash Functions from DL, PRGs from DDH Lecturer: Daniel Wichs Scribe: Biswaroop Maiti 1 Topics Covered • Public Key Encryption • A Public Key Encryption from the DDH Assumption • El Gamal Encryption • CRHF from Discrete Log • PRG from DDH 2 Recall Recall the three number theoretic assumptions we saw last time. We will build Crypto- graphic schemes or protocols based on the hardness of these problems. Definition 1 (G; g; q) Groupgen(1n) } Assumption 1 DL Given g; gX , it is hard to find X. Assumption 2 Computational Diffie Hellman Given g; gX ; gY , it is hard to find gXY . Assumption 3 Decisional Diffie Hellman Given g; gX ; gY , it is hard to distinguish between gXY and gZ , where Z is chosen at random. (g; gX ; gY ; gXY ) ≈ (g; gX ; gY ; gZ ) 3 Key Agreement from the Diffie Helman scheme AB x Zq X hA = g −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−£ Y hB = g ¡−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Y Zq X XY Y XY hB = g hA = g The keys agreed upon by A and B is gXY . Lecture 14, Page 1 It is interesting to note that in this scheme, A and B were able to agree upon a key without communicating about it. Each party generates a puzzle uniformly at random: A X Y generates hA = g , and B generates hB = g . Then, they send their puzzles to each other, and establish the key to be gXY . Proving this scheme is secure is equivalent to showing that the DDH assumption holds. 4 Public Key Encryption The general syntax of Public Key Encryption is the following. -
Implementing Several Attacks on Plain Elgamal Encryption Bryce D
Iowa State University Capstones, Theses and Graduate Theses and Dissertations Dissertations 2008 Implementing several attacks on plain ElGamal encryption Bryce D. Allen Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/etd Part of the Mathematics Commons Recommended Citation Allen, Bryce D., "Implementing several attacks on plain ElGamal encryption" (2008). Graduate Theses and Dissertations. 11535. https://lib.dr.iastate.edu/etd/11535 This Thesis is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Implementing several attacks on plain ElGamal encryption by Bryce Allen A thesis submitted to the graduate faculty in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Major: Mathematics Program of Study Committee: Clifford Bergman, Major Professor Paul Sacks Sung-Yell Song Iowa State University Ames, Iowa 2008 Copyright c Bryce Allen, 2008. All rights reserved. ii Contents CHAPTER 1. OVERVIEW . 1 1.1 Introduction . .1 1.2 Hybrid Cryptosystems . .2 1.2.1 Symmetric key cryptosystems . .2 1.2.2 Public key cryptosystems . .3 1.2.3 Combining the two systems . .3 1.2.4 Short messages and public key systems . .4 1.3 Implementation . .4 1.4 Splitting Probabilities . .5 CHAPTER 2. THE ELGAMAL CRYPTOSYSTEM . 7 2.1 The Discrete Log Problem . .7 2.2 Encryption and Decryption . .8 2.3 Security . .9 2.4 Efficiency . -
Comparison of Two Public Key Cryptosystems
Journal of Optoelectronical Nanostructures Summer 2018 / Vol. 3, No. 3 Islamic Azad University Comparison of two Public Key Cryptosystems 1 *,2 1 Mahnaz Mohammadi , Alireza Zolghadr , Mohammad Ali Purmina 1 Department of Electrical and Electronic Eng., Science and Research Branch, Islamic Azad University, Tehran, Iran 2 Faculty of Computer and Electrical Eng., Department of Communication and Electronics, Shiraz University, Shiraz, Iran (Received 10 Jun. 2018; Revised 11 Jul. 2018; Accepted 26 Aug. 2018; Published 15 Sep. 2018) Abstract: Since the time public-key cryptography was introduced by Diffie and Hellman in 1976, numerous public-key algorithms have been proposed. Some of these algorithms are insecure and the others that seem secure, many are impractical, either they have too large keys or the cipher text they produce is much longer than the plaintext. This paper focuses on efficient implementation and analysis of two most popular of these algorithms, RSA and ElGamal for key generation and the encryption scheme (encryption/decryption operation). RSA relies on the difficulty of prime factorization of a very large number, and the hardness of ElGamal algorithm is essentially equivalent to the hardness of finding discrete logarithm modulo a large prime. These two systems are compared to each other from different parameters points of view such as performance, security, speed and applications. To have a good comparison and also to have a good level of security correspond to users need the systems implemented are designed flexibly in terms of the key size. Keywords: Cryptography, Public Key Cryptosystems, RSA, ElGamal. 1. INTRODUCTION The security is a necessary for the network to do all the works related to ATM cards, computer passwords and electronic commerce. -
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. -
Lecture 19: Public-Key Cryptography (Diffie-Hellman Key Exchange & Elgamal Encryption)
Lecture 19: Public-key Cryptography (Diffie-Hellman Key Exchange & ElGamal Encryption) Public-key Cryptography Recall In private-key cryptography the secret-key sk is always established ahead of time The secrecy of the private-key cryptography relies on the fact that the adversary does not have access to the secret key sk For example, consider a private-key encryption scheme $ 1 The Alice and Bob generate sk Gen() ahead of time 2 Later, when Alice wants to encrypt and send a message to Bob, she computes the cipher-text c = Encsk(m) 3 The eavesdropping adversary see c but gains no additional information about the message m 4 Bob can decrypt the message me = Decsk(c) 5 Note that the knowledge of sk distinguishes Bob from the eavesdropping adversary Public-key Cryptography Perspective If jskj >jmj, then we can construct private-key encryption schemes (like, one-time pad) that is secure even against adversaries with unbounded computational power If jskj = O(jmj"), where " 2 (0; 1) is a constant, then we can construction private-key encryption schemes using pseudorandom generators (PRGs) What if, jskj = 0? That is, what if Alice and Bob never met? How is “Bob” any different from an “adversary”? Public-key Cryptography In this Lecture We shall introduce the Decisional Diffie-Hellmann (DDH) Assumption and the Diffie-Hellman key-exchange protocol, We shall introduce the El Gamal (public-key) Encryption Scheme, and Finally, abstract out the principal design principles learned. Public-key Cryptography Decisional Diffie-Hellman (DDH) Computational Hardness AssumptionI Let (G; ◦) be a group of size N that is generated by g. -
Public-Key Cryptography
Public-key Cryptogra; Theory and Practice ABHIJIT DAS Department of Computer Science and Engineering Indian Institute of Technology Kharagpur C. E. VENIMADHAVAN Department of Computer Science and Automation Indian Institute ofScience, Bangalore PEARSON Chennai • Delhi • Chandigarh Upper Saddle River • Boston • London Sydney • Singapore • Hong Kong • Toronto • Tokyo Contents Preface xiii Notations xv 1 Overview 1 1.1 Introduction 2 1.2 Common Cryptographic Primitives 2 1.2.1 The Classical Problem: Secure Transmission of Messages 2 Symmetric-key or secret-key cryptography 4 Asymmetric-key or public-key cryptography 4 1.2.2 Key Exchange 5 1.2.3 Digital Signatures 5 1.2.4 Entity Authentication 6 1.2.5 Secret Sharing 8 1.2.6 Hashing 8 1.2.7 Certification 9 1.3 Public-key Cryptography 9 1.3.1 The Mathematical Problems 9 1.3.2 Realization of Key Pairs 10 1.3.3 Public-key Cryptanalysis 11 1.4 Some Cryptographic Terms 11 1.4.1 Models of Attacks 12 1.4.2 Models of Passive Attacks 12 1.4.3 Public Versus Private Algorithms 13 2 Mathematical Concepts 15 2.1 Introduction 16 2.2 Sets, Relations and Functions 16 2.2.1 Set Operations 17 2.2.2 Relations 17 2.2.3 Functions 18 2.2.4 The Axioms of Mathematics 19 Exercise Set 2.2 20 2.3 Groups 21 2.3.1 Definition and Basic Properties . 21 2.3.2 Subgroups, Cosets and Quotient Groups 23 2.3.3 Homomorphisms 25 2.3.4 Generators and Orders 26 2.3.5 Sylow's Theorem 27 Exercise Set 2.3 29 2.4 Rings 31 2.4.1 Definition and Basic Properties 31 2.4.2 Subrings, Ideals and Quotient Rings 34 2.4.3 Homomorphisms 37 2.4.4 -
Another Look at Tightness Ii: Practical Issues in Cryptography
ANOTHER LOOK AT TIGHTNESS II: PRACTICAL ISSUES IN CRYPTOGRAPHY SANJIT CHATTERJEE, NEAL KOBLITZ, ALFRED MENEZES, AND PALASH SARKAR Abstract. How to deal with large tightness gaps in security proofs is a vexing issue in cryptography. Even when analyzing protocols that are of practical importance, leading researchers often fail to treat this question with the seriousness that it deserves. We discuss nontightness in connection with complexity leveraging, HMAC, lattice-based cryptography, identity-based encryption, and hybrid encryption. 1. Introduction The purpose of this paper is to address practicality issues in cryptography that are related to nontight security reductions. A typical security reduction (often called a “proof of security”) for a protocol has the following form: A certain mathematical task reduces to the task of successfully mounting a certain class of attacks on the protocolP — that is, of being aQ successful adversary in a certain security model. More precisely, the security reduction is an algorithm for solving the mathematical problem that has access to a hypothetical oracle for R. If the oracle takes time at most T andP is successful with probability at least ǫ (hereQ T and ǫ are functions of the security parameter k), then R solves in time at most T ′ with probability at least ǫ′ (where again T ′ and ǫ′ are functions of k).P We call (T ǫ)/(Tǫ ) the tightness gap. The reduction is said to be tight if the ′ ′ R tightness gap is 1 (or is small); otherwise it is nontight. Usually T ′ T and ǫ′ ǫ in a tight reduction. ≈ ≈ A tight security reduction is often very useful in establishing confidence in a protocol. -
Rethinking Verifiably Encrypted Signatures
Rethinking Verifiably Encrypted Signatures: A Gap in Functionality and Potential Solutions Theresa Calderon1 and Sarah Meiklejohn1 and Hovav Shacham1 and Brent Waters2 1 UC San Diego ftcaldero, smeiklej, [email protected] 2 UT Austin [email protected] Abstract. Verifiably encrypted signatures were introduced by Boneh, Gentry, Lynn, and Shacham in 2003, as a non-interactive analogue to in- teractive protocols for verifiable encryption of signatures. As their name suggests, verifiably encrypted signatures were intended to capture a no- tion of encryption, and constructions in the literature use public-key encryption as a building block. In this paper, we show that previous definitions for verifiably encrypted signatures do not capture the intuition that encryption is necessary, by presenting a generic construction of verifiably encrypted signatures from any signature scheme. We then argue that signatures extracted by the arbiter from a verifiably encrypted signature object should be distributed identically to ordinary signatures produced by the original signer, a prop- erty that we call resolution independence. Our generic construction of verifiably encrypted signatures does not satisfy resolution independence, whereas all previous constructions do. Finally, we introduce a stronger but less general version of resolution independence, which we call res- olution duplication. We show that verifiably encrypted signatures that satisfy resolution duplication generically imply public-key encryption. Keywords: Verifiably encrypted signatures, signatures, public-key en- cryption 1 Introduction Verifiably encrypted signatures were introduced by Boneh, Gentry, Lynn, and Shacham in 2003 [5] as a non-interactive analogue to interactive protocols for verifiable encryption of signatures [3,4] and of other cryptographic objects [7]. -
Choosing Parameters for Ntruencrypt Jeff Hoffstein, Jill Pipher, John Schanck, Joseph H
Choosing Parameters for NTRUEncrypt Jeff Hoffstein, Jill Pipher, John Schanck, Joseph H. Silverman, William Whyte, Zhenfei Zhang OnBoard Security / Brown University Security Innovation Embedded Business Unit is becoming Onboard Security! §Two sister companies being formed – OnBoard Security: Cryptography, Hardware Roots of Trust and Automotive Security – Security Innovation: Application Security Services and Education §Reasons – Increase strategic focus on core competencies – Unlock latent value – Attract pure-play investors Goal of presentation § Present new parameters as in published paper § Discuss parameter choices at a higher level to explore difference between published approaches – LWE – NTRU – NTRU Prime § Make a mysterious announcement A Lattice! (F,G) (f,g) Symmetric encryption with lattices: The Close Vector Problem Example over integers Lattice Basis B ((f,g), (F,G)) = ((7,1), (2,18)) • Pick m = (-2, 2). • (maximum norm of m < norm of shortest basis vector) • Pick random lattice point 5* (7,1) + 1*(2, 18) = (37, 23) • Add m to get e = (35, 25). 4.6 (f,g) 5 (f,g) + To decrypt: (F,G) 1 (F,G) • e = 4.6*(f,g) + 1.3*(F, G) 1.3 (F,G) … we get this by dividing: B-1 = ((G,-g), (-F, f)).[det(B)] -1. (f,g) • Round to closest lattice point = 5* (7,1) + 1*(2, 18) = (37, 23) • Subtract from e • Recover m = (-2, 2) Lattice-based crypto motivation § If I take E = a*H + b where H is known and a, b are random and “big enough”, then 1. For some size of a and b It is hard to recover a, b (the assumption used in NTRU) 2.