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See detailPakeMail: Authentication and Key Management in Decentralized Secure Email and Messaging via PAKE
Vazquez Sandoval, Itzel UL; Atashpendar, Arash; Lenzini, Gabriele UL et al

in Obaidat, Mohammad S.; Ben-Othman, Jalel (Eds.) E-Business and Telecommunications - 17th International Conference on E-Business and Telecommunications, ICETE 2020, Online Event, July 8-10, 2020, Revised Selected Papers. (2021, October)

We propose the use of password-authenticated key exchange (PAKE) for achieving and enhancing entity authentication (EA) and key management (KM) in the context of decentralized end-to-end encrypted email ... [more ▼]

We propose the use of password-authenticated key exchange (PAKE) for achieving and enhancing entity authentication (EA) and key management (KM) in the context of decentralized end-to-end encrypted email and secure messaging, i.e., without a public key infrastructure or a trusted third party. This not only simplifies the EA process by requiring users to share only a low-entropy secret such as a memorable word, but it also allows us to establish a high-entropy secret key. This approach enables a series of cryptographic enhancements and security properties, which are hard to achieve using out-of-band (OOB) authentication. We first study a few vulnerabilities in voice-based OOB authentication, in particular a combinatorial attack against lazy users, which we analyze in the context of a secure email solution. We then propose tackling public key authentication by solving the problem of secure equality test using PAKE and discuss various protocols and their properties. This method enables the automation of important KM tasks such as key renewal and future key pair authentications, reduces the impact of human errors and lends itself to the asynchronous nature of email and modern messaging. It also provides cryptographic enhancements including multi-device synchronization, and secure secret storage/retrieval, and paves the path for forward secrecy, deniability and post-quantum security.We also discuss the use of auditable PAKEs for mitigating a class of online guess and abort attacks in authentication protocols. We present an implementation of our proposal, called PakeMail, to demonstrate the feasibility of the core idea and discuss some of its cryptographic details, implemented features and efficiency aspects. We conclude with some design and security considerations, followed by future lines of work. [less ▲]

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See detail"Just for the sake of transparency": Exploring Voter Mental Models Of Verifiability
Zollinger, Marie-Laure UL; Estaji, Ehsan UL; Ryan, Peter Y A UL et al

in Electronic Voting, Sixth International Joint Conference, E-Vote-ID 2021, Bregenz, Austria, October 5-8 (2021, October)

Verifiable voting schemes allow voters to verify their individual votes and the election outcome. The voting protocol Selene offers verification of plaintext votes while preserving privacy. Misconceptions ... [more ▼]

Verifiable voting schemes allow voters to verify their individual votes and the election outcome. The voting protocol Selene offers verification of plaintext votes while preserving privacy. Misconceptions of verification mechanisms might result in voters mistrust of the system or abstaining from using it. In this paper, we interviewed 24 participants and invited them to illustrate their mental models of Selene. The drawings demonstrated different levels of sophistication and four mental models: 1) technology understanding, 2) meaning of the verification phase, 3) security concerns, and 4) unnecessary steps. We highlight the misconceptions expressed regarding Internet voting technologies and the system design. Based on our findings, we conclude with recommendations for future implementations of Selene as well as for the design of Internet voting systems in general. [less ▲]

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See detailInvestigating Usability and User Experience of Individually Verifiable Internet Voting Schemes
Marky, Karola; Zollinger, Marie-Laure UL; Roenne, Peter et al

in ACM Transactions on Computer-Human Interaction (2021), 28(5), 1-36

Internet voting can afford more inclusive and inexpensive elections. The flip side is that the integrity of the election can be compromised by adversarial attacks and malfunctioning voting infrastructure ... [more ▼]

Internet voting can afford more inclusive and inexpensive elections. The flip side is that the integrity of the election can be compromised by adversarial attacks and malfunctioning voting infrastructure. Individual verifiability aims to protect against such risks by letting voters verify that their votes are correctly registered in the electronic ballot box. Therefore, voters need to carry out additional tasks making human factors crucial for security. In this article, we establish a categorization of individually verifiable Internet voting schemes based on voter interactions. For each category in our proposed categorization, we evaluate a voting scheme in a user study with a total of 100 participants. In our study, we assessed usability, user experience, trust, and further qualitative data to gain deeper insights into voting schemes. Based on our results, we conclude with recommendations for developers and policymakers to inform the choices and design of individually verifiable Internet voting schemes. [less ▲]

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See detailBatching CSIDH Group Actions using AVX-512
Cheng, Hao UL; Fotiadis, Georgios UL; Groszschädl, Johann UL et al

in IACR Transactions on Cryptographic Hardware and Embedded Systems (TCHES) (2021, August), 2021(4), 618-649

Commutative Supersingular Isogeny Diffie-Hellman (or CSIDH for short) is a recently-proposed post-quantum key establishment scheme that belongs to the family of isogeny-based cryptosystems. The CSIDH ... [more ▼]

Commutative Supersingular Isogeny Diffie-Hellman (or CSIDH for short) is a recently-proposed post-quantum key establishment scheme that belongs to the family of isogeny-based cryptosystems. The CSIDH protocol is based on the action of an ideal class group on a set of supersingular elliptic curves and comes with some very attractive features, e.g. the ability to serve as a “drop-in” replacement for the standard elliptic curve Diffie-Hellman protocol. Unfortunately, the execution time of CSIDH is prohibitively high for many real-world applications, mainly due to the enormous computational cost of the underlying group action. Consequently, there is a strong demand for optimizations that increase the efficiency of the class group action evaluation, which is not only important for CSIDH, but also for related cryptosystems like the signature schemes CSI-FiSh and SeaSign. In this paper, we explore how the AVX-512 vector extensions (incl. AVX-512F and AVX-512IFMA) can be utilized to optimize constant-time evaluation of the CSIDH-512 class group action with the goal of, respectively, maximizing throughput and minimizing latency. We introduce different approaches for batching group actions and computing them in SIMD fashion on modern Intel processors. In particular, we present a hybrid batching technique that, when combined with optimized (8 × 1)-way prime-field arithmetic, increases the throughput by a factor of 3.64 compared to a state-of-the-art (non-vectorized) x64 implementation. On the other hand, vectorization in a 2-way fashion aimed to reduce latency makes our AVX-512 implementation of the group action evaluation about 1.54 times faster than the state-of-the-art. To the best of our knowledge, this paper is the first to demonstrate the high potential of using vector instructions to increase the throughput (resp. decrease the latency) of constant-time CSIDH. [less ▲]

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See detailAVRNTRU: Lightweight NTRU-based Post-Quantum Cryptography for 8-bit AVR Microcontrollers
Cheng, Hao UL; Groszschädl, Johann UL; Roenne, Peter UL et al

in 2021 Design, Automation and Test in Europe Conference and Exhibition, DATE 2021, Grenoble, France, February 1-5, 2021, Proceedings (2021, February)

Introduced in 1996, NTRUEncrypt is not only one of the earliest but also one of the most scrutinized lattice-based cryptosystems and expected to remain secure in the upcoming era of quantum computing ... [more ▼]

Introduced in 1996, NTRUEncrypt is not only one of the earliest but also one of the most scrutinized lattice-based cryptosystems and expected to remain secure in the upcoming era of quantum computing. Furthermore, NTRUEncrypt offers some efficiency benefits over “pre-quantum” cryptosystems like RSA or ECC since the low-level arithmetic operations are less computation-intensive and, thus, more suitable for constrained devices. In this paper we present AVR N TRU, a highly-optimized implementation of NTRUEncrypt for 8-bit AVR microcontrollers that we developed from scratch to reach high performance and resistance to timing attacks. AVR N TRU complies with the EESS #1 v3.1 specification and supports product-form parameter sets such as ees443ep1, ees587ep1, and ees743ep1. An entire encryption (including mask generation and blinding-polynomial generation) using the ees443ep1 parameters requires 847973 clock cycles on an ATmega1281 microcontroller; the decryption is more costly and has an execution time of 1051871 cycles. We achieved these results with the help of a novel hybrid technique for multiplication in a truncated polynomial ring, whereby one of the operands is a sparse ternary polynomial in product form and the other an arbitrary element of the ring. A constant-time multiplication in the ring given by the ees443ep1 parameters takes only 192577 cycles, which sets a new speed record for the arithmetic part of a lattice-based cryptosystem on AVR. [less ▲]

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See detailA Survey of Requirements for COVID-19 Mitigation Strategies
Jamroga, Wojciech UL; Mestel, David UL; Roenne, Peter UL et al

in Bulletin of The Polish Academy of Sciences: Technical Science (2021), 69(4), 137724

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See detailA Declaration of Software Independence
Jamroga, Wojciech UL; Ryan, Peter Y A UL; Schneider, Steve et al

in Protocols, Strands, and Logic - Essays Dedicated to Joshua Guttman on the Occasion of his 66.66th Birthday (2021)

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See detailLightweight Post-quantum Key Encapsulation for 8-bit AVR Microcontrollers
Cheng, Hao UL; Groszschädl, Johann UL; Roenne, Peter UL et al

in Liardet, Pierre-Yvan; Mentens, Nele (Eds.) Smart Card Research and Advanced Applications, 19th International Conference, CARDIS 2020, Virtual Event, November 18–19, 2020, Revised Selected Papers (2020, November)

Recent progress in quantum computing has increased interest in the question of how well the existing proposals for post-quantum cryptosystems are suited to replace RSA and ECC. While some aspects of this ... [more ▼]

Recent progress in quantum computing has increased interest in the question of how well the existing proposals for post-quantum cryptosystems are suited to replace RSA and ECC. While some aspects of this question have already been researched in detail (e.g. the relative computational cost of pre- and post-quantum algorithms), very little is known about the RAM footprint of the proposals and what execution time they can reach when low memory consumption rather than speed is the main optimization goal. This question is particularly important in the context of the Internet of Things (IoT) since many IoT devices are extremely constrained and possess only a few kB of RAM. We aim to contribute to answering this question by exploring the software design space of the lattice-based key-encapsulation scheme ThreeBears on an 8-bit AVR microcontroller. More concretely, we provide new techniques for the optimization of the ring arithmetic of ThreeBears (which is, in essence, a 3120-bit modular multiplication) to achieve either high speed or low RAM footprint, and we analyze in detail the trade-offs between these two metrics. A low-memory implementation of BabyBear that is secure against Chosen Plaintext Attacks (CPA) needs just about 1.7 kB RAM, which is significantly below the RAM footprint of other lattice-based cryptosystems reported in the literature. Yet, the encapsulation time of this RAM-optimized BabyBear version is below 12.5 million cycles, which is less than the execution time of scalar multiplication on Curve25519. The decapsulation is more than four times faster and takes roughly 3.4 million cycles on an ATmega1284 microcontroller. [less ▲]

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See detailHigh-Throughput Elliptic Curve Cryptography Using AVX2 Vector Instructions
Cheng, Hao UL; Groszschädl, Johann UL; Tian, Jiaqi UL et al

in Dunkelman, Orr; Jacobson Jr., Michael J.; O'Flynn, Colin (Eds.) Selected Areas in Cryptography, 27th International Conference, Halifax, NS, Canada (Virtual Event), October 21-23, 2020, Revised Selected Papers (2020, October)

Single Instruction Multiple Data (SIMD) execution engines like Intel’s Advanced Vector Extensions 2 (AVX2) offer a great potential to accelerate elliptic curve cryptography compared to implementations ... [more ▼]

Single Instruction Multiple Data (SIMD) execution engines like Intel’s Advanced Vector Extensions 2 (AVX2) offer a great potential to accelerate elliptic curve cryptography compared to implementations using only basic x64 instructions. All existing AVX2 implementations of scalar multiplication on e.g. Curve25519 (and alternative curves) are optimized for low latency. We argue in this paper that many real-world applications, such as server-side SSL/TLS handshake processing, would benefit more from throughput-optimized implementations than latency-optimized ones. To support this argument, we introduce a throughput-optimized AVX2 implementation of variable-base scalar multiplication on Curve25519 and fixed-base scalar multiplication on Ed25519. Both implementations perform four scalar multiplications in parallel, where each uses a 64-bit element of a 256-bit vector. The field arithmetic is based on a radix-2^29 representation of the field elements, which makes it possible to carry out four parallel multiplications modulo a multiple of p=2^255−19 in just 88 cycles on a Skylake CPU. Four variable-base scalar multiplications on Curve25519 require less than 250,000 Skylake cycles, which translates to a throughput of 32,318 scalar multiplications per second at a clock frequency of 2 GHz. For comparison, the to-date best latency-optimized AVX2 implementation has a throughput of some 21,000 scalar multiplications per second on the same Skylake CPU. [less ▲]

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See detailShort paper: Mechanized Proofs of Verifiability and Privacy in a paper-based e-voting Scheme
Zollinger, Marie-Laure UL; Roenne, Peter UL; Ryan, Peter UL

in International Conference on Financial Crypto Workshop on Advances in Secure Electronic Voting (2020, February)

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See detailCoercion-Resistant Voting in Linear Time via Fully Homomorphic Encryption: Towards a Quantum-Safe Scheme
Roenne, Peter UL; Atashpendar, Arash UL; Kristian, Gjøsteen et al

in Financial Cryptography and Data Security 2019. FC 2019: International Workshops, CIW, VOTING, and WTSC (2020)

We present an approach for performing the tallying work in the coercion-resistant JCJ voting protocol, introduced by Juels, Catalano, and Jakobsson, in linear time using fully homomorphic encryption (FHE ... [more ▼]

We present an approach for performing the tallying work in the coercion-resistant JCJ voting protocol, introduced by Juels, Catalano, and Jakobsson, in linear time using fully homomorphic encryption (FHE). The suggested enhancement also paves the path towards making JCJ quantum-resistant, while leaving the underlying structure of JCJ intact. The pairwise comparison-based approach of JCJ using plaintext equivalence tests leads to a quadratic blow-up in the number of votes, which makes the tallying process rather impractical in realistic settings with a large number of voters. We show how the removal of invalid votes can be done in linear time via a solution based on recent advances in various FHE primitives such as hashing, zero-knowledge proofs of correct decryption, verifiable shuffles and threshold FHE. We conclude by touching upon some of the advantages and challenges of such an approach, followed by a discussion of further security and post-quantum considerations. [less ▲]

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See detail(Universal) Unconditional Verifiability in E-Voting without Trusted Parties
Iovino, Vincenzo; Rial, Alfredo UL; Roenne, Peter UL et al

in 2020 IEEE 33rd Computer Security Foundations Symposium (2020)

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See detailTowards Model Checking of Voting Protocols in Uppaal
Jamroga, Wojciech UL; Kim, Yan UL; Kurpiewski, Damian et al

in Proceedings of the Fifth International Joint Conference on Electronic Voting E-VOTE-ID 2020 (2020)

The design and implementation of a trustworthy e-voting system is a challenging task. Formal analysis can be of great help here. In particular, it can lead to a better understanding of how the voting ... [more ▼]

The design and implementation of a trustworthy e-voting system is a challenging task. Formal analysis can be of great help here. In particular, it can lead to a better understanding of how the voting system works, and what requirements on the system are relevant. In this paper, we propose that the state-of-art model checker Uppaal provides a good environment for modelling and preliminary verification of voting protocols. To illustrate this, we demonstrate how to model a version of Pret-a-Voter in Uppaal, together with some natural extensions. We also show how to verify a variant of receipt-freeness, despite the severe limitations of the property specification language in the model checker. The aim of this work is to open a new path, rather then deliver the ultimate outcome of formal analysis. A comprehensive model of Pret-a-Voter, more accurate specification of requirements, and exhaustive verification are planned for the future. [less ▲]

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See detailVerifiable Inner Product Encryption Scheme
Soroush, Najmeh UL; Iovino, Vincenzo; Rial, Alfredo UL et al

in Public-Key Cryptography – PKC 2020 (2020)

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See detailPost-Quantum Anonymous Veto Networks
Ding, Jintai; Emery, Doug; Mueller, Johannes UL et al

in E-Vote-ID 2020 (2020)

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See detailRevisiting Practical and Usable Coercion-Resistant Remote E-Voting
Estaji, Ehsan UL; Haines, Thomas; Gjoesteen, Kristian et al

in Electronic Voting - 5th International Joint Conference, E-Vote-ID 2020, Bregenz, Austria, October 6-9, 2020, Proceedings (2020)

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See detailPreservation of DNA Privacy During the Large Scale Detection of COVID-19
Hollenstein, Marcel; Naccache, David; Roenne, Peter UL et al

E-print/Working paper (2020)

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See detailA Lightweight Implementation of NTRU Prime for the Post-Quantum Internet of Things
Cheng, Hao UL; Dinu, Dumitru-Daniel; Groszschädl, Johann UL et al

in Laurent, Maryline; Giannetsos, Thanassis (Eds.) Information Security Theory and Practice, 13th IFIP WG 11.2 International Conference, WISTP 2019, Paris, France, December 11–12, 2019, Proceedings (2019, December)

The dawning era of quantum computing has initiated various initiatives for the standardization of post-quantum cryptosystems with the goal of (eventually) replacing RSA and ECC. NTRU Prime is a variant of ... [more ▼]

The dawning era of quantum computing has initiated various initiatives for the standardization of post-quantum cryptosystems with the goal of (eventually) replacing RSA and ECC. NTRU Prime is a variant of the classical NTRU cryptosystem that comes with a couple of tweaks to minimize the attack surface; most notably, it avoids rings with "worrisome" structure. This paper presents, to our knowledge, the first assembler-optimized implementation of Streamlined NTRU Prime for an 8-bit AVR microcontroller and shows that high-security lattice-based cryptography is feasible for small IoT devices. An encapsulation operation using parameters for 128-bit post-quantum security requires 8.2 million clock cycles when executed on an 8-bit ATmega1284 microcontroller. The decapsulation is approximately twice as costly and has an execution time of 15.6 million cycles. We achieved this performance through (i) new low-level software optimization techniques to accelerate Karatsuba-based polynomial multiplication on the 8-bit AVR platform and (ii) an efficient implementation of the coefficient modular reduction written in assembly language. The execution time of encapsulation and decapsulation is independent of secret data, which makes our software resistant against timing attacks. Finally, we assess the performance one could theoretically gain by using a so-called product-form polynomial as part of the secret key and discuss potential security implications. [less ▲]

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See detailAuthenticated Key Distribution: When the Coupon Collector is Your Enemy
Beunardeau, Marc; El Orche, Fatima Ezzahra UL; Maimut, Diana et al

in Innovative Security Solutions for Information Technology and Communications (2019, November 14)

We introduce new authenticated key exchange protocols which on the one hand do not resort to standard public key setups with corresponding assumptions of computationally hard problems, but on the other ... [more ▼]

We introduce new authenticated key exchange protocols which on the one hand do not resort to standard public key setups with corresponding assumptions of computationally hard problems, but on the other hand, are more efficient than distributing symmetric keys among the participants. To this end, we rely on a trusted central authority distributing key material whose size is independent of the total number of users, and which allows the users to obtain shared secret keys. We analyze the security of our construction, taking into account various attack models. Importantly, only symmetric primitives are needed in the protocol making it an alternative to quantum-safe key exchange protocols which rely on hardness assumptions. [less ▲]

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