International Association
for Cryptologic Research

Fair exchange protocols let two mutually distrusted parties exchange digital data in a way that neither can cheat. At CCS 2017, Campanelli et al. proposed two blockchain-based protocols for the fair exchange of digital coins and a certain service, i.e., “proofs of retrievability” (PoR), that take place between a buyer and seller. In this work, we identify two serious issues of these schemes; namely, (1) a malicious client can waste the seller’s resources, and (2) real-time leakage of information to non-participants in the exchange. To rectify the issues, we propose “recurring contingent PoR payment” (RC-PoR-P). It lets the fair exchange reoccur while ensuring that the seller’s resources are not wasted, and the parties’ privacy is preserved. We implemented the RC- PoR-P. Our cost analysis indicates that the RC-PoR-P is efficient. The RC-PoR-P is the first of its kind that offers all the above features.

The Oil and Vinegar signature scheme, proposed in 1997 by Patarin, is one of the oldest and best understood multivariate quadratic signature schemes. It has excellent performance and signature sizes but suffers from large key sizes on the order of 50 KB, which makes it less practical as a general-purpose signature scheme. To solve this problem, this paper proposes MAYO, a variant of the UOV signature scheme whose public keys are two orders of magnitude smaller. MAYO works by using a UOV map with an unusually small oil space, which makes it possible to represent the public key very compactly. The usual UOV signing algorithm fails if the oil space is too small, but MAYO works around this problem by ``whipping up'' the base oil and vinegar map into a larger map, that does have a sufficiently large oil space. With parameters targeting NISTPQC security level I, MAYO has a public key size of only 614 Bytes and a signature size of 392 Bytes. This makes MAYO more compact than state-of-the-art lattice-based signature schemes such as Falcon and Dilithium. Moreover, we can choose MAYO parameters such that, unlike traditional UOV signatures, signatures provably only leak a negligible amount of information about the private key.

Reliable voter identification is one of the key requirements to guarantee eligibility and uniformity of elections. In a remote setting, this task becomes more complicated compared to voter identification at a physical polling station. In case strong cryptographic mechanisms are not available, biometrics is one of the available alternatives to consider. In this paper, we take a closer look at facial recognition as a possible remote voter identification measure. We cover technical aspects of facial recognition relevant to voting, discuss the main architectural decisions, and analyse some of the remaining open problems, including dispute resolution and privacy issues.

Pairings have been widely used since their introduction to cryptography. They can be applied to identity-based encryption, tripartite Diffie-Hellman key agreement, blockchain and other cryptographic schemes. The Acceleration of pairing computations is crucial for these cryptographic schemes or protocols. In this paper, we will focus on the Elliptic Net algorithm which can compute pairings in polynomial time, but it requires more storage than Miller’s algorithm. We use several methods to speed up the Elliptic Net algorithm. Firstly, we eliminate the inverse operation in the improved Elliptic Net algorithm. In some ircumstance, this finding can achieve further improvements. Secondly, we apply lazy reduction technique to the Elliptic Net algorithm, which helps us achieve a faster implementation. Finally, we propose a new derivation of the formulas for the computation of the Optimal Ate pairing on the twisted curve. Results show that the Elliptic Net algorithm can be significantly accelerated especially on the twisted curve. The algorithm can be 80% faster than the previous ones on the twisted 381-bit BLS12 curve and 71:5% faster on the twisted 676-bit KSS18 curve respectively.

Protocols for Byzantine agreement (BA) and secure multi-party computation (MPC) can be classified according to the underlying communication model. The two most commonly considered models are the synchronous one and the asynchronous one. Synchronous protocols typically lose their security guarantees as soon as the network violates the synchrony assumptions. Asynchronous protocols remain secure regardless of the network conditions, but achieve weaker security guarantees even when the network is synchronous.

Recent works by Blum, Katz and Loss [TCC'19], and Blum, Liu-Zhang and Loss [CRYPTO'20] introduced BA and MPC protocols achieving security guarantees in both settings: security up to $t_s$ corruptions in a synchronous network, and up to $t_a$ corruptions in an asynchronous network, under the provably optimal threshold trade-offs $t_a \le t_s$ and $t_a + 2t_s < n$. However, current solutions incur a high synchronous round complexity when compared to state-of-the-art purely synchronous protocols. When the network is synchronous, the round complexity of BA protocols is linear in the number of parties, and the round complexity of MPC protocols also depends linearly on the depth of the circuit to evaluate.

In this work, we provide round-efficient constructions for both primitives with optimal resilience: fixed-round and expected constant-round BA protocols, and an MPC protocol whose round complexity is independent of the circuit depth.

We describe some cryptographically relevant discrete logarithm problems (DLPs) and present some of the key ideas and constructions behind the most efficient algorithms known that solve them. Since the topic encompasses such a large volume of literature, for the finite field DLP we limit ourselves to a selection of results reflecting recent advances in fixed characteristic finite fields.

Event date: 13 September 2021

Clearmatics is a protocol engineering company. We are building a new financial market architecture that is more open, fair, and resilient than the legacy systems that are in use today. We develop protocols and software that create new markets for risk and more efficient infrastructure for trading, backed by a robust and scalable blockchain network, and secured with modern cryptographic techniques and economic mechanism design.

The Research group at Clearmatics is dedicated to developing solutions to the hard problems needed to advance our mission. We are academics and protocol engineers collaborating with teams inside and outside the company to translate theoretical results into running software implementations.

RESPONSIBILITIES

- Assist in the design of cryptographic protocols

- Collaborate with your colleagues on the implementation of cryptographic primitives and protocols

- Produce technical design specifications

- Produce externally facing artefacts (e.g. blog posts, papers, documentation excerpts etc.)

- Support research colleagues in conducting their research

- Interface with the Engineering team to ease the transition of the research pieces of code into robust production software fully integrated with our stack

- Keep up with new research in the space

REQUIREMENTS​

- Fluency in English (written and spoken)

- Background in applied Computer Science

- Experience with system programming (C/C++/Rust)

- Strong applied cryptography skills (experience implementing robust elliptic curve cryptography)

- Outstanding algorithmic thinking

- Strong focus on code quality/documentation and simplicity

Nice to haves​

- Knowledge of Unix and bash

- Experience with constant time cryptography

- Experience with cryptography on embedded systems

- Experience with Ethereum or other blockchain projects

- Experience contributing to open-source cryptography libraries

- Experience with Python/SageMath

Closing date for applications:

Contact: https://boards.greenhouse.io/clearmatics/jobs/5326634002

More information: https://grnh.se/e40fe3cb2us

Cryptography and Information Security Laboratory is currently looking for a Post-doctoral researcher. Our laboratory is conducting the latest research on the development of cyber threat prediction and response technologies, lightweight cryptography for IoT environment, field-oriented digital forensic, design and development of encryption technologies, etc. We are highly recognized externally for excellent research results. The applicant will have the opportunity to work on our ongoing projects with a team of scientists in the lab and collaborators. We offer an excellent research environment and a highly competitive salary.

Current Research Directions:

Analysis of malware and malicious traffic based on machine learning

Cyber threat prediction and threat intelligence analysis

Design and cryptanalysis of symmetric-key cryptosystems

Fast and efficient implementation of ciphers

Mobile, memory, AI forensics

IoT and Convergence security
Current Research Directions:

Candidate must have recently received (or expect soon) PhD degree in or related to Information Security, Computer Science fields.

Good publication record and prior development experience are highly desirable.
Appointment term: 1 year commitment to postdoctoral training is expected (can be extended depending on performance).
Appointment start date: September 2021
Required Application Materials:

CV

Statement of research interests

Contact information

Closing date for applications:

Contact: Interested candidates should email their application materials to professor Changhoon Lee (chlee@seoultech.ac.kr).

More information: https://cis.seoultech.ac.kr/index.do

The successful candidate for this position will participate in developing cutting edge blockchain methods and tools to provide for world-class new product introduction (NPI), new-to-industry (NTI), and services/support capabilities throughout the company. You will work in a multi-disciplinary team contributing to the applications of designing new better blockchain-based systems, to improve existing designs, and to disseminate knowledge into the community to stand out as thought leaders in the space. Applications include web3, decentralized finance, layer 2 technology, cryptography, proof of work, distributed ledger technology, lending and borrowing, incentivization, with more.

Closing date for applications:

Contact: Martina Burghi (martina@advancedblockchain.com)

More information: https://incredulous.bamboohr.com/jobs/view.php?id=36

Computing the count of distinct elements in large data sets is a common task but naive approaches are memory-expensive. The HyperLogLog (HLL) algorithm (Flajolet et al., 2007) estimates a data set's cardinality while using significantly less memory than a naive approach, at the cost of some accuracy. This trade-off makes the HLL algorithm very attractive for a wide range of applications such as database management and network monitoring, where an exact count may not be needed. The HLL algorithm and variants of it are implemented in systems such as Redis and Google Big Query. Recently, the HLL algorithm has started to be proposed for use in scenarios where the inputs may be adversarially generated, for example counting social network users or detection of network scanning attacks. This prompts an examination of the performance of the HLL algorithm in the face of adversarial inputs. We show that in such a setting, the HLL algorithm's estimate of cardinality can be exponentially bad: when an adversary has access to the internals of the HLL algorithm and has some flexibility in choosing what inputs will be recorded, it can manipulate the cardinality estimate to be exponentially smaller than the true cardinality. We study both the original HLL algorithm and a more modern version of it (Ertl, 2017) that is used in Redis. We present experimental results confirming our theoretical analysis. Finally, we consider attack prevention: we show how to modify HLL in a simple way that provably prevents cardinality estimate manipulation attacks.

This paper explores the good-case latency of synchronous Byzantine Fault Tolerant (BFT) consensus protocols in the rotating leader setting. We first present a lower bound that relates the latency of a broadcast when the sender is honest and the latency of switching to the next sender. We then present a matching upper bound with a latency of $2\Delta$ ($\Delta$ is the pessimistic synchronous delay) with an optimistically responsive change to the next sender. The results imply that both our lower and upper bounds are tight. We implement and evaluate our protocol and show that our protocol obtains similar latency compared to state-of-the-art stable-leader protocol Sync~HotStuff while allowing optimistically responsive leader rotation.

Due to the advent of quantum computers, the security of existing public-key cryptography is threatened since quantum computers are expected to be able to solve the underlying mathematical problems efficiently. Hence, quantum resistant alternatives are required. Consequently, about 70 post-quantum scheme candidates were submitted to the National Institute of Standards and Technology (NIST) standardization effort. One candidate is the qTESLA signature scheme. We present an efficient shared-memory parallelization of qTESLA’s core routines, analyze the speedup in-depth and show that it can compete with the two most commonly used signature schemes RSA and ECDSA which are quantum-vulnerable. The speed is further increased by semi-automatic tuning of qTESLA’s configuration parameters based on results of multi-parameter performance models. We show how to considerably increase qTESLA’s usability through the Java Native Interface (JNI) without performance penalty. The analysis on x86 and ARM architecture employing three operating systems demonstrates the achieved portability. The enhanced performance, its straight forward usability and the high portability of our implementation make it a quantum-safe replacement for the state-of-the-art schemes.

Since quantum computers will be able to break all public-key encryption schemes employed today efficiently, quantum-safe cryptographic alternatives are required. One group of candidates are lattice-based schemes since they are efficient and versatile. To make them practical, their security level must be assessed on classical HPC systems in order to determine efficient but secure parameterization. In this paper, we propose a novel parallelization strategy for the open source framework p3Enum which is designed to solve the important lattice problem of finding the shortest non-zero vector in a lattice (SVP). We also present the p3Enum extreme pruning function generator (p3Enum-epfg) which generates optimized extreme pruning functions for p3Enum’s pruned lattice enumeration by employing a parallelized simulated annealing approach. We demonstrate the quality of the pruning functions delivered. Combining the new parallelization with optimized pruning functions speeds up p3Enum by a factor up to 3 compared to the previous version. Additionally, we compare the required runtime to solve the SVPs with state-of-the art tools and, for the first time, also visualize the statistical effects in the runtime of the algorithms under consideration. This allows a considerably better understanding of the behavior of the implementations than previous average-value considerations and demonstrates the relative stability of p3Enum’s parallel runtimes which improve reproducibility and predictability. All these advancements make it the fastest SVP solver for lattice dimensions 66 to 92 and a suitable building block as SVP-oracle in lattice basis reduction.

Computation on ciphertexts of all known fully homomorphic encryption (FHE) schemes induces some noise, which, if too large, will destroy the plaintext. Therefore, the bootstrapping technique that re-encrypts a ciphertext and reduces the noise level remains the only known way of building FHE schemes for arbitrary unbounded computations. The bootstrapping step is also the major efficiency bottleneck in current FHE schemes. A promising direction towards improving concrete efficiency is to exploit the bootstrapping process to perform useful computation while reducing the noise at the same time. We show a bootstrapping algorithm, which embeds a lookup table and evaluates arbitrary functions of the plaintext while reducing the noise. Depending on the choice of parameters, the resulting homomorphic encryption scheme may be either an exact FHE or homomorphic encryption for approximate arithmetic. Since we can evaluate arbitrary functions over the plaintext space, we can use the natural homomorphism of Regev encryption to compute affine functions without bootstrapping almost for free. Consequently, our algorithms are particularly suitable for circuits with many additions and scalar multiplication gates. We achieve record speeds for such circuits. For example, in the exact FHE setting, we achieve a speedup of a factor of over 3000x over state-of-the-art methods. Effectively, we bring the evaluation time from weeks or days down to a few hours or minutes. Furthermore, we note that the speedup gets more significant with the size of the affine function. We provide a tight error analysis and show several parameter sets for our bootstrapping. Finally, we implement our algorithm and provide extensive tests. We demonstrate our algorithms by evaluating different neural networks in several parameter and accuracy settings.

In this short paper we find an efficient binary approximation of the FSM of ZUC-256 with high correlation around $2^{-21.1}$ between the keystream words and the LFSR. Thereafter, we make a conjecture on a theoretical complexity of a hypothetical correlation attack on ZUC-256.

We argue that for all integers $N \geq 2$ and $g \geq 1$ there exist "multiradical" isogeny formulae, that can be iteratively applied to compute $(N^k, \ldots, N^k)$-isogenies between principally polarized $g$-dimensional abelian varieties, for any value of $k \geq 2$. The formulae are complete: each iteration involves the extraction of $g(g+1)/2$ different $N$th roots (whence the epithet multiradical) and by varying which roots are chosen one computes all $N^{g(g+1)/2}$ extensions to an $(N^k, \ldots, N^k)$-isogeny of the incoming $(N^{k-1}, \ldots, N^{k-1})$-isogeny. Our argumentation is heuristic, but we provide concrete formulae for several prominent families. As our main application, we illustrate the use of multiradical isogenies by implementing a hash function from $(3,3)$-isogenies between Jacobians of superspecial genus-$2$ curves, showing that it outperforms its $(2,2)$-counterpart by an asymptotic factor $\approx 9$ in terms of speed.

The isogeny-based post-quantum schemes SIKE (NIST PQC round 3 alternate candidate) and CSIDH (Asiacrypt 2018) have received only little attention with respect to their fault attack resilience so far. We aim to &#64257;ll this gap and provide a better understanding of their vulnerability by analyzing their resistance towards safe-error attacks. We present four safe-error attacks, two against SIKE and two against a constant-time implementation of CSIDH that uses dummy isogenies. The attacks use targeted bit&#64258;ips during the respective isogeny-graph traversals. All four attacks lead to full key recovery. By using voltage and clock glitching, we physically carried out two of the attacks - one against each scheme -, thus demonstrate that full key recovery is also possible in practice.

The 2021 election is being held to fill the three IACR Director positions currently held by Mark Fischlin, Nadia Heninger and Anna Lysyanskaya, whose 3-year terms are ending.

Nominations are due by October 1st, 2021.
Information about nomination is available at https://iacr.org/elections/2021/announcement.html.

Multi-Key fully homomorphic encryption (MKFHE) allows computation on data encrypted under different and independent keys. The previous researches show that the ciphertext size of MKFHE scheme usually increases linearly or squarely with the number of parties, which restricts the application of the MKFHE scheme. In this paper, we propose a general construction of MKFHE scheme with compact ciphertext. Firstly, we construct the accumulated public key of the parties set with compact by accumulating every party’s public key under the CRS model. Secondly, all parties provide the ciphertext of their secret keys key which is encrypted by the accumulated public-key as the accumulated evaluation key. Thirdly, we run the bootstrapping process (or key switching process) on each party's ciphertext and accumulated evaluation key to refresh the ciphertext. Finally, We homomorphically calculate the refreshed ciphertext and decrypt it by the joint secret key. Furthermore, according to the advantages of TFHE-type scheme’s efficient bootstrapping and CKKS scheme supporting approximate data homomorphic computation, we improve the bootstrapping in our general scheme and specifically propose two efficient MKFHE schemes with compact ciphertext. Our work has two advantages. The one is that the ciphertext size of the proposed general scheme is independent of the number of parties, and the homomorphic computation is as efficient as the single-party full homomorphic encryption scheme. When the parties' set is updated, the ciphertext of the original set can continue to be used for homomorphic computation of the new parties' set after refreshed. Another advantage is that only by authorization can a party’s data be used in the homomorphic operation of a set, i.e., all parties need to regenerate their accumulated evaluation key with the set. Compared with the fully dynamic MKFHE scheme, the authorized MKFHE scheme we proposed supports parties to effectively control which set their data.