International Association
for Cryptologic Research

Cube attacks exploit the algebraic properties of symmetric ciphers by recovering a special polynomial, the superpoly, and subsequently the secret key. When the algebraic normal forms of the corresponding Boolean functions are not available, the division property based approach allows to recover the exact superpoly in a clever way. However, the computational cost to recover the superpoly becomes prohibitive as the number of rounds of the cipher increases. For example, the nested monomial predictions (NMP) proposed at ASIACRYPT 2021 stuck at round 845 for Trivium. To alleviate the bottleneck of the NMP technique, i.e., the unsolvable model due to the excessive number of monomial trails, we shift our focus to the so-called valuable terms of a specific middle round that contribute to the superpoly. Two new techniques are introduced, namely, Non-zero Bit-based Division Property (NBDP) and Core Monomial Prediction (CMP), both of which result in a simpler MILP model compared to the MILP model of MP. It can be shown that the CMP technique offers a substantial improvement over the monomial prediction technique in terms of computational complexity of recovering valuable terms. Combining the divide-and-conquer strategy with these two new techniques, we catch the valuable terms more effectively and thus avoid wasting computational resources on intermediate terms contributing nothing to the superpoly. As an illustration of the power of our techniques, we apply our framework to Trivium, Grain, Kreyvium and Acorn. As a result, the computational cost of earlier attacks can be significantly reduced and the exact ANFs of the superpolies for 846-, 847- and 848-round Trivium, 192-round Grain, 895-round Kreyvium and 776-round Acorn can be recovered in practical time, even though the superpoly of 848-round Trivium contains over 500 million terms; this corresponds to respectively 3, 1, 1 and 1 rounds more than the previous best results. Moreover, by investigating the internal properties of Möbius transformation, we show how to perform key recovery using superpolies involving full key bits, which leads to the best key recovery attacks on the targeted ciphers.

Privacy-Preserving Authenticated Key Exchange (PPAKE) provides protection both for the session keys and the identity information of the involved parties. In this paper, we introduce the concept of robustness into PPAKE. Robustness enables each user to confirm whether itself is the target recipient of the first round message in the protocol. With the help of robustness, a PPAKE protocol can successfully avoid the heavy redundant communications and computations caused by the ambiguity of communicants in the existing PPAKE, especially in broadcast channels.

We propose a generic construction of robust PPAKE from key encapsulation mechanism (KEM), digital signature (SIG), message authentication code (MAC), pseudo-random generator (PRG) and symmetric encryption (SE). By instantiating KEM, MAC, PRG from the DDH assumption and SIG from the CDH assumption, we obtain a specific robust PPAKE scheme in the standard model, which enjoys forward security for session keys, explicit authentication and forward privacy for user identities. Thanks to the robustness of our PPAKE, the number of broadcast messages per run and the computational complexity per user are constant, and in particular, independent of the number of users in the system.

The Eurocrypt 2023 organizing committee is soliciting for affiliated events to be held in conjunction with Eurocrypt 2023, on Saturday, April 22 and/or Sunday, April 23, in Lyon, France.

Each such event is expected to provide a forum discussing a specific topic of the broad cryptographic world (theory, practice, implementation, standardizations, etc.). The format of the event (e.g. workshop, tutorial, etc.) is up to the organizers.

Proposals for events should be submitted by email to the Eurocrypt 2023 workshop chair at eurocrypt2023workshops@iacr.org by September 30, 2022.

For more information, please visit: https://eurocrypt.iacr.org/2023/affiliated.php

This document is an informal summary on the FRI low degree test [BSBHR18a], [BSCI+20], and DEEP algebraic linking from [BSGKS20]. Based on its most recent soundness analysis [BSCI+20], we discuss parameter settings for practical security levels, how FRI is turned into a polynomial commitment scheme, and the soundness of DEEP sampling in the list decoding regime. In particular, we illustrate the DEEP method applied to proving satisfiability of algebraic intermediate representations and prove a soundness error bound which slightly improves the one in [Sta21].

Secure messaging schemes such as the Signal protocol rely on out-of-band channels to verify the authenticity of long-running communication. Such out-of-band checks however are only rarely actually performed by users in practice.

In this paper, we propose a new method for performing continuous authentication during a secure messaging session, without the need for an out-of-band channel. Leveraging the users' long-term secrets, our Authentication Steps extension guarantees authenticity as long as long-term secrets are not compromised, strengthening Signal's post-compromise security. Our mechanism further allows to detect a potential compromise of long-term secrets after the fact via an out-of-band channel.

Our protocol comes with a novel, formal security definition capturing continuous authentication, a general construction for Signal-like protocols, and a security proof for the proposed instantiation. We further provide a prototype implementation which seamlessly integrates on top of the official Signal Java library, together with bandwidth and storage overhead benchmarks.

In ASIACRYPT 2016, Bellare, Fuchsbauer, and Scafuro studied the security of NIZK arguments under subverted Structured Reference String (SRS) and presented some positive and negative results. In their best positive result, they showed that by defining an SRS as a tuple of knowledge assumption in bilinear groups (e.g. $g^a, g^b, g^{ab}$), and then using a Non-Interactive (NI) zap to prove that either there is a witness for the statement $\mathsf{x}$ or one knows the trapdoor of SRS (e.g. $a$ or $b$), one can build NIZK arguments that can achieve soundness and $\textit{subversion zero-knowledge}$ (zero-knowledge without trusting a third party; Sub-ZK). In this paper, we expand their idea and use NI zaps (of knowledge) to build NIZK arguments (of knowledge) with $\textit{updatable}$, $\textit{universal}$, and $\textit{succinct}$ SRS. To this end, we first show that their proposed sound and Sub-ZK NIZK argument can also achieve $\textit{updatable}$ soundness, which is a more desired notion than the plain soundness. Updatable soundness allows the verifier to update the SRS one time and bypass the need for a trusted third party. Then, we show that using a similar OR language, given a NI zap (of knowledge) and a $\textit{key-updatable}$ signature scheme, one can build NIZK arguments that can achieve Sub-ZK and $\textit{updatable}$ simulation soundness (resp. $\textit{updatable}$ simulation extractability). The proposed constructions are the first NIZK arguments that have updatable and succinct SRS, and do not require a random oracle. Our instantiations show that in the resulting NIZK arguments the computational cost for the parties to verify/update the SRS is negligible, namely, a few exponentiations and pairing checks. The run times of the prover and verifier, as well as the size of the proof, are asymptotically the same as those of the underlying NI zap.

In the Nostradamus attack, introduced by Kelsey and Kohno (Eurocrypt 2006), the adversary has to commit to a hash value y of an iterated hash function H such that, when later given a message prefix P, the adversary is able to find a suitable "suffix explanation" S with H(P||S)=y. Kelsey and Kohno show a herding attack with $2^{2n/3}$ evaluations of the compression function of H (with n bits output and state), locating the attack between preimage attacks and collision search in terms of complexity. Here we investigate the security of Nostradamus attacks for quantum adversaries. We present a quantum herding algorithm for the Nostradamus problem making approximately $\sqrt[3]{n}\cdot 2^{3n/7}$ compression function evaluations, significantly improving over the classical bound. We also prove that quantum herding attacks cannot do better than $2^{3n/7}$ evaluations for random compression functions, showing that our algorithm is (essentially) optimal. We also discuss a slightly less tight bound of roughly $2^{3n/7-s}$ for general Nostradamus attacks against random compression functions, where s is the maximal block length of the adversarially chosen suffix S.

We solve a long-standing challenge to the integrity of votes cast without the supervision of a voting booth: "it improper influence,'' which refers to any combination of vote buying and voter coercion. Our approach allows each voter, or their trusted agents, to cancel their vote in a way that is unstoppable, irrevocable, and forever unattributable to the voter. In particular, our approach enhances security of online, remote, public-sector elections, for which there is a growing need and the threat of improper influence is most acute. In this extended abstract, we introduce the new approach, compare it with previous methods, and concisely summarize the protocols. In our full paper, give detailed cryptographic protocols, show how they can be applied to several voting settings, describe our implementation in a full voting system called Votexx, and provide UC proofs of security. Our system protects against the strongest adversary considered in prior related work and is suitable for widespread use in public elections.

We sketch a method for creating a zero-knowledge proof of knowledge for the correct execution of a program within a model of higher-order, recursive, purely functional programming by leveraging Halo 2. To our knowledge, this is the first ZKP for general purpose computation based on purely functional computation. This is an attractive alternative to using a von Neumann architecture based zero-knowledge virtual machine for verified computing of functional programs, as compilation will be more direct, making it more easily verifiable and potentially more efficient. Interaction nets are a natural setting for recursive, higher-order functional programming where all computation steps are linear and local. Interaction nets are graphs and traces for such programs are hyper-graphs. Correctness of a trace is a simple syntactic check over the structure of the trace represented as a hyper-graph. We reformulate this syntactic check as a Halo 2 circuit which is universal over all traces.

Recent practical applications using advanced cryptographic protocols such as multi-party computations (MPC) and zero-knowledge proofs (ZKP) have prompted a range of novel symmetric primitives described over large finite fields, characterized as arithmetization-oriented AO ciphers. Such designs, aiming to minimize the number of multiplications over fields, have a high risk of being vulnerable to algebraic attacks, especially to the higher-order differential attack. Thus, it is significant to carefully evaluate the growth of their algebraic degree. However, the degree estimation for AO ciphers has been a challenge for cryptanalysts due to the lack of general and accurate methods.

In this paper, we extend the division property, a state-of-the-art framework for finding the upper bound of the algebraic degree over binary fields, to the scope of $\mathbb{F}_{2^n}$. It is a generic method to detect the algebraic degree for AO ciphers, even applicable to Feistel ciphers which have no better bounds than the trivial exponential one. In this general division property, our idea is to evaluate whether the polynomial representation of a block cipher contains some specific monomials. With a deep investigation of the arithmetical feature, we introduce the propagation rules of monomials for field-based operations, which can be efficiently modeled using the bit-vector theory of SMT. Then the new searching tool for degree estimation can be constructed due to the relationship between the algebraic degree and the exponents of monomials.

We apply our new framework to some important AO ciphers, including Feistel MiMC, GMiMC, and MiMC. For Feistel MiMC, we show that the algebraic degree grows significantly slower than the native exponential bound. For the first time, we present a secret-key higher-order differential distinguisher for up to 124 rounds, much better than the 83-round distinguisher for Feistel MiMC permutation proposed at CRYPTO 2020. We also exhibit a full-round zero-sum distinguisher with a data complexity of $2^{251}$. Our method can be further extended for the general Feistel structure with more branches and exhibit higher-order differential distinguishers against the practical instance of GMiMC for up to 50 rounds. For MiMC in SP-networks, our results correspond to the exact algebraic degree proved by Bouvier et al. We also point out that the number of rounds in MiMC's specification is not sufficient to guarantee the security against the higher-order differential attack for MiMC-like schemes with different exponents. The investigation of different exponents provides some guidance on the cipher design.

We introduce puncturable key wrapping (PKW), a new cryptographic primitive that supports fine-grained forward security properties in symmetric key hierarchies. We develop syntax and security definitions, along with provably secure constructions for PKW from simpler components (AEAD schemes and puncturable PRFs). We show how PKW can be applied in two distinct scenarios. First, we show how to use PKW to achieve forward security for TLS 1.3 0-RTT session resumption, even when the server's long-term key for generating session tickets gets compromised. This extends and corrects a recent work of Aviram, Gellert, and Jager (Journal of Cryptology, 2021). Second, we show how to use PKW to build a protected file storage system with file shredding, wherein a client can outsource encrypted files to a potentially malicious or corrupted cloud server whilst achieving strong forward-security guarantees, relying only on local key updates.

Garbling is a cryptographic primitive which has many applications. It is mainly used for scenes of limited authority, such as multi-party computation (MPC), attribute-based encryption (ABE), functional encryption (FE), indistinguishability obfuscation (IO), etc. Garbling schemes before 2013 are of one-time garbling. Goldwasser et al and Agrawal presented a reusable garbling scheme, which made use of a symmetric encryption scheme and an FE scheme as the components.

In this paper we discuss the validity and the efficiency of reusable garbling scheme. We present the following three notes on the scheme.

(1) Reusable garbling scheme does not provide new applications, and it is still a one-time garbling scheme.

(2) Even reusable garbling scheme is taken as a one-time garbling scheme, sometimes it is not usable. More detailedly, it can only be used for Basic Scene 2, and cannot be used for Basic Scene 1. For example, it cannot be used for MPC.

(3) Even reusable garbling scheme is taken as a one-time garbling scheme used for Basic Scene 2, there is no evidence to show that its efficiency is better than a former one-time garbling scheme.

In the classical notion of multiparty computation (MPC), an honest party learning private inputs of others, either as a part of protocol specification or due to a malicious party's unspecified messages, is not considered a potential breach. Several works in the literature exploit this seemingly minor loophole to achieve the strongest security of guaranteed output delivery via a trusted third party, which nullifies the purpose of MPC. Alon et al. (CRYPTO 2020) presented the notion of Friends and Foes ($\mathtt{FaF}$) security, which accounts for such undesired leakage towards honest parties by modelling them as semi-honest (friends) who do not collude with malicious parties (foes). With real-world applications in mind, it's more realistic to assume parties are semi-honest rather than completely honest, hence it is imperative to design efficient protocols conforming to the $\mathtt{FaF}$ security model.

Our contributions are not only motivated by the practical viewpoint, but also consider the theoretical aspects of $\mathtt{FaF}$ security. We prove the necessity of semi-honest oblivious transfer for $\mathtt{FaF}$-secure protocols with optimal resiliency. On the practical side, we present QuadSquad, a ring-based 4PC protocol, which achieves fairness and GOD in the $\mathtt{FaF}$ model, with an optimal corruption of $1$ malicious and $1$ semi-honest party. QuadSquad is, to the best of our knowledge, the first practically efficient $\mathtt{FaF}$ secure protocol with optimal resiliency. Its performance is comparable to the state-of-the-art dishonest majority protocols while improving the security guarantee from abort to fairness and GOD. Further, QuadSquad elevates the security by tackling a stronger adversarial model over the state-of-the-art honest-majority protocols, while offering a comparable performance for the input-dependent computation. We corroborate these claims by benchmarking the performance of QuadSquad. We also consider the application of liquidity matching that deals with highly sensitive financial transaction data, where $\mathtt{FaF}$ security is apt. We design a range of $\mathtt{FaF}$ secure building blocks to securely realize liquidity matching as well as other popular applications such as privacy-preserving machine learning (PPML). Inclusion of these blocks makes QuadSquad a comprehensive framework.

An $\ell$-server Private Information Retrieval (PIR) scheme enables a client to retrieve a data item from a database replicated among $\ell$ servers while hiding the identity of the item. It is called $b$-error-correcting if a client can correctly compute the data item even in the presence of $b$ malicious servers. It is known that $b$-error correction is possible if and only if $\ell>2b$. In this paper, we first prove that if error correction is perfect, i.e., the client always corrects errors, the minimum communication cost of $b$-error-correcting $\ell$-server PIR is asymptotically equal to that of regular $(\ell-2b)$-server PIR as a function of the database size $n$. Secondly, we formalize a relaxed notion of statistical $b$-error-correcting PIR, which allows non-zero failure probability. We show that as a function of $n$, the minimum communication cost of statistical $b$-error-correcting $\ell$-server PIR is asymptotically equal to that of regular $(\ell-b)$-server one, which is at most that of $(\ell-2b)$-server one. Our main technical contribution is a generic construction of statistical $b$-error-correcting $\ell$-server PIR for any $\ell>2b$ from regular $(\ell-b)$-server PIR. We can therefore reduce the problem of determining the optimal communication complexity of error-correcting PIR to determining that of regular PIR. In particular, our construction instantiated with the state-of-the-art PIR schemes and the previous lower bound for single-server PIR result in a separation in terms of communication cost between perfect and statistical error correction for any $\ell>2b$.

A major challenge for blockchain interoperability is having an on-chain light client protocol that is both efficient and secure. We present a protocol that provides short proofs about the state of a decentralised consensus protocol while being able to detect misbehaving parties. To do this naively, a verifier would need to maintain an updated list of all participants' public keys which makes the corresponding proofs long. In general, existing solutions either lack accountability or are not efficient. We define and design a committee key scheme with short proofs that do not include any of the individual participants' public keys in plain. Our committee key scheme, in turn, uses a custom designed SNARK which has a fast prover time. Moreover, using our committee key scheme, we define and design an accountable light client system as the main cryptographic core for building bridges between proof of stake blockchains. Finally, we implement a prototype of our custom SNARK for which we provide benchmarks.

Doctoral student Position at School of Computer Science, University College Dublin, Ireland, focusing on Blockchain and Federated Learning for CONFIDENTIAL6G Project. We are looking for a candidate for a four-year direct Ph.D. position at the School of Computer Science, University College Dublin, Ireland, focusing on Blockchain uses for radio spectrum sharing and learning data integrity assurance for AI/ML approaches. This PhD position is attached to the project CONFIDENTIAL6G; a HORIZON EUROPE project funded by the EU commission. This project emphasizes privacy preservation and security of sensitive data focusing on the protection of data in use, in transit, and processed or stored at the edge. The selected student will work on a topic related to the CONFIDENTIAL6G project. #Funding The student will receive a four-year scholarship (where university tuition fees are fully covered along with living allowances of 18,500 Euros per annum) for the total duration of the Ph.D. program. Start Date By January 2023 Requirements for the doctoral student - Candidates should have a B.Sc (with a first-class) or a M.Sc. in one of the following fields: computer science, software engineering, or any other relevant subject by the time of the start date; - Proven DLT software (e.g., Blockchain, Ethereum, hyperledger…etc.) development skills with at least one relevant programming language such as Python, or Java; - Proven ability to document and publish the research findings in top conference proceedings and journals; - Motivation and dedication to pursue doctoral degree studies and research work that has the potential to be published in high-ranking publications; - Formidable communication skills to enable networking and knowledge dissemination plausible. Applying If you are interested, please contact me with the following documen

Closing date for applications:

Contact: The position is supervised by Asst. Prof. Dr. Madhusanka Liyanage (https://scholar.google.fi/citations?user=p1n0ioUAAAAJ&hl=en) and Asst. Prof. Dr. Shen Wang (https://scholar.google.com/citations?user=rPAOzIwAAAAJ&h).

This is an opportunity for a high-achieving postdoctoral researcher to join a world-leading research group within the area of computer security and cryptography. In this role you will design, develop, implement, and assess tools and procedures for secure implementation of cryptographic primitives. The position will support our research program to improve hardware and software security and promote secure designs.

This is a fixed term (18 months) position with a flexible start date up to January 2023.

Apply at: https://careers.adelaide.edu.au/cw/en/job/510702

Closing date for applications:

Contact: Yuval Yarom yval(at)cs.adelaide.edu.au

Job Description
The Cryptography Architect will be responsible for guiding how advanced and innovative cryptography is leveraged at JPMorgan Chase. As an experienced member of the Emerging Technologies Security group within the Cybersecurity & Technology Controls organization, you will interact with like-minded cryptographers and a group of passionate security engineers to work on concrete applications of advanced cryptography schemes. You will also have the opportunity to collaborate with other cryptographers on research projects.
The position requires strong academic knowledge as well as some industry experience in vetting and applying advanced cryptography schemes to secure complex IT infrastructure, customer-facing services, and sensitive customer and enterprise data.
Knowledge, experience, and capability required for the role include:

• Expertise in both mainstream encryption schemes and key exchange protocols as well as quantum-safe cryptography
• Strong familiarity with NIST post-quantum cryptography standardization & migration efforts
• Hands-on experience with implementing, testing and deploying advanced cryptographic schemes
• Familiarity with NIST Cryptographic Standards and Guidelines
• Proficiency in multiple programming languages, e.g., Java, C#, JavaScript, C/C++
• Ability to convey complex concepts in a clear & concise manner to a wide range of audience
• Proven track record in publishing papers (academia, whitepaper, position paper etc.)
• Proven track record in working with diverse teams to achieve goals
• Driving enterprise-wide transformative security technology initiatives
• PhD (preferred) or MS in computer science

Closing date for applications:

Contact: Hubert Le Van Gong, Ph.D. | Managing Director | Cybersecurity & Technology Controls

More information: https://jpmc.fa.oraclecloud.com/hcmUI/CandidateExperience/en/sites/CX_1001/job/210337824/?utm_medium=jobshare

Job Description

The Applied Cryptography Architect will be responsible for leveraging innovative cryptography at JPMorgan Chase. As a member of the Emerging Technologies Security group within the Cybersecurity & Technology Controls organization, you will work alongside cryptographers and a group of passionate security engineers to solve complex security problems and support the deployment of cryptography-based solutions.

The position requires extensive knowledge and industry experience in combining cryptography and security best-practices to secure complex IT infrastructure, customer-facing services, and sensitive customer and enterprise data.

Knowledge, experience, and capability required for the role include:

• Expertise in applying mainstream cryptographic primitives, including digital signatures, public-key ciphers, block ciphers Good understanding and hands-on experience of network security protocols (TLS etc.)
• Familiarity with NIST post-quantum cryptography standardization & migration efforts
• Security solution development utilizing cryptographic agility principles and elements
• Proficiency in multiple programming languages, e.g., Java, C#, JavaScript, C/C++
• Hands-on data protection solution development utilizing industry standard security protocol and best-practices
• Application knowledge of public key infrastructure (PKI) and digital certificates (e.g., X.509)
• Ability to convey complex concepts and ideas in a clear and concise manner to a wide range of audience
• Proven track record in working with diverse teams to achieve goals
• Driving enterprise-wide transformative security technology initiatives
• MS (preferred) or BS in computer science

Closing date for applications:

Contact: Hubert Le Van Gong, Ph.D. | Managing Director | Cybersecurity & Technology Controls

More information: https://jpmc.fa.oraclecloud.com/hcmUI/CandidateExperience/en/sites/CX_1001/job/210337262/?utm_medium=jobshare

Oxford University’s Computer Science Department is hiring four new faculty. The positions are open to all areas of computer science and the closing date is 12 noon on 14 December 2022. For more information, see https://www.cs.ox.ac.uk/aboutus/vacancies/vacancy-faculty-hiring.html

Closing date for applications:

Contact: James Worrell