International Association
for Cryptologic Research

Physically related functions~(PReFs) are hardware primitives proposed to establish key-exchange between resource-constrained devices with no pre-established secrets. In this paper, we introduce XOR composition of PReFs to eliminate the requirement of revealing the complete functionality of the hardware primitive during the setup phase, which is a prerequisite to setup PReFs. We evaluate the quality of XOR\_PReF design by implementing them on Artix-7 FPGAs.

Event date: 11 December to 14 December 2022
Submission deadline: 1 September 2022
Notification: 15 October 2022

The Applied Cryptography Group at Technical University of Darmstadt offers a fully funded position as PhD student in Cryptography. The positions is to be filled as soon as possible for 3 years with the possibility of extension. You will conduct research and publish/present the results at top venues for research in cryptography and IT Security.

Topics of particular interest include (but are not limited to):

• Leakage/tamper resilient cryptography
• Cryptography for blockchains and cryptocurrencies
• Multiparty computation & threshold cryptography

Your profile is ideally:

• Completed Master's degree (or equivalent) with excellent grades in computer science, mathematics or a similar area.
• Strong mathematical and/or algorithmic/theoretical CS background
• Good knowledge of cryptography. Knowledge in concepts of provable security is a plus.
• Fluent written and verbal communication skills in English

TU Darmstadt is a top research university for IT Security, Cryptography and Computer Science in Europe. We offer excellent working environment in the heart of the Frankfurt Metropolitan Area, which is internationally well-known for a high quality of life.

Review of applications starts immediately until the position is filled. For further information please visit: https://www.informatik.tu-darmstadt.de/cac/cac/index.en.jsp

Closing date for applications:

Contact: Sebastian Faust (office.cac@cysec.de)

Huawei German Research Center in Munich is looking for a PhD student on Security & Trust - Connected, Cooperative, Automated Mobility (m/f/d).

The ideal candidate would have background in probabilistic reasoning and logic or formal methods and understanding of security.

The position is connected to a new EU Project starting in September 2022 on Security and Trust in Connected, Cooperative, Automated Mobility (CCAM). The PhD candidate will be funded by the project and PhD topic will be connected directly to the research inside this project. Goal is to complete it in 3 years.

Research Topic

• Perform research and develop new solutions for Trust Management in the Next-Generation CCAM technologies.
• Contribute to new mechanisms for assessing dynamic trust relationship based on Zero Trust and Subjective Logic.
• Define a trust model and trust reasoning framework based on which involved entities can establish trust for cooperatively executing safety-critical functions.

Responsibilities

• Contribute to the research and development of technologies in the upcoming domain of Connected, Cooperative and Automated Mobility (CCAM).
• Being involved in international initiatives including industry groups such as 5GAA, Gaia-X, DIF and Horizon Europe research projects.

Your Profile

• Completed master studies (or equivalent) in computer science, information technology, electrical engineering, or mathematics;
• Background in probabilistic reasoning and logic or formal methods
• Exposure and understanding of data protection and security development technologies;
• Good programming skill;
• Fluent in English;

Closing date for applications:

Contact: Ioannis Krontiris (ioannis.krontiris@huawei.com)

More information: https://huaweiresearchcentergermanyaustria.teamtailor.com/jobs/1732783-phd-student-security-trust-connected-cooperative-automated-mobility-m-f-d

With the advent of Malicious (Peyrin and Wang, Crypto'20), the question of a cipher with an intentional weakness which is only known to its designer has gained its momentum. In their work, the authors discuss how an otherwise secure cipher can be broken by its designer with the help of a secret backdoor (which is not known to the user/attacker). The contribution of Malicious is to propose a cipher-level construction with a backdoor, where it is computationally infeasible to retrieve the backdoor entry despite knowing how the mechanism works.

In this work, we revisit the work by Peyrin and Wang in a greater depth. We discuss the relevant aspects with more clarity, thereby addressing some of the important issues connected to a backdoor construction. The main contribution, however, comes as a new proof-of-concept block cipher with an innate backdoor, named ZUGZWANG. Unlike Malicious, which needs new/experimental concepts like partially non-linear layer; our cipher entirely relies on concepts which are well-established for decades (such as, using an one-way function as a Feistel cipher's state-update), and also offers quite a few advantages over Malicious (easy to visualise, succeeds with probability 1, and so on). Having known the secret backdoor entry, one can recover the secret key with only 1 plaintext query to our cipher; but it is secure otherwise. As the icing on the cake, we show the provable security claims for our cipher.

In this work, we recover the private key material of the FrodoKEM key exchange mechanism as submitted to the NIST Post Quantum Cryptography (PQC) standardization process. The new mechanism that allows for this is a Rowhammer-assisted \emph{poisoning} of the FrodoKEM Key Generation (KeyGen) process. The Rowhammer side-channel is a hardware-based security exploit that allows flipping bits in DRAM by “hammering” rows of memory adjacent to some target-victim memory location by repeated memory accesses. Using Rowhammer, we induce the FrodoKEM software to output a higher-error Public Key (PK), $(\mathbf{A}, \mathbf{B} = \mathbf{A}\mathbf{S}+\mathbf{\widetilde{E}}),$ where the error $\widetilde{\mathbf{E}}$ is modified by Rowhammer.

Then, we perform a decryption failure attack, using a variety of publicly-accessible supercomputing resources running on the order of only 200,000 core-hours. We delicately attenuate the decryption failure rate to ensure that the adversary's attack succeeds practically, but so honest users cannot easily detect the manipulation.

Achieving this public key "poisoning" requires an extreme engineering effort, as FrodoKEM's KeyGen runs on the order of 8 milliseconds. (Prior Rowhammer-assisted attacks against cryptography require as long as 8 hours of persistent access.) In order to handle this real-world timing condition, we require a wide variety of prior and brand new, low-level engineering techniques, including e.g. memory massaging algorithms -- i.e. "Feng Shui" -- and a precisely-targeted performance degradation attack on the extendable output function SHAKE.

We explore the applicability of our techniques to other lattice-based KEMs in the NIST PQC Round 3 candidate-pool, e.g. Kyber, Saber, etc, as well as the difficulties that arise in the various settings. To conclude, we discuss various simple countermeasures to protect implementations against this, and similar, attacks.

Mixing protocols serve as a promising solution to the unlinkability in blockchains. They work by hiding one transaction among a set of transactions and enjoy the advantage of high compatibility with the underlying system. However, due to the inherently public nature of the blockchains built on the account-based model, the unlinkability is highly restricted to non-confidential transactions. In the account-based model, blockchains supporting confidential payments need to trade their compatibility for unlinkability.

In this paper, we propose MixCT, a generic protocol that provides the mixing service for confidential payment systems built from homomorphic commitment in the account-based model. We formally define the security goals including safety and availability, and prove that our generic construction satisfies them. Furthermore, we provide an efficient instantiation of MixCT by the Pedersen commitment and the one-out-of-many proof. The evaluation results show that MixCT introduces a small cost for its users while being highly compatible with the underlying confidential blockchain.

A transaction record in a sharded blockchain can be represented as a two-dimensional array of integers with row-index associated to an account, column-index to a shard and the entry to the transaction amount. In a blockchain-based cryptocurrency system with coded sharding, a transaction record of a given epoch of time is encoded using a block code considering the entries as finite-field symbols. Each column of the resultant coded array is then stored in a server. In the particular case of PolyShard scheme, the block code turns out to be a maximum-distance-separable code. In this paper, we propose a privacy-preserving multi-round protocol that allows a remote client to retrieve from a coded blockchain system the sum of transaction amounts belonging to two different epochs of time, but to the same account. At the core of the protocol lies an algorithm for a remote client to privately compute a non-linear function referred to as integer-addition of two finite-field symbols representing integer numbers, in the presence of curious-but-honest adversaries. Applying it to balance-checking in a cryptocurrency system, the protocol guarantees information-theoretic privacy on account number and shard number thereby ensuring perfect user anonymity, and also maintains confidentiality of half of the input bits on average. The protocol turns out to be a useful primitive for balance-checking in lightweight clients of a PolyShard-ed blockchain.

We present SimplePIR, the fastest private information retrieval (PIR) scheme known to date. SimplePIR is a single-server PIR scheme, whose security holds under the learning-with-errors assumption. To answer a client’s PIR query, the SimplePIR server performs one 32-bit multiplication and one 32-bit addition per database byte. SimplePIR achieves 6.5 GB/s/core server throughput, which is 7% faster than the fastest two-server PIR schemes (that require non-colluding servers). SimplePIR has relatively large communication costs: to make queries to a 1 GB database, the client must download a 124 MB “hint” about the database contents; thereafter, the client may make an unbounded number of queries, each requiring 242 KB of communication. We present a second single-server scheme, DoublePIR, that shrinks the hint to 16 MB at the cost of slightly higher per-query communication (345 KB) and slightly lower throughput (5.2 GB/s/core). Finally, we apply our PIR schemes, together with a new data structure for approximate set membership, to the problem of private auditing in Certificate Transparency. We achieve a strictly stronger notion of privacy than Google Chrome’s current approach with a modest, 13× larger communication overhead.

Grover famously showed that any unsorted list, of finite size $N$, can be searched in O($\sqrt{N})$ time via quantum computation. Bennett et. al. demonstrated that any algorithm general enough to search any finite unsorted list must take at least O($\sqrt{N})$ time via quantum computation. We demonstrate a quantum algorithm that can search a proper subclass of finite, unsorted lists, of size $N$, in a time that is polynomial in $log(N)$. We demonstrate how it can be used to search the keyspace of any block cipher that can be implemented on a quantum computer with the keyspace in superpositon. In particular we give a polynomial time attack on $AES-128$, $AES-192$ and $AES-256$.

Searchable Encryption schemes provide secure search over encrypted databases while allowing admitted information leakages. Generally, the leakages can be categorized into access and volume pattern. In most existing SE schemes, these leakages are caused by practical designs but are considered an acceptable price to achieve high search efficiency. Recent attacks have shown that such leakages could be easily exploited to retrieve the underlying keywords for search queries. Under the umbrella of attacking SE, we design a new Volume and Access Pattern Leakage-Abuse Attack (VAL-Attack) that improves the matching technique of LEAP (CCS ’21) and exploits both the access and volume patterns. Our proposed attack only leverages leaked documents and the keywords present in those documents as auxiliary knowledge and can effectively retrieve document and keyword matches from leaked data. Furthermore, the recovery performs without false positives. We further compare VAL-Attack with two recent well-defined attacks on several real-world datasets to highlight the effectiveness of our attack and present the performance under popular countermeasures.

Physical attacks can compromise the security of cryptographic devices. Depending on the attack’s requirements, adversaries might need to (i) place probes in the proximity of the integrated circuits (ICs) package, (ii) create physical connections between their probes/wires and the system’s PCB, or (iii) physically tamper with the PCB’s components, chip’s package, or substitute the entire PCB to prepare the device for the attack. While tamper-proof enclosures prevent and detect physical access to the system, their high manufacturing cost and incompatibility with legacy systems make them unattractive for many low-cost scenarios. In this paper, inspired by methods known from the field of power integrity analysis, we demonstrate how the impedance characterization of the system’s power distribution network (PDN) using on-chip circuit-based network analyzers can detect various classes of tamper events. We explain how these embedded network analyzers, without any modifications to the system, can be deployed on FPGAs to extract the frequency response of the PDN. The analysis of these frequency responses reveals different classes of tamper events from board to chip level. To validate our claims, we run an embedded network analyzer on FPGAs of a family of commercial development kits and perform extensive measurements for various classes of PCB and IC package tampering required for conducting different side-channel or fault attacks. Using the Wasserstein Distance as a statistical metric, we further show that we can confidently detect tamper events. Our results, interestingly, show that even environment-level tampering activities, such as the proximity of contactless EM probes to the IC package or slightly polished IC package, can be detected using on-chip impedance sensing.

The notion of public key encryption with keyword search (PEKS) was introduced to efficiently search over encrypted data. In this paper, we propose a PEKS scheme in which both the encrypted keyword and the trapdoor are randomized, so that the cloud server is not able to recognize identical queries. Our scheme is CI-secure in the single-user setting and TI-secure in the multi-user setting with multi-trapdoor.

The application security and cryptography group at the Lucerne School of Information Technology has the following open research positions:

Senior Research Associate Cryptography and Quantum Information (https://recruitingapp-2678.umantis.com/Vacancies/2466/Description/1)

Senior Research Associate Security Software Engineer (https://recruitingapp-2678.umantis.com/Vacancies/2465/Description/1)

Doctoral Position in Cryptography & Quantum Information (https://recruitingapp-2678.umantis.com/Vacancies/2467/Description/1)
Candidates should have a strong background in IT security and cryptography and/or good software engineering skills; knowledge in quantum information is advantageous. Both junior and more senior candidates are considered. For junior candidates, there exists the possibility to combine the employment with enrollment in a study-programm towards a PhD or a Master of Science in Engineering (MSE).

Closing date for applications:

Contact: Please apply online via the links provided above. For any further Information contact Prof. Dr. Esther Hänggi, esther.haenggi@hslu.ch

More information: https://recruitingapp-2678.umantis.com/Vacancies/2466/Description/1

The Department of Computer Science within the Faculty of Engineering and Physical Sciences has an international reputation for research and teaching. Research in the department is focused on three main areas - Nature Inspired Computing and Engineering (NICE), Distributed and Networked Systems, and Secure Systems, with Surrey hosting UK Academic Centres of Excellence both in Research and in Education, both recognised by GCHQ.

This post offers an exciting opportunity for an appointment in the Secure Systems group. Suitable areas of expertise that complement and extend strengths of the group include (but are not limited to): software security, program analysis, formal verification of software/systems, practical system security, trusted systems, distributed systems, complex systems and networks, as well as the interface between security and machine learning.

Candidates to the post should have a PhD in a relevant subject or equivalent professional experience. An ability to secure research funding and produce high quality outputs and manage research projects and supervise research students is also required. It is expected that the post-holder will also contribute to high quality teaching in cyber security and fundamental topics in computer science at undergraduate and post-graduate level and to supervise undergraduate projects and dissertations.

The University and the Department specifically are committed to building a culturally diverse organisation and strongly encourages applications from female and minority candidates. The Department of Computer Science was awarded a Bronze Athena SWAN award, in recognition of our commitment to equality and diversity.

The University of Surrey is committed to providing an inclusive environment that offers equal opportunities for all. We place great value on diversity and are seeking to increase the diversity within our community. Therefore, we particularly encourage applications from under-represented groups, such as people from Black, Asian and minority ethnic groups and people with disabilities.

Closing date for applications:

Contact: Professor Steve Schneider

s.schneider@surrey.ac.uk

More information: https://jobs.surrey.ac.uk/vacancy.aspx?ref=045822

Recent works have made exciting progress on the construction of round optimal, *two-round*, Multi-Party Computation (MPC) protocols. However, most proposals so far are still complex and inefficient.

In this work, we improve the simplicity and efficiency of two-round MPC in the setting with dishonest majority and malicious security. Our protocols make use of the Random Oracle (RO) and a generalization of the Oblivious Linear Evaluation (OLE) correlated randomness, called tensor OLE, over a finite field $\mathbb{F}$, and achieve the following:

- MPC for Boolean Circuits: Our two-round, maliciously secure MPC protocols for computing Boolean circuits, has overall (asymptotic) computational cost $O(S\cdot n^3 \cdot \log |\mathbb{F}|)$, where $S$ is the size of the circuit computed, $n$ the number of parties, and $\mathbb{F}$ a field of characteristic two. The protocols also make black-box calls to a Pseudo-Random Function (PRF).

- MPC for Arithmetic Branching Programs (ABPs): Our two-round, information theoretically and maliciously secure protocols for computing ABPs over a general field $\mathbb{F}$ has overall computational cost $O(S^{1.5}\cdot n^3\cdot \log |\mathbb{F}|)$, where $S$ is the size of ABP computed.

Both protocols achieve security levels inverse proportional to the size of the field $|\mathbb{F}|$.

Our construction is built upon the simple two-round MPC protocols of [Lin-Liu-Wee TCC'20], which are only semi-honest secure. Our main technical contribution lies in ensuring malicious security using simple and lightweight checks, which incur only a constant overhead over the complexity of the protocols by Lin, Liu, and Wee. In particular, in the case of computing Boolean circuits, our malicious MPC protocols have the same complexity (up to a constant overhead) as (insecurely) computing Yao's garbled circuits in a distributed fashion.

Finally, as an additional contribution, we show how to efficiently generate tensor OLE correlation in fields of characteristic two using OT.

It can be tricky to trust elliptic curves standardized in a non-transparent way. To rectify this, we propose a systematic methodology for analyzing curves and statistically comparing them to the expected values of a large number of generic curves with the aim of identifying any deviations in the standard curves.

For this purpose, we put together the largest publicly available database of standard curves. To identify unexpected properties of standard generation methods and curves, we simulate over 250 000 curves by mimicking the generation process of four standards. We compute 22 different properties of curves and analyze them with automated methods to pinpoint deviations in standard curves, pointing to possible weaknesses.

Coin mixing services allow users to mix their cryptocurrency coins and thus enable unlinkable payments in a way that prevents tracking of honest users' coins by both the service provider and the users themselves. The easy bootstrapping of new users and backwards compatibility with cryptocurrencies (such as Bitcoin) with limited support for scripts are attractive features of this architecture, which has recently gained considerable attention in both academia and industry.

A recent work of Tairi et al. [IEEE S&P 2021] formalizes the notion of a coin mixing service and proposes A$^{2}$L, a new cryptographic protocol that simultaneously achieves high efficiency and interoperability. In this work, we identify a gap in their formal model and substantiate the issue by showing two concrete counterexamples: we show how to construct two encryption schemes that satisfy their definitions but lead to a completely insecure system.

To amend this situation, we investigate secure constructions of coin mixing services. First, we develop the notion of blind conditional signatures (BCS), which acts as the cryptographic core for coin mixing services. We propose game-based security definitions for BCS and propose A$^{2}$L$^{+}$, a modified version of the protocol by Tairi et al. that satisfies our security definitions. Our analysis is in an idealized model (akin to the algebraic group model) and assumes the hardness of the one-more discrete logarithm problem. Finally, we propose A$^{2}$L$^\text{UC}$, another construction of BCS that achieves the stronger notion of UC-security (in the standard model), albeit with a significant increase in computation cost. This suggests that constructing a coin mixing service protocol secure under composition requires more complex cryptographic machinery than initially thought.

A succinct non-interactive argument of knowledge (SNARK) allows a prover to produce a short proof that certifies the veracity of a certain NP-statement. In the last decade, a large body of work has studied candidate constructions that are secure against quantum attackers. Unfortunately, no known candidate matches the efficiency and desirable features of (pre-quantum) constructions based on bilinear pairings.

In this work, we make progress on this question. We propose the first lattice-based SNARK that simultaneously satisfies many desirable properties: It (i) is tentatively post-quantum secure, (ii) is publicly-verifiable, (iii) has a logarithmic-time verifier and (iv) has a purely algebraic structure making it amenable to efficient recursive composition. Our construction stems from a general technical toolkit that we develop to translate pairing-based schemes to lattice-based ones. At the heart of our SNARK is a new lattice-based vector commitment (VC) scheme supporting openings to constant-degree multivariate polynomial maps, which is a candidate solution for the open problem of constructing VC schemes with openings to beyond linear functions. However, the security of our constructions is based on a new family of lattice-based computational assumptions which naturally generalises the standard Short Integer Solution (SIS) assumption.

This paper presents a side-channel analysis (SCA) on key encapsulation mechanisms (KEMs) based on the Fujisaki–Okamoto (FO) transformation and its variants. Many post-quantum KEMs usually perform re-encryption during key decapsulation to achieve CCA security. It has been shown that the side-channel leakage of re-encryption can be exploited for mounting a key-recovery plaintext-checking attack (KR-PCA), even if the CPA secure decryption constructing the KEM is securely implemented. In this paper, we propose an efficient side-channel-assisted KR-PCA on post-quantum KEMs, which achieves a key recovery with significantly fewer attack traces than the existing one. The basic ideas of the proposed attack are to present a new KR-PCA based on a multiple-valued (MV-)PC oracle and to utilize a dedicated multi-classification neural network (NN) to implement an MV-PC oracle. This paper also presents how to realize a sufficiently reliable MV-PC oracle from not completely accurate NN model outputs, and analyzes the tradeoff between the key recovery success rate and the number of attack traces, with its application to NIST PQC selected algorithm Kyber and similar lattice-based Saber, FrodoKEM and NTRU Prime, as well as SIKE, a candidate for the fourth round. Furthermore, the feasibility of the proposed attack is assessed through attack experiments on three typical PRF implementations (i.e., SHAKE, SHA3, and AES software). In consequence, we confirm that the proposed attack reduces the number of attack traces required for a reliable key recovery by up to 87% compared to the existing attacks against Kyber and other lattice-based KEMs under the condition of 99.9999% success rate for key recovery. We also confirm that the proposed attack can reduce the number of attack traces by 85% for SIKE.