International Association for Cryptologic Research

International Association
for Cryptologic Research

IACR News

Here you can see all recent updates to the IACR webpage. These updates are also available:

email icon
via email
RSS symbol icon
via RSS feed

21 September 2023

University of Luxembourg, Esch-sur-Alzette, Luxembourg
Job Posting Job Posting

The CryptoLux group of the University of Luxembourg has a vacancy for a post-doctoral researcher in the area of security/privacy of blockchains and smart contracts. The successful candidate will contribute to a research project entitled Advanced Cryptography for Finance and Privacy (CryptoFin), which is funded by the Fonds National de la Recherche (FNR). Starting in September 2023, CryptoFin will run over a period of 3 years and be carried out in collaboration with the cryptography teams of Stanford University and Ethereum foundation. The mission of the CryptoFin project is to develop innovative solutions for some of the most pressing research problems in the blockchain domain, especially in the context of layer-2 protocols for off-chain transactions and the design of advanced cryptographic techniques like verifiable delay functions, proof-of-X systems with special features, and new MPC/SNARK-friendly primitives.

Candidates must hold a Ph.D. degree in cryptography, IT security, or a related field. Preference will be given to candidates with a strong publication record that includes at least one paper at an IACR conference/workshop or one of the top-4 security conferences. Experience in blockchains and/or smart contracts is a plus. Candidates with an interest to conduct research in one of the following areas are particularly encouraged to apply:

  • Applied cryptography (especially design/analysis of symmetric cryptosystems)
  • Cryptofinance and cryptoeconomics
  • Privacy and anonymity on the Internet

The position is initially offered for 1 year, but an extension by 2 years is possible. The University of Luxembourg offers excellent working conditions and a highly competitive salary. Interested candidates are invited to send their application by email to Prof. Alex Biryukov before October 15, 2023 (early submission is encouraged). The application material should contain a cover letter explaining the candidate's research interests, a CV (incl. photo), a list of publications, scans of diploma certificates, and contact details of 3 references.

Closing date for applications:

Contact: Prof. Alex Biryukov (alex.biryukov@uni.lu)

Expand
AIT Austrian Institute of Technology; Vienna, Austria
Job Posting Job Posting
AIT is Austria's largest non-universitary research institute. Its Cyber Security team focuses on various aspects of security, including anomaly detection, cyber ranges, penetration testing, and cryptography. The cryptography group is conducting research in various directions, including secure communication, privacy-enhancing technologies, and long-term and post-quantum security. The group seeks to grow and thus has a vacancy for a researcher in related areas.

Requirements:
  • PhD degree in Computer Science, Cyber Security, or a related field, with a specialization on cryptology
  • Profound knowledge in (public key) cryptography, including, e.g., federated computation, long-term and post-quantum secure communication, privacy-enhancing technologies, real-world crypto, zero-knowledge proofs and zkSNARKs
  • Strong track record with publications at competitive academic conferences or journals (e.g., Crypto, Eurocrypt, Asiacrypt, TCC, PKC, CCS, S&P, USENIX, ESORICS, ...)
  • Experience in the acquisition and execution of national and transnational research projects (e.g., H2020) is a plus
  • Good knowledge of a programming language (e.g., C/C++, Rust, Java, Python) and software development is a plus
  • Very good written and oral English skills; knowledge of German is not a requirement but willingness to learn German is expected
The salary starts from ~61k€/year, depending on experience. The review process will begin immediately and will continue open until the position has been filled.

Please submit your application including CV, cover letter, full list of publications, and contact details of at least 2 references via email to: stephan.krenn[at]ait.ac.at

Closing date for applications:

Contact: Stephan Krenn; stephan.krenn[at]ait.ac.at

Expand
University of Birmingham, UK
Job Posting Job Posting

This is an exciting opportunity to join the University of Birmingham’s Centre for Cyber Security and Privacy on the EPSRC funded project "IOTEE: Securing and analysing trusted execution beyond the CPU", led by Prof Oswald and Prof Ryan.

Trusted Execution Environments (TEEs) allow users to run their software in a secure enclave while assuring the integrity and confidentiality of data and applications. However, cloud computing these days relies heavily on peripherals (connected through PCIe) such as GPUs and FPGAs. In this project, together with researchers at the University of Southampton, we will thoroughly evaluate the security guarantees of the new TEE support in the PCIe standard. This could involve the use of formal modelling, as well as researching various software and hardware attacks and countermeasures against them.

We are looking for a person with a PhD in cyber security/computer science/electrical engineering. The candidate must have experience areas such as embedded security, binary analysis, physical attacks such as side-channel analysis and fault injection, and/or formal modelling. This needs to be evidenced through publications in highly ranked conferences/journals in the field. We also welcome experience in writing system level or low-level code in programming languages such as C, C++, or Rust.

The successful candidate will be employed on a full-time, fixed-term contract up to August 2026. Full-time starting salary is normally in the range £33,348 to £43,155. (Some) remote work is possible, depending on the circumstances. The University provides a range of employee benefits, as well as opportunities for career development and training. The project includes substantial funding for conference travel and equipment.

The post-doc will be working in the Centre for Cyber Security and Privacy, which currently has 14 permanent academics as well as 21 postdocs/PhD students.

The application deadline is 12 Oct 2023. Applications have to be made online at: https://edzz.fa.em3.oraclecloud.com/hcmUI/CandidateExperience/en/sites/CX_6001/job/2681/

Closing date for applications:

Contact: Informal enquiries can be made to David Oswald d.f.oswald@bham.ac.uk.

More information: https://edzz.fa.em3.oraclecloud.com/hcmUI/CandidateExperience/en/sites/CX_6001/job/2681/

Expand
Paderborn University, Department of Computer Science, Paderborn, Germany
Job Posting Job Posting
With the Institute for Photonic Quantum Systems (PhoQS), Paderborn University wants to establish an international research centre in the field of photonic quantum technologies. The aim is to develop new technologies for photon-based quantum applications as well as new theoretical and experimental concepts and research approaches. Ultimately, the focus is on understanding and controlling photonic quantum simulators and quantum computers.

Postdoc (f/m/d) (salary is according to E13 TV-L)

A position with 100 % of the regular working hours is available as of the next possible date. The employment is initially limited to three years and is based on the legal regulations of the Wissen-schaftszeitvertragsgesetzes (WissZeitVG).

Your duties and responsibilities:
• Establishment and expansion of an infrastructure for the integration of quantum computing in high-performance computing.
• Interface of PhoQS to the Paderborn Center for Parallel Computing (PC2) of the Paderborn University
• Supporting users, especially in the natural sciences, in the development and implementation of quantum algorithms
• Optimisation of quantum software platforms for photonic and gate-based quantum computing such as Strawberry Fields, Parceval or Qiskit in collaboration with HPC experts of the PC2
• Organisation and delivery of tutorials and workshops on the use of quantum software plat-forms (basic to advanced)
• Leading a team for the technical integration of quantum computing and high-performance computing

Hiring requirements:
• Completed PhD in computer science, mathematics or physics or comparable qualification
• Solid understanding of many-body quantum mechanics
• Practical experience in high-performance computing and/or in the use of quantum software platforms
• High motivation and willingness for interdisciplinary cooperation between computer science and physics
• Good knowledge of German and English, both written and spoken
• Friendliness, flexibility, ability to work in a team, initiative and willingness to work independently

Closing date for applications:

Contact: Please send your application including a CV (preferably in a single pdf file) using the Ref. No. 6105 by 30th September, 2023 to: bloemer@upb.de

More information: https://cs.uni-paderborn.de/en/cuk

Expand

18 September 2023

Omer Paneth, Rafael Pass
ePrint Report ePrint Report
Non-interactive delegation schemes enable producing succinct proofs (that can be efficiently verified) that a machine $M$ transitions from $c_1$ to $c_2$ in a certain number of deterministic steps. We here consider the problem of efficiently \emph{merging} such proofs: given a proof $\Pi_1$ that $M$ transitions from $c_1$ to $c_2$, and a proof $\Pi_2$ that $M$ transitions from $c_2$ to $c_3$, can these proofs be efficiently merged into a single short proof (of roughly the same size as the original proofs) that $M$ transitions from $c_1$ to $c_3$? To date, the only known constructions of such a mergeable delegation scheme rely on strong non-falsifiable ``knowledge extraction" assumptions. In this work, we present a provably secure construction based on the standard LWE assumption.

As an application of mergeable delegation, we obtain a construction of incrementally verifiable computation (IVC) (with polylogarithmic length proofs) for any (unbounded) polynomial number of steps based on LWE; as far as we know, this is the first such construction based on any falsifiable (as opposed to knowledge-extraction) assumption. The central building block that we rely on, and construct based on LWE, is a rate-1 batch argument (BARG): this is a non-interactive argument for NP that enables proving $k$ NP statements $x_1,..., x_k$ with communication/verifier complexity $m+o(m)$, where $m$ is the length of one witness. Rate-1 BARGs are particularly useful as they can be recursively composed a super-constant number of times.
Expand
Prashant Agrawal, Kabir Tomer, Abhinav Nakarmi, Mahabir Prasad Jhanwar, Subodh Sharma, Subhashis Banerjee
ePrint Report ePrint Report
In this paper we address the problem of recovery from failures without re-running entire elections when elections fail to verify. We consider the setting of $\textit{dual voting}$ protocols, where the cryptographic guarantees of end-to-end verifiable voting (E2E-V) are combined with the simplicity of audit using voter-verified paper records (VVPR). We first consider the design requirements of such a system and then suggest a protocol called $\textit{OpenVoting}$, which identifies a verifiable subset of error-free votes consistent with the VVPRs, and the polling booths corresponding to the votes that fail to verify with possible reasons for the failures.
Expand
Yi Liu, Junzuo Lai, Qi Wang, Xianrui Qin, Anjia Yang, Jian Weng
ePrint Report ePrint Report
Protocols with \emph{publicly verifiable covert (PVC) security} offer high efficiency and an appealing feature: a covert party may deviate from the protocol, but with a probability (\eg $90\%$, referred to as the \emph{deterrence factor}), the honest party can identify this deviation and expose it using a publicly verifiable certificate. These protocols are particularly suitable for practical applications involving reputation-conscious parties.

However, in the cases where misbehavior goes undetected (\eg with a probability of $10\%$), \emph{no security guarantee is provided for the honest party}, potentially resulting in a complete loss of input privacy and output correctness.

In this paper, we tackle this critical problem by presenting a highly effective solution. We introduce and formally define an enhanced notion called \emph{robust PVC security}, such that even if the misbehavior remains undetected, the malicious party can only gain an additional $1$-bit of information about the honest party's input while maintaining the correctness of the output. We propose a novel approach leveraging \emph{dual execution} and \emph{time-lock puzzles} to design a robust PVC-secure two-party protocol with \emph{low overhead} (depending on the deterrence factor). For instance, with a deterrence factor of $90\%$, our robust PVC-secure protocol incurs \emph{only additional ${\sim}10\%$ overhead} compared to the state-of-the-art PVC-secure protocol.

Given the stronger security guarantees with low overhead, our protocol is highly suitable for practical applications of secure two-party computation.
Expand
Zhenzhen Bao, Jinyu Lu, Yiran Yao, Liu Zhang
ePrint Report ePrint Report
In CRYPTO 2019, Gohr showed that well-trained neural networks could perform cryptanalytic distinguishing tasks superior to differential distribution table (DDT)-based distinguishers. This suggests that the differential-neural distinguisher (ND) may use additional information besides pure ciphertext differences. However, the explicit knowledge beyond differential distribution is still unclear. In this work, we provide explicit rules that can be used alongside DDTs to enhance the effectiveness of distinguishers compared to pure DDT-based distinguishers. These rules are based on strong correlations between bit values in right pairs of XOR-differential propagation through addition modulo $2^n$. Interestingly, they can be closely linked to the earlier study of the multi-bit constraints and the recent study of the fixed-key differential probability. In contrast, combining these rules does not improve the NDs' performance. This suggests that these rules or their equivalent form have already been exploited by NDs, highlighting the power of neural networks in cryptanalysis. In addition, we find that to enhance the differential-neural distinguisher's accuracy and the number of rounds, regulating the differential propagation is imperative. Introducing differences into the keys is typically believed to help eliminate differences in encryption states, resulting in stronger differential propagations. However, differential-neural attacks differ from traditional ones as they don't specify output differences or follow a single differential trail. This questions the usefulness of introducing differences in a key in differential-neural attacks and the resistance of Speck against such attacks in the related-key setting. This work shows that the power of differential-neural cryptanalysis in the related-key setting can exceed that in the single-key setting by successfully conducting a 14-round key recovery attack on Speck32/64.
Expand
Théophile Wallez, Jonathan Protzenko, Karthikeyan Bhargavan
ePrint Report ePrint Report
Data formats used for cryptographic inputs have historically been the source of many attacks on cryptographic protocols, but their security guarantees remain poorly studied. One reason is that, due to their low-level nature, formats often fall outside of the security model. Another reason is that studying all of the uses of all of the formats within one protocol is too difficult to do by hand, and requires a comprehensive, automated framework.

We propose a new framework, “Comparse”, that specifically tackles the security analysis of data formats in cryptographic protocols. Comparse forces the protocol analyst to systematically think about data formats, formalize them precisely, and show that they enjoy strong enough properties to guarantee the security of the protocol.

Our methodology is developed in three steps. First, we introduce a high-level cryptographic API that lifts the traditional game-based cryptographic assumptions over bitstrings to work over high-level messages, using formats. This allows us to derive the conditions that secure formats must obey in order for their usage to be secure. Second, equipped with these security criteria, we implement a framework for specifying and verifying secure formats in the F* proof assistant. Our approach is based on format combinators, which enable compositional and modular proofs. In many cases, we relieve the user of having to write those combinators by hand, using compile-time term synthesis via Meta-F*. Finally, we show that our F* implementation can replace the symbolic notion of message formats previously implemented in the DY* protocol analysis framework. Our newer, bit-level precise accounting of formats closes the modeling gap, and allows DY* to reason about concrete messages and identify protocol flaws that it was previously oblivious to.

We evaluate Comparse over several classic and real-world protocols. Our largest case studies use Comparse to formalize and provide security proofs for the formats used in TLS 1.3, as well as upcoming protocols like MLS and Compact TLS 1.3 (cTLS), providing confidence and feedback in the design of these protocols.
Expand
Dario Fiore, Dimitris Kolonelos, Paola de Perthuis
ePrint Report ePrint Report
Registration-Based Encryption (RBE) [Garg et al. TCC'18] is a public-key encryption mechanism in which users generate their own public and secret keys, and register their public keys with a central authority called the key curator. Similarly to Identity-Based Encryption (IBE), in RBE users can encrypt by only knowing the public parameters and the public identity of the recipient. Unlike IBE, though, RBE does not suffer the key escrow problem — one of the main obstacles of IBE's adoption in practice — since the key curator holds no secret.

In this work, we put forward a new methodology to construct RBE schemes that support large users identities (i.e., arbitrary strings). Our main result is the first efficient pairing-based RBE for large identities. Prior to our work, the most efficient RBE is that of [Glaeser et al. ePrint'22] which only supports small identities. The only known RBE schemes with large identities are realized either through expensive non-black-box techniques (ciphertexts of 3.6 TB for 1000 users), or via a specialized lattice-based construction [Döttling et al. Eurocrypt'23] (ciphertexts of 2.4 GB). By unlocking the use of pairings for RBE with large identity space, we enable a further improvement of three orders of magnitude, as our ciphertexts for a system with 1000 users are $1.7$ MB.

The core technique of our approach is a novel use of cuckoo hashing in cryptography that can be of independent interest. We give two main applications. The first one is the aforementioned RBE methodology, where we use cuckoo hashing to compile an RBE with small identities into one for large identities. The second one is a way to convert any vector commitment scheme into a key-value map commitment. For instance, this leads to the first algebraic pairing-based key-value map commitments.
Expand
Min Zhang, Yu Chen, Chuanzhou Yao, Zhichao Wang
ePrint Report ePrint Report
Sigma protocols are one of the most common and efficient zero-knowledge proofs (ZKPs). Over the decades, a large number of efficient Sigma protocols are proposed, yet few works pay attention to the common design principal. In this work, we propose a generic framework of Sigma protocols for algebraic statements from verifiable secret sharing (VSS) schemes. Our framework provides a general and unified approach to understanding Sigma protocols for proving knowledge of openings of algebraic commitments. It not only neatly explains the classic protocols such as Schnorr, Guillou–Quisquater and Okamoto protocols, but also leads to new Sigma protocols that were not previously known.

Furthermore, we show an application of our framework in designing ZKPs for composite statements, which contain both algebraic and non-algebraic statements. We give a generic construction of ZKPs for composite statements by combining Sigma protocols from VSS and ZKPs following MPC-in-the-head paradigm seamlessly via a technique of witness sharing reusing. Our construction has advantages of requiring no trusted setup, being public-coin and having a fast prover runtime. By instantiating our construction using Ligero++ (Bhadauria et al., CCS 2020), we obtain a new ZK protocol for composite statements, which achieves a new balance between running time and the proof size, thus resolving the open problem left by Backes et al. (PKC 2019). Concretely, the proof size is polylogarithmic to the circuit size and the number of public-key operations that both the prover and the verifier require is independent to the circuit size.
Expand
Yongcheng Song, Jiang Zhang, Xinyi Huang, Wei Wu
ePrint Report ePrint Report
In this paper, we initiate the study of the Rank Decoding (RD) problem and LRPC codes with blockwise structures in rank-based cryptosystems. First, we introduce the blockwise errors ($\ell$-errors) where each error consists of $\ell$ blocks of coordinates with disjoint supports, and define the blockwise RD ($\ell$-RD) problem as a natural generalization of the RD problem whose solutions are $\ell$-errors (note that the standard RD problem is actually a special $\ell$-RD problem with $\ell=1$). We adapt the typical attacks on the RD problem to the $\ell$-RD problem, and find that the blockwise structures do not ease the problem too much: the $\ell$-RD problem is still exponentially hard for appropriate choices of $\ell>1$. Second, we introduce blockwise LRPC ($\ell$-LRPC) codes as generalizations of the standard LPRC codes whose parity-check matrices can be divided into $\ell$ sub-matrices with disjoint supports, i.e., the intersection of two subspaces generated by the entries of any two sub-matrices is a null space, and investigate the decoding algorithms for $\ell$-errors. We find that the gain of using $\ell$-errors in decoding capacity outweighs the complexity loss in solving the $\ell$-RD problem, which makes it possible to design more efficient rank-based cryptosystems with flexible choices of parameters.

As an application, we show that the two rank-based cryptosystems submitted to the NIST PQC competition, namely, RQC and ROLLO, can be greatly improved by using the ideal variants of the $\ell$-RD problem and $\ell$-LRPC codes. Concretely, for 128-bit security, our RQC has total public key and ciphertext sizes of 2.5 KB, which is not only about 50% more compact than the original RQC, but also smaller than the NIST Round 4 code-based submissions HQC, BIKE, and Classic McEliece.
Expand
Shichen Wu, Zhiying Song, Puwen Wei, Peng Tang, Quan Yuan
ePrint Report ePrint Report
The proof of stake (PoS) mechanism, which allows stakeholders to issue a block with a probability proportional to their wealth instead of computational power, is believed to be an energy-efficient alternative to the proof of work (PoW). The privacy concern of PoS, however, is more subtle than that of PoW. Recent research has shown that current anonymous PoS (APoS) protocols do not suffice to protect the stakeholder's identity and stake, and the loss of privacy is theoretically inherent for any (deterministic) PoS protocol that provides liveness guarantees. In this paper, we consider the concrete stake privacy of PoS when considering the limitations of attacks in practice. To quantify the concrete stake privacy of PoS, we introduce the notion of $(T, \delta, \epsilon)$-privacy. Our analysis of $(T, \delta, \epsilon)$-privacy on Cardano shows to what extent the stake privacy can be broken in practice, which also implies possible parameters setting of rational $(T, \delta, \epsilon)$-privacy for PoS in the real world. The data analysis of Cardano demonstrates that the $(T, \delta, \epsilon)$-privacy of current APoS is not satisfactory, mainly due to the deterministic leader election predicate in current PoS constructions. Inspired by the differential privacy technique, we propose an efficient non-deterministic leader election predicate, which can be used as a plugin to APoS protocols to protect stakes against frequency analysis. Based on our leader election predicate, we construct anonymous PoS with noise (APoS-N), which can offer better $(T, \delta, \epsilon)$-privacy than state-of-the-art works. Furthermore, we propose a method of proving the basic security properties of PoS in the noise setting, which can minimize the impact of the noise on the security threshold. This method can also be applied to the setting of PoS with variable stakes, which is of independent interest.
Expand
David Balbás, Daniel Collins, Phillip Gajland
ePrint Report ePrint Report
Developing end-to-end encrypted instant messaging solutions for group conversations is an ongoing challenge that has garnered significant attention from practitioners and the cryptographic community alike. Notably, industry-leading messaging apps such as WhatsApp and Signal Messenger have adopted the Sender Keys protocol, where each group member shares their own symmetric encryption key with others. Despite its widespread adoption, Sender Keys has never been formally modelled in the cryptographic literature, raising the following natural question:

What can be proven about the security of the Sender Keys protocol, and how can we practically mitigate its shortcomings?

In addressing this question, we first introduce a novel security model to suit protocols like Sender Keys, deviating from conventional group key agreement-based abstractions. Our framework allows for a natural integration of two-party messaging within group messaging sessions that may be of independent interest. Leveraging this framework, we conduct the first formal analysis of the Sender Keys protocol, and prove it satisfies a weak notion of security. Towards improving security, we propose a series of efficient modifications to Sender Keys without imposing significant performance overhead. We combine these refinements into a new protocol that we call Sender Keys+, which may be of interest both in theory and practice.
Expand
Dmitrii Koshelev
ePrint Report ePrint Report
This article aims to speed up (the precomputation stage of) multi-scalar multiplication (MSM) on ordinary elliptic curves of $j$-invariant $0$ with respect to specific ''independent'' (a.k.a. ''basis'') points. For this purpose, so-called Mordell--Weil lattices (up to rank $8$) with large kissing numbers (up to $240$) are employed. In a nutshell, the new approach consists in obtaining more efficiently a considerable number (up to $240$) of certain elementary linear combinations of the ``independent'' points. By scaling the point (re)generation process, it is thus possible to get a significant performance gain. As usual, the resulting curve points can be then regularly used in the main stage of an MSM algorithm to avoid repeating computations. Seemingly, this is the first usage of lattices with large kissing numbers in cryptography, while such lattices have already found numerous applications in other mathematical domains. Without exaggeration, the article results can strongly affect performance of today's real-world elliptic cryptography, since MSM is a widespread primitive (often the unique bottleneck) in modern protocols. Moreover, the new (re)generation technique is prone to further improvements by considering Mordell--Weil lattices with even greater kissing numbers.
Expand
Ziqi Zhu, Kai Zhang, Junqing Gong, Haifeng Qian
ePrint Report ePrint Report
This paper presents the first generic black-box construction of registered attribute-based encryption (Reg-ABE) via predicate encoding [TCC'14]. The generic scheme is based on $k$-Lin assumption in the prime-order bilinear group and implies the following concrete schemes that improve existing results:

- the first Reg-ABE scheme for span program in the prime-order group; prior work uses composite-order group;

- the first Reg-ABE scheme for zero inner-product predicate from $k$-Lin assumption; prior work relies on generic group model (GGM);

- the first Reg-ABE scheme for arithmetic branching program (ABP) which has not been achieved previously.

Technically, we follow the blueprint of Hohenberger et al. [EUROCRYPT'23] but start from the prime-order dual-system ABE by Chen et al. [EUROCRYPT'15], which transforms a predicate encoding into an ABE. The proof follows the dual-system method in the context of Reg-ABE: we conceptually consider helper keys as secret keys; furthermore, malicious public keys are handled via pairing-based quasi-adaptive non-interactive zero-knowledge argument by Kiltz and Wee [EUROCRYPT'15].
Expand
Charles Gouert, Dimitris Mouris, Nektarios Georgios Tsoutsos
ePrint Report ePrint Report
As cloud computing continues to gain widespread adoption, safeguarding the confidentiality of data entrusted to third-party cloud service providers becomes a critical concern. While traditional encryption methods offer protection for data at rest and in transit, they fall short when it comes to where it matters the most, i.e., during data processing. To address this limitation, we present HELM, a framework for privacy-preserving data processing using homomorphic encryption. HELM automatically transforms arbitrary programs expressed in a Hardware Description Language (HDL), such as Verilog, into equivalent homomorphic circuits, which can then be efficiently evaluated using encrypted inputs. HELM features two modes of encrypted evaluation: a) a gate mode that consists of standard Boolean gates, and b) a lookup table mode which significantly reduces the size of the circuit by combining multiple gates into lookup tables. Finally, HELM introduces a scheduler that enables embarrassingly parallel processing in the encrypted domain. We evaluate HELM with the ISCAS'85 and ISCAS'89 benchmark suites as well as real-world applications such as AES and image filtering. Our results outperform prior works by up to $65\times$.
Expand
Jack Doerner, Yashvanth Kondi, Leah Namisa Rosenbloom
ePrint Report ePrint Report
We investigate the conditions under which straight-line extractable NIZKs in the random oracle model (i.e. without a CRS) permit multiparty realizations that are black-box in the same random oracle. We show that even in the semi-honest setting, any MPC protocol to compute such a NIZK cannot make black-box use of the random oracle or a hash function instantiating it if security against all-but-one corruptions is desired, unless the size of the NIZK grows with the number of parties. This presents a fundamental barrier to constructing efficient protocols to securely distribute the computation of NIZKs (and signatures) based on MPC-in-the-head, PCPs/IOPs, and sigma protocols compiled with transformations due to Fischlin, Pass, or Unruh.

When the adversary is restricted to corrupt only a constant fraction of parties, we give a positive result by means of a tailored construction, which demonstrates that our impossibility does not extend to weaker corruptions models in general.
Expand
Jiaxin Pan, Benedikt Wagner, Runzhi Zeng
ePrint Report ePrint Report
We give a tighter security proof for authenticated key exchange (AKE) protocols that are generically constructed from key encapsulation mechanisms (KEMs) in the quantum random oracle model (QROM). Previous works (Hövelmanns et al., PKC 2020) gave reductions for such a KEM-based AKE protocol in the QROM to the underlying primitives with square-root loss and a security loss in the number of users and total sessions. Our proof is much tighter and does not have square-root loss. Namely, it only loses a factor depending on the number of users, not on the number of sessions.

Our main enabler is a new variant of lossy encryption which we call parameter lossy encryption. In this variant, there are not only lossy public keys but also lossy system parameters. This allows us to embed a computational assumption into the system parameters, and the lossy public keys are statistically close to the normal public keys. Combining with the Fujisaki-Okamoto transformation, we obtain the first tightly IND-CCA secure KEM in the QROM in a multi-user (without corruption), multi-challenge setting.

Finally, we show that a multi-user, multi-challenge KEM implies a square-root-tight and session-tight AKE protocol in the QROM. By implementing the parameter lossy encryption tightly from lattices, we obtain the first square-root-tight and session-tight AKE from lattices in the QROM.
Expand
Nanyang Technological University, Singapore
Job Posting Job Posting

The Symmetric Key and Lightweight Cryptography Lab (SyLLab) at NTU Singapore is looking for candidates for several Research Fellow/Post-Doc (from fresh Post-Docs to Senior Research Fellows, flexible contract duration) as well as PhD student positions on various topics:
  • symmetric-key cryptography (cryptanalysis, design),
  • machine learning,
  • side-channels attacks,
  • fully homomorphic encryption.

Postdoc candidates are expected to have a proven record of publications in top cryptography/security venues.

The positions will be funded by the 5-year National Research Foundation (NRF) Investigatorship grant from Singapore. Salaries are competitive and are determined according to the successful applicant's accomplishments, experience and qualifications. We offer an excellent research environment with a highly international team, with flexible working conditions, budget for conferences/equipment, etc.

Interested applicants should send their detailed CVs and references to Prof. Thomas Peyrin (thomas.peyrin@ntu.edu.sg). The review of applications starts immediately and will continue until positions are filled.

Closing date for applications:

Contact: Thomas Peyrin (thomas.peyrin@ntu.edu.sg)

Expand
◄ Previous Next ►