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15 August 2023
Nikolaos Makriyannis, Oren Yomtov
We present four novel key-extraction attacks on popular MPC signing protocols showing how a single corrupted party may extract the secret in full during the MPC signing process. Our attacks are highly practical (the practicality of the attack depends on the number of signature-generation ceremonies the attacker participates in before extracting the key). Namely, we show key-extraction attacks against different threshold-ECDSA protocols/implementations requiring $10^6$, $256$, $16$, and *one signature*, respectively. In addition, we provide proof-of-concept code that implements our attacks.
Ashwin Jha, Mridul Nandi, Abishanka Saha
Tarek Galal, Anja Lehmann
In our work, we propose and formally model a privacy-preserving variant of such an outsourced validation service. Therein the validator learns the attributes it is supposed to verify, but not the users identity. Still, the validator's assertion is blindly bound to the user's identity to ensure the desired user-binding. We analyze the EU specification in our model and show that it only meets a subset of those goals. Our analysis further shows that the EU protocol is unnecessarily complex and can be significantly simplified while maintaining the same (weak) level of security. Finally, we propose a new construction for privacy-preserving certificate validation that provably satisfies all desired goals.
Fangan Yssouf Dosso, Alexandre Berzati, Nadia El Mrabet, Julien Proy
Shuai Han, Shengli Liu, Zhedong Wang, Dawu Gu
To obtain our schemes from LWE, we propose new frameworks for constructing SIG and PKE with a core technical tool named probabilistic quasi-adaptive hash proof system (pr-QA-HPS). As a new variant of HPS, our pr-QA-HPS provides probabilistic public and private evaluation modes that may toss coins. This is in stark contrast to the traditional HPS [Cramer and Shoup, Eurocrypt 2002] and existing variants like approximate HPS [Katz and Vaikuntanathan, Asiacrypt 2009], whose public and private evaluations are deterministic in their inputs. Moreover, we formalize a new property called evaluation indistinguishability by requiring statistical indistinguishability of the two probabilistic evaluation modes, even in the presence of the secret key. The evaluation indistinguishability, as well as other nice properties resulting from the probabilistic features of pr-QA-HPS, are crucial for the multi-user security proof of our frameworks under adaptive corruptions.
As for instantiations, we construct pr-QA-HPS from the LWE assumption and prove its properties with almost tight reductions, which admit almost tightly secure LWE-based SIG and PKE schemes under our frameworks. Along the way, we also provide new almost-tight reductions from LWE to multi-secret LWE, which may be of independent interest.
Francesco Sica
A further idea of parametrizing solutions of the norm equation will show that these conditions can be fulfilled under the same heuristics of these previous works. Our contribution is a theoretical one. It doesn't invalidate the attack, which works as well in practice, but gives a correct mathematical justification for it.
We also simplify the argument of Theorem 3 in [dQuehen-etal21] to show that the requirement that $m$ be small is unnecessary.
Elizabeth Crites, Chelsea Komlo, Mary Maller, Stefano Tessaro, Chenzhi Zhu
Kosei Sakamoto, Ryoma Ito, Takanori Isobe
Huayi Qi, Minghui Xu, Dongxiao Yu, Xiuzhen Cheng
Yuval Ishai, Mahimna Kelkar, Varun Narayanan, Liav Zafar
Different kinds of correlations can vary greatly in terms of usefulness and ease of generation. While there has been major progress on efficiently generating oblivious transfer (OT) correlations, other useful kinds of correlations are much more costly to generate. Thus, it is highly desirable to develop efficient techniques for securely converting copies of a given source correlation into copies of a given target correlation, especially when the former are cheaper to generate than the latter.
In this work, we initiate a systematic study of such conversions that only involve a single uni-directional message. We refer to such a conversion as a one-message secure reduction (OMSR). Recent works (Agarwal et al, Eurocrypt 2022; Khorasgani et al, Eurocrypt 2022) studied a similar problem when no communication is allowed; this setting is quite restrictive, however, with few non-trivial conversions being feasible. The OMSR setting substantially expands the scope of feasible results, allowing for direct applications to existing MPC protocols.
We obtain the following positive and negative results. - OMSR constructions. We present a general rejection-sampling based technique for OMSR with OT source correlations. We apply it to substantially improve in the communication complexity of optimized protocols for distributed symmetric cryptography (Dinur et al., Crypto 2021).
- OMSR lower bounds. We develop general techniques for proving lower bounds on the communication complexity of OMSR, matching our positive results up to small constant factors.
Kirill Vedenev, Yury Kosolapov
Johannes Mono, Kamil Kluczniak, Tim Güneysu
More specifically, we significantly simplify the bootstrapping idea by Carpov, Izabach`ene, and Mollimard [1] for Boolean-based FHE schemes such as FHEW or TFHE, making the concept usable in practice. Based on our simplifications, we provide an easy-to-use interface for amortized bootstrapping implementing our improvements in the open-source library FHE-Deck and provide new parameter sets for multi-bit encryptions with state-of-the-art security.
We build a toolset that compiles high-level code such as C++ to code that executes operations on encrypted data. For this toolset, we propose the first non-trivial FHE-specific optimizations in synthesizing privacy-preserving circuits from high-level code, namely look-up table (LUT) grouping and adder substitution. Using LUT grouping, we reduce the number of bootstrapping required by almost 35 % on average, while for adder substitution, we reduce the number of required bootstrapping by up to 80 % for certain use cases. Overall, the execution time is up to 3.8× faster using our optimizations compared to previous state-of-the-art circuit synthesis.
Zhipeng Wang, Marko Cirkovic, Duc V. Le, William Knottenbelt, Christian Cachin
In this work, we introduce the Merkle Pyramid Builder approach, to incrementally build the Merkle tree in an on-chain mixer and update the tree per batch of deposits, which can therefore decrease the overall cost of using the mixer. Our evaluation results highlight the effectiveness of this approach, showcasing a significant reduction of up to $7\times$ in the amortized cost of depositing compared to state-of-the-art on-chain mixers. Importantly, these improvements are achieved without compromising users' privacy. Furthermore, we propose the utilization of verifiable computations to shift the responsibility of Merkle tree updates from on-chain smart contracts to off-chain clients, which can further reduce deposit costs. Additionally, our analysis demonstrates that our designs ensure fairness by distributing Merkle tree update costs among clients over time.
Mario Mastriani
14 August 2023
Nominations are due by October 1st, 2023.
Information about nomination is available at https://iacr.org/elections/2023/announcement.html.
Department of Information Security and Communication Technology at NTNU in Trondheim, Norway
The NIST Post Quantum Cryptography Standardization is expected to end in 2024, and post-quantum cryptography will be required to secure all sensitive information in the years to come shortly after, e.g., in protocols such as TLS, SSH, FIDO and other systems. Additionally, NIST have announces a new call for quantum secure digital signature algorithms.
This project aims to conduct research on lightweight post-quantum protocols and primitives, including symmetric key primitives, and improve upon the frameworks used today regarding communication size, computation complexity and secure and efficient implementation of long-term security cryptographic primitives.
The postdoc will be part of the NTNU Applied Cryptology Lab, a multidisciplinary research group consisting of members from the Department of Information Security and Communication Technology and the Department of Mathematical Sciences at NTNU.
A list of possible, but not limited to, post-quantum cryptography research topics for the postdoctoral position are:
Your hosts will be Professor Danilo Gligoroski, Professor Stig Frode Mjølsnes, and/or Associate Professor Tjerand Silde.
Closing date for applications:
Contact: Associate Professor Tjerand Silde (tjerand.silde@ntnu.no)
More information: https://www.jobbnorge.no/en/available-jobs/job/248833/postdoctoral-fellow-in-lightweight-post-quantum-cryptography
IT University of Copenhagen (ITU)
We are hiring a PhD student to work on a project investigating privacy preserving yet auditable cryptographic protocols for decentralized applications. The student will be working in one (or more) of the following areas: secure multiparty computation, zero knowledge, anonymous credentials, blockchain consensus, cryptocurrencies, differential privacy.
The ideal candidate should have a background in computer science or mathematics, with a focus on complexity theory, number theory, algebra and probability theory. Previous research experience in security and cryptography (specially in cryptographic protocols) is most welcome. Moreover, the candidate should be motivated and enthusiastic about theoretical research in cryptography.
ITU is located in beautiful Copenhagen, which is well connected by flight to many locations. We offer a competitive salary following Danish standards as well as travel funding for scientific visits and events. As a resident in Denmark, the student will also have access to the excellent public education and health systems.
Candidates are welcome to contact Bernardo David by email for any questions. Notice, however, that all applications must be submitted via the official URL.
Closing date for applications:
Contact: Bernardo David (beda@itu.dk)
More information: https://candidate.hr-manager.net/ApplicationInit.aspx?cid=119&ProjectId=181605&DepartmentId=3439&MediaId=5
IDEAS NCBR
Closing date for applications:
Contact: Marta Krzyżycka
More information: https://ideas-ncbr.softgarden.io/job/34064687?l=pl
Quantum-Safe Migration Center, Chelpis Quantum Tech, Taipei, Taiwan
Chelpis Quantum Tech was established in 2017, drawing its team from the Fast Cryptography Laboratory at National Taiwan University. Our primary focus has been research and development of post-quantum cryptographic systems and the creation of related cryptographic applications.
QSMC is looking for an applied post-quantum cryptography researcher to join our research team in Taipei, Taiwan.
We currently have three research focus areas and candidates should be experienced in at least one:
- PQC Hardware
- Formally-verified PQC Software
- New PQC primitives (in particular, candidates of the recent NIST PQC digital signature competition)
- Work on research projects and publish at top-tier cryptography and security conferences
- Collaborate with researchers in Taiwan and internationally
- Present research on international workshops and conferences
- Contribute to standardization efforts such as NIST PQC
- Consult Chelpis' other teams in all aspects of post-quantum cryptography
Closing date for applications:
Contact:
- Ming Chih (my.chih@chelpis.com)
- Matthias Kannwischer (matthias@chelpis.com)
More information: https://www.qsmc.org/
National Research Council Canada
Closing date for applications:
Contact: https://recruitment-recrutement.nrc-cnrc.gc.ca/job/Various-Locations-Applied-Cryptography-Research-Officer-ON/572782617/
More information: https://recruitment-recrutement.nrc-cnrc.gc.ca/job/Various-Locations-Applied-Cryptography-Research-Officer-ON/572782617/