IACR News
Here you can see all recent updates to the IACR webpage. These updates are also available:
02 March 2021
Ling Sun, Wei Wang, Meiqin Wang
Ryoma Ito, Rentaro Shiba, Kosei Sakamoto, Fukang Liu, Takanori Isobe
Bernardo David, Bernardo Magri, Christian Matt, Jesper Buus Nielsen, Daniel Tschudi
In this vein, we propose a novel approach that leverages the sharding safety-liveness dichotomy. We separate the liveness and safety in shard consensus, allowing us to dynamically tune shard parameters to achieve essentially optimal efficiency for the current corruption ratio of the system. We start by sampling a relatively small shard (possibly with a small honesty ratio), and we carefully trade-off safety for liveness in the consensus mechanism to tolerate small honesty without losing safety. However, for a shard to be live, a higher honesty ratio is required in the worst case. To detect liveness failures, we use a so-called control chain that is always live and safe. Shards that are detected to be not live are resampled with increased shard size and liveness tolerance until they are live, ensuring that all shards are always safe and run with optimal efficiency. As a concrete example, considering a population of 10K parties, 30% corruption and 60-bit security, our design permits shards of size 200 parties in contrast to 6K parties in previous designs.
Moreover, in this highly concurrent execution setting, it is paramount to guarantee that both the sharded ledger protocol and its sub protocols (e.g., the shards) are secure under composition. To prove the security of our approach, we present ideal functionalities capturing a sharded ledger as well as ideal functionalities capturing the control chain and individual shard consensus, which needs adjustable liveness. We further formalize our protocols and prove that they securely realize the sharded ledger functionality in the UC framework.
Craig Gentry, Shai Halevi, Hugo Krawczyk, Bernardo Magri, Jesper Buus Nielsen, Tal Rabin, Sophia Yakoubov
We refer to this as the You-Only-Speak-Once (YOSO) property, and initiate the formal study of it within a new model that we call the YOSO model. Our model is centered around the notion of roles, which are stateless parties that can only send a single message. Crucially, our modelling separates the protocol design, that only uses roles, from the role-assignment mechanism, that assigns roles to actual physical entities. This separation enables studying these two aspects separately, and our YOSO model in this work only deals with the protocol-design aspect.
We describe several techniques for achieving YOSO MPC; both computational and information theoretic. Our protocols are synchronous and provide guaranteed output delivery (which is important for application domains such as blockchains), assuming honest majority of roles in every time step. We describe a practically efficient computationally-secure protocol, as well as a proof-of-concept information theoretically secure protocol.
George Marinakis
Modern cryptographic algorithms have an enormous key diversity, so if we want to test their strength for all the keys, it will take practically an infinite time. To avoid this, we use the sampling method, in which we examine a much smaller number of keys n and then we make estimation for the total key population N with a predetermined sampling error. For the generation of the n cipher outputs (samples) with the n corresponding keys, the critical questions are how many samples we will test and how large must be the size of each sample. The general rule is that, the sampling error is reduced as we increase the number of the samples. But since the tests must be executed in an acceptable time, we must compromise the above rule with some additional factors, such as the type of the cryptographic cipher, the kind and the size of the plain information and of course the available computer power. In this study we examine the interrelations of all the above factors, and we propose applicable solutions.
Keywords: Cryptography, Data encryption, Communication security, Computer security, Data security, Information security.
Esch-sur-Alzette, Luxembourg, 21 August - 16 August 2021
Submission deadline: 25 April 2021
Virtual event, Anywhere on Earth, 19 July - 20 July 2021
Virtual event, Anywhere on Earth, 4 October - 6 October 2021
Submission deadline: 10 May 2021
Notification: 30 June 2021
Naval Postgraduate School, Monterey, California, USA
Closing date for applications:
Contact: Geoff Xie, Search Committee Chair
More information: https://main.hercjobs.org/jobs/14480892
University of Bern
Postdoc positions are available in the Cryptology and Data Security research group at the Institute of Computer Science, University of Bern, led by Christian Cachin.
Our research addresses all aspects of security in distributed systems, especially cryptographic protocols, consistency, consensus, and cloud-computing security. We are particularly interested in blockchains, distributed ledger technology, cryptocurrencies, and their security and economics.
Candidates should have a strong background in computer science. They should like conceptual, rigorous thinking for working theoretically, or be interested in building innovative systems for working practically. Demonstrated expertise in cryptography, distributed computing, or blockchain technology is a plus. Applicants should hold a Ph.D., with contributions in the relevant research topics.
Positions are available starting immediately and come with a competitive salary. The selection process runs until suitable candidates have been found. The University of Bern conducts excellent research and lives up its vision that “Knowledge generates value”. The city of Bern lies in the center of Switzerland and offers some of the highest quality of life worldwide.
If you are interested, please apply be sending email with one single PDF file and subject line set to Application for Postdoc addressed directly to Prof. Christian Cachin at crypto (at) inf.unibe.ch.
Closing date for applications:
Contact: For more information, please contact Christian Cachin (https://crypto.unibe.ch/cc/).
More information: https://crypto.unibe.ch/jobs/
Hasso-Plattner-Institute, University of Potsdam (Potsdam/Berlin, Germany)
The Cybersecurity - Identity Management group at the Hasso-Plattner-Institute (HPI), University of Potsdam is looking for a motivated PhD student or Postdoc in the area of cryptography and privacy.
Your future tasks- Development and analysis of provably secure cryptographic protocols for real-world problems. Topics of interest include (but are not limited to):
- Privacy-enhancing technologies
- Password-based cryptography
- Foundations and solutions for real-world cryptography
- Publish and present results at top-tier international conferences
- Participate in teaching activities
- Master’s degree (or PhD for postdoctoral position) in Computer Science, Mathematics, or a related area by the time of appointment
- Profound knowledge in the areas of cryptography and IT security (for postdoctoral candidates proven in the form of publications in these areas)
- Excellent English language skills
We look forward to your application including a CV and motivation letter. Applications for the PhD position should also include a list of attended Master courses and grades, whereas applications for the Postdoc position should include contact information for two references. Please submit your application documents in a single PDF file via email.
Closing date for applications:
Contact: Anja Lehmann (anja.lehmann [at] hpi.de)
More information: https://hpi.de/lehmann/home.html
University of Luxembourg
The APSIA group led by Peter Y.A. Ryan is offering a post-doc position in a research project on future-proofing privacy of secure electronic voting led by Johannes Müller. The position is fully funded for 2 years and may be extended up to 5 years.
Your RoleThe candidate will shape research directions and produce results in one or more of the following topics:
- Protocol security
- Post-quantum cryptography
- Information-theoretic security
- Implementation of security protocols
- A PhD degree in Computer Science, Applied Mathematics or a related field
- Competitive research record in (applied) cryptography or protocol security
- Experience with secure e-voting or protocol security proofs is a plus
- Experience with post-quantum cryptography or information-theoretic security is a plus
- Experience with implementation of security protocols is a plus
Closing date for applications:
Contact: Johannes Müller
More information: https://recruitment.uni.lu/en/details.html?id=QMUFK026203F3VBQB7V7VV4S8&nPostingID=57676&nPostingTargetID=80219&mask=karriereseiten&lg=UK
DTU Denmark
Closing date for applications:
Contact: Professor Lars Ramkilde Knudsen, lrkn@dtu.dk. Please use the above link when applying for the position. Applications sent by email will not be considered.
More information: https://www.dtu.dk/english/about/job-and-career/vacant-positions/job?id=fa3c2175-2322-42c9-b822-167147cf4e70
01 March 2021
Mahimna Kelkar, Phi Hung Le, Mariana Raykova, Karn Seth
Our construction relies on new protocols for secure fixed-point exponentiation and correlated matrix multiplications. Our secure exponentiation construction avoids expensive bit decomposition and achieves orders of magnitude improvement in both online and offline costs over state of the art works. As a result, the dominant cost for our secure Poisson regression are matrix multiplications with one fixed matrix. We introduce a new technique, called correlated Beaver triples, which enables many such multiplications at the cost of roughly one matrix multiplication. This further brings down the cost of secure Poisson regression.
We implement our constructions and show their extreme efficiency. Our secure exponentiation for 20-bit fractional precision takes less than 0.07ms. One iteration of Poisson regression on a dataset with 10,000 samples with 1000 binary features, requires 16.47s offline time, 23.73s online computation and 7.279MB communication. For several real datasets this translates into training that takes seconds and only a couple of MB communication.
Daniele Cozzo, Nigel P. Smart, Younes Talibi Alaoui
Ádám Ficsór, Yuval Kogman, Lucas Ontivero, István András Seres
Tsz Hon Yuen, Handong Cui, Xiang Xie
When applied to two-party ECDSA, we can lower the bandwidth of the key generation algorithm by 47%, and the running time for the key generation and signing algorithms are boosted by about 35% and 104% respectively. When applied to threshold ECDSA, our first scheme is more optimized for the key generation algorithm (about 70% lower bandwidth and 70% faster computation in key generation, at a cost of 20% larger bandwidth in signing), while our second scheme has an all-rounded performance improvement (about 60% lower bandwidth, 27% faster computation in key generation without additional cost in signing).
Andrey Kim, Yuriy Polyakov, Vincent Zucca
More precisely, we propose an improved variant of BFV where the encryption operation is modified to significantly reduce the noise growth, which makes the BFV noise growth somewhat better than for BGV (in contrast to prior results showing that BGV has smaller noise growth for larger plaintext moduli). We also modify the homomorphic multiplication procedure, which is the main bottleneck in BFV, to reduce its algorithmic complexity. Our work introduces several other novel optimizations, including lazy scaling in BFV homomorphic multiplication and an improved BFV decryption procedure in the Residue Number System (RNS) representation. We also develop a usable variant of BGV as a more efficient alternative to BFV for common practical scenarios.
We implement our improved variants of BFV and BGV in PALISADE and evaluate their experimental performance for several benchmark computations. Our results suggest that BGV is faster for intermediate and large plaintext moduli, which are often used in practical scenarios with ciphertext packing, while BFV is faster for small plaintext moduli.
Tjerand Silde, Martin Strand
Additional contributions include expanded definitions and a description of how anonymous tokens can improve the privacy in dp3t-like digital contact tracing applications. We also show how to create efficient and conceptually simple tokens with public metadata and public verifiability from pairings.
Martin R. Albrecht, Russell W. F. Lai
By constructing families of $(s,t)$-subtractive sets $S$ of size $n = $ poly over cyclotomic rings $\mathcal{R} = \mathbb{Z}[\zeta_{p^\ell}]$ for prime $p$, we construct Schnorr-like lattice-based proofs of knowledge for the SIS relation ${A} \cdot \vec{x} = s \cdot \vec{y} \bmod q$ with $O(1/n)$ knowledge error, and $s = 1$ in case $p = $ poly. Our technique slots naturally into the lattice Bulletproof framework from Crypto'20, producing lattice-based succinct arguments for NP with better parameters.
We then give matching impossibility results constraining $n$ relative to $s$, which suggest that our Bulletproof-compatible protocols are optimal unless fundamentally new techniques are discovered. Noting that the knowledge error of lattice Bulletproofs is \(\Omega(\log k/n)\) for witnesses in \(\mathcal{R}^k\) and subtractive set size \(n\), our result represents a barrier to practically efficient lattice-based succinct arguments in the Bulletproof framework.
Beyond these main results, the concept of $(s,t)$-subtractive sets bridges group-based threshold cryptography to lattice settings, which we demonstrate by relating it to distributed pseudorandom functions.