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26 September 2022
Muhammad Haris Mughees, Ling Ren
Dana Dachman-Soled, Julian Loss, Adam O'Neill, Nikki Sigurdson
Our main result rules this out with respect to algorithms in a natural adaptation of the generic ring model to the preprocessing setting. In particular, in this setting we show the existence of a factoring algorithm (albeit in the random oracle model) with polynomially related parameters, for any setting of RSA parameters.
John Chan, Phillip Rogaway
Wouter Castryck, Thomas Decru, Marc Houben, Frederik Vercauteren
Xiangyu Liu, Shengli Liu, Dawu Gu
Harry Eldridge, Aarushi Goel, Matthew Green, Abhishek Jain, Maximilian Zinkus
In this work we investigate the possibility of realizing one-time programs from a recent and now more commonly available hardware functionality: the counter lockbox. A counter lockbox is a stateful functionality that protects an encryption key under a user-specified password, and enforces a limited number of incorrect guesses. Counter lockboxes have become widely available in consumer devices and cloud platforms.
We show that counter lockboxes can be used to realize one-time programs for general functionalities. We develop a number of techniques to reduce the number of counter lockboxes required for our constructions, that may be of independent interest.
Seonghak Kim, Minji Park, Jaehyung Kim, Taekyung Kim, Chohong Min
CKKS scheme is a levelled homomorphic encryption scheme, consuming one level for each homomorphic multiplication. When the level runs out, a special computational circuit called bootstrapping is required in order to conduct further multiplications. The algorithm proposed by Cheon et al. has been regarded as a standard way to do bootstrapping in the CKKS scheme, and it consists of the following four steps: ModRaise, CoeffToSlot, EvalMod and SlotToCoeff. However, the steps consume a number of levels themselves, and thus optimizing this extra consumption has been a major focus of the series of recent research.
Among the total levels consumed in the bootstrapping steps, about a half of them is spent in CoeffToSlot and SlotToCoeff steps to scale up the real number components of DFT matrices and round them to the nearest integers. Each scale-up factor is very large so that it takes up one level to rescale it down. Scale-up factors can be taken smaller to save levels, but the error of rounding would be transmitted to EvalMod and eventually corrupt the accuracy of bootstrapping.
EvalMod aims to get rid of the superfluous $qI$ term from a plaintext $pt + qI$ resulting from ModRaise, where $q$ is the bottom modulus and $I$ is a polynomial with small integer coefficients. EvalRound is referred to as its opposite, obtaining $qI$. We introduce a novel bootstrapping algorithm consisting of ModRaise, CoeffToSlot, EvalRound and SlotToCoeff, which yields taking smaller scale-up factors without the damage of rounding errors.
Aayush Gupta, Kobi Gurkan
Nullifiers are used as a public commitment to a specific anonymous account, to forbid actions like double spending, or allow a consistent identity between anonymous actions. We identify a new deterministic signature algorithm that both uniquely identifies the keypair, and keeps the account identity secret. In this work, we will define the full DDH-VRF construction, and prove uniqueness, secrecy, and existential unforgeability. We will also demonstrate a proof of concept of the nullifier.
Estuardo Alpirez Bock, Lukasz Chmielewski, Konstantina Miteloudi
Akinori Hosoyamada, Takanori Isobe, Yosuke Todo, Kan Yasuda
Fuyuki Kitagawa, Ryo Nishimaki
In this work, we introduce the notion of secret-key functional encryption (SKFE) with secure key leasing, where a decryption key can be securely leased in the sense of secure software leasing. We also instantiate it with standard cryptographic assumptions. More specifically, our contribution is as follows.
- We define the syntax and security definitions for SKFE with secure key leasing. - We achieve a transformation from standard SKFE into SKFE with secure key leasing without using additional assumptions. Especially, we obtain bounded collusion-resistant SKFE for $\mathsf{P/poly}$ with secure key leasing based on post-quantum one-way functions since we can instantiate bounded collusion-resistant SKFE for $\mathsf{P/poly}$ with the assumption.
Some previous secure software leasing schemes capture only pirate software that runs on an honest evaluation algorithm (on a legitimate platform). However, our secure key leasing notion captures arbitrary attack strategies and does not have such a limitation.
As an additional contribution, we introduce the notion of single-decryptor FE (SDFE), where each functional decryption key is copy-protected. Since copy-protection is a stronger primitive than secure software leasing, this notion can be seen as a stronger cryptographic primitive than FE with secure key leasing. More specifically, our additional contribution is as follows.
- We define the syntax and security definitions for SDFE. - We achieve collusion-resistant single-decryptor PKFE for $\mathsf{P/poly}$ from post-quantum indistinguishability obfuscation and quantum hardness of the learning with errors problem.
Nan Wang, Sid Chi-Kin Chau
Yun Lu, Yu Wei, Malik Magdon-Ismail, Vassilis Zikas
Our work aims to address the above limitation. In a nutshell we devise a methodology for domain experts with limited knowledge of security to estimate the (differential) privacy of an arbitrary mechanism. Our Eureka moment is the utilization of a link---which we prove---between the problems of DP parameter-estimation and Bayes optimal classifiers in machine learning, which we believe can be of independent interest. Our estimator methodology uses this link to achieve two desirable properties: (1) it is black-box, i.e., does not require knowledge of the underlying mechanism, and (2) it has a theoretically-proven accuracy, which depends on the underlying classifier used. This allows domain experts to design mechanisms that they conjecture offer certain (differential) privacy guarantees---but maybe cannot prove it---and apply our method to confirm (or disprove) their conjecture.
More concretely, we first prove a new impossibility result, stating that for the classical DP notion there is no black-box poly-time estimator of $(\epsilon,\delta)$-DP. This motivates a natural relaxation of DP, which we term relative DP. Relative DP preserves the desirable properties of DP---composition, robustness to post processing, and robustness to the discovery disclosure of new data---and applies in most practical settings where privacy is desired. We then devise a black-box poly-time $(\epsilon,\delta)$-relative DP estimator---the first to support mechanisms with large output spaces while having tight accuracy bounds. As a result of independent interest, we apply this theory to develop the first approximate estimator for the standard, i.e., non-relative, definition of Distributional Differential Privacy (DDP) -- aka noiseless privacy.
To demonstrate both our theory and its potential for practical impact, we devised a proof-of-concept implementation of our estimator and benchmarked it against well-studied DP mechanisms. We show that in reasonable execution time our estimator can reproduce the tight, analytically computed $\epsilon, \delta$ trade-off of Laplacian and Gaussian mechanisms---to our knowledge, the first black box estimator to do so, and for the Sparse Vector Technique, our outputs are comparable to that of a more specialized state-of-the-art $(\epsilon, \delta)$-DP estimator.
Julien Devevey, Omar Fawzi, Alain Passelègue, Damien Stehlé
Yuval Ishai, Arpita Patra, Sikhar Patranabis, Divya Ravi, Akshayaram Srinivasan
-- For a natural class of protocols, specifically, those with a universal output decoder, we show that the size of the TP must necessarily be exponential in the number of parties. This result holds irrespective of the computational assumptions used in the protocol. The class of protocols to which our lower bound applies is broad enough to capture prior results in the area, implying that the prior techniques necessitate the use of an exponential-sized TP. We additionally rule out the possibility of achieving information-theoretic full security (without the restriction of using a universal output decoder) using a “small” TP in the plain model (i.e., without any setup).
-- In order to get around the above negative result, we consider protocols without a universal output decoder. The main positive result in our work is a construction of such a fully-secure MPC protocol assuming the existence of a succinct Functional Encryption scheme. We also give evidence that such an assumption is likely to be necessary for fully-secure MPC in certain restricted settings.
-- Finally, we explore the possibility of achieving full-security with a semi-honest TP that could collude with other malicious parties (which form a dishonest majority). In this setting, we show that even fairness is impossible to achieve regardless of the “small TP” requirement.
Trevor Yap, Adrien Benamira, Shivam Bhasin, Thomas Peyrin
University of St.Gallen, Switzerland
The student is expected to work on topics that include security and privacy issues in biometric authentication. More precisely, the student will be working on investigating efficient and privacy-preserving authentication that provides: i) provable security guarantees, and ii) rigorous privacy guarantees.
Key Responsibilities:
- Perform exciting and challenging research in the domain of information security and cryptography.
- Support and assist in teaching computer security and cryptography courses.
- The PhD student is expected to have a MSc degree or equivalent, and strong background in cryptography, network security and mathematics.
- Experience in one or more domains such as cryptography, design of protocols, secure multi-party computation and differential privacy is beneficial.
- Excellent programming skills.
- Excellent written and verbal communication skills in English
Please apply by 15th October 2022.
Closing date for applications:
Contact:
Eriane Breu, eriane.breu@unisg.ch (Administrative matters)
Prof. Katerina Mitrokotsa, katerina.mitrokotsa@unisg.ch (Research related questions)
IHUB NTIHAC FOUNDATION, IIT Kanpur, Kanpur-208016, U.P., INDIA
Closing date for applications:
Contact: Submissions are accepted only through an email to Professor Manindra Agrawal (manindra@cse.iitk.ac.in), Director, C3iHub, IIT Kanpur.
More information: https://www.linkedin.com/jobs/view/cryptanalyst-at-c3i-hub-3243352185/?originalSubdomain=in
24 September 2022
Okinawa Institute of Science and Technology Graduate University
The Okinawa Institute of Science and Technology (OIST) is a dynamic and growing graduate university in Japan. We are inviting applications for tenure-track and tenured faculty positions in the areas of Quantum Information Science and Quantum Technology, Applied Cryptography and Cyber Security.
Successful candidates will have an opportunity to join our vibrant, collaborative, interdisciplinary research community. They will:
- establish and run an active independent Research Unit with generous internal funding, including funds for several research staff;
- supervise and mentor PhD students, develop and teach graduate courses, and actively contribute to university services;
- receive access to cutting-edge core research facilities, including imaging, sequencing, instrumentation, nanofabrication, and high-performance computing, with dedicated support staff;
- enjoy a competitive remuneration package with additional benefits, such as housing allowance.
OIST is actively seeking applications from women and underrepresented groups.
Deadline for applications: 30 Nov 2022 at 12:59 PM JST.
About OIST
OIST is a dynamic and growing graduate university in Japan, offering a world-class research environment and opportunities for cross-disciplinary research. We have no departments, and we currently have 89 Research Units. English is the official language of the university, and the research community is fully international, with more than 50 countries represented. The campus is located on 85 hectares of protected forestland overlooking beautiful shorelines and coral reefs in subtropical Okinawa, Japan. To learn more about OIST, visit www.oist.jp
Closing date for applications:
Contact: Dr. Milind Purohit, Dean of Faculty Affairs (faculty-recruiting at oist.jp)
More information: https://groups.oist.jp/facultypositions
National University of Singapore
Closing date for applications:
Contact: Faculty search committee chair Prof. Joxan Jaffar (joxan@comp.nus.edu.sg) Head, Prof. Lee Wee Sun (leews@comp.nus.edu.sg)
More information: https://www.comp.nus.edu.sg/images/resources/content/dept-compscience/20210923_DCS_Poster_v4.pdf