Blockchain Papers

Farzaliyev, Valeh

Electronic voting solutions are built on complex cryptographic tools to guarantee security and fairness. Currently, those tools are based on hardness assumptions of discrete logarithm, factorization and other classical problems. While they are hard to break in classical computers, there are efficient quantum algorithms to solve using quantum computers of the near future. Thus, there is a need to develop voting protocols that are resistant to quantum attacks. Verifiable shuffling based voting systems are a popular use-case of mix-networks first proposed by Chaum four decades ago [Cha81] as a general tool for building anonymous communication systems. A decade later the quantum threat was known and since then only a few studies searched for post-quantum secure mix-nets. Recently, Costa, Martinez and Morillo introduced new arguments of shuffle for RLWE ciphertexts and how to prove the correctness of the shuffling without leaking sensitive info [CMM17]. In this thesis, we provide exact, shorter proof of Costa et al.’s lattice-based shuffling arguments. As a result, we obtain a practical non-interactive zero-knowledge proof having a runtime of 1 second per voter.

Gil Segev, Ido Shahaf

The hardness of highly-structured computational problems gives rise to a variety of public-key primitives. On one hand, the structure exhibited by such problems underlies the basic functionality of public-key primitives, but on the other hand it may endanger public-key cryptography in its entirety via potential algorithmic advances. This subtle interplay initiated a fundamental line of research on whether structure is inherently necessary for cryptography, starting with Rudich’s early work (PhD Thesis '88) and recently leading to that of Bitansky, Degwekar and Vaikuntanathan (CRYPTO '17). Identifying the structure of computational problems with their corresponding complexity classes, Bitansky et al. proved that a variety of public-key primitives (e.g., public-key encryption, oblivious transfer and even functional encryption) cannot be used in a black-box manner to construct either any hard language that has NP-verifiers both for the language itself and for its complement, or any hard language (and even promise problem) that has a statistical zero-knowledge proof system - corresponding to hardness in the structured classes NP ∩ coNP or SZK, respectively, from a black-box perspective. In this work we prove that the same variety of public-key primitives do not inherently require even very little structure in a black-box manner: We prove that they do not imply any hard language that has multi-prover interactive proof systems both for the language and for its complement - corresponding to hardness in the class MIP ∩ coMIP from a black-box perspective. Conceptually, given that MIP = NEXP, our result rules out languages with very little structure. Already the cases of languages that have IP or AM proof systems both for the language itself and for its complement, which we rule out as immediate corollaries, lead to intriguing insights. For the case of IP, where our result can be circumvented using non-black-box techniques, we reveal a gap between black-box and non-black-box techniques. For the case of AM, where circumventing our result via non-black-box techniques would be a major development, we both strengthen and unify the proofs of Bitansky et al. for languages that have NP-verifiers both for the language itself and for its complement and for languages that have a statistical zero-knowledge proof system.

Nïkhil Gupta, Chandan Saha, Bhargav Thankey

We show an Ω̃(n^2.5) lower bound for general depth four arithmetic circuits computing an explicit n-variate degree-Θ(n) multilinear polynomial over any field of characteristic zero. To our knowledge, and as stated in the survey [Amir Shpilka and Amir Yehudayoff, 2010], no super-quadratic lower bound was known for depth four circuits over fields of characteristic ≠ 2 before this work. The previous best lower bound is Ω̃(n^1.5) [Abhijat Sharma, 2017], which is a slight quantitative improvement over the roughly Ω(n^1.33) bound obtained by invoking the super-linear lower bound for constant depth circuits in [Ran Raz, 2010; Victor Shoup and Roman Smolensky, 1997]. Our lower bound proof follows the approach of the almost cubic lower bound for depth three circuits in [Neeraj Kayal et al., 2016] by replacing the shifted partials measure with a suitable variant of the projected shifted partials measure, but it differs from [Neeraj Kayal et al., 2016]’s proof at a crucial step - namely, the way "heavy" product gates are handled. Loosely speaking, a heavy product gate has a relatively high fan-in. Product gates of a depth three circuit compute products of affine forms, and so, it is easy to prune Θ(n) many heavy product gates by projecting the circuit to a low-dimensional affine subspace [Neeraj Kayal et al., 2016; Amir Shpilka and Avi Wigderson, 2001]. However, in a depth four circuit, the second (from the top) layer of product gates compute products of polynomials having arbitrary degree, and hence it was not clear how to prune such heavy product gates from the circuit. We show that heavy product gates can also be eliminated from a depth four circuit by projecting the circuit to a low-dimensional affine subspace, unless the heavy gates together account for Ω̃(n^2.5) size. This part of our argument is inspired by a well-known greedy approximation algorithm for the weighted set-cover problem.

Tian Qiu, Lin Hou, Dongdai Lin

No abstract is available for this record.

Luis Luna, Erick Asiain, R. Garrido

This paper describes preliminary results on a Proportional plus Adaptive Disturbance Observer (P+ADOB) controller applied to velocity regulation tasks in a servo system. Adaptation law is obtained to estimate the servo system input gain, which is subsequently employed in the design of a Disturbance Observer. Compared with previous approaches, this feature relaxes the assumption on exact knowledge on the input gain, and only upper and lower bounds on this term are assumed known. A stability proof assuming constant disturbances allows concluding that the estimate of the input gain is bounded, and the velocity tracking error converges to zero. Real-time experiments illustrate the performance of the proposed controller.

Kazuhiko Shibuya

No abstract is available for this record.

Nir Bitansky, Arka Rai Choudhuri

Randomness is typically thought to be essential for zero knowledge protocols. Following this intuition, Goldreich and Oren (Journal of Cryptology 94) proved that auxiliary-input zero knowledge cannot be achieved with a deterministic prover. On the other hand, positive results are only known in the honest-verifier setting, or when the prover is given at least a restricted source of entropy. We prove that removing (or just bounding) the verifier’s auxiliary input, deterministic-prover zero knowledge becomes feasible: Assuming non-interactive witness-indistinguishable proofs and subexponential indistinguishability obfuscation and one-way functions, we construct deterministic-prover zero-knowledge arguments for Open image in new window against verifiers with bounded non-uniform auxiliary input. Assuming also keyless hash functions that are collision-resistant against bounded-auxiliary-input quasipolynomial-time attackers, we construct similar arguments for all of Open image in new window .

Max Hoffmann, Michael Klooß, Markus Raiber, Andy Rupp

Abstract Black-box accumulation (BBA) is a building block which enables a privacy-preserving implementation of point collection and redemption, a functionality required in a variety of user-centric applications including loyalty programs, incentive systems, and mobile payments. By definition, BBA+ schemes (Hartung et al. CCS ‘17) offer strong privacy and security guarantees, such as unlinkability of transactions and correctness of the balance flows of all (even malicious) users. Unfortunately, the instantiation of BBA+ presented at CCS ‘17 is, on modern smartphones, just fast enough for comfortable use. It is too slow for wearables, let alone smart-cards. Moreover, it lacks a crucial property: For the sake of efficiency, the user’s balance is presented in the clear when points are deducted. This may allow to track owners by just observing revealed balances, even though privacy is otherwise guaranteed. The authors intentionally forgo the use of costly range proofs, which would remedy this problem. We present an instantiation of BBA+ with some extensions following a different technical approach which significantly improves efficiency. To this end, we get rid of pairing groups, rely on different zero-knowledge and fast range proofs, along with a slightly modified version of Baldimtsi-Lysyanskaya blind signatures (CCS ‘13). Our prototype implementation with range proofs (for 16 bit balances) outperforms BBA+ without range proofs by a factor of 2.5. Moreover, we give estimates showing that smart-card implementations are within reach.

Zvika Brakerski, Sanjam Garg, Rotem Tsabary

We present a novel tree-based technique that can convert any designated-prover NIZK proof system (DP-NIZK) which maintains zero-knowledge only for single statement, into one that allows to prove an unlimited number of statements in ZK, while maintaining all parameters succinct. Our transformation requires leveled fully-homomorphic encryption. We note that single-statement DP-NIZK can be constructed from any one-way function. We also observe a two-way derivation between DP-NIZK and attribute-based signatures (ABS), and as a result derive now constructions of ABS and homomorphic signatures (HS).

Aditya Damodaran, Alfredo Rial

No abstract is available for this record.

Yang Qin, Tiantian Zhang, Mengya Li

No abstract is available for this record.

Sébastien Canard, Adela Georgescu, Guillaume Kaim, Adeline Roux-Langlois · 5 authors

No abstract is available for this record.

Sébastien Canard, Adel Hamdi, Fabien Laguillaumie

No abstract is available for this record.

Xiangbin Xian, Zhenguo Yang, Guipeng Zhang, Tucua Miro de Nelio S. · 5 authors

No abstract is available for this record.

Ellerson

Fifty Years of Women's Engagement at FESPACO Beti Ellerson (bio) Click for larger view View full resolution Figure G. Women gather at FESPACO. Courtesy of FESPACO. [End Page 245] Our role as an elder is to transmit our knowledge to the younger ones…I am very happy to see that I am a model for the youth and especially for young girls. Alimata Salambéré at the UNESCO reception at FESPACO in her honor on March 4, 2019 and on February 26 during the launching of the book by Yacouba Traoré about her journey as cinematic and cultural advocate: Alimata Salembéré / Ouedraogo: itinéraire et leçons de vie d'une femme debout [translation from French: Alimata Salembéré-Ouedraogo: the journey and life lessons of a woman of principle]. The words of Burkinabe Alimata Salembéré, as the title of the book dedicated to her work indicate, reflect her seminal role in FESPACO's development, setting the stage for women who follow in her footsteps as cultural workers in the myriad missions of the world of cinema. Her trajectory is indicative of the essential function African women perform as founders, organizers, curators, and stakeholders of film festivals and film-focused events. In addition, her work puts a spotlight on film festival practices and their importance in empowering women in cinema as well as encouraging and developing future women film specialists. Hence, since its inception, FESPACO, as well as the cinema-related structures that it has initiated and supported, play a paramount role in women's empowerment in all sectors of the moving image. The grand prize of FESPACO is in the image of Princess Yennenga, which is very significant. It demonstrates the importance of women in society. To have this prize, the Étalon de Yennenga, is a crowning achievement … Princess Yennenga was the proof of courage and bravery, the proof of endurance … To fight for a woman to obtain the Yennenga is truly a step forward, and it will be for the greater welfare and development of women in general.1 Franceline Oubda [End Page 246] So, "when will a woman receive this honor?" one asks, fifty years since the creation of FESPACO. Every two years, during the weeks before the start of the festival, with journalists abuzz, eager for information on the status of African women in cinema, and in particular their representation at the festival, this question is often posed, along with a catalog of queries regarding African women's accomplishments. My response has always been by way of suggested readings, presenting a list of sources offering a more comprehensive perspective on African women's place in African cinema history. Nonetheless, there appears to be a bit of impatience to peruse this ever-growing research on the timeline of African women in cinema. At the start of the celebration of the fiftieth anniversary of the creation of FESPACO in 2019, a provocative announcement in large letters circulated on social media (in French, hence the translation): Did you know? In the fifty years of FESPACO, the number of Gold Yennengas conferred to: Male filmmakers: twenty-five. Female filmmakers: zero.2 Though the balance sheet was not quite accurate, as the Yennenga was bestowed for the first time in 1972 and not at the first event in 1969. Hence at the start of the twenty-fifth edition in 2019, twenty-three Gold Yennengas had been awarded. To note, the Étalon de Yennenga was the sole grand prize until 2005; during which second and third prizes were established. Hence, the names of the three prizes for feature films: Gold Yennenga, Silver Yennenga and Bronze Yennenga. And while the core of the debate is accurate, that no woman to date has yet to win the Gold Yennenga, I suggest that rather than focusing on how many and why not more, it may be useful to trace the development of African women in cinema and the role that they have played within it, highlighting what they have achieved—as well as to analyze how they have evolved during these past fifty years. A strength-based approach, which I find both empowering and encouraging, also reposes questions that take...

Aditya Damodaran, Alfredo Rial

No abstract is available for this record.

Jayamine Alupotha, Xavier Boyen, Ernest Foo

No abstract is available for this record.

Shunli Ma, Yi Deng, Mengqiu Bai, Debiao He · 6 authors

No abstract is available for this record.

Yi Deng

No abstract is available for this record.

Jonathan Bootle, Anja Lehmann, Vadim Lyubashevsky, Gregor Seiler

No abstract is available for this record.

Jíntai Ding, Albrecht Petzoldt, Dieter Schmidt

No abstract is available for this record.

Fabrice Benhamouda, Huijia Lin

No abstract is available for this record.

Peter Fenteany, Benjamin Fuller

No abstract is available for this record.

Guangyao Yuan, Lihong Guo, Gang Wang

No abstract is available for this record.