ePrint Report: Revisiting Beimel-Weinreb Weighted Threshold Secret Sharing Schemes Oriol Farràs, Miquel Guiot A secret sharing scheme is a cryptographic primitive that allows a dealer to share a secret among a set of parties, so that only authorized subsets of them can recover it. The access structure of the scheme is the family of authorized…

ePrint Report: Shuffle Shamir Secret Shares Uniformly with Linear Online Communication Jiacheng Gao, Yuan Zhang, Sheng Zhong In this paper, we revisit shuffle protocol for Shamir secret sharing. Upon examining previous works, we observe that existing constructions either produce non-uniform shuffle or require large communication and round complexity, e.g. exponential in the number of parties.…

ePrint Report: Polynomial Inversion Algorithms in Constant Time for Post-Quantum Cryptography Abhraneel Dutta, Emrah Karagoz, Edoardo Persichetti, Pakize Sanal The computation of the inverse of a polynomial over a quotient ring or a finite field plays a very important role during the key generation of post-quantum cryptosystems like NTRU, BIKE, and LEDACrypt. It is therefore…

ePrint Report: Multi-Authority Functional Encryption with Bounded Collusions from Standard Assumptions Rishab Goyal, Saikumar Yadugiri Multi-Authority Functional Encryption ($mathsf{MA}$-$mathsf{FE}$) [Chase, TCC’07; Lewko-Waters, Eurocrypt’11; Brakerski et al., ITCS’17] is a popular generalization of functional encryption ($mathsf{FE}$) with the central goal of decentralizing the trust assumption from a single central trusted key authority to a group of…

ePrint Report: Learning from Functionality Outputs: Private Join and Compute in the Real World Francesca Falzon, Tianxin Tang Private Join and Compute (PJC) is a two-party protocol recently proposed by Google for various use-cases, including ad conversion (Asiacrypt 2021) and which generalizes their deployed private set intersection sum (PSI-SUM) protocol (EuroS&P 2020). PJC allows two…

ePrint Report: Bootstrapping (T)FHE Ciphertexts via Automorphisms: Closing the Gap Between Binary and Gaussian Keys Olivier Bernard, Marc Joye The GINX method in TFHE offers low-latency ciphertext bootstrapping with relatively small bootstrapping keys, but is limited to binary or ternary key distributions. In contrast, the AP method supports arbitrary key distributions, however at the cost…

ePrint Report: A Holistic Framework for Impossible Boomerang Attacks Yincen Chen, Qinggan Fu, Ning Zhao, Jiahao Zhao, Ling Song, Qianqian Yang In 2011, Lu introduced the impossible boomerang attack at DCC. This powerful cryptanalysis technique combines the strengths of the impossible differential and boomerang attacks, thereby inheriting the advantages of both cryptographic techniques. In this…

ePrint Report: The Nonlinear Filter Model of Stream Cipher Redivivus Claude Carlet, Palash Sarkar The nonlinear filter model is an old and well understood approach to the design of secure stream ciphers. Extensive research over several decades has shown how to attack stream ciphers based on this model and has identified the security properties required…

ePrint Report: Secure Showing of Partial Attributes Foteini Baldimtsi, Julia Kastner, Julian Loss, Omar Renawi Anonymous Attribute-Based Credentials (ABCs) allow users to prove possession of attributes while adhering to various authentication policies and without revealing unnecessary information. Single-use ABCs are particularly appealing for their lightweight nature and practical efficiency. These credentials are typically built using…

ePrint Report: Cycles and Cuts in Supersingular L-Isogeny Graphs Sarah Arpin, Ross Bowden, James Clements, Wissam Ghantous, Jason T. LeGrow, Krystal Maughan Supersingular elliptic curve isogeny graphs underlie isogeny-based cryptography. For isogenies of a single prime degree $ell$, their structure has been investigated graph-theoretically. We generalise the notion of $ell$-isogeny graphs to $L$-isogeny graphs (studied…