Multi-User BBB Security of Public Permutations Based MAC

At CRYPTO 2019, Chen et al. have shown a beyond the birthday bound secure $n$-bit to $n$-bit PRF based on public random permutations. Followed by the work, Dutta and Nandi have proposed a beyond the birthday bound secure nonce based MAC $\textsf{nEHtM}_p$ based on public random permutation. In particular, the authors have shown that $\textsf{nEHtM}_p$ achieves tight $2n/3$-bit security ({\em with respect to the state size of the permutation}) in the single-user setting, and their proven bound gracefully degrades with the repetition of the nonces. However, we have pointed out that their security proof is not complete (albeit it does not invalidate their security claim). In this paper, we propose a minor variant of $\textsf{nEHtM}_p$ construction, called $\textsf{nEHtM}^*_p$ and show that it achieves a tight $2n/3$ bit security in the multi-user setting. Moreover, the security bound of our construction also degrades gracefully with the repetition of nonces. Finally, we have instantiated our construction with the PolyHash function to realize a concrete beyond the birthday bound secure public permutation-based MAC, $\textsf{nEHtM}_p^+$ in the multi-user setting

A multivariate noise-free HE proposal

Recently, new ideas to build homomorphic noise-free encryption schemes have been proposed. The starting point of these schemes deals with private-key encryption schemes whose secret key is a rational function. By construction, these schemes are not homomorphic. To get homomorphic properties, nonlinear homomorphic operators are derived from the secret key. In this paper, we adopt the same approach to build a HE. We obtain a multivariate encryption scheme in the sense that the knowledge of the CPA attacker can be turned into an over-defined system of nonlinear equations. The factoring assumption is introduced in order to make a large class of attacks based on Groebner basis irrelevant. While we did not propose a formal security proof relying on a classical cryptographic assumption, we hopefully provide convincing evidence for security

Progress in Cryptology - AFRICACRYPT 2020 [electronic resource] : 12th International Conference on Cryptology in Africa, Cairo, Egypt, July 20 – 22, 2020, Proceedings /

This book constitutes the refereed proceedings of the 12th International Conference on the Theory and Application of Cryptographic Techniques in Africa, AFRICACRYPT 2020, held in Cairo, Egypt, in July 2020. The 21 papers presented in this book were carefully reviewed and selected from 49 submissions. The papers are organized in topical sections on zero knowledge, symmetric key cryptography, elliptic curves, post quantum cryptography, lattice based cryptography, side channel attacks, cryptanalysis and new algorithms and schemes. AFRICACRYPT is a major scientific event that seeks to advance and promote the field of cryptology on the African continent. The conference has systematically drawn some excellent contributions to the field. The conference has always been organized in cooperation with the International Association for Cryptologic Research (IACR).QA-NIZK Arguments of Same Opening for Bilateral Commitments -- Signatures of Knowledge for Boolean Circuits under Standard Assumptions -- LESS is More: Code-Based Signatures without Syndromes -- UC Updatable Databases and Applications -- Symmetric Key Cryptography -- Impossible Di erential Cryptanalysis of Reduced-Round Tweakable TWINE -- MixColumns Coe cient Property and Security of the AES with A Secret S-Box -- New Results on the SymSum Distinguisher on Round-Reduced SHA3 -- Cryptanalysis of FlexAEAD -- BBB Secure Nonce Based MAC Using Public Permutations -- Elliptic Curves -- On Adaptive Attacks against Jao-Urbanik's Isogeny-Based Protocol -- A SAT-Based Approach for Index Calculus on Binary Elliptic Curves -- Post Quantum Cryptography -- Hash-based Signatures Revisited: A Dynamic FORS with Adaptive Chosen Message Security -- LMS vs XMSS: Comparison of Stateful Hash-Based Signature Schemes on ARM Cortex-M4 -- Lattice Based Cryptography -- Round Optimal Secure Multisignature Schemes from Lattice with Public Key Aggregation and Signature Compression -- Sieve, Enumerate, Slice, and Lift: Hybrid Lattice Algorithms for SVP via CVPP -- Side Channel Attacks -- Online Template Attack On ECDSA: Extracting Keys Via The Other Side -- When similarities among devices are taken for granted: Another look at portability -- A Tale of Three Signatures: Practical Attack of ECDSA with wNAF -- Attacking RSA Using an Arbitrary Parameter -- New Algorithms and Schemes -- A New Encoding Algorithm for a Multidimensional Version of the Montgomery Ladder -- New Ideas to Build Noise-Free Homomorphic Cryptosystems -- Zero Knowledge.This book constitutes the refereed proceedings of the 12th International Conference on the Theory and Application of Cryptographic Techniques in Africa, AFRICACRYPT 2020, held in Cairo, Egypt, in July 2020. The 21 papers presented in this book were carefully reviewed and selected from 49 submissions. The papers are organized in topical sections on zero knowledge, symmetric key cryptography, elliptic curves, post quantum cryptography, lattice based cryptography, side channel attacks, cryptanalysis and new algorithms and schemes. AFRICACRYPT is a major scientific event that seeks to advance and promote the field of cryptology on the African continent. The conference has systematically drawn some excellent contributions to the field. The conference has always been organized in cooperation with the International Association for Cryptologic Research (IACR)