EHE: nonce misuse-resistant message authentication

We propose a nonce misuse-resistant message authentication scheme called EHE (Encrypt-Hash-Encrypt). In EHE, a message-dependent polynomial is evaluated at the point which is an encrypted nonce. The resulting polynomial hash value is encrypted again and becomes an authentication tag. We prove the prf-security of the EHE scheme and extend it to two authenticated encryption modes which follow the “encrypt-then-authenticate” paradigm

Mathematical methods in solutions of the problems from the Third International Students' Olympiad in Cryptography

The mathematical problems and their solutions of the Third International Students' Olympiad in Cryptography NSUCRYPTO'2016 are presented. We consider mathematical problems related to the construction of algebraic immune vectorial Boolean functions and big Fermat numbers, problems about secrete sharing schemes and pseudorandom binary sequences, biometric cryptosystems and the blockchain technology, etc. Two open problems in mathematical cryptography are also discussed and a solution for one of them proposed by a participant during the Olympiad is described. It was the first time in the Olympiad history

The Seventh International Olympiad in Cryptography: problems and solutions

The International Olympiad in Cryptography NSUCRYPTO is the unique Olympiad containing scientific mathematical problems for professionals, school and university students from any country. Its aim is to involve young researchers in solving curious and tough scientific problems of modern cryptography. In 2020, it was held for the seventh time. Prizes and diplomas were awarded to 84 participants in the first round and 49 teams in the second round from 32 countries. In this paper, problems and their solutions of NSUCRYPTO'2020 are presented. We consider problems related to attacks on ciphers and hash functions, protocols, permutations, primality tests, etc. We discuss several open problems on JPEG encoding, Miller -- Rabin primality test, special bases in the vector space, AES-GCM. The problem of a modified Miller -- Rabin primality test was solved during the Olympiad. The problem for finding special bases was partially solved

EHE: nonce misuse-resistant message authentication

We propose a nonce misuse-resistant message authentication scheme called EHE (Encrypt-Hash-Encrypt). In EHE, a message-dependent polynomial is evaluated at the point which is an encrypted nonce. The resulting polynomial hash value is encrypted again and becomes an authentication tag. We prove the prf-security of the EHE scheme and extend it to two authenticated encryption modes which follow the “encrypt-then-authenticate” paradigm

On the Connection Between the Maximal Coefficients of the Fourier and Walsh–Hadamard Transforms

Let the Fourier and Walsh–Hadamard transforms be applied to the same sequence. We obtain upper bounds for the maximal Fourier coefficient via the maximal Walsh–Hadamard coefficient

Оценка сверху числа бент-функций с помощью 2-строчных бент-прямоугольников

Using the representation of bent functions (maximum nonlinear functions) by bent rectangles, that is, special matrices with restrictions on columns and rows, we obtain herein an upper bound on the number of bent functions that improves the previously known bounds in a practical range of dimensions. The core of our method is the following fact based on the recent observation by V. Potapov (arXiv:2107.14583): a 2-row bent rectangle is completely determined by one of its rows and the remaining values in slightly more than half of the columns. С помощью представления бент-функций (максимально нелинейных функций) бент-прямоугольниками (специальными матрицами с ограничениями на строки и столбцы) получена оценка сверху для числа бент-функций, которая улучшает ранее известные оценки в практическом диапазоне размерностей. Используется следующий факт, основанный на недавнем наблюдении В. Потапова (arXiv:2107.14583): 2-строчный бент-прямоугольник полностью определяется одной из своих строк и оставшимися значениями в немногим более половине столбцов.

Mathematical methods in solutions of the problems presented at the Third International Students' Olympiad in Cryptography

The mathematical problems, presented at the Third International Students’ Olympiad in Cryptography NSUCRYPTO’2016, and their solutions are considered. They are related to the construction of algebraic immune vectorial Boolean functions and big Fermat numbers, the secrete sharing schemes and pseudorandom binary sequences, biometric cryptosystems and the blockchain technology, etc. Two open problems in mathematical cryptography are also discussed and a solution for one of them proposed by a participant during the Olympiad is described. It was the first time in the Olympiad history. The problem is the following: construct F : ^ with maximum possible component algebraic immunity 3 or prove that it does not exist. Alexey Udovenko from University of Luxembourg has found such a function