On semigroups of multivariate transformations constructed in terms of time dependent linguistic graphs and solutions of Post Quantum Multivariate Cryptography.

Abstract

Time dependent linguistic graphs over abelian group H are introduced. In the case $H=K*$ such bipartite graph with point set $P=H^n$ can be used for generation of Eulerian transformation of $(K*)^n$, i.e. the endomorphism of $K[x_1, x_2,… , x_n]$ sending each variable to a monomial term. Subsemigroups of such endomorphisms together with their special homomorphic images are used as platforms of cryptographic protocols of noncommutative cryptography. The security of these protocol is evaluated via complexity of hard problem of decomposition of Eulerian transformation into the product of known generators of the semigroup. Nowadays the problem is intractable one in the Postquantum setting. The symbiotic combination of such protocols with special graph based stream ciphers working with plaintext space of kind $K^m$ where $m=n^t$ for arbitrarily chosen parameter $t$ is proposed. This way we obtained a cryptosystem with encryption/decryption procedure of complexity $O(m^{1+2/t})$