Algorithmic recognition of infinite cyclic extensions

We prove that one cannot algorithmically decide whether a finitely presented $\mathbb{Z}$-extension admits a finitely generated base group, and we use this fact to prove the undecidability of the BNS invariant. Furthermore, we show the equivalence between the isomorphism problem within the subclass of unique $\mathbb{Z}$-extensions, and the semi-conjugacy problem for deranged outer automorphisms.Comment: 24 page

Algorithmic properties of poly-Z groups and secret sharing using non-commutative groups

Computational aspects of polycyclic groups have been used to study cryptography since 2004 when Eick and Kahrobaei proposed polycyclic groups as a platform for conjugacy based cryptographic protocols. In the first chapter we study the conjugacy problem in polycyclic groups and construct a family of torsion-free polycyclic groups where the uniform conjugacy problem over the entire family is at least as hard as the subset sum problem. We further show that the conjugacy problem in these groups is in NP, implying that the uniform conjugacy problem is NP-complete over these groups. This is joint work with Delaram Kahrobaei. We also present an algorithm for the conjugacy problem in groups of the form $\Z^n \rtimes_\phi \Z$. We continue by studying automorphisms of poly-$\Z$ groups and successive cyclic extensions of arbitrary groups. We study a certain kind of extension that we call deranged , and show that the automorphisms of the resulting group have a strict form. We also show that the automorphism group of a group obtained by iterated extensions of this type contains a non-abelian free group if and only if the original base group does. Finally we show that it is possible to verify that a finitely presented by infinite cyclic group is finitely presented by infinite cyclic, but that determining that a general finitely presented group is finitely generated by infinite cyclic is undecidable. We then discuss implications the latter result has for calculating the Bieri-Neumann-Strebel invariant. This is joint work with Jordi Delgado, Delaram Kahrobaei, Ha Lam, and Enric Ventura and is currently in preparation. In the final chapter we discuss secret sharing schemes and variations. We begin with classical secret sharing schemes and present variations that allow them to be more practical. We then present a secret sharing scheme due to Habeeb, Kahrobaei, and Shpilrain. Finally, we present an original adjustment to their scheme that involves the shortlex order on a group and allows less information to be transmitted each time a secret is shared. Additionally, we propose additional steps that allow participants to update their information independently so that the scheme remains secure over multiple rounds. This is joint work with Delaram Kahrobaei

Efficient and Secure Delegation of Group Exponentiation to a Single Server

We consider the problem of delegating computation of group operations from a computationally weaker client holding an input and a description of a function, to a {\em single} computationally stronger server holding a description of the same function. Solutions need to satisfy natural correctness, security, privacy and efficiency requirements. We obtain delegated computation protocols for the following functions, defined for an {\em arbitrary} commutative group: \begin{enumerate} \item Group inverses, with security and privacy holding against any computationally unrestricted malicious server. \item Group exponentiation, with security and privacy holding against any computationally unrestricted ``partially honest server. \item Group exponentiation, with security and privacy holding against any polynomial-time malicious server, under a pseudorandom generation assumption, and security holding with constant probability. \end{enumerate

A polynomial time algorithm for the conjugacy problem in Zn o Z

-In this paper we introduce a polynomial time algorithm that solves both the conjugacy decision and search problems in free abelian-by-innite cyclic groups where the input is elements in normal form. We do this by adapting the work of Bogopolski, Martino, Maslakova, and Ventura in [1] and Bogopolski, Martino, and Ventura in [2], to free abelian-by-innite cyclic groups, and in certain cases apply a polynomial time algorithm for the orbit problem over Zn by Kannan and Lipton [7].Keywords: Conjugacy problem, semidirect product. MSC (2010): Primary 20F10, Secondary 20E06

Algorithmic recognition of infinite cyclic extensions

We prove that one cannot algorithmically decide whether a finitely presented Z-extension admits a finitely generated base group, and we use this fact to prove the undecidability of the BNS invariant. Furthermore, we show the equivalence between the isomorphism problem within the subclass of unique Z-extensions, and the semi-conjugacy problem for deranged outer automorphisms.Peer Reviewe

Contemporary Mathematics: Algebra and Computer Science-volume 677

Benjamin Fine is a contributing author, On secret sharing protocols with Chi Sing Chum, Anja IS Moldenhauer, Gerhard Rosenberger, and Xiaowen Zhang. Book description: This volume contains the proceedings of three special sessions: Algebra and Computer Science, held during the Joint AMS-EMS-SPM meeting in Porto, Portugal, June 10-13, 2015; Groups, Algorithms, and Cryptography, held during the Joint Mathematics Meeting in San Antonio, TX, January 10-13, 2015; and Applications of Algebra to Cryptography, held during the Joint AMS-Israel Mathematical Union meeting in Tel-Aviv, Israel, June 16-19, 2014. Papers contained in this volume address a wide range of topics, from theoretical aspects of algebra, namely group theory, universal algebra and related areas, to applications in several different areas of computer science. From the computational side, the book aims to reflect the rapidly emerging area of algorithmic problems in algebra, their computational complexity and applications, including information security, constraint satisfaction problems, and decision theory. The book gives special attention to recent advances in quantum computing that highlight the need for a variety of new intractability assumptions and have resulted in a new area called group-based cryptography.https://digitalcommons.fairfield.edu/mathandcomputerscience-books/1005/thumbnail.jp