Circular external difference families, graceful labellings and cyclotomy

(Strong) circular external difference families (which we denote as CEDFs and SCEDFs) can be used to construct nonmalleable threshold schemes. They are a variation of (strong) external difference families, which have been extensively studied in recent years. We provide a variety of constructions for CEDFs based on graceful labellings ($\alpha$-valuations) of lexicographic products $C_n \boldsymbol{\cdot} K_{\ell}^c$, where $C_n$ denotes a cycle of length $n$. SCEDFs having more than two subsets do not exist. However, we can construct close approximations (more specifically, certain types of circular algebraic manipulation detection (AMD) codes) using the theory of cyclotomic numbers in finite fields

Circular External Difference Families: Construction and Non-Existence

The circular external difference family and its strong version, which themselves are of independent combinatorial interest, were proposed as variants of the difference family to construct new unconditionally secure non-malleable threshold schemes. In this paper, we present new results regarding the construction and non-existence of (strong) circular external difference families, thereby solving several open problems on this topic

Computational investigation of 0-APN monomials

This thesis is dedicated to exploring methods for deciding whether a power function $F(x) = x^d$ is 0-APN. Any APN function is 0-APN, and so 0-APN-ness is a necessary condition for APN-ness. APN functions are cryptographically optimal, and are thus an object of significant interest. Deciding whether a given power function is 0-APN, or APN, is a very difficult computational problem in dimensions greater than e.g. 30. Methods which allow this to be resolved more efficiently are thus instrumental to resolving open problems such as Dobbertin's conjecture. Dobbertin's conjecture states that any APN power function must be equivalent to a representative from one of the six known infinite families. This has been verified for all dimensions up to 34, and up to 42 for even dimensions. There have, however, been no further developments, and so Dobbertin's conjecture remains one of the oldest and most well-known open problems in the area. In this work, we investigate some methods for efficiently testing 0-APN-ness. A 0-APN function can be characterized as one that does not vanish on any 2-dimensional linear subspace. We determine the minimum number of linear subspaces that have to be considered in order to check whether a power function is 0-APN. We characterize the elements of this minimal set of linear subspaces, and formulate and implement efficient procedures for generating it. We computationally test the efficiency of this method for dimension 35, and conclude that it can be used to decide 0-APN-ness much faster than by conventional methods, although a dedicated effort would be needed to exploit this further due to the huge number of exponents that need to be checked in high dimensions such as 35. Based on our computational results, we observe that most of the cubic power functions are 0-APN. We generalize this observation into a ``doubly infinite'' family of 0-APN functions, i.e. a construction giving infinitely many exponents, each of which is 0-APN over infinitely many dimensions. We also present some computational results on the differential uniformity of these exponents, and observe that the Gold and Inverse power functions can be expressed using the doubly infinite family.Masteroppgave i informatikkINF399MAMN-PROGMAMN-IN

Parsing a sequence of qubits

We develop a theoretical framework for frame synchronization, also known as block synchronization, in the quantum domain which makes it possible to attach classical and quantum metadata to quantum information over a noisy channel even when the information source and sink are frame-wise asynchronous. This eliminates the need of frame synchronization at the hardware level and allows for parsing qubit sequences during quantum information processing. Our framework exploits binary constant-weight codes that are self-synchronizing. Possible applications may include asynchronous quantum communication such as a self-synchronizing quantum network where one can hop into the channel at any time, catch the next coming quantum information with a label indicating the sender, and reply by routing her quantum information with control qubits for quantum switches all without assuming prior frame synchronization between users.Comment: 11 pages, 2 figures, 1 table. Final accepted version for publication in the IEEE Transactions on Information Theor