Alphabet Size Reduction for Secure Network Coding: A Graph Theoretic Approach

TL;DR

This paper introduces a graph-theoretic method to improve the lower bounds on alphabet size needed for secure network coding, making it more practical by reducing complexity and storage requirements.

Contribution

It develops a systematic graph-based approach to tighten lower bounds on alphabet size for secure network coding, improving upon previous bounds and providing an efficient computation algorithm.

Findings

New lower bound depends only on network topology and wiretap sets

The bound can be significantly smaller than previous bounds

A polynomial-time algorithm for computing the bound is provided

Abstract

We consider a communication network where there exist wiretappers who can access a subset of channels, called a wiretap set, which is chosen from a given collection of wiretap sets. The collection of wiretap sets can be arbitrary. Secure network coding is applied to prevent the source information from being leaked to the wiretappers. In secure network coding, the required alphabet size is an open problem not only of theoretical interest but also of practical importance, because it is closely related to the implementation of such coding schemes in terms of computational complexity and storage requirement. In this paper, we develop a systematic graph-theoretic approach for improving Cai and Yeung's lower bound on the required alphabet size for the existence of secure network codes. The new lower bound thus obtained, which depends only on the network topology and the collection of wiretap sets, can be significantly smaller than Cai and Yeung's lower bound. A polynomial-time algorithm is devised for efficient computation of the new lower bound.