Abstract
Security aspects of the index coding with side information (ICSI) problem are investigated. Building on the results of Bar-Yossef et al. (2006), the properties of linear index codes are further explored. The notion of weak security, considered by Bhattad and Narayanan (2005) in the context of network coding, is generalized to block security. It is shown that the linear index code based on a matrix L, whose column space code C(L) has length, minimum distance D, and dual distance d(perpendicular to), is (d - 1 - t)-block secure (and hence also weakly secure) if the adversary knows in advance t <= d - 2 messages, and is completely insecure if the adversary knows in advance more than n - d(perpendicular to) messages. Strong security is examined under the conditions that the adversary: 1) possesses t messages in advance; 2) eavesdrops at most mu transmissions; 3) corrupts at most delta transmissions. We prove that for sufficiently large, an optimal linear index code which is strongly secure against such an adversary has length kappa(q) + mu + 2 delta. Here, kappa(q) is a generalization of the min-rank over F-q of the side information graph for the ICSI problem in its original formulation in the work of Bar-Yossef et al.