On the robustness of three classes of rateless codes against pollution attacks in P2P networks

Rateless codes (a.k.a. fountain codes, digital fountain) have found their way in numerous peer-to-peer based applications although their robustness to the so called pollution attack has not been deeply investigated because they have been originally devised as a solution for dealing with block erasures and not for block modification. In this paper we provide an analysis of the intrinsic robustness of three rateless codes algorithms, i.e., random linear network codes (RLNC), Luby transform (LT), and band codes (BC) against intentional data modification. By intrinsic robustness we mean the ability of detecting as soon as possible that modification of at least one equation has occurred as well as the possibility a receiver can decode from the set of equations with and without the modified ones. We focus on bare rateless codes where no additional information is added to equations (e.g., tags) or higher level protocol are used (e.g., verification keys to pre-distribute to receivers) to detect and recover from data modification. We consider several scenarios that combine both random and targeted selection of equations to alter and modification of an equation that can either change the rank of the coding matrix or not. Our analysis reveals that a high percentage of attacks goes undetected unless a minimum code redundancy is achieved, LT codes are the most fragile in virtually all scenarios, RLNC and BC are quite insensitive to the victim selection and type of alteration of chosen equations and exhibit virtually identical robustness although BC offer a low complexity of the decoding algorithm.