Reliable and Secure Multishot Network Coding using Linearized Reed-Solomon Codes

Multishot network coding is considered in a worst-case adversarial setting in which an omniscient adversary with unbounded computational resources may inject erroneous packets in up to $t$ links, erase up to $ρ$ packets, and wire-tap up to $μ$ links, all throughout $\ell$ shots of a linearly-coded network. Assuming no knowledge of the underlying linear network code (in particular, the network topology and underlying linear code may be random and change with time), a coding scheme achieving zero-error communication and perfect secrecy is obtained based on linearized Reed-Solomon codes. The scheme achieves the maximum possible secret message size of $ \ell n^\prime - 2t - ρ- μ$ packets for coherent communication, where $ n^\prime $ is the number of outgoing links at the source, for any packet length $ m \geq n^\prime $ (largest possible range). By lifting this construction, coding schemes for non-coherent communication are obtained with information rates close to optimal for practical instances. The required field size is $ q^m $, where $ q > \ell $, thus $ q^m \approx \ell^{n^\prime} $, which is always smaller than that of a Gabidulin code tailored for $ \ell $ shots, which would be at least $ 2^{\ell n^\prime} $. A Welch-Berlekamp sum-rank decoding algorithm for linearized Reed-Solomon codes is provided, having quadratic complexity in the total length $n = \ell n^\prime $, and which can be adapted to handle not only errors, but also erasures, wire-tap observations and non-coherent communication. Combined with the obtained field size, the given decoding complexity is of $ \mathcal{O}(n^{\prime 4} \ell^2 \log(\ell)^2) $ operations in $ \mathbb{F}_2 $.