We consider a communication network with random network coding which can be attacked by adversaries of two types. One of them can wiretap original packets outgoing from source to destination. The other can insert its own packets into information flow, which are wrong messages for the receiver. To provide secure communication, we use a scheme based on combining the GPT (Gabidulin-Paramonov-Tretjakov) public key cryptosystem and SKK (Silva-Kschischang-Koetter) codes. Encrypted packets are transmitted to the destination through wired channels. Performance of this system is investigated. The main result is that the proposed scheme is secure against wiretapping and insertion attacks under some conditions which depend on rank code parameters.