In near future, industrial wireless sensor networks will be commonly deployed, so that the security improvements in these networks will gain much importance. With respect to the physical layer solutions, the standard system model that includes an eavesdropper is updated by adding trustful intermediate relays between legitimate nodes. This updated model is operated with a scheme based on the working principle of McEliece cryptosystem and the error correction capability of legitimate receiver. As a performance metric, the decoding error probability of eavesdropper is obtained analytically and with simulations based on the effects of noisy channels between eavesdropper and relays.