The invention relates to a method for a communication system comprising a first device and a second device. The method comprises transferring a packet from a first device to a second device, which packet comprises an authentication request having a challenge; encrypting the challenge from the authentication request by the second device; including the determined challenge as a challenge-response to a response packet by the second device; sending the response packet from the second device to the first device; determining whether the challenge matches with the challenge-response, and if so, authenticating the second device.