There is disclosed a technique of providing message authentication in a communication system comprising the steps of: transmitting a first message from a first device to a second device; transmitting a second message from the second device to the first device, the second message including a message authentication code determined using said first and second messages; transmitting a third message from the first device to the second device, the third messages including a message authentication code determined using the third message. The message authentication code of the third message may be additionally based on the second or the second and first messages.
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