  Polar codes have been proven to be capacity achieving for any binary-input
discrete memoryless channel, while at the same time they can reassure secure
and reliable transmission over the single-input single-output wireless channel.
However, the use of polar codes to secure multiple-antenna transmission and
reception has not yet been reported in the open literature. In this paper, we
assume a multiple-input multiple-output wiretap channel, where the legitimate
receiver and the eavesdropper are equipped with the same number of antennas. We
introduce a protocol that exploits the properties of both physical and media
access control layer security by employing polar coding and encryption
techniques in a hybrid manner in order to guarantee secure transmission. A
novel security technique is also proposed, where a cryptographic key is
generated based on the information transmitted and renewed every transmission
block without the need for a separate key exchange method. Finally, to
illustrate the effectiveness of the proposed protocol, we prove the weak and
strong security conditions, and we provide a practical method to achieve
computational security for the cases where these conditions cannot be
established.
