  In this paper, we consider a two-way wiretap Multi-Input Multi-Output
Multi-antenna Eve (MIMOME) channel, where both nodes (Alice and Bob) transmit
and receive in an in-band full-duplex (IBFD) manner. For this system with
keyless security, we provide a novel artificial noise (AN) based signal design,
where the AN is injected in both signal and null spaces. We present an ergodic
secrecy rate approximation to derive the power allocation algorithm. We
consider scenarios where AN is known and unknown to legitimate users and
include imperfect channel information effects. To maximize secrecy rates
subject to the transmit power constraint, a two-step power allocation solution
is proposed, where the first step is known at Eve, and the second step helps to
improve the secrecy further. We also consider scenarios where partial
information is known by Eve and the effects of non-ideal self-interference
cancellation. The usefulness and limitations of the resulting power allocation
solution are analyzed and verified via simulations. Results show that secrecy
rates are less when AN is unknown to receivers or Eve has more information
about legitimate users. Since the ergodic approximation only considers Eves
distance, the resulting power allocation provides secrecy rates close to the
actual ones.
