  We consider a two-user multiple-input multiple-output (MIMO) multiple access
wiretap channel with $N$ antennas at each transmitter, $N$ antennas at the
legitimate receiver, and $K$ antennas at the eavesdropper. We determine the
optimal sum secure degrees of freedom (s.d.o.f.) for this model for all values
of $N$ and $K$. We subdivide our problem into several regimes based on the
values of $N$ and $K$, and provide achievable schemes based on real and vector
space alignment techniques for fixed and fading channel gains, respectively. To
prove the optimality of the achievable schemes, we provide matching converses
for each regime. Our results show how the number of eavesdropper antennas
affects the optimal sum s.d.o.f. of the multiple access wiretap channel.
