  A two-transmitter Gaussian multiple access wiretap channel with multiple
antennas at each of the nodes is investigated. The channel matrices at the
legitimate terminals are fixed and revealed to all the terminals, whereas the
channel matrix of the eavesdropper is arbitrarily varying and only known to the
eavesdropper. The secrecy degrees of freedom (s.d.o.f.) region under a strong
secrecy constraint is characterized. A transmission scheme that orthogonalizes
the transmit signals of the two users at the intended receiver and uses a
single-user wiretap code is shown to be sufficient to achieve the s.d.o.f.
region. The converse involves establishing an upper bound on a
weighted-sum-rate expression. This is accomplished by using induction, where at
each step one combines the secrecy and multiple-access constraints associated
with an adversary eavesdropping a carefully selected group of sub-channels.
