  We study private classical communication over quantum multiple-access
channels. For an arbitrary number of transmitters, we derive a regularized
expression of the capacity region. In the case of degradable channels, we
establish a single-letter expression for the best achievable sum-rate and prove
that this quantity also corresponds to the best achievable sum-rate for quantum
communication over degradable quantum multiple-access channels. In our
achievability result, we decouple the reliability and privacy constraints,
which are handled via source coding with quantum side information and universal
hashing, respectively. Hence, we also establish that the multi-user coding
problem under consideration can be handled solely via point-to-point coding
techniques. As a by-product of independent interest, we derive a distributed
leftover hash lemma against quantum side information that ensures privacy in
our achievability result.
