  We introduce and analyze an information theoretical task that we call the
quantum multiple-access one-time pad. Here, a number of senders initially share
a correlated quantum state with a receiver and an eavesdropper. Each sender
performs a local operation to encode a classical message and sends their system
to the receiver, who subsequently performs a measurement to decode the
messages. The receiver will be able to decode the messages almost perfectly,
while the eavesdropper must not be able to extract information about the
messages even if they have access to the quantum systems transmitted. We
consider a ''conditional'' scenario in which a portion of the receiver's side
information is also accessible to the eavesdropper. We investigate the maximum
amount of classical information that can be encoded by each of the senders. We
derive a single-letter characterization for the achievable rate region in an
asymptotic limit of infinitely many copies and vanishingly small error.
