  We propose a covert communication protocol for the spread-spectrum multiple
random access with additive white Gaussian noise (AWGN) channel. No existing
paper has studied covert communication for the random access channel. Our
protocol assumes binary discrete phase-shift keying (BPSK) modulation, and it
works well under imperfect channel state information (I-CSI) for both the
legitimate and adversary receivers, which is a realistic assumption in the low
power regime. Also, our method assumes that the legitimate users share secret
variables in a similar way as the preceding studies. Although several studies
investigated the covert communication for the point-to-point communication, no
existing paper considers the covert communication under the above uncertainty
assumption even for point-to-point communication. Our protocol under the above
uncertainty assumption allows O(n) legitimate senders and O(n/log n) active
legitimate senders. Furthermore, our protocol can be converted to a protocol
for point-to-point communication that works under the above uncertainty
assumption.
