  We consider covert communication using a queuing timing channel in the
presence of a warden. The covert message is encoded using the inter-arrival
times of the packets, and the legitimate receiver and the warden observe the
inter-departure times of the packets from their respective queues. The
transmitter and the legitimate receiver also share a secret key to facilitate
covert communication. We propose achievable schemes that obtain non-zero covert
rate for both exponential and general queues when a sufficiently high rate
secret key is available. This is in contrast to other channel models such as
the Gaussian channel or the discrete memoryless channel where only
$\mathcal{O}(\sqrt{n})$ covert bits can be sent over $n$ channel uses, yielding
a zero covert rate.
