A commonly proposed covert channel is allocation of space. It is often the case that any program in a position to ask for space is also in a position to determine how much space is available. If the receiver for a covert channel is able to make this query then the sender merely allocates and frees space. The sender thus provides a step function of time. Other programs that allocate produce additive noise to this transmission. Most of signal detection tecnology is devoted to detecting the signal in the presence of additive noise.