The security in satellite communications is a key issue due to the large footprint of the beams. This it is specially critical in IoT devices that transmit data directly to satellite. Take into account that IoT devices are characterized by transmitting packets of short length. Consequently, it means that it is not feasible to augment the security level of the IoT packets via complex cryptographic algorithms. Otherwise, their packed length may be increased in a non-negligible way which could augment their collision probability, latency and energy consumption. For this reason, this paper proposes to take advantage of the time-packing technique. By doing so, it is possible to use the overlapping degree among the pulse-shapes to boost the secrecy-capacity. In particular, the overlapping degree between the pulse-shapes introduces an artificial interference that degrades the eavesdropper's channel. In this regard, it is necessary to highlight that there is a residual co-channel interference in the satellite beams. So, it means that these two sources of impairments make difficult to estimate the legitimate user's transmission parameters by the eavesdropper.