Communication system, transmitter, receiver, communication method, transmission method, and reception method

In order to ensure security even when packet communication is performed using multiple communication channels of a public network, the communication system (1) has a configuration wherein: the transmitter (2) is equipped with a first storage unit (11) for storing a first communication pattern, first and second communication units (12, 13) for performing packet communication with a receiver (3), and a first processor (16) for controlling communication units (12, 13); and the receiver (3) is equipped with a second storage unit (21) for storing a second communication pattern, third and fourth communication units (22, 23) for performing the packet communication with the transmitter (2), and a second processor (26) for controlling communication units (22, 23), whereby processor (16) transmits packets from communication units as selected in accordance with the first communication pattern and inserts dummy packets into at least one of the groups of packets to be transmitted, and the second processor (26) restores original data from valid packets, that is, the remaining packets after the dummy packets are removed from the received packets in accordance with the second communication pattern.