A data transmitting apparatus include a measurement control unit to measure an amount relating to biological information； an encryption key generation control unit to generate, as an encryption key, information calculated from first shared information and second shared information that is shared with a receiving apparatus； an encryption control unit to encrypt the biological information with the encryption key and generate encryption data； a packet generation control unit to generate a one-way transmission packet that includes the first shared information and the encryption data； and a transmitter to transmit the packet.
