A packets sending/receiving apparatus, comprising: authentication and key
exchange means; encryption means for producing an encryption sending
data; sending condition setting management means for producing sending
condition setting information for setting sending condition of the
sending packets; packetization means for producing the sending packets
using the encryption sending data; receiving condition setting management
means for producing receiving condition setting information for setting
receiving condition of the receiving packets; packets reception means for
receiving the reception packets; and decoding means for decoding the
reception data using the decoding key.