Method and its system for transmission-reception of data packet between computer systems

PROBLEM TO BE SOLVED: To attain ciphering and decoding automatically for a data packet sent from a sender source host to a destination host via a public internet. SOLUTION: A tunnel bridge TB is arranged to each network to interruptingly received all packet sent through each network N. When a 1st host sends a packet to its network, the tunnel bridge arranged in the network of the host interruptingly receives the packet to discriminate whether or not the packet to be sent to a destination host designated by the host requires ciphering or whether or not the packet sent from the network of the destination host from the network of the sender source host requires ciphering, based on an information header.