Patent ID: 7143282

Claim:
A gateway device for carrying out a packet relaying at a transport or upper layer between a sender device and a destination device which are capable of carrying out communications through networks with data secrecy based on a security association set up therebetween, the gateway device comprising: a security information management unit configured to obtain and manage information regarding the security association; a data receiving unit configured to receive a first packet which includes a first header and an encrypted packet from the sender device; a data decryption unit configured to decrypt the encrypted packet to obtain a second packet including a second header and data by utilizing the information regarding the security association and to check the second header; a packet relay unit configured to carry out the packet relaying at the transport or upper layer according to the second header; a data encryption unit configured to encrypt the second packet to obtain an encrypted second packet by utilizing the information regarding the security association, no header being newly attached to the encrypted second packet; and a data transmitting unit configured to transmit the encrypted second packet with attaching the first header to the destination device.