Patent ID: 8654755

Claim:
A communication device, comprising: a first transmitting unit that transmits to a server a first message created according to a first protocol, the first protocol being a protocol in which a network forwarding device translates a source port number, the network forwarding device translating each source port number contained in a protocol header of transmitted messages into a source port number for communicating with an external network; a receiving unit that receives a port number message including a translated port number from the server via the network forwarding device, the translated port number being a source port number obtained after the network forwarding device performs an address translation when the first message is transmitted to the server; a storing unit that stores the translated port number; a first protocol processing unit that generates a second message that is to be transmitted according to the first protocol and in which a source port number contained in a protocol header according to the first protocol is specified as a same value as the stored translated port number, which differs for each source, the second message being transmitted to the server by an application that communicates with the server using the translated port number; a second protocol processing unit that generates a third message, in which the first protocol is concealed, by appending, to the generated second message, a header encrypted according to a second protocol which is not decrypted by the server; a third protocol processing unit that generates a fourth message, in which the first protocol is concealed, by appending a header according to a third protocol to the generated third message, the third protocol being a protocol in which the network forwarding device translates a source port number contained in the header according to the third protocol, and the source port number contained in the header according to the third protocol being a value to be translated to the translated port number; and a second transmitting unit that transmits the generated fourth message to the server via the network forwarding device.