Address-authentification-information issuing apparatus, address-authentification-information adding apparatus, false-address checking apparatus, and network system

An address-authentication-information adding apparatus comprising:

• a receiving unit that receives an address to be assigned to a user and authentication information that verifies the address, from a network;
• a storage unit that stores the authentication information;
• an adding unit that adds the authentication information stored in the storage unit to data transmitted from the user;
• a transmitting unit that transmits the data to which the authentication information is added, to the network;
• a checking unit that checks length of the data;
• and
• an error sending unit that sends a message instructing to make the length of the data to predetermined length or less when it is found that the length of the data exceeds the predetermined length as a result of checking by the checking unit.

A false-address checking apparatus comprising:

• a receiving unit that receives data transmitted from a user;
• an extracting unit that extracts a source address and first authentication information that verifies the source address, from the data;
• and
• a checking unit that creates second authentication information based on the source address, and that checks the second authentication information against the first authentication information.

A network system comprising:

• an address-authentication-information issuing apparatus that issues an address to be assigned to a user and first authentication information that verifies the address;
• an address-authentication-information adding apparatus that adds the address and the first authentication information to data that is transmitted from the user;
• and
• a false-address checking apparatus that receives the data from the address-authentication-information adding apparatus and that checks second authentication information against the first authentication information, the second authentication information created based on a source address extracted from the data.