Abstract: Multiple service servers can store identification tags, which identify each user, after associating the identification tags with the identification tags of other users; and can also store identification data, which uniquely identifies users across multiple service servers, after associating the identification data with an encryption key for each identification datum. A management server device stores as identification data the user address data encrypted by means of an encryption key that has been generated for each identification datum. A gateway server device receives the identification tags from a first service server, receives the other identification tags associated with the first identification tags, receives the encryption keys associated with the other identification tags, and obtains the encrypted data from the management server. The gateway server device then decodes the encrypted information, and commands delivery that uses the obtained address data.

Abstract: Multiple service servers can store identification tags, which identify each user, after associating the identification tags with the identification tags of other users; and can also store identification data, which uniquely identifies users across multiple service servers, after associating the identification data with an encryption key for each identification datum. A management server device stores as identification data the user address data encrypted by means of an encryption key that has been generated for each identification datum. A gateway server device receives the identification tags from a first service server, receives the other identification tags associated with the first identification tags, receives the encryption keys associated with the other identification tags, and obtains the encrypted data from the management server. The gateway server device then decodes the encrypted information, and commands delivery that uses the obtained address data.

Abstract: A service server can: associate identification tags which identify users, with other-user identification tags, and store said identification tags; and associate the identification tags with identification data uniquely identifying users in service servers, and an encryption key for identification data and store said identification tags. A control server device stores a table for storing encryption data, encrypted identifiers of service servers used by users. The gateway server device receives an other-user identification tag associated with an identification tag and stored in a service server.

Abstract: Multiple service servers can store identification tags, which identify each user, after associating the identification tags with the identification tags of other users; and can also store identification data, which uniquely identifies users across multiple service servers, after associating the identification data with an encryption key for each identification datum. A management server device stores as identification data the user address data encrypted by means of an encryption key that has been generated for each identification datum. A gateway server device receives the identification tags from a first service server, receives the other identification tags associated with the first identification tags, receives the encryption keys associated with the other identification tags, and obtains the encrypted data from the management server. The gateway server device then decodes the encrypted information, and commands delivery that uses the obtained address data.

Abstract: An information terminal of a user B who permits a user A to search the person B calculates a calculation result G(Pa?, Pb) by using information Pa? related to the user A and information Pb of the user B, both Pa? and Pb being stored in the information terminal of the user B and transmits to a server the calculation result G(Pa?, Pb). Further, the information terminal of the user B receives trust information expressing that Pb is authenticated and calculates a calculation result F(Pb) and transmits to the server. The information terminal of the user A calculates G(Pa, Pb?) and transmits it to the server. When the server receives G(Pa, Pb?) from the information terminal of the user A, the server searches G(Pa?, Pb) which matches G(Pa, Pb?) and the search result with F(Pb) to the information terminal of the user A. The information terminal of the user A calculates F(Pb?) and compares it with F(Pb) which is sent by the server.

Abstract: A technique for synchronization of the information on multiple information terminal devices is disclosed. The information to be stored is stored in encrypted format in a server unit, and thus the server unit administrator cannot access this information. In the information terminal device where information is to be synchronized, encrypted changed information, where difference information or any set of difference information generated due to changes in the information, is encrypted, and is sent to the server unit. Then the server unit stores this encrypted changed information by correlating a revision number with it. A terminal device receives the revision number correlated with the encrypted changed information, and stores it by correlating it with the difference information or any set of difference information.