Patent Publication Number: US-7913093-B2

Title: Method and system for providing access to information on an article to which a tag is coupled

Description:
DETAILED DESCRIPTION OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to information processing technology, and more particularly to a method for accessing information on article with a tag attached thereon, a local server, an ONS proxy, a program, a tag creation method, a tag writer, a tag and a program for controlling an apparatus including a tag writer. 
     2. Background Art 
     In order to promote the efficiency of article circulation and the spread of article quality control by use of RFID (Radio Frequency Identification) tag, EPCglobal, a standardization group, has established the specifications (shown in  FIG. 17 ) of EPC code that includes version information (VER)  1701  indicating tag data bit assignment, manufacturer ID (MID)  1702 , product ID (PID)  1703  and product serial number (SNO)  1704  (refer to non-patent document 1). 
     Also, the standardization group, EPCglobal has proposed a framework (shown in  FIG. 16 ) for accessing information on article with an RFID tag in which an Electronic Product Code (EPC) code is stored attached thereon. According to the framework, a local server  103  acquires an EPC code serving as article ID from data that is stored in an RFID tag  101  received via a tag reader  102 . Subsequently, by use of the EPC code, the local server  103  requests the network address of a Physical Markup Language (PML) server  107  recording information on article with an RFID tag attached thereon via a network  104  from an Object Naming Service (ONS) server  105 . Then, by use of the EPC code and the network address of the PML server  107  acquired from the ONS server  105 , the local server  103  accesses the information on article with the tag attached thereon, which is stored in the PML server  107 . 
     Data recorded onto an RFID tag can generally be read with an RFID tag reader of any type. Consequently, an EPC code recorded onto an RFID tag attached to an article worn by an individual may be read with a tag reader installed in a public space. Concerned about the privacy problem that an article worn by an individual may be grasped by anyone else, consumer groups have staged boycott movements against articles with an RFID tag, interfering with promotion of the efficiency of article circulation and the spread of article quality control by use of RFID tag. 
     As a method for coping with the privacy problem regarding RFID tag, there has been proposed Kill-Command for halting the function of RFID tag at the time when the article is bought by a consumer (refer to non-patent document 2). As another method, there has been proposed a function such that a blocker tag, which interferes with tag readers, blocks other tag data from being read (refer to non-patent document 3). As still another method for coping with the privacy problem, there has been proposed a method in which whenever data recorded onto an RFID tag is read, the data contents are rewritten with an external tag writer or by the tag itself (refer to non-patent documents 4 and 5).
     [Non-patent document 1] Bud Babcock et al, “EPC Tag Data Standards Version 1.1 Rev. 1. 24,” EPCglobal, Apr. 1, 2004   [Non-patent document 2] Auto-ID centre, “860-960 MHz Class I Radio Frequency Identification Tag Radio Frequency &amp; Logical Communication Interface Specification Proposed Recommendation, Version 1. 0. 0,”Technical Report MIT-Auto ID=TR007, 2002   [Non-patent document 3] A. Juels et al, “The Blocker Tag: Selective Blocking of RFID Tags for Consumer Privacy,” MIT RFID Privacy Summit, 2003   [Non-patent document 4] M. Ohkubo et al, “Cryptographic Approach to a Privacy Friendly Tag,” MIT RFID Privacy Workshop, 2003   [Non-patent document 5] S. Weis, “Security and Privacy in Radio-Frequency Identification: Security Risks and Challenges,” RSA Cryptobytes, Vol. 6, No. 1, 2003   

     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     The above described methods for coping with the privacy problem will sacrifice traceability that is the main object of introducing RFID tag, and/or will involve increased cost associated with introducing additional hardware mechanism. 
     An objective of the invention is to provide a method for accessing information on an article with a tag attached thereon, the method making it possible to prevent information on article worn by an individual from being grasped with a tag reader installed in a public space, without sacrificing traceability and without involving much increase in cost, a local server, an ONS proxy, a program, a tag creation method, a tag writer and a tag writer control program. 
     The above object can be achieved by combinations of the features described in the independent claims. The dependent claims define additional advantageous embodiments of the invention. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention, in a network system including a local server, an ONS proxy, an ONS server and at least one PML server, there is provided a method for providing access to information on an article associated with a tag, comprising the steps of: reading, by the local server, at least one encrypted virtual ID included in a tag; sending an ONS service request including the virtual ID from the local server to the ONS proxy; acquiring, by the ONS proxy, an article ID by decrypting the virtual ID by use of a key K; generating, by the ONS proxy, based on the article ID, a network address request for acquiring the network address of a PML server in which the information on article associated with the tag is stored, to send the request to the ONS server; receiving, by the local server, the network address of a PML server which the ONS server has returned in response to the network address request; sending, by the local server, based on the network address of a PML server, a PML service request including the virtual ID to the PML server; and providing, by the PML server, access to the information on article associated with the tag, which has been specified with the article ID acquired by decrypting the virtual ID by use of the key K, for the local server. 
     The first embodiment of the invention can be perceived as a network system, a local server, an ONS proxy, a program, a storage medium in which the program is stored, or as other program products. 
     According to a second aspect of the invention, there is provided a method for making, by using a tag writer, a tag including a virtual ID with a length of N bits is stored, the method comprising the steps of: storing an article ID with a length of (N−r) bits in a storage device; generating a random number R of r bits; generating a bit string with a length of N bits by distributing digits of the random number R of r bits within the bit string of the article ID with a length of (N−r) bits; generating a virtual ID with a length of N bits by encrypting the bit string with a length of N bits in a manner that decryption of the encrypted bit string with a key K stored in the ONS proxy and the PML server is possible; and writing the virtual ID with a length of N bits to a tag by use of a tag writer. 
     The second embodiment of the invention can be perceived as an apparatus including a tag writer, a tag itself, a program for controlling an apparatus including a tag writer, a recording medium in which the program is stored, or as other program products. 
     In the above described outlines of the invention, all essential features of the invention are not listed. Subcombinations of these feature groups can also become an invention. 
     PREFERRED EMBODIMENT 
     The invention will now be described through embodiments of the invention. The embodiments described below, however, does not limit the invention according to the claims, and not all the combinations of the features described in the embodiments are essential as the means of the invention for solving the problems. 
     Embodiment 1 
       FIG. 1  is a high-level schematic diagram showing a network system according to a first embodiment of the invention. The network system includes a local server  103 , an Object Naming Service (ONS) server  105 , an ONS proxy  106  and a Physical Markup Language (PML) server  107  being communicatable with each other via a network  104 . The local server  103  is connected to a tag reader  102  capable of reading data recorded on a Radio Frequency Identification (RFID) tag  101  that is coupled to (i.e., on or attached to) an article. 
     (Hardware Configuration) 
       FIG. 2  is an external view of a first exemplary RFID tag  101  being usable in the first embodiment of the invention.  FIG. 3  is an external view of a second exemplary RFID tag  101  being usable in the first embodiment of the invention.  FIG. 4  is an external view of an exemplary RFID tag reader/writer  102  being usable in the first embodiment of the invention. 
     According to the first embodiment, the RFID tag  101  includes an IC chip  201  or  301  and an antenna  202  or  302 , each of the IC chips  201  and  301  including a logic circuit and a memory. The RFID tag  101  has a function of the logic circuit performing reading/writing from/to the memory based on the contents of communication with the RFID tag reader/writer  102  via the antenna  202  or  302 . The first exemplary RFID tag  101  performs the communication with the RFID tag reader/writer  102  through electromagnetic induction. The second exemplary RFID tag  101  performs the communication with the RFID tag reader/writer  102  through microwave. Based on the standard specifications or the like, a person skilled in the art can arbitrarily design, manufacture or obtain the above described RFID tag  101  and RFID tag reader/writer  102 , and hence detailed description thereof is omitted in the present specifications. 
       FIG. 5  is a diagram showing an exemplary hardware configuration of a computer that appropriately functions as the local server  103 , ONS server  105 , ONS proxy  106  or PML server  107  in the first embodiment of the invention. The computer apparatus includes a central processing unit (CPU)  1  and a main memory  4 . The CPU  1  and main memory  4  are connected via a bus  2  to a hard disk device  13  serving as an auxiliary storage unit. Also, removal storages (external storage systems with exchangeable recording medium) including a flexible disk unit  20 , a MO unit  28  and CD-ROM units  26  and  29  are connected to the bus  2  via a flexible disk controller  19 , an IDE controller  25 , a SCSI controller  27  and the like, which are related to the removal storages, respectively. 
     Storage media such as flexible disk, MO and CD-ROM are inserted into removal storages such as the flexible disk unit  20 , MO unit  28  and CD-ROM units  26  and  29 , respectively. On the flexible disk and the like, hard disk device  13  and ROM  14 , there can be recorded computer program codes for giving instructions to the CPU, etc. in conjunction with operating system to implement the invention. The storage media with the recorded computer program therein is a computer program product. In order to execute the computer program, it is loaded into the main memory  4 . The computer program can be compressed, and can also be divided to be recorded on plural media. 
     Further, the computer apparatus can include as user interface hardware a pointing device  7  such as a mouse, a keyboard  6  and a display  12  for providing visual data for the user. Also, a printer (not shown) can be connected via a parallel port  16 , and a modem (not shown) can be connected via a serial port  15 . The computer apparatus can communicate with another computer or the like through connection with a network via the serial port  15  and modem or via a communication adapter  18  (Ethernet® card or token ring card) or the like. 
     A loudspeaker  23  receives via an amplifier  22  audio signals obtained by performing D/A conversion (digital/analog conversion) by an audio controller  21 , and outputs sounds. The audio controller  21  A/D converts (analog/digital converts) audio information received from a microphone  24 , thus making it possible to capture audio information from outside the system into the system. 
     According to the above description, it will be easily understood that the computer apparatus according to the embodiment of the invention can be implemented by an information processing apparatus such as mainframe, workstation, ordinary personal computer (PC) or by a combination of these apparatuses. It is noted that these components are shown as an example and all the components are not essential for the invention. 
     Particularly, among the hardware components described above, even when removal storages such as flexible disk unit  20 , MO unit  28  and CD-ROM units  26  and  29 , parallel port  16 , printer, serial port  15 , modem, communication adapter  18 , loudspeaker  23 , audio controller  21 , amplifier  22 , microphone  24 , etc. are removed, the embodiment of the invention is implementable. Thus, the above components may not be included in the computer apparatus according to the embodiment of the invention. 
     Various modifications such as distributing the function of each hardware component of the computer apparatus used to implement the invention to a combination of plural machines for implementation can be easily conceived by those skilled in the art. Of course, these modifications are concepts that can be included in the technical scope of the invention. 
     The computer apparatus can employ, as operating system, Window (®) operating system provided by Microsoft corp., AIX provided by International Business Machines Corp., MacOS provided by Apple Computer, Inc. or Linux or the like that supports GUI multi-window environment. The computer apparatus can also employ, as operating system, PC-DOS provided by International Business Machines Corp. or one with character-based environment such as MS-DOS provided by Microsoft corp. Also, the server  300  can employ OS Open provided by International Business Machines Corp., a real time OS such as Vx Works of Wind River Systems, Inc. or an operating system incorporated into a network computer such as Java (®) OS. 
     It can be understood from the above description that the computer apparatus is not limited to a particular operating system environment. Of course, the local server  103 , ONS server  105 , ONS proxy  106  or PML server  107  can be operated under a different operating system environment from each other. 
     The network  104  is a communication path that connects the local server  103 , ONS server  105 , ONS proxy  106  and PML server  107 ; it can be implemented by the Internet, for example. As is commonly known, the network  104  being the Internet performs connection between systems by use of TCP/IP (Transmission Control Protocol/Internet Protocol). In the network  104 , mutually communicating systems are specified by use of IP address represented by global address or local address. 
     (Functional Block Configuration) 
       FIG. 6  is a functional block diagram of a network system according to the first embodiment of the invention. According to the embodiment of the invention, the local server  103  includes a tag reader/writer controller  1031 , an ONS resolver  1032  and a PML requester  1033 . The local server  103  is connected to the tag reader  102  capable of reading data recorded on the RFID tag  101 . In order to acquire a virtual identifier (ID) to be described later, the tag reader/writer controller  1031  acquires data recorded on the RFID tag by controlling the tag reader/writer  102 , wherein the data acquired by the tag reader/writer controller  1031  from the RFID tag includes a virtual ID. 
     In order to acquire the network address (IP address in this embodiment) of the PML server  107 , the ONS resolver  1032  sends a network address request including the virtual ID (VID) acquired by the tag reader/writer controller  1031  to the network and obtains the network address of the PML server  107 . 
     The PML requester  1033  accesses, by use of the network address of the PML server  107  which is obtained by the ONS resolver  1032  and the virtual ID, information (hereinafter referred to as PML information) on an article having an RFID tag attached thereon and being associated with the RFID tag, which information is recorded on the PML server  107 . 
     On the ONS proxy  106 , there is securely recorded a common key (K)  1061 . In response to the request including the virtual ID from the ONS resolver  1032  of the local server  103 , the ONS proxy  106  decrypts the virtual ID by use of the common key  1061  to acquire an article ID. Then, in order to generate a network address request to request the network address of the PML server which provides access to the information on article associated with the article ID, the ONS proxy  106  extracts a manufacturer ID (MID) from the article ID. The ONS proxy sends the network address request in which the extracted MID is included to the ONS server  105 . 
     The ONS server  105  is constructed according to the specifications based on DNS server established by the standardization group, EPCGlobal. On the ONS server  105 , there is recorded data to associate each manufacturer ID (MID) with the network address of a PML server  107  managed by a manufacturer indicated by the manufacturer ID. According to the first embodiment, in response to the network address request including the MID, the ONS server  105  returns the network address of the PML server  107  that provides access to the information on article associated with the article ID. 
     The PML server  107  includes a PML manager  1071  and a PML database  1072  that records PML information corresponding to each article ID. Also, on the PML server  107 , there is securely recorded a common key (K)  1073 . According to the embodiment, in response to the PML information request from the local server  103 , the PML manager  1071  decrypts the virtual ID included in the PML information request by use of the common key (K)  1073  to acquire the article ID. Then, the PML manager  1071  identifies PML information corresponding to the article ID, retrieves the identified PML information from the PML database  1072 , and provides (i.e., transmits) the retrieved PML information to the local server  103 . 
     (Generation of Tag Data Including Virtual ID) 
       FIG. 7  is a first exemplary data structure of data recorded on an RFID tag  101  according to the first embodiment of the invention. According to the specifications established by the standardization group, EPCGlobal, by use of version number (VER)  701  of 8 bits, the data contents assigned to the remaining 88 bits can be defined. In the first example, in the remaining 88 bits, there is stored one virtual ID (VID)  702  generated based on article ID; in version number  701 , there is stored a bit string indicating employment of such data structure. 
       FIG. 8  is a second exemplary data structure of data recorded on an RFID tag  101  according to the first embodiment of the invention. In the second example, in the remaining 88 bits, there is stored a virtual ID consisting of a first virtual ID (VID- 1 )  802  of 52 bits generated from manufacturer ID (MID) and product ID (PID) each included in article ID and a second virtual ID (VID- 2 )  803  of 36 bits generated from serial number (SNO) included in article ID; in version number (VER)  801 , there is stored a bit string indicating employment of such data structure. 
     According to the embodiment, virtual ID is generated by applying an appropriate encryption process to article ID. Article ID can be calculated by applying an appropriate decryption process to virtual ID. Also, according to the embodiment of the invention, for the purpose of protecting privacy, virtual ID preferably fulfills a condition, i.e. Indistiguishable, in which even when mapping with respect to a pair of a given article ID and virtual ID is known, mapping with respect to another virtual ID can not be known. If the above described Indistiguishable is fulfilled, for example, even when the user makes public the retrieval result of a virtual ID, the user can know only the mapping of the above virtual ID and article ID and can not know any mapping with respect to another virtual ID. According to the first embodiment, to meet the above described requirement, a bit string of a virtual ID is generated according to the following method. 
       FIG. 10  is a flowchart showing an exemplary flow of a method for generating a virtual ID according to the first embodiment of the invention. 
     The process starts with step  1001 , and an article ID is acquired (step  1002 ). Here, if a correspondence between article ID and virtual ID is one—one, Indistinguishable can not be fulfilled. Thus, in order to associate one article ID with plural virtual IDs, the number of bits of article ID is smaller than that of virtual ID, as shown in  FIG. 9 . According to the embodiment, in order to associate one article ID with virtual IDs on the order of 220, when a virtual ID of 88 bits is generated, an article ID of 68 bits consisting of MID  901  of 24 bits, PID  902  of 20 bits and SNO  903  of 24 bits is employed. Subsequently, a random number R of 20 bits is generated (step  1003 ) and then digits of the random number R is distributed within the article ID (step  1004 ) according to an “All-or-Nothing Transformation (AONT)” algorithm, and then the article ID having the random number R distributed therein is encrypted with the key K in a manner that decryption with the common key stored in the ONS proxy and PML server is possible (step  1005 ). 
     The above process is expressed by the following formula, where known block cipher OFB mode such as DES can be employed as encryption function E, and K is a key of DES, and IV is the initial vector.
 
 VID=E   K,IV ( AONT ( MID∥PID∥SNO,R ))
 
     In AONT algorithm, the random number effect of the random number R is distributed over the entire cipher text, whereby when any single bit of the cipher text is lost, the cipher text can not be decrypted into a clear text. For example, OAEP known as cipher padding of RSA is one of the methods for implementing AONT. According to the embodiment, as AONT function used in step  1004 , there is employed OAEP to be described below in detail. 
       FIG. 11  is a flowchart showing OAEP algorithm used to generate a virtual ID according to the first embodiment of the invention. 
     The process starts with step  1101 . First the random number R generated in step  1003  is hashed by a hash function F()that outputs a hash value of 68 bits to obtain F(R) (step  1102 ), and then there is generated X being an exclusive OR between the article ID of 68 bits and the F(R) (step  1103 ). The article ID is denoted as RID in step  1103  in  FIG. 11 . Further, X is hashed by a hash function G( ) that outputs a hash value of 20 bits to generate G(X) (step  1104 ), and then there is generated Y being an exclusive OR between the random number R of 20 bits and G(X) (step  1105 ). Finally, X and Y are joined together (e.g., by concatenating X and Y) (step  1106 ) to generate a bit string Z, wherein Z is the article ID (RID) having the random number R distributed therein. By executing the above steps, there is generated the bit string Z with a length of 88 bits to be encrypted using the key K in step  1005 , thereby finishing the process (step  1107 ). The above described process is expressed by the following formulas.
 
 X=XOR ( MID∥PID∥SNO,F ( R )
 
 Y=XOR ( R,G ( X ))
 
 Z=X∥Y  
 
     Taking into consideration the first exemplary data structure of data recorded on RFID tag, the method for generating a virtual ID was described above. However, it will be easily understood by those skilled in the art that also in the second example, by use of a similar method as illustrated in  FIG. 8 , VID- 1  is generated by applying a random number of 8 bits to one part (44 bits) of the article ID consisting of MID (24 bits) and PID (20 bits), and VID- 2  is generated by applying a random number of 12 bits to SNO part (24 bits) of the article ID. 
     By executing the above described steps, a virtual ID of 88 bits is obtained, and the process for the first example is finished (step  1006 ). The virtual ID generated by the above described method is written into the RFID tag  101  together with the version number by use of the tag writer  102 . 
     (Method for Accessing Information on Article with a Tag Attached Thereon) 
       FIG. 12  is a flowchart showing an exemplary flow of a method for accessing PML information according to the first embodiment of the invention. 
     The process starts with step  1201 , and the tag reader  102  reads tag data from the RFID tag  101 . The read tag data is given to the local server  103  (step  1202 ). The local server  103  generates an ONS proxy address request having “VID. VER. onsroot. org” including virtual ID (VID) and version number (VER) as target URL (Uniform Resource Locator) and sends it to the ONS server  105  (step  1203 ). 
     When receiving the ONS proxy address request sent from the local server  103  in step  1203 , the ONS server returns, in response to the version information (VER) indicating that virtual ID is included in the tag being included in the request, the IP address of the ONS proxy  106  to the local server  103 . Then, by use of the IP address of the ONS proxy  106 , the local server  103  returns an ONS service request including VID to the ONS proxy (step  1204 ). 
     When receiving the ONS service request, the ONS proxy  106  decrypts the VID included in the request by use of the common key  1061  which the ONS proxy  106  holds to obtain an article ID (step  1205 ), and then extracts manufacturer ID (MID) included in the article ID to return a request having “MID.onsroot.org” including the MID as target URL to the ONS server  105  (step  1206 ). The ONS server  105  identifies the IP address of the PML server from the MID included in the request and returns it to the local server  103  (step  1207 ). 
     By use of the IP address of the PML server  107 , the local server  103  sends a PML service request including VID to the PML server  107  (step  1208 ). By use of the common key  1073 , the PML server  107  decrypts the VID included in the received PML service request to obtain an article ID. By use of the article ID, the PML server  107  identifies PML information to be provided and provides it for the local server  103  (step  1209 ), thereby finishing the process (step  1210 ). According to the embodiment, by executing the above described steps, the local server  103  can access the PML information stored in the PML database of the PML server  107 . 
     Embodiment 2 
       FIG. 13  is a high-level schematic diagram showing a network system according to a second embodiment of the invention. According to the second embodiment of the invention, the network system includes local servers  103   a  to  103   c , an ONS server  105 , an ONS proxy  106  and a PML servers  107   a  to  107   c , which are communicatable with each other via a network  104 . 
     It should be noted that according to the second embodiment of the invention, the network system includes a plurality of local servers each with a tag reader/writer connected thereto and a plurality of PML servers. In explaining the second embodiment of the invention, tag reader/writers  102   a  to  102   c , local servers  103   a  to  103   c  and PML servers  107   a  to  107   c  are often generically referred to as tag reader/writer  102 , local server  103  and PML server  107 , respectively. 
     (Hardware Configuration) 
     According to the second embodiment of the invention, RFID tag  101 , tag reader/writer  102 , local server  103 , network  104 , ONS server  105 , ONS proxy  106  and PML server  107  can be realized with hardware similar to that of the first embodiment. Thus, regarding the second embodiment, the description of hardware configuration of each component is omitted. 
     (Functional Block Configuration) 
       FIG. 14  is a functional block diagram of a network system according to the second embodiment of the invention. According to the second embodiment of the invention, similarly to the first embodiment, the local server  103  includes a tag reader/writer controller  1031 , an ONS resolver  1032  and a PML requester  1033 . Also, according to the second embodiment, the local server  103  includes an authentication mechanism  1034 . The authentication mechanism  1034  performs authentication with the ONS proxy  106  and stores a credential obtained as a result of authentication. The credential stored in the authentication mechanism  1034  is used by the PML server  107  determining, in response that a PML information request is received from PML requester  1033 , whether or not access to recorded PML information is permissible. 
     According to the second embodiment, a different security level is given to each of the local servers  103   a  to  103   c  (or tag readers/writers  102   a  to  102   c ). Specifically, assume that: with the connected tag reader/writer  102   a  installed in a public space, the local server  103   a  is anon-secure one with no credential given thereto; with the connected tag reader/writer  102   b  installed in an ordinary retail shop, the local server  103   b  is a low-level secure one with a low-level credential given thereto; and with the connected tag reader/writer  102   c  managed by the manufacturer of article with a tag attached thereon, the local server  103   c  is a high-level secure one with a high-level credential given thereto. 
     Similarly to the first embodiment, on the ONS proxy  106 , there is securely recorded a common key (K)  1061 . According to the second embodiment, the ONS proxy  106  further includes an authentication mechanism  1062 , and supplies a credential in accordance with authentication level to the local server  103  in response that authentication is properly performed with the authentication mechanism  1034  of the local server  103 . The ONS proxy  106  according to the second embodiment has a function of requesting the network address of a different PML server  107  from the ONS server  105  based on a result of authentication performed with the local server  103 . 
     The ONS server  105 , which can be realized by a configuration similar to that of the first embodiment, has a function of sending back the network address of a PML server  107  in response to a request. 
     According to the first embodiment, the PML server  107  includes a PML manager  1071 , a PML database  1072  and a securely recorded common key (K)  1073 . According to the second embodiment, the PML server  107  further includes an authentication mechanism  1074 . The authentication mechanism  1074  has a function of determining, according to a credential that a local server  103  requesting PML information holds, whether or not access to PML information recorded on the PML database  1072  is permissible. 
       FIG. 15  is a flowchart showing an exemplary flow of a method for accessing PML information according to the second embodiment. 
     The process starts with step  1501 . The tag reader  102  reads tag data including at least one virtual ID (VID) from the RFID tag  101 . VID can be generated by a method similar to one which was described regarding the first embodiment. 
     The read tag data is given to the local server  103  (step  1502 ). The local server  103  generates a request having “VID.VER.onsroot.org” including virtual ID (VID) and version number (VER) as target URL (Uniform Resource Locator) and sends it to the ONS server  105  (step  1503 ). 
     When receiving the request sent from the local server  103  in step  1503 , the ONS server  105  returns the IP address of the ONS proxy  106  to the local server  103  based on the request. Then, by use of the IP address of the ONS proxy  106 , the local server  103  sends an ONS service request including VID to the ONS proxy  106  (step  1504 ). 
     The above described steps are similar to those in the first embodiment. Subsequently, according to the second embodiment, the ONS proxy  106  performs authentication with the local server  103  which sent the ONS service request (step  1505 ). If authentication fails in step  1505 , then the flow proceeds from step  1506  through arrow No to step  1508  without issuing any credential. In the second embodiment, assume that the authentication between the non-secure local server  103   a  and ONS proxy  105  fails, thus issuing no credential. 
     If the authentication is properly performed in step  1505 , then the flow proceeds from step  1506  to arrow Yes, and authentication level is determined. Those skilled in the art can appropriately design and implement a method for determining authentication level. For example, authentication level can be determined by the IP address of local server, the ID of tag reader/writer or the like, which are preliminarily registered. Then, a credential corresponding to the determined authentication level is issued to the local server  103  (step  1507 ). 
     In the second embodiment, assume that: low-level authentication is properly performed with respect to the local server  103   b  with low-security level given thereto, whereby a low-level credential is issued; high-level authentication is properly performed with respect to the local server  103   c  with high-security level given thereto, whereby a high-level credential is issued. 
     Subsequently, the ONS proxy  106  decrypts VID included in the request by use of common key (K)  1061  to obtain an article ID (step  1508 ), and extracts manufacturer ID (MID) included in the article ID to send a request having “MID.onsroot.org” including the MID as target URL to the ONS server  105  (step  1509 ). According to the second embodiment, the ONS proxy  106  generates a different target URL based on a result of authentication of step  1506 . 
     Specifically, the ONS proxy  106  generates “MID.non_secure.onsroot.org” with respect to the local server  103   a  for which authentication has failed, and generates “MID.low_secure.onsroot.org” with respect to the local server  103   b  for which low-level authentication has been properly performed, and generates “MID.high_secure.onsroot.org” with respect to the local server  103   c  for which high-level authentication has been properly performed. 
     When receiving the request, the ONS server  105  identifies the IP address of an appropriate PML server  107  from the MID and security level included in the request and returns it to the local server  103  (step  1510 ). It should be noted that the returned IP address can change according to the contents of target URL. 
     Specifically, according to the second embodiment, the ONS server  105  returns the IP address of PML server  107   a  to the local server  103   a , and returns the IP address of PML server  107   b  to the local server  103   b , and returns the IP address of PML server  107   c  to the local server  103   c.    
     By use of the acquired IP address of PML server  107 , the local server  103  sends a PML service request including VID to the PML server  107  (step  1511 ). When receiving the PML service request, the PML server  107  firstly determines whether or not the server itself is a secure site (step  1512 ). 
     If it is determined in step  1512  that the PML server  107  is not a secure site, then the flow proceeds through arrow No to step  1514  because the PML information stored in the above PML server  107  is accessible by anyone. If it is determined in step  1512  that the PML server  107  is a secure site, then the PML server  107  certifies, by use of authentication mechanism  1074  whether or not the local server  103  which has sent the PML service request holds an appropriate credential (step  1513 ). 
     If the authentication mechanism  1074  of PML server  107  determines in step  1513  that the local server  103  holds an appropriate credential, the flow proceeds through arrow Yes to step  1514 . In step  1514 , the PML server  107  decrypts VID included in the PML service request by use of the common key (K)  1073  to obtain an article ID. By use of the article ID, the PML server  107  identifies PML information to be provided, and then provides it for the local server  103 , thereby finishing the process (step  1516 ). 
     If the authentication mechanism  1074  of PML server  107  determines in step  1513  that the local server  103  does not holds an appropriate credential, then the flow proceeds through arrow No to step  1515 , and the PML server  107  rejects access to PML information by the local server  103  (step  1515 ), thereby finishing the process (step  1516 ). 
     The previous description is of preferred examples for implementing the invention, and the technical scope of the invention should not be restrictively interpreted by the description of the embodiment but be defined by the claims. Those skilled in the art will recognize that many changes or modifications to the embodiments described above are possible. For example, while the above embodiments are described under an assumption that encryption and decryption of virtual ID are performed with a secret key cryptography using a common key, encryption and decryption of virtual ID may of course be performed with a public key cryptography using a pair of secret key and public key. Further, for example, while ONS proxy and ONS server is constructed as separate hardware in the above described embodiments, the functions of ONS proxy and ONS server may be implemented by the same hardware. Specifically, those skilled in the art can easily and properly design the hardware arrangement and implementation of servers, functional blocks, program modules and the like each described above in the embodiments. It will be apparent from the description of the claims that an embodiment with such changes or modifications applied thereto can also be included in the technical scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a high-level schematic diagram showing a network system according to a first embodiment of the invention; 
         FIG. 2  is an external view of a first exemplary RFID tag being usable in the first embodiment of the invention; 
         FIG. 3  is an external view of a second exemplary RFID tag being usable in the first embodiment of the invention; 
         FIG. 4  is an external view of an exemplary tag reader/writer being usable in the first embodiment of the invention; 
         FIG. 5  is a diagram showing an exemplary hardware configuration of a computer apparatus that functions as a local server, etc. in the first embodiment of the invention; 
         FIG. 6  is a functional block diagram of the network system according to the first embodiment of the invention; 
         FIG. 7  is an image of a first exemplary data structure of data stored in RFID tag according to the first embodiment of the invention; 
         FIG. 8  is an image of a second exemplary data structure of data stored in RFID tag according to the first embodiment of the invention; 
         FIG. 9  is an image of data structure of an article ID according to the first embodiment of the invention; 
         FIG. 10  is a flowchart showing an exemplary flow of a method for generating a virtual ID according to the first embodiment of the invention; 
         FIG. 11  is a flowchart showing OAEP algorithm used to generate a virtual ID according to the first embodiment of the invention; 
         FIG. 12  is a flowchart showing an exemplary flow of a method for accessing PML information according to the first embodiment of the invention; 
         FIG. 13  is a high-level schematic diagram showing a network system according to a second embodiment of the invention; 
         FIG. 14  is a functional block diagram of the network system according to the second embodiment of the invention; 
         FIG. 15  is a flowchart showing an exemplary flow of a method for accessing PML information according to the second embodiment of the invention; 
         FIG. 16  is an overall image of a network system according to prior art; and 
         FIG. 17  is an image of data structure of data stored in RFID tag according to prior art. 
     
    
    
     DESCRIPTION OF SYMBOLS 
     
         
           101  . . . RFID tag 
           102  . . . Tag reader/writer 
           103  . . . Local server 
           104  . . . Internet 
           105  . . . ONS server 
           106  . . . ONS proxy 
           107  . . . PML server 
           201 ,  301  . . . IC chip 
           202 ,  302  . . . Antenna