Abstract:
This invention allows a toll authority to monitor transaction numbers which are sent from a transponder ( 14 ) to an interrogator ( 12 ). By incrementing the transaction counter stored in the transponder with successful transactions the toll authority can ascertain whether accounting of a transaction has been missed (i.e., a transaction number missing from the sequence), or double-counted (i.e., two transactions with the same transaction number).

Description:
This application is a division of Ser. No. 08/518,068, filed Aug. 22, 1995, now U.S. Pat. No. 6,317,721, which is a continuation-in-part of Ser. No. 08/420,849, filed Apr. 10, 1995, now abandoned. 
    
    
     CROSS-REFERENCE TO RELATED PATENTS 
     The following commonly assigned patent applications are hereby incorporated herein by reference: 
     
       
         
               
               
               
             
           
               
                   
               
               
                 Pat No./Serial No. 
                 Filing Date 
                 TI-Case No. 
               
               
                   
               
             
             
               
                 08/021,123 - 5701127 
                 February 23, 1993 
                 TI-17529 
               
               
                 08/233,839 - 5471212 
                 April, 26, 1994 
                 TI-18205 
               
               
                 08/339,091 - 5525992 
                 November 11, 1994 
                 TI-18332 
               
               
                   
               
             
          
         
       
     
     FIELD OF THE INVENTION 
     This invention generally relates to recognition systems of the type which include an interrogator and a transponder, and more particularly to such a system in which the interrogator transmits an interrogation signal to the transponder in response to which the interrogator transmits back to the interrogator a response signal. The invention further generally relates to systems and methods implementing smartcards with the recognition system. In specific embodiments, the invention relates to an Automatic Vehicle Identification (AVI) type of recognition system. 
     BACKGROUND OF THE INVENTION 
     The invention will be described in the context of an Automatic Vehicle Identification (AVI) system capable of exchanging data codes between an interrogator and a transponder. The AVI field is but one environment in which the inventive concepts described herein can be applied. Systems using batteryless transponders, as well as transponders with batteries, may be used for identifying or locating objects bearing the transponders such as cattle, luggage or other items. 
     With respect to AVI systems, generally, the interrogator is provided in a toll booth of a toll road, parking garage or other limited access facility. The interrogator (reader) identifies passing automobiles by sending wireless interrogation signals to a transponder (tag), which would normally be a small, self-contained unit placed, for example, on the dashboard or windshield of the car. In this way the car (or other vehicle or object) can be identified in a speedy and efficient manner. Depending on the use of the system, an account associated with the driver, owner, or other designated person can be debited with an access charge. Compatibility standards for one such AVI system are set out in Title 21, Division 2, Chapter 16, Articles 1-4 of the California Code of Regulations, herein known as the Caltrans specification or Caltrans spec. The AVI equipment for toll collection typically consists of two functional elements: vehicle-mounted transponders and fixed-position interrogators. 
     In prior art applications there have been so-called “money on the tag” applications. In these applications the user would take his transponder to a toll agency where special equipment could program data, representing a certain amount of money, into the transponder. The main disadvantage to this prior art application is the loss of privacy in that the user would have to take his transponder to another person, that person typically being the tollway agent. See e.g., U.S, Pat. No. 5,144,5,53 to Hassett et al. This prior art application also has a substantial disadvantage in that it does not provide the convenience of the smartcard. 
     Within the prior art of payment systems, it is known to use “smartcards” for exchanges of goods and services. Smartcards are generally about the size of a credit card and have a microprocessor embedded in them. The smartcard can generally read, write and store information. In a typical application, the user will access an automated machine through which data representing an amount of money may be written into the smartcard memory. Each time a good or service is purchased using the smartcard, the data in the smartcard memory is debited to reflect the amount of the transaction. An advantage of using smartcards, in addition to potential increases in user privacy, is the potential to eliminate point-of-sale equipment. Smartcards have been implemented, or are anticipated to be implemented, in numerous applications: pay phones, automated banking, automated vending and the like. Automated machines for storing data in smartcards might be placed in post offices or stores. 
     In prior art AVI applications using smartcards, dual gantry systems are used. In the dual gantry system the transponder smartcard access is begun at a first gantry. Because of the slowness of the transponder smartcard interface the transaction must be completed at a later gantry. The disadvantages of such a prior system is the cost associated with construction of multiple gantries per toll plaza. Another disadvantage of such a system is the complexity of coordinating actions between the first gantry and the later gantry. 
     SUMMARY OF THE INVENTION 
     This invention allows a user to have a smartcard and a smartcard-based transponder. This smartcard-based transponder can accept money from the smartcard. The amount transferred from the smartcard can be stored in the transponder memory. At a toll plaza, a toll amount can be subtracted within a short period of time, so that a vehicle bearing the transponder will not pass through an interrogator read zone (the zone in which the transponder and interrogator may perform RF communications) before an appropriate toll amount can be decremented from the amount stored within the transponder. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a block circuit diagram of an interrogator and transponder arrangement according to the present invention; 
     FIG. 2 is a generalized side elevation of a typical installation of an Automatic Vehicle Identification (AVI) System in accordance with FIG. 1; 
     FIG. 3 is a block circuit diagram of the transponder and interrogator arrangement usable in the systems of FIGS. 1-2; 
     FIG. 4 is a more detailed block circuit diagram of the transponder of FIG. 3, depicting the transponder&#39;s internal components and a smartcard operable to communicate with the transponder; and 
     FIG. 5 is a generalized timing diagram describing the method of using the preferred embodiment transponder in a smartcard application. 
     Corresponding numerals and symbols in the different figures refer to corresponding parts unless otherwise indicated. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a block diagram of an AVI system  10  in which an interrogator  12  communicates with a remote transponder  14  by transmitting an interrogation signal  15   a  to the transponder  14  in response to which the interrogator  12  transmits back to the interrogator  12  a response signal  15   b  containing a transponder-unique identifying code (ID). In a typical AVI system, the interrogator  12  will convey this information into a host computer (host)  16  for maintaining accounting information with respect to the transponder  14  and the smartcard  66  (see FIG. 4) associated with the transponder  14 . 
     Referring to FIG. 2, traffic lanes  28  are located at a traffic control point such as a toll plaza  29 . Each traffic lane  28  has an associated interrogator  12 . Each interrogator  12  initiates and maintains communication via an RF data link with transponders  14  carried on vehicles  26  travelling within the interrogator&#39;s  12  associated lane  28 . The interrogators  12  may have unique internal electrical parameters such as interrogator lane position, interrogator control parameters, and interrogator reference frequency. The role of the interrogator  12  in this application is: to trigger or activate a transponder  14 , to interrogate or poll the transponder  14  for specific information, and if a valid data exchange has taken place, to acknowledge that fact to the transponder  14 . As shown in FIGS. 1-2, the interrogator  12  has an antenna  18  which is preferably mounted above the roadway. Interrogator electronics  20  are connected to the antenna  18  by suitable cable, such as for example an RF coax  22 . 
     The interrogator  12  communicates in a wireless fashion with the transponder  14  by sending on/off keyed modulated signals to the transponder  14 . Interrogator  12  then sends a continuous wave RF signal to the transponder  14 . The transponder  14  may respond to the interrogator  12  by backscatter modulating the continuous wave RF signal such as described in U.S. Pat. No. 4,739,328 by Koelle, et al. Details of the communication between the interrogator  12  and the transponder  14  will be further described herein. The function of the optional host  16  is to control the operations of the interrogator  12  and the peripheral functions of the toll plaza. Such peripheral functions might include operation of traffic control gates and other lane enforcement equipment such as cameras and traffic lights. Still other peripheral functions might include communications between interrogators  12  and communications with a central office computer (not shown) that might maintain accounting information. Connection  24  between the interrogator  12  and the host  16  as shown in FIG. 1 may be an ethernet, token ring, RS232, RS422 or other connection. 
     FIG. 2 shows a side view of a typical AVI system  10  installation. In this figure a vehicle  26  travels on a vehicle lane  28  and approaches the antenna  18 . A transponder  14  is located on or within a vehicle  26 . Preferably the transponder  14  is mounted to the vehicle front window. In certain applications such as in unusually large vehicles other locations such as on a truck&#39;s bumper might be appropriate to reduce variation in height of transponder  14 . As shown in the figure, the vehicle  26  carrying the transponder  14  approaches the interrogator  18  at the toll plaza  29 . Further details regarding the communication between the transponder  14  and the interrogator  12  will be discussed herein. The components of the interrogator  12  and transponder  14  will also be discussed in greater detail. 
     FIG. 3 provides a block diagram of the major components of the AVI system  10 . First, a transponder  14  will be described with reference to FIG. 4 together with FIGS. 2 and 3. The AVI system  10  preferably comprises directional antennas  18 , each antenna  18  focused on an associated vehicle lane  28 . A vehicle  26  or vehicles  26  may travel on each lane  28 , each vehicle  26  carrying one or more transponders  14 . Each transponder  14  preferably comprises: an antenna  30 , an analog or analog/digital ASIC  32 , a digital ASIC  34 , and a modulated reflector  41 . Antenna  30  and modulated reflector  41  may form a single integrated antenna  31 . Preferably ASIC  32  and ASIC  34  are integrated as a single ASIC. 
     With further reference to FIGS. 3, the transponder antenna  30  is operable to receive RF transmissions from the interrogator  12 . The analog ASIC  32  converts a signal supplied by the transponder antenna  30  to a voltage which upon exceeding a threshold activates the transponder  14 . Preferably, the analog ASIC  32  senses high frequency modulation present upon the signal from the transponder antenna  30  and will only activate the transponder  14  upon presence of that specific modulation frequency. In this way, the transponder is relatively immune to being awakened by spurious RF transmissions not originating in the interrogator  12 , but only is activated when a particular frequency is transmitted by the interrogator  12 . The voltage threshold may be adjustable. 
     Referring still to FIG. 3, the analog ASIC  32  and digital ASIC  34  typically process the interrogation signal received from the transmitter  52  and formulate the necessary reply data. The digital ASIC  34  then provides a formatted reply data stream to the modulated reflector  41 . This ASIC  34  might be a simple digital system using a fixed format, or a more versatile digital processing system which can incorporate a number of options. Many functions can be envisioned for the ASIC  34  to accomplish. Examples of such functions include but are not limited to: data storage, data exchange history, and battery capacity warning. The modulated reflector  41  is modulated by changing its apparent wave length, preferably between one fourth and one half the carrier wave length. When the apparent wave length of the modulated reflector  41  is ½, then the antenna  30  reflects a large portion of the incident carrier energy. When the modulated reflector  41  has an apparent length of ¼, it reflects very little of the incident carrier. As is well known in the art, a switching of an antenna between ½ and ¼ can be accomplished by connecting or disconnecting two ¼ stubs. For the described embodiment, the change in Reflective Cross Section (RCS) is preferably between 45 cm 2  and 100 cm 2 . By varying the RCS according to the specified format, data is sent from the transponder  14  to the interrogator  12 . The transponders  14  are typically self-contained on a small credit card size assembly that is completely portable. Preferably an internal battery is provided to give operating power to the transponder  14 . Alternatively the transponder  14  might gain its operating power directly from the RF signal as set forth in commonly assigned U.S. Pat. No. 5,053,774 to Schuermann. 
     Now that the components of the transponder  14  have been generally described, with further reference to FIG. 3, a preferred embodiment interrogator  12  will be generally described. The interrogator  12  is located at a specific point where data exchange is desired, such as a toll plaza. The AVI system  10  may include a common reference oscillator  50  which generates at its output  51  a reference carrier wave for coordination between interrogators  12 . Each interrogator  12  has a directional antenna  18  and a transmitter  52 , which transmit a trigger signal of sufficient field strength at a pre-selected distance to trigger or activate a transponder  14  being carried in a vehicle  26  in the interrogator&#39;s associated vehicle lane  28 . 
     FIG. 4 illustrates, in block diagram form, a preferred embodiment of a transponder  14  in communication with the smartcard  66  through interface  68 . Preferably the smartcard  66  will be provided by the system user. The smartcard  66  will slip into socket  70  so that communication may be effected through interface  68 . Transponder  14  comprises a user interface  72 , which in turn has an LCD  74  and a keyboard  76 . The LCD  74  is preferably used to show the user the amount of money stored in the transponder  14  or the amount last debited. After the microcontroller  78  of the transponder  14  “authenticates” that the smartcard  66  is compatible with the transponder  14  application, the microcontroller  78  may optionally begin an “authorization” process by which the user may input a PIN through the keyboard  76 . Other “authorization” processes may be used to assure that the smartcard  66  may permissibly be used with the transponder  14 . Upon entering of the PIN, the microcontroller  78  of the transponder  14  will compare this PIN to an encoded identification value stored on the smartcard  66  and transmitted to the microcontroller  78  as a part of the smartcard certificate before allowing any money or other data to be downloaded from the smartcard  66 . Preferably this authentication and authorization process will be effected through the interface  68 , which is preferably a serial interface. 
     In an embodiment of the invention the smartcard  66  would transfer data representing an amount that is preferably two to three times the amount of a typical toll in the transponder&#39;s  14  intended environment. This transaction will generate information representing such things as the amount of the transaction, the toll agency, the smartcard identification, and other information. 
     Initially, information is generated by the smartcard  66  and stored in the transponder  14 . The information actually generated by the smartcard  66  is called a smartcard certificate. This smartcard certificate will generally comprise: 1) a portion of unencrypted data representing location, time, smartcard number, or other information necessary for the system administrator to ensure that a valid transaction took place; and 2) an encrypted portion comprising command and other information. If the microcontroller  78  is able to successfully read this encrypted portion, the certificate is then stored in the transponder  14  under control of the transponder microcontroller  78 . This smartcard certificate may be stored in the RAM  80  or the EEPROM  82 . The advantage of storing in the EEPROM is the permanent non-volatile characteristics of storage within EEPROM. 
     For security and privacy reasons, an encrypter/decrypter  84  is provided in communication with microcontroller  78 . The encrypter/decrypter  84  will encrypt and decrypt data which is transferred to and from the smartcard  66 . This will prevent individuals from being able to circumvent use of the smartcard by tampering with the transponder  14  so as to increase the amount of money stored in the transponder and also from being able to transfer an apparently larger amount of money back into the smartcard  66  from the transponder  14 . The transponder  14  will preferably run on batteries, but may also be connected into the automotive or other system main power supply. The transponder  14  also may be integrated into a vehicle or other system. 
     The smartcard  66  may be taken by the user to a machine similar to automatic teller machines (ATM) into which money may be placed and value units representing that same amount of money or another amount of money may be placed in the smartcard  66 . Alternatively, money may be debited from an account or charged to a credit account and the data representing that amount of money or another amount of money may be placed in the smartcard  66 . Once this data has been placed in the smartcard  66  from the external card machine, then the user may take the smartcard with him and use it in conjunction with his transponder  14  or perhaps in other applications using compatible smartcards  66 . 
     The advantage of using a smartcard  66  in this manner is that it gives the user a certain degree of privacy not available in prior art systems. In systems where an external machine such as an ATM is used for instance, the money (cash) may be placed into the machine directly and no identification of the user would be necessary. 
     In a typical toll transaction sequence, upon entering a toll area, the toll booth interrogator  10  will interrogate the transponder  14 . The interrogation will begin with an approach, or wake-up, message to alert the transponder  14  that it is in the toll area. The interrogator  10  then sends a presentation request comprising gantry identification and location detail, acceptable contracts or payment methods (credit card, debit card, or other payment systems). In the presentation response, the transponder  14  informs the interrogator  10  of its identity, the payment method it wishes to use, the vehicle classification information, an authorization code, and similar information, a random number, and the account authorization Message Authentication Code (MAC), which is an encrypted confirmation code using an encryption method such as the Data Encryption Standard (DES). 
     Next the interrogator  10  sends to the transponder  14  a transaction request, which comprises the fee to be charged, date and time, and a cipher code, which is an encrypted representation of the random number sent from the transponder  14  to the interrogator  10  during the presentation response. At this time the transponder  14  unencrypts the code, and if the code matches the random number sent during the presentation response, the authorization is complete. 
     The transponder  14  will thereupon send a transaction response comprising a status code, a payment ID, and an encrypted MAC to act as a receipt for the transaction. The transaction response will either be the transponder certificate or an error code explaining why a transponder certificate could not be generated and the transaction failed. 
     The interrogator  10  will process that information and send back a transaction receipt to terminate the transaction. The transponder  14  may then find an opportune moment to subtract from the running total of value units stored in the transponder memory  80 , 82 . Alternatively in a system such as the Kansas Turnpike, where the amount of the toll is proportional to the distance traveled on the toll road, perhaps upon entering the toll facility nothing more than the location code of the entrance point will be stored in the transponder  14 . In this scenario, upon approaching the toll area the transponder  14  will report its entry point to the interrogator  10 . The interrogator  10  will then compute the proper toll and transmit it back to the transponder  14 . At this time, the toll amount will be subtracted from the running total stored within the transponder  14  as described above. In the toll booth transaction, two certificates are transmitted from the transponder  14  to the interrogator  10 . 
     Transferring both the smartcard certificate and the transponder certificate from the transponder  14  to the interrogator  10  allows the managing entities to keep a “shadow balance” or a running count of how many times a given smartcard  66  has been debited and that the amount of money charged on a given smartcard is equivalent to the money put into that same smartcard  66 . This would not necessarily violate the users&#39; privacy, since it is not a requirement that a name ever be associated with a given smartcard  66 . Each transaction will have a transaction number associated with it so that when an accounting is made of all the transactions, missing transactions can be easily identified. 
     This method of tracking transactions using transaction numbers, proceeds as follows. Initially, an initial transaction count is established in a transaction register of said transponder  14 . The interrogator  12  subsequently transmits an interrogation and thereafter the responder  14  sends a response. Preferably this response would also comprise data representing the value of the transaction count that is presently stored in said transaction register. The transaction register would preferably operate under control of the transponder microcontroller  78 . Alternatively the transponder  14  could transmit the transaction count to the interrogator  12  in a separate transmission. 
     In this embodiment, the value stored in the transaction register will be incremented or otherwise modified each time a successful interrogation and response transaction is completed between the transponder  14  and an interrogator  12 , more specifically, the value stored in the transaction register might only be updated when a toll is debited from the transponder, thus a new receipt number will only be generated to accord with a single toll transaction. The modification of the transaction register might be effected by command from the interrogator to the transponder upon an acknowledgement signal from said interrogator indicating that a successful interrogation and response cycle had been completed. 
     One application of this transaction number data would be to submit all or some transactions from the interrogator to a host or processing unit for analysis. By this method the processing unit can compile the submitted transponder responses along with their associated transaction numbers or receipt numbers. In the event of a double inclusion of a certain number or in the event of a certain receipt number being skipped, it is likely that an error or a fraud has been committed. 
     By transmission of the approach message, presentation request, transaction request, transaction response, and transaction receipt, and handling the updating of information directly between the transponder memory  80 ,  82  and the interrogator  10  instead of directly between the smartcard  66  and the interrogator  10 , the problems associated with effecting data transfers within a communications window during which the transponder lies within a interrogators beam is overcome. By the extensive security, protocols, and handshaking between the interrogator  10  and the transponder  14 , security concerns associated with traditional “money on tag” applications have been largely overcome. 
     The transaction speed is vastly improved in this embodiment relative to systems in which the smartcard  66  communicates directly with the interrogator  10  through the transponder modulator and demodulator. This is because most smartcards  66  have slow, standard serial interfaces. It is important that the data transfer time between the interrogator  10  and the transponder  14  not depend on the access time for retrieving and storing data from and to the smartcard  66 . By keeping the data temporarily within the memory of the transponder, the memories  80 ,  82  of the transponder  14 , the slower communications between the transponder  14  and the smartcards  66  may take place after the communication is with the toll plaza is complete. 
     In one embodiment the entire value stored within the smartcard  66  may be transferred to the transponder  14 . Upon removal of the smartcard  66 , any remaining money could be transferred back into the smartcards  66 . This is Where the importance of encryption of the data stored within the transponder  14  comes into play. It is very desirable that an individual not be able to manipulate the data which is stored in the transponder  14  and then upon transferring the money back from the transponder  14  to the smartcard  66 , a larger amount of money does not appear because of tampering. The role of the encrypter  84  is to encrypt this data. 
     Preferably an entire data transaction is accomplished within  10  milli-seconds. During this time the transponder  14  will respond to an interrogation signal from the interrogator  10 . The toll is determined and transmitted to the transponder  14 . The certificates are generated and the proper amount is debited from the running total within the transponder  14 . Where this invention preferably allows these transactions to be performed within approximately 10 milliseconds, prior art smartcard transponder applications typically took 300 to 500 milliseconds. Once this transaction has been completed, the transponder  14  may update the smartcard  66  when the criticality of the communication speed is not as great, i.e., when the transponder is no longer within the interrogator  10  reading range. 
     The smartcard  66  could be interchanged between users and between applications. Thus this application overcomes the problem of storing money actually and directly on the transponder  14 , which has a disadvantage of its lack of mobility in that the transponder would generally be stored in a single automobile and would not be able to be used in other applications. In the current embodiment, a user may take his smartcard  66  and use it with his transponder  14  for tolling applications, as well as perhaps in vending machines, public pay telephones, or other applications. 
     This embodiment further has the advantage of increased privacy and flexibility with respect to “money on tag” systems in which the money alone is stored directly on the tags. In such prior systems, special agents are required with special machines to input money into the transponder  14 . In this embodiment, the transponder  14  is loaded with money from the smartcard  66 , which may have money placed in it through automatic machines similar to automatic teller machines (ATM). 
     FIG. 5 gives a broad-level timing diagram for an embodiment of this invention. The timing may be considered as being divided into  3  distinct phases. The first phase, phase “A”—Insertion describes the part of the user operation when the user inserts the smartcard  66  into the transponder  14 . This step is designated as block  102  in FIG.  5 . 
     Next the user may optionally input a personal identification number (PIN) into the keyboard  76 . This is designated as block  104 . Upon the user&#39;s entrance of the PIN, the microcontroller  78  of the transponder  14  will compare this PIN to an encoded identification value stored on the smartcard  66  and transmitted from the smartcard to the microcontroller  78  as a part of the “authorization” process. Depending on the desired level of security this authorization process may be foregone. 
     At block  106  the smartcard  66  generates a smartcard certificate comprising: 1) a portion of unencrypted data representing location, time, smartcard number, value units representing the amount of money stored on the smartcard, and other information necessary for the system administrator to ensure that a valid transaction took place; and 2) an encrypted portion comprising command and other information. If the microcontroller  78  is able to successfully read this encrypted portion, the certificate is then stored in the transponder  14  under control of the transponder microcontroller  78 . The microcontroller  78  receives this value and generates a certificate storing this certificate in either RAM  80  or EEPROM  82 . Once this has been done, the transponder  14  is ready to undergo transactions with an interrogator  12 . 
     The transactions phase is shown as phase “B” in FIG.  5 . This phase is entered when the transponder enters a toll zone as shown in block  110 . The interrogation will begin with an approach, or wake-up, message to alert the transponder  14  that it is in the toll area. The interrogator  10  then sends a presentation request comprising gantry identification and location detail, acceptable contracts or payment methods. The transponder  14  then in its presentation response informs the interrogator  10  of its identity, the payment method it wishes to use, the vehicle classification information, an authorization code, and similar information, a random number, and the account authorization Message Authentication Code (MAC), which is an encrypted confirmation code using an encryption method such as the Data Encryption Standard (DES). Next the interrogator  10  sends to the transponder  14  a transaction request, which comprises the fee to be charged, date and time, and a cypher code, which is an encrypted representation of the random number sent from the transponder  14  to the interrogator  10  during the presentation response. At this time the transponder  14  unencrypts the code, and if the code matches the random number sent during the presentation response, the authorization is complete. 
     At block  112  the transponder  14  will provide a transaction response comprising a status code, a payment ID, and an encrypted MAC to act as a receipt for the transaction. The transaction response will either be the transponder certificate or an error code explaining why a transponder certificate could not be generated and the transaction failed. 
     The interrogator  10  will process that information and send back a transaction receipt to terminate the transaction (block  114 ). The transponder  14  may then find an opportune moment to subtract from the running total of value units stored in the transponder memory  80 , 82 . The microcontroller  78  performs mathematical operations to make this deduction and again stores the information in the RAM  80  or the EEPROM  82 . Steps  110 - 118  may be repeated as long as the amount of currency in the tag has not been subtracted below its minimum balance. 
     Phase “C” designates the removal of the smartcard upon the user request at block  120 . At this time any amount of money remaining in the transponder is preferably credited back to the smartcard  66  via the interface  68 . This transfer may preferably be encrypted. The money in the smartcard  66  is updated by generation at block  124  of another certificate and the storage of the certificate in the smartcard  66 . The smartcard may now be removed from the transponder  14  at block  126 . 
     A few preferred embodiments have been described in detail hereinabove. It is to be understood that the scope of the invention also comprehends embodiments different from those described, yet within the scope of the claims. 
     For example, display devices can be cathode ray tubes or other raster-scanned devices, liquid crystal displays, or plasma displays. “Microcomputer” in some contexts is used to mean that microcomputer requires a memory and “microprocessor” does not. The usage herein is that these terms can also be synonymous and refer to equivalent things. The terms “controller,” “processing circuitry,” and “control circuitry” comprehend ASICs (application specific integrated circuits), PAL (programmable array logic), PLAs (programmable logic arrays), decoders, memories, non-software based processors, or other circuitry, or digital computers including microprocessors and microcomputers of any architecture, or combinations thereof. Memory devices include SRAM (static random access memory), DRAM (dynamic random access memory), pseudo-static RAM, latches, EEPROM (electrically-erasable programmable read-only memory), EPROM (erasable programmable read-only memory), registers, or any other memory device known in the art. Words of inclusion are to be interpreted as nonexhaustive in considering the scope of the invention. 
     Frequency shift keyed (FSK) modulation is envisioned as a possible data modulation scheme, as well as pulse-pause modulation, amplitude shift keying (ASK), quadrature AM (QAM) modulation, phase shift keying (PSK), quadrature phase shift keying (QPSK), or any other modulation. Different types of multiplexing such as time or frequency modulation might be effected to avoid cross-signal interference. Modulation might be effected by back-scatter modulation, by active modulation of a carrier, or by another method. 
     Implementation is contemplated in discrete components or fully integrated circuits in silicon, gallium arsenide, or other electronic materials families, as well as in optical-based or other technology-based forms and embodiments. It should be understood that various embodiments of the invention can employ or be embodied in hardware, software or microcoded firmware. 
     While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.