Abstract:
Methods and systems are provided for information access control. Information read from a portable device is received. One portion of the information includes optical information read optically from the portable device and another portion of the information includes electromagnetic information read electromagnetically from the device. A cryptographic key is determined from the received information. The portable device is communicated with electromagnetically to retrieve an electromagnetic transmission packet that includes encrypted data. The retrieved encrypted data are decrypted using the determined cryptographic key.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of U.S. patent application Ser. No. 10/997,770, entitled “METHODS AND SYSTEMS FOR ELECTROMAGNETIC INITIATION OF SECURE TRANSACTIONS,” filed Nov. 23, 2004 by Brian T. Kean (“the &#39;770 application”). The &#39;770 application is a nonprovisional of, and claims the benefit of the filing date of, U.S. Prov. Pat. Appl. No. 60/530,510, entitled “METHODS AND SYSTEMS FOR ELECTROMAGNETIC INITIATION OF SECURE TRANSACTIONS,” filed Dec. 17, 2003 by Brian T. Kean, the entire disclosure of which is incorporated herein by reference for all purposes. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This application relates generally to information security. More specifically, this application relates to methods and systems for electromagnetic initiation of secure transactions.  
         [0003]     In recent years, a number of proposals have been put forth to expand the flexibility with which consumers may provide access to accounts when engaging in financial transactions. Currently, there are a number of different types of transactions that permit such access, such as debit transactions, credit transactions, and stored-value transactions. For example, debit transactions may provide information during the transaction regarding a demand-deposit, checking, or savings account so that a debit of funds may be applied directly to the account substantially contemporaneously with the transaction. In the case of a credit transaction, account information provided during the transaction may define a credit account against which the customer may charge funds up to a predefined credit limit. Similarly, account information provided during a stored-value transaction identifies a stored-value account against which the customer is authorized to debit finds.  
         [0004]     Because of its sensitive nature, a major concern when handling financial-account information during such transactions is the security of the information. Currently, the most common way to ensure that the information is treated securely is to provide the information on a magnetic stripe that is affixed to a plastic card entrusted to the control of the customer. The magnetic-stripe image on the card is read during a transaction with a magnetic-stripe reader and transmitted for approval by an entity responsible for the identified financial account. In some instances, a personal identification number may be required to support the transaction, but not in other instances.  
         [0005]     Many proposals to allow radio-frequency (“rf”) initiation of transactions do nothing more than suggest loading the magnetic-stripe image onto an rf chip. These suggestions fail to account for additional security and authentication schemes that would add extra processing to the authorization system or add extra complexity to the chip, but which would be needed to ensure the security of the financial-account information. There is accordingly, a general need in the art for methods and systems that provide for electromagnetic initiation of transactions that maintain the security of the information.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     Embodiments of the invention thus provide methods and systems for processing secure transactions that make use of electromagnetic initiation of the transactions. In a first set of embodiments, a method is provided for processing a secure transaction. An electromagnetic transmission packet is received from a portable device at a processing device. The electromagnetic transmission packet includes an encrypted magnetic-stripe image and an encrypted version of an alphanumerical identifier. A keyed nonencrypted version of the alphanumerical identifier is received at the processing device, and the encrypted version of the alphanumerical identifier is decrypted. The decryption of the encrypted version of the alphanumerical identifier is compared with the nonencrypted version of the alphanumerical identifier. Thereafter, a decryption of the encrypted magnetic-stripe image is transmitted to a host system for processing the secure transaction using an account identified by the decryption of the magnetic-stripe image.  
         [0007]     In some instances, the electromagnetic transmission packet is received at a radio frequency. Further, in some embodiments, a barcode scan of a barcode may also be received, with a barcode value that corresponds to the barcode being transmitted with the decryption of the encrypted magnetic-stripe image. The validity of the barcode may also be verified, such as by calculating a check digit from characters comprised by the scanned barcode and comparing the calculated check digit with a comparison check digit comprised by the scanned barcode. In one embodiment, an antenna is activated to receive the electromagnetic transmission packet only after verifying the validity of the barcode, with the antenna being deactivated after receiving the electromagnetic transmission packet, thereby providing electrical savings and reducing signal-pollution radiation. In other embodiments, the alphanumerical identifier may be transmitted with the decryption of the encrypted magnetic-stripe image.  
         [0008]     In some cases, an identification of the processing device and a transaction identifier may be transmitted to the portable device. The electromagnetic transmission packet further includes an encryption of the transaction identifier and the identification of the processing device. The encryption of the transaction identifier and the identification of the processing device may be decrypted by the processing device. The decryption of the transaction identifier and the identification of the processing device may then be compared with the identification of the processing device and the transaction identifier transmitted to the portable device. In one embodiment, a symmetric-key encrypted portable-device transaction counter and incremented processing-device transaction counter are received. The portable-device transaction counter and incremented processing-device transaction counter are decrypted. A different is calculated between the decrypted portable-device transaction counter and the decrypted incremented processing-device transaction counter to verify that the portable device was able to decrypt an original encrypted value. In one embodiment, the portable-device transaction counter is further transmitted to a host for fraud detection.  
         [0009]     In various embodiments, the electromagnetic transmission packet may further include a digital signature, the authenticity of which may be verified as part of the method. The encrypted magnetic-stripe image may be encrypted with a variety of techniques, including an elliptic-curve cryptographic technique. Also, in some embodiments, the electromagnetic transmission packet may additionally included nonencrypted information. For example, the nonencrypted information may comprise a key identification that defines a key for decrypting the encrypted magnetic-stripe image.  
         [0010]     In a second set of embodiments, a processing device is provided for processing a secure transaction. The processing device comprises a radio-frequency antenna, a keypad equipped for receipt of entry of alphanumerical strings, a communications system, and a processor. The processor is provided in communication with the radio-frequency antenna, the keypad, and the communications system and is coupled with a computer-readable storage medium. The computer-readable storage medium has a computer-readable program embodied therein for directing operation of the processor to implement the methods described above.  
         [0011]     In a third set of embodiments, a portable device is provided for use in processing a secure transaction. The portable device comprises a radio-frequency antenna, a memory device, an activation switch, and a processor. The processor is provided in communication with the radio-frequency antenna, the memory device, and the activation switch. The memory device has a computer-readable program embodied therein for transmitting a radio-frequency transmission packet that includes an encrypted magnetic-stripe image and an encrypted version of an alphanumerical identifier to a processing device. The transmission is performed with the radio-frequency antenna and in accordance with a state of the activation switch.  
         [0012]     In some such embodiments, the computer-readable program further includes instruction for receiving, with the radio-frequency antenna, an identification of the processing device and a transaction identifier. The identification of the processing device and the transaction identifier are encrypted, with the encrypted versions being transmitted to the processing device as part of the radio-frequency transmission packet. The states of the activation switch may define on and off states of the portable device in some embodiments. In other embodiments, the states of the activation switch define which of a plurality of accounts is to be used for the secure transaction. A default of the plurality of accounts may require correct identification of the alphanumerical identifier. The activation switch may comprise a membrane switch. In some cases, the portable device may also comprise a plurality of input ports for payment modules, with the encrypted magnetic-stripe image defining at least one of the payment modules. The payment modules may comprise stored-value modules, debit modules, credit modules, and the like, and may be provided in the form of support interface modules (“SIMs”).  
         [0013]     In a fourth set of embodiments, a system is provided for processing secure transactions. The system comprises a host system, a plurality of processing devices such as those described above, and a plurality of portable devices such as those described above. Processors comprised by the processing devices and the portable devices are configured to process the secure transactions in accordance with the methods described above. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings wherein like reference numerals are used throughout the several drawings to refer to similar components. In some instances, a sublabel is associated with a reference numeral and follows a hyphen to denote one of multiple similar components. When reference is made to a reference numeral without specification to an existing sublabel, it is intended to refer to all such multiple similar components.  
         [0015]      FIG. 1  provides a schematic illustration of the structure of a system that allows processing of secure transactions in an embodiment of the invention;  
         [0016]      FIG. 2A  provides an illustration of a structure for a processing device used in processing secure transactions in an embodiment of the invention;  
         [0017]      FIG. 2B  provides a schematic illustration of a computational structure embodied by the processing device in embodiments of the invention;  
         [0018]      FIG. 3  provides an illustration of a structure for a portable device used in processing secure transactions in an embodiment of the invention;  
         [0019]      FIGS. 4A and 4B  provide illustrations of switching structures that may be used in the portable device in different embodiments of the invention; and  
         [0020]      FIGS. 5A-5C  proved a flow diagram illustration how secure transactions may be processed in certain embodiments of the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]     Embodiments of the invention provide methods and systems for processing secure transactions that use electromagnetic initiation. These embodiments make use of a combination of a processing device that is typically located at a transaction point and a portable device that is typically carried by the customer. Sometimes, the transaction point is referred to herein as a “point of sale,” although such usage is not intended to limit the nature of the transaction, which may be for a sale of goods, for a service, or for any transaction in which funds are exchanged between parties. The description below sometimes makes specific reference to electromagnetic communications at radio frequencies, although the invention is not intended to be limited to rf applications and may be used at other frequencies in alternative embodiments.  
         [0022]     An overview of a system that allows the use of the processing device and the portable device in processing secure transactions is provided in  FIG. 1 , in which the overall architecture of the system is denoted  100 . As this figure illustrates, the processing device may be provided in some instances as a satellite device in communication with an existing point-of-sale terminal; alternatively, it may be provided as part of an integrated point-of-sale terminal that combines the functionality described herein with that of existing point-of-sale devices. Such versatility advantageously allows existing systems to be upgraded to accommodate the embodiments described herein by interfacing the satellite device with existing equipment. At the same time, it is possible to substitute existing equipment with the integrated point-of-sale terminals when equipment is undergoing an upgrade.  
         [0023]     In  FIG. 1 , there are three examples where the process device  200  is provided as a satellite device in communication with an existing point-of-sale terminal  120 , i.e. in the case of process devices  200 - 1 ,  200 - 2 , and  200 - 3 . In each of these instances, the point-of-sale terminal  120  may have the structure and functionality of existing equipment configured for communication with a host system  104  in processing transactions. In some cases, such existing equipment may already be configured to accommodate a variety of different transaction instruments by including, for example, payment-information-entry components, signature-capture components, keypads, keyboards, display screens, biometric-data-capture components, speakers, printers, processors, software, memory, communication devices, and the like. Examples of such multifunction point-of-sale terminals are provided in the following commonly assigned applications, the entire disclosures of which are incorporated herein by reference for all purposes: U.S. Prov. Pat. Appl. No. 60/147,889, entitled “INTEGRATED POINT OF SALE DEVICE,” filed Aug. 9, 1999 by Randy J. Templeton et al.; U.S. patent application Ser. No. 09/634,901, entitled “POINT OF SALE PAYMENT SYSTEM,” filed Aug. 9, 2000 by Randy J. Templeton et al.; U.S. patent application Ser. No. 10/116,689, entitled “SYSTEMS AND METHODS FOR PERFORMING TRANSACTIONS AT A POINT-OF-SALE,” filed Apr. 3, 2002 by Earney Stoutenburg et al.; U.S. patent application Ser. No. 10/116,733, entitled “SYSTEMS AND METHODS FOR DEPLOYING A POINT-OF-SALE SYSTEM,” filed Apr. 3, 2002 by Earney Stoutenburg et al.; U.S. patent application Ser. No. 10/116,686, entitled “SYSTEMS AND METHODS FOR UTILIZING A POINT-OF-SALE SYSTEM,” filed Apr. 3, 2002 by Earney Stoutenburg et al.; and U.S. patent application Ser. No. 10/116,735, entitled “SYSTEMS AND METHODS FOR CONFIGURING A POINT-OF-SALE SYSTEM,” filed Apr. 3, 2002 by Earney Stoutenburg.  FIG. 1  also provides three examples where the process device is integrated as part of a multifunction point-of-sale terminal  124 , i.e. in the case of integrated point-of-sale terminals  124 - 1 ,  124 - 2 , and  124 - 3 . The point-of-sale terminals  120  and integrated point-of-sale terminals  124  are sometimes referred to collectively herein as “transaction-point devices.” 
         [0024]     In addition,  FIG. 1  illustrates that there may be a variety of different ways in which communications may be effected between the transaction-point devices and a host system  104  that manages interactions with a financial network in processing the transactions. For instance, the transaction-point devices may be provided in direct communication with the host system, as illustrated for point-of-sale terminal  120 - 3  and integrated point-of-sale terminal  124 - 3 . More usually, however, interactions with the host system  104  proceed through one or more intermediary systems, such as through the merchant systems  116  shown in the drawing. Such a merchant system  116  may be used, for instance, to coordinate transactions received at a single merchant location that has multiple transaction-point devices, or may be used to coordinate transactions received at multiple merchant locations for a single merchant entity. In some cases, there may be a hierarchy of such systems intermediate between the transaction-point devices and the host system  104 , with each of such systems being configured to route information to or from the host system  104  as appropriate.  
         [0025]     In processing transactions, the host system  104  is provided in communication with one or more financial institutions  112 , usually through a private financial network  108  that so that it is less likely to be compromised than a public network. The financial institutions  112  usually maintain or have access to maintenance information for financial accounts identified in information transmitted to the host system  104  from the transaction-point devices. For example, in the case of a debit transaction, the financial institution  112  may comprise a bank that maintains a demand-deposit account to be debited in accordance with the terms of the transaction. In the case of a credit transaction, the financial institution  112  may comprise a credit-card company that provides funds on a credit basis to customers in accordance with preset credit limits. In the case of a stored-value transaction, the financial institution may be a company that maintains records of stored-value balances for a variety of different merchant labels, perhaps providing mechanisms for reloading value and performing other maintenance functions.  
         [0026]     An example of a structure that may conveniently be used for the processing devices  200  is shown for one embodiment in  FIGS. 2A and 2B . While  FIG. 2A  provides an illustration of an external physical structure for the processing device  200 ,  FIG. 2B  provides an illustration of components that are usually included internal to the device. The external structure shown in  FIG. 2A  provides a number of elements that conveniently allow the customer to interface with the device. An antenna  224 , which may be optimized for operation at radio frequencies in some instances, allows the processing device  200  to interact with the portable device as described in greater detail below. In addition to the electromagnetic interactions enabled by the antenna  224 , the processing device includes a keypad  216  that allows entry of a nonencrypted version of an alphanumerical identifier. As used herein, an “alphanumerical identifier” may have only alphabetic components, may have only numerical components, or may have a combination of alphabetic and numerical components. The illustration in  FIG. 2A  provides an example where the keypad  216  is equipped to permit entry of an alphanumerical identifier consisting of numerical components. A display  208  permits instructions to be communicated to the customer and a status bar  212  provides an indication that processing steps are being taken. The status bar  212  may be adapted for display in different colors, such as red and green, depending on operations that are being performed and to indicate the successful completion of those operations, progressively illuminating more of the status bar as the terminal completes each phase of the transaction. A set of transaction-selection buttons  204  may be used to select among a number of different services accommodated by the processing device, one of which, i.e. button  204 - 1 , corresponds to the specific service described herein. A terminal interface cable  220  may be used to provide a mechanism for exchange of information between the processing device  200  and a point-of-sale terminal  120 , although other mechanisms may alternatively be used, including wireless mechanisms.  
         [0027]      FIG. 2B  provides one example of a functional arrangement of components that may be embodied by the processing device  200  to implement the functions described herein, although other functional arrangements may be used in alternative embodiments.  FIG. 2B  broadly illustrates how individual system elements for the processing device  200  may be implemented in a separated or more integrated manner. The processing device  200  is shown comprised of hardware elements that are electrically coupled via bus  258 , including a processor  250 , one or more input devices  254 , one or more storage devices  256 , and the antenna system  224 . Information used in implementing the methods described below, such as encryption-key information, is stored on the storage devices  256 , which may, for instance, comprise secure-access memory (“SAM”)  257 . In addition to the keypad  216 , for example, the input devices  254  might comprise a smart-card reader slot to allow injection of data to the processing device  200 , such as the encryption keys, software upgrades, and the like.  
         [0028]     The processing device  200  also comprises software elements, shown as being currently located within working memory  260 , including program code  268  designed to implement methods of the invention. It will be apparent to those skilled in the art that substantial variations may be used in accordance with specific requirements. For example, customized hardware might also be used and/or particular elements might be implemented in hardware, software (including portable software, such as applets), or both. Further, connection to other computing devices such as network input/output devices may be employed.  
         [0029]     It is noted that the structure shown in  FIG. 2B  may also be used in embodiments where an integrated point-of-sale terminal  124  is provided. In such embodiments, a number of output devices may be provided in communication with the bus  258  and a greater number of input devices  254  may be available, such as payment-information-entry components, signature-capture components, keypads, keyboards, display screens, biometric-data-capture components, speakers, printers, processors, software, memory, communication devices, and the like. In addition, the program code  268  may include instructions that implement functions of a separated point-of-sale terminal  120  as well functions of the processing device.  
         [0030]     An example of the portable device is provided in  FIG. 3  in the form of a key fob  304 , which may conveniently be carried by customers. The portable device includes memory that may be used to hold encrypted versions of the magnetic-stripe image and alphanumerical identifier. The magnetic-stripe image and alphanumerical identifier may conveniently be encrypted using the same key, although this is not required. As used herein, the “magnetic-stripe image” that is stored in memory by the portable device is intended to refer to account information of the type that is commonly stored on magnetic-stripe tracks. For example, the information may be stored in a format that has a correspondence to the ISO/IEC 7810, 11, 12, and 13 series of standards, which specify a three-track format, storage scheme, and bit density for all financial card applications. While the information may conveniently be stored in a format that mimics the magnetic-stripe organization, with different types of information being associated with different tracks, references to such a magnetic-stripe image are intended more broadly to encompass any organization of the information. For example, the magnetic-stripe image may comprise an identification of a financial account and of a financial institution that holds the financial account in the form of an account number coupled with a bank identification number (“BIN”). In addition, information identifying the customer by name, an expiration date, and various check characters may be included, although the specific information content of the magnetic-stripe image may vary according to such factors as the issuer, the type of accounts accommodated, the status of the customer, and the like.  
         [0031]     The encryption of the magnetic-stripe image and of the alphanumerical identifier may result from a variety of different types of encryption methods in different embodiments. For example, in one embodiment, they are encrypted according to an elliptical curve cryptography (“ECC”) scheme, which is an example of an asymmetric encryption scheme. In cases where there are potentially multiple issuers to be accommodated by the host system  104 , the use ECC encryption may function by implementing an elliptical curve master public/private ECC key pair, which may be rotated periodically to enhance security. Key pointers are then used to associate individual issuers with a master ECC key index number. By using ECC keys in this way, it is sufficient to load the master ECC public key(s) onto the processing devices  200 . The individual issuer ECC key is then encrypted under the master ECC private key and included on the portable devices  304 . This thereby limits the number of keys that need to be loaded and managed on the processing devices  200  and SAM module  257 , and enhances the scalability of the system. Encryption of the magnetic-stripe image and alphanumerical identifier may then be encrypted by the master ECC private key, creating an ECC certificate that incorporates the individual issuers&#39; key pointers.  
         [0032]     In other embodiments, such a hierarchy of encryptions may be avoided, with appropriate public and private keys being loaded onto the processing and portable devices  200  and  304 . Also, a variety of other types of encryption techniques well known to those of skill in the art may alternatively be used, such as with the well-known Data Encryption Standard (“DES”) and the like. One use of a symmetric key is in the encryption of an identifier for the portable device, which may comprise a barcode as described further below, when sending it from the terminal to the portable device, as described in detail below.  
         [0033]     The portable device  304  shown in  FIG. 3  may include a variety of mechanisms that enhance the security of the transactions even beyond the use of encryption. For instance, a switch  308  may be used to prevent “pocket surfing,” in which electromagnetic transmissions from the portable device are captured with the intention of using the received information fraudulently. The switch  308  acts as a physical security measure that may be implemented so that useable electromagnetic signals are only transmitted when the switch is activated. A light-emitting device (“LED”)  312  or other indicator may be provided on the portable device to indicate activation by the switch. In one embodiment, the switch  308  comprises a membrane switch, although other switch configurations may alternatively be used.  
         [0034]     There are a number of different ways in which such a switch may function, as illustrated with  FIGS. 4A and 4B  for different embodiments. For example, in the embodiment illustrated in  FIG. 4A , the switch  406  may be configured so that no signal is provided from a processor  410  comprised by the portable device  304  to an antenna  402  comprised by the portable device  304  unless activated. In such an embodiment, no electromagnetic signal is thus transmitted, and therefore cannot be pocket surfed, unless the customer is activating the switch at the time of the transaction. In the embodiment illustrated in  FIG. 4B , the switch  414  may instead be configured so that a magnetic-stripe image associated with different accounts is transmitted depending on a state of the switch  414 . For example, the default account  418  might correspond to an account that requires a PIN in order to effect transactions so that the magnetic-stripe image alone is insufficient. Protection against pocket surfing is thereby provided by assigning such an account as the default, and by requiring activation of the switch  414  to access the magnetic-stripe image for a different account  418 ′ or  418 ″. In some cases, as  FIG. 4B  illustrates, the switch may comprise a multiposition switch so that more than two states may be accommodated, permitting access to a greater number of accounts with a single portable device  304 .  
         [0035]      FIG. 3  also illustrates a further security feature that may be included in the form of a barcode that is printed on the portable device  304 . Confirmation of a valid barcode during a transaction may be used as described below to confirm that a transaction is being performed while the portable device.  304  is present. Confirmation of such presence thus acts as a further mechanism that prevents pocket surfing from being used to commit fraud since the printed barcode cannot be appropriated simply by detecting ambient electromagnetic signals (sometimes referred to as a “pocket-surfing attack”).  
         [0036]     In some embodiments, the portable device  304  may be equipped with input ports that allow for access of payment modules  314 . In such an embodiment, the modules  314  may be accessible with a bladelike configuration that permits individual modules to be removed from an interior of the portable device  304 . Identification of a particular module may result in identification of a corresponding account by the portable device  304 , such as by using the swivel action to trigger a switch within the portable device  304  to identify the account. The magnetic-stripe image that is communicated by the portable device  304  may then correspond to the magnetic-stripe image for the identified account. In this way, the portable device  304  may act as a convenient holder for payment modules  314 , thereby simplifying organization of multiple stored-value accounts that may be maintained by a customer.  
         [0037]     Furthermore, in some embodiments, the modules  314  and/or the portable device  304  may be sold with an automated dispenser that allows consumer selection of gift or other stored-value cards for specific merchants, initial values, and the like. For example, the modules  314  may be sold in such a device located in a mall or other place, and equipped to activate and release a selected payment module  314  upon payment by a customer. The payment could be made with a cash receiver, a magnetic-stripe card reader, or, in some cases, with a processing device  200  such as the one described herein for enabling electromagnetic initiation of secure transactions. Upon receipt of payment, a financial institution responsible for administering the purchased stored-value is notified of the sale so that the corresponding account may be loaded with the purchased amount. The dispensing machine reads electromagnetic identifications from the modules as they are dispensed and associates those identifications with the corresponding stored-value accounts. Such an arrangement thus provides a convenient mechanism for the sale of payment modules, and relieves customers who maintain multiple stored-value accounts of the need to hold multiple magnetic-stripe cards.  
         [0038]      FIGS. 5A-5C  provide a flow diagram that illustrates how secure transactions may be processed with electromagnetic initiation using the structural arrangements described above. Such processing may be initiated using an arrangement having a separated processing device  200  and point-of-sale terminal  120 , or may be initiated using an integrated point-of-sale terminal  124  equipped with combined functionality. The flow diagram presented in  FIGS. 5A-5C  may be considered to provide a single flow despite its presentation in multiple parts, and certain portions of the flow diagram are additionally identified by labels corresponding to logical portions of the process flow. While the order of the blocks in the flow diagram sets forth an exemplary order, this order is not necessary and in some alternative embodiments a different order may be followed, or some of the steps represented by the blocks may be performed simultaneously. Furthermore, some alternative embodiments include steps in addition to those depicted explicitly in the drawing and other alternative embodiments omit some steps that are depicted in the figures.  
         [0039]     Blocks  502 - 510  of  FIG. 5A  collectively correspond to an initiation phase of a transaction when a customer presents himself at a point of sale and indicates a desire to engage in a transaction. At block  502 , a scan of the barcode printed on the portable device  304  may be received by having the customer respond to a request to present the barcode to the barcode scanner on the processing device  200 . In some instances, the validity of the barcode may be verified as indicated at block  504 , usually at this stage by verifying a structure of the barcode. For example, the barcode may be checked to ensure that it has a required number of characters and that its format is as otherwise expected. In addition, the barcode may sometimes comprise a check character that is defined by application of a specified algorithm to other characters comprised by the bar code; the check character may be verified by comparing it with the result of applying the specified algorithm. If the barcode is found not to be valid as a result of such checks, a request may be made to have the barcode rescanned as indicated at block  506 . At block  508 , a request is presented to the customer on the display of the processing device  200  to key in an alphanumerical identifier, which may take the form of a numerical identifier such as a PIN. The processing device  200  initiates an electromagnetic transmission to the portable device  304  at block  510 . The electromagnetic transmission may take place at radio frequencies and includes an identifier for the processing device and a transaction number.  
         [0040]     At blocks  512 - 516 , the portable device  304  responds to the transmission from the processing device  200  in a manner that enhances the security of the transaction by ensuring that it is not a replay or a deliberate hack. The processing-device identifier and transaction number are received by the portable device  304  at block  512 . The portable device  304  concatenates the processing-device identifier and the transaction number and signs the combination with a first private key at block  514 . At block  516 , this signed combination is transmitted electromagnetically back to the processing device  200  as part of an electromagnetic transmission packet that additionally includes information to be used in effecting the transaction. In particular, a payment-option digital certificate with encrypted magnetic-stripe image are included as part of the electromagnetic transmission packet. Which of a plurality of magnetic-stripe images is included may depend on a state of the portable device  304 , such as described above in connection with different states that may be realized by the customer selecting different states of the switch  308 . The magnetic-stripe image is encrypted using a second private key, usually prior to being stored on the portable device  304 .  
         [0041]     Alternatively, a symmetric key, such as a DES key, may be used to encrypt the portable-device identifier and transaction number being sent to the portable device. The portable device decrypts using a stored DES key, increments the transaction count by an internally held portable-device transaction counter, and sends it back to the terminal encrypted under the same or a different DES key. The internally held transaction counter is itself incremented by one. The transmission may include the portable-device transaction counter together with the incremented terminal transaction counter. The terminal determines the difference between the two values to verify that the portable device was able to decrypt the original value, and the portable-device transaction counter may be sent to the host for various fraud-detection purposes. In addition, during this process, the barcode value or other identifier may be verified as being correct.  
         [0042]     At blocks  518 - 524 , the processing device  200  performs a set of verification functions to ensure the authenticity of the information received, to ensure that the received transmission is not the result of a replay or hack, and to ensure that the presence of the portable device  304  during the transaction. At block  518 , the processing device  200  verifies that the payment-option certificate conforms to a predetermined set of requirements, thereby ensuring that the portable device  304  is one recognized within the system. At block  520 , the processing device  200  decrypts the combination of the processing-device identifier and the transaction number with a first public key. The first private key and the first public key define a private/public key combination within whatever encryption scheme is used. At block  522 , the decrypted processing-device identifier and transaction number are compared with what the processing device  304  previously transmitted, thereby verifying that the received transmission is not a replay or hack. At block  524 , the signature affixed to the combination by the portable device  304  is verified in accordance with the decryption to verify the presence of the portable device  304 .  
         [0043]     After performing such verifications, the processing device packages an authentication package to be transmitted to the host system  104  to seek authorization for the transaction in accordance with the policies of the responsible financial institution and  112  and the status of the identified account. Thus, at block  526 , the processing device  200  decrypts the received magnetic-stripe image with a second public key, the second private key and second public key defining a private/public key combination within the applicable encryption scheme. At block  528 , the alphanumerical identifier is extracted from the decrypted payment digital certificate by the processing device  200 . This allows a comparison to be performed between the extracted alphanumerical identifier and the alphanumerical identifier that was keyed at block  508 . If the two fail to match, as checked at block  530 , the transaction is declined at block  532 . If there is a match, then the processing device  200  generates the authentication package at block  534  for transmission at block  536 . In the illustrated embodiment, the processing device  200  is a satellite device provided in communication with a point-of-sale terminal  120  so that the transmission is made to the point-of-sale terminal  120 , which performs certain authorization functions described below. In other embodiments, the transmission may be made in a manner to transmit the necessary authorization information to the host system  104  through the architecture discussed in connection with  FIG. 1 . The authentication package may include whatever pieces of information are needed or requested by the host system  104  to coordinate soliciting authentication for the transaction. In the illustrated embodiment, the authentication package includes a barcode value corresponding to the barcode, the processing-device identifier, the transaction number, the portable-device signature, and the alphanumerical identifier.  
         [0044]     According to embodiments of the invention, the comparison of the keyed alphanumerical identifier with the decrypted alphanumerical identifier is performed offline, meaning that such a comparison is performed prior to transmission of the authorization package to the host system  104 . Conveniently, such an offline comparison is performed in the illustrated embodiment by the processing device  200 , although more generally the offline comparison may be performed by any component of the system architecture  100 , such as by the merchant system  116 , prior to transmission of the authorization package to the host system  104 . There are a number of benefits to performing the comparison of alphanumerical identifiers offline. For example, the offline comparison provides a fast and efficient mechanism by which it can be verified both that the portable device  304  is present during the transaction and that the individual presenting it is authorized to do so.  
         [0045]     As previously noted, there are some transactions in which authorization may be provided without an alphanumerical identifier. For example, credit transactions and stored-value transactions are frequently authorized without alphanumerical identifiers while debit transactions typically require validation of an alphanumerical identifier in the form of a numerical PIN by the financial institution  112 . Thus, in some embodiments, the authorization package may omit the alphanumerical identifier even where it has been verified offline. In other embodiments, inclusion of the alphanumerical identifier in the authorization package may be avoided for all transactions by instead including a flag that indicates that the alphanumerical identifier has been confirmed offline. In other embodiments, the offline comparison may be avoided altogether in order to increase the transaction time. In such alternative embodiments, the presence of the portable device  304  may be verified by decryption of the magnetic-stripe image and checking check values embedded within the magnetic-stripe image. Such check values might correspond to different magnetic-stripe tracks or could be global check values that apply to the magnetic-stripe image as a whole. In some embodiments, an additional control mechanism is provided by imposing a maximum transaction dollar limit for transactions executed without validation of an alphanumeric identifier. Such a maximum transaction dollar limit may be conveniently stored on the portable device  304  and transmitted to the processing device  200  during a transaction with the information at block  516 . The processing device  200  may then include additional programming to decline any transaction that exceeds the limit unless an alphanumerical identifier is verified. Thus, if a portable device is lost, the potential fraud exposure is limited to the maximum amount. Known fraud-detection mechanisms that identify such scenarios as attempting a large number of small transactions in a short period of time may also be implemented.  
         [0046]     After the authorization package is transmitted from the processing device  200 , the transaction may be authorized at blocks  538 - 550  of  FIG. 5C . Initially, as indicated at block  538 , the processing-device identifier and transaction number may be verified by one of the intermediary devices between the processing device  200  and the host system  104 . In this example, where the processing device  200  is a satellite device connected with a point-of-sale terminal  120 , the verification of the processing-device identifier and transaction number are performed by the connected point-of-sale terminal  120 . At block  540 , the point-of-sale terminal  120  increments a counter, which may ensure that duplicate transmissions resulting from receipt of stray electromagnetic signals are not treated as additional transactions. In cases where the authorization requires presentation of an alphanumerical identifier, the alphanumerical identifier is extracted from the received authorization package at block  542 . The point-of-sale terminal  120  then transmits an authorization request through the architecture discussed in connection with  FIG. 1  to the host system  104  as indicated at block  544 . In cases where an alphanumerical identifier is required for authorization, the alphanumerical identifier is transmitted with the authorization request at block  544 .  
         [0047]     The authorization request at this point may be processed in a fashion identical to processing for magnetic-stripe transactions. The point-of-sale terminal  120  thus awaits a return response at block  546  specifying whether the transaction has been authorized. If so, the transaction is executed at block  550 , with appropriate debits and credits being settled in accordance with well-established settlement practices. If the transaction has not been authorized, the point-of-sale terminal  120  declines to execute the transaction as indicated at block  548 .  
         [0048]     Having described several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Accordingly, the above description should not be taken as limiting the scope of the invention, which is defined in the following claims.