Patent Publication Number: US-7222331-B2

Title: Linking of virtual methods

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is related to the following:
     U.S. patent application Ser. No. 10/346,581, filed Jan. 16, 2003 in the name of inventor Eduard de Jong, entitled “System for Communicating Program Data Between a First Device and a Second Device”, commonly assigned herewith.   U.S. patent application Ser. No. 10/346,230, filed Jan. 16, 2003 in the name of inventor Eduard de Jong, entitled “Signing Program Data Payload Sequence in Program Loading”, commonly assigned herewith.   U.S. patent application Ser. No. 10/346,238, filed Jan. 16, 2003 in the name of inventor Eduard de Jong, entitled “Using a Digital Fingerprint to Commit Loaded Data in a Device”, commonly assigned herewith.   U.S. patent application Ser. No. 10/346,586, filed Jan. 16, 2003 in the name of inventor Eduard de Jong, entitled “Ordering Program Data for Loading on a Device”, commonly assigned herewith.   U.S. patent application Ser. No. 10/346,227, filed Jan. 16, 2003 in the name of inventor Eduard de Jong, entitled “Optimized Representation of Data Type Information in Program Verification”, commonly assigned herewith.   U.S. patent application Ser. No. 10/346,243, filed Jan. 16, 2003 in the name of inventor Eduard de Jong, entitled “Run Time Code Integrity Checks”, commonly assigned herewith.   

   FIELD OF THE INVENTION 
   The present invention relates to the field of computer science. More particularly, the present invention relates to linking of virtual methods. 
   BACKGROUND OF THE INVENTION 
     FIG. 1  is a block diagram that illustrates a typical mechanism for communicating program data between a host computer and a smart card. Smart cards  110  typically communicate with other computers  100  via APDUs (Application Protocol Data Units). The APDU protocol is specified in International Standard ISO/IEC 7816-3. An APDU includes either a command  115  or a response  120  message. A smart card  110  receives a command APDU  115  from a host computer  100 , executes the instruction specified in the command  115  and replies to the host computer  100  with a response APDU  120 . Command APDUs  115  and response APDUs  120  are exchanged alternately between a card  110  and a host computer  100 . 
   According to the APDU protocol, APDU messages comprise two structures. One structure is used by a host application on a loading terminal to send commands to the card. The other structure is used by the card to send responses back to the host application. The former is referred to as the command APDU (C-APDU) and the latter is referred to as the response APDU (R-APDU). Their structures are illustrated in  FIGS. 2A and 2B , respectively. Some C-APDU components are optional. 
   Java Card™ technology enables programs written in the Java™ programming language to run on smart cards and other resource-constrained devices. Java Card™ technology is described in Z. Chen, Java Card™ Technology for Smart Cards (2000). 
   Turning now to  FIG. 3 , a block diagram that illustrates loading a converted applet (CAP) file is presented. The Java Card™ Virtual Machine (JCVM) comprises an on-card portion that includes the Java Card™ bytecode interpreter  345  and an off-card portion called a converter  310 . Taken together, the interpreter  345  and the converter  310  implement all the virtual machine functions, including loading Java™ class files  300  and executing them with a particular set of semantics. The converter  310  loads and pre-processes the class files  300  that comprise a Java Card™ program that may be structured in one or more packages and produces a CAP (converted applet) file  350 . The CAP file  350  is then loaded on a Java Card™ technology-enabled smart card  330  and executed by the interpreter  345 . The CAP file  350  includes an executable binary representation of the classes in a Java™ package  350 . The Java Card™ interpreter  345  provides runtime support of the Java™ language execution model. 
   In Java Card™ technology, the mechanisms to download and install a CAP file  350  are embodied in a unit called the installer  340 . The Java Card™ installer  340  resides within the card  330 . It cooperates with an off-card installation program  320 . The off-card installation program  320  transmits the executable binary and possibly other data in a CAP file  350  to the installer  340  running on the card  330  via a loading terminal  325 . The installer  340  writes the binary into the smart card memory, links it with the other classes that have already been placed on the card  330  and creates and initializes any data structures that are used internally by the Java Card™ runtime environment. An optional on-card verifier  335  performs bytecode verification of downloaded code before the downloaded code is interpreted by bytecode interpreter  345 . 
   The APDU protocol limits the size of the payload or data field (reference numeral  240  of  FIG. 2 ) to a small number of bytes (typically less than 128) determined by the restricted size of RAM. Data structures larger than the limitation must be split among the payload portion of multiple APDUs. This splitting is typically performed without regard to the data content. For example, a particular APDU may contain a portion of one data structure and a portion of another data structure. This is explained in more detail below, with reference to  FIG. 4 . 
   Turning now to  FIG. 4 , a flow diagram that illustrates loading a CAP file from the perspective of a loading terminal is presented. At  400 , a CAP file is received. At  405 , the CAP file and associated authentication data is split amongst multiple APDUs. At  410 , the APDUs are transmitted to the target smart card according to the APDU protocol. 
   Turning now to  FIG. 5 , a flow diagram that illustrates loading a CAP file from the perspective of a smart card is presented. At  500 , the CAP file is reassembled in the smart card. At  505 , the reassembled CAP file is decrypted. At  510 , the decrypted CAP file data is authenticated. In another solution, the CAP file is authenticated and then decrypted. In yet another solution, the CAP file is communicated without encryption. At  515 , the content of the authenticated CAP file is installed on the smart card. 
   Turning now to  FIG. 6 , a flow diagram that illustrates reassembling a CAP file in a smart card is presented. At  600 , an APDU is received. At  605 , the APDU is stored in a persistent mutable memory such as an EEPROM (electrically erasable programmable read-only memory). Alternatively, the APDU payload is not stored in a persistent mutable memory. At  610 , receipt of the APDU is acknowledged. At  615 , a determination is made regarding whether another APDU needs to be processed. Additional APDUs are processed beginning at  600 . 
   Turning now to  FIG. 7 , a block diagram that illustrates modifying a stored program having link data to resolve static references is presented. Card memory  700  represents card memory before using embedded link data ( 704 ,  712 ,  728 ) to link executable code segments ( 702 ,  706 ,  708 ,  710 ,  712 ,  716 ,  718 ,  720 ,  722 ,  724 ,  726 ,  728 ,  732 ). Card memory  750  represents card memory after the embedded link data ( 704 ,  712 ,  728 ) has been used to link executable code segments ( 702 ,  706 ,  708 ,  710 ,  712 ,  716 ,  718 ,  720 ,  722 ,  724 ,  726 ,  728 ,  732 ). Referring to card memory  700 , method “A1A” code  702  calls method “A1C”  708 , method “A2A” code  712  calls method “B1A”  720  and method “B2A” code  728  calls method “B1D”  726 . Method “A1A” link data  704  comprises an indication of how to resolve the reference to method “A1C”  708 . Method “A1A” link data  704  may additionally comprise an indication of how method “A1A” code  702  must be modified. Likewise, method “A2A” link data  714  comprises an indication of how to resolve the reference to method “B1A”  720 . Method “A2A” link data  714  may additionally comprise an indication of how method “A2A” code  712  must be modified. Additionally, method “B2A” link data  730  comprises an indication of how to resolve the reference to method “B1D”  726 . Method “B2A” link data  730  may additionally comprise an indication of how method “B2A” code  728  must be modified. Referring to card memory  750  of  FIG. 7 , symbolic references to called methods have been replaced with the addresses of the called methods and the link data is not stored. 
   Unfortunately, storing the re-created CAP file in a persistent mutable memory and then processing the CAP file contents to create linked executable code requires a significant amount of available memory and is time consuming. 
   Accordingly, a need exists in the prior art for a method and apparatus for communicating program data between a host computer and a smart card that is relatively efficient. A further need exists for such a solution that is relatively secure. Yet another need exists for such a solution that detects when program data has been tampered with. 
   SUMMARY OF THE INVENTION 
   Linking a virtual method comprises receiving a program comprising multiple program units, enumerating classes of the program, determining whether a virtual method of the program has been overridden at least once, creating a virtual method jump table indexed by a type indicator if the virtual method has been overridden and rewriting at least one call instruction that calls the virtual method. The at least one call instruction is rewritten to include the type indicator of a called object. The table comprises at least one entry including an address of a virtual method. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more embodiments of the present invention and, together with the detailed description, serve to explain the principles and implementations of the invention. 
     In the drawings: 
       FIG. 1  is a block diagram that illustrates a typical mechanism for communicating program data between a host computer and a smart card. 
       FIG. 2A  is a block diagram that illustrates a typical Command Application Protocol Data Unit (C-APDU). 
       FIG. 2B  is a block diagram that illustrates a typical Response Application Protocol Data Unit (R-APDU). 
       FIG. 3  is a block diagram that illustrates loading a converted applet (CAP) file. 
       FIG. 4  is a flow diagram that illustrates loading a CAP file from the perspective of a loading terminal. 
       FIG. 5  is a flow diagram that illustrates loading a CAP file from the perspective of a smart card. 
       FIG. 6  is a flow diagram that illustrates reassembling a CAP file in a smart card. 
       FIG. 7  is a block diagram that illustrates modifying a stored program having link data to resolve static references. 
       FIG. 8  is a block diagram of a computer system suitable for implementing aspects of the present invention. 
       FIG. 9  is a block diagram that illustrates a system for communicating program data between a host computer and a smart card in accordance with one embodiment of the present invention. 
       FIG. 10  is a high level flow diagram that illustrates communicating program data from a host computer to a smart card in accordance with one embodiment of the present invention. 
       FIG. 11  is a low level flow diagram that illustrates communicating program data from a host computer to a smart card in accordance with one embodiment of the present invention. 
       FIG. 12  is a flow diagram that illustrates a method for communicating program data from a host computer to a loading terminal from the perspective of a host computer in accordance with one embodiment of the present invention. 
       FIG. 13  is a block diagram that illustrates partitioning a CAP file into one or more logical APDUs in accordance with one embodiment of the present invention. 
       FIG. 14  is a flow diagram that illustrates a method for using program unit type map information in accordance with one embodiment of the present invention. 
       FIG. 15A  is a block diagram that illustrates a CAP file comprising package-structured data. 
       FIG. 15B  is a use diagram corresponding to the program within the CAP file of  FIG. 15A . 
       FIG. 15C  is a block diagram that illustrates the CAP file of  FIG. 15A  ordered based upon the use diagram of  FIG. 15B  in accordance with one embodiment of the present invention. 
       FIG. 16  is a flow diagram that illustrates a method for ordering program units for optimized verification and linking in accordance with one embodiment of the present invention. 
       FIG. 17A  is a block diagram that illustrates a CAP file comprising package-structured data. 
       FIG. 17B  is a use diagram corresponding to the program within the CAP file of  FIG. 17A . 
       FIG. 17C  is a block diagram that illustrates the CAP file of  FIG. 17A  ordered based upon the use diagram of  FIG. 17B  in accordance with one embodiment of the present invention. 
       FIG. 18  is a flow diagram that illustrates a method for disassembling a CAP file into one or more logical APDUs in accordance with one embodiment of the present invention. 
       FIG. 19  is a flow diagram that illustrates a method for disassembling a CAP file into one or more logical APDUs including APDUs comprising verification data in accordance with one embodiment of the present invention. 
       FIG. 20A  is a flow diagram that illustrates a method for computing an authentication fingerprint over an APDU data stream where verification APDUs are included in the fingerprint in accordance with one embodiment of the present invention. 
       FIG. 20B  is a flow diagram that illustrates a method for computing an authentication fingerprint over an APDU data stream where verification APDUs are excluded from the fingerprint in accordance with one embodiment of the present invention. 
       FIG. 21  is a flow diagram that illustrates a method for communicating program data from a host computer to a loading terminal from the perspective of a loading terminal in accordance with one embodiment of the present invention. 
       FIG. 22  is a flow diagram that illustrates a method for disassembling an augmented CAP file into one or more logical APDUs in accordance with one embodiment of the present invention. 
       FIG. 23  is a flow diagram that illustrates a method for disassembling an augmented CAP file including verification data into one or more logical APDUs including APDUs comprising verification data in accordance with one embodiment of the present invention. 
       FIG. 24  is a flow diagram that illustrates a method for disassembling an augmented CAP file not including verification data into one or more logical APDUs including APDUs comprising verification data in accordance with one embodiment of the present invention. 
       FIG. 25  is a flow diagram that illustrates a method for disassembling an augmented CAP file into one or more logical APDUs including APDUs comprising link data in accordance with one embodiment of the present invention. 
       FIG. 26  is a flow diagram that illustrates a method for disassembling an augmented CAP file including verification data into one or more logical APDUs including APDUs comprising verification data and APDUs comprising link data in accordance with one embodiment of the present invention. 
       FIG. 27  is a flow diagram that illustrates a method for disassembling an augmented CAP file not including verification data into one or more logical APDUs including APDUs comprising verification data and APDUs comprising link data in accordance with one embodiment of the present invention. 
       FIG. 28  is a flow diagram that illustrates a method for creating one or more method link APDUs in accordance with one embodiment of the present invention. 
       FIG. 29  is a flow diagram that illustrates a method for communicating program data from a loading terminal to a smart card from the perspective of a smart card in accordance with one embodiment of the present invention. 
       FIG. 30  is a flow diagram that illustrates a method for communicating program data from a loading terminal to a smart card from the perspective of a smart card using an authentication fingerprint that is a HMAC in accordance with one embodiment of the present invention. 
       FIG. 31  is a flow diagram that illustrates a method for performing load initialization in accordance with one embodiment of the present invention. 
       FIG. 32  is a flow diagram that illustrates a method for processing a logical APDU stream in accordance with one embodiment of the present invention. 
       FIG. 33  is a flow diagram that illustrates a method for computing an authentication fingerprint in accordance with one embodiment of the present invention. 
       FIG. 34  is a flow diagram that illustrates a method for processing a logical APDU in accordance with one embodiment of the present invention. 
       FIG. 35  is a block diagram that illustrates data structures for linking a program including virtual methods in accordance with one embodiment of the present invention. 
       FIG. 36  is a block diagram that illustrates modifying a stored program having link data to resolve dynamic references in accordance with one embodiment of the present invention. 
       FIG. 37  is a flow diagram that illustrates modifying a stored program having link data to resolve dynamic references in accordance with one embodiment of the present invention. 
       FIG. 38  is a block diagram that illustrates a hierarchy of program unit commitment fingerprints in accordance with one embodiment of the present invention. 
       FIG. 39  is a block diagram that illustrates a data structure including program code and program unit commitment fingerprints in accordance with one embodiment of the present invention. 
       FIG. 40  is a block diagram that illustrates a data structure including program code and a load storage commitment fingerprint in accordance with one embodiment of the present invention. 
       FIG. 41  is a flow diagram that illustrates a method for using a program unit commitment fingerprint to determine whether a program unit may be used, in accordance with one embodiment of the present invention. 
       FIG. 42  is a flow diagram that illustrates a method for determining whether stored program unit data is valid in accordance with one embodiment of the present invention. 
       FIG. 43  is a block diagram that illustrates a smart card configured to ensure a called method has been verified prior to execution in accordance with one embodiment of the present invention. 
       FIG. 44  is a flow diagram that illustrates a method for ensuring a called method has been verified prior to execution in accordance with one embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   Embodiments of the present invention are described herein in the context of linking virtual methods. Those of ordinary skill in the art will realize that the following detailed description of the present invention is illustrative only and is not intended to be in any way limiting. Other embodiments of the present invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to implementations of the present invention as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts. 
   In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer&#39;s specific goals, such as compliance with application- and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure. 
   In accordance with one embodiment of the present invention, the components, process steps, and/or data structures may be implemented using various types of operating systems (OS), computing platforms, firmware, computer programs, computer languages, and/or general-purpose machines. The method can be run as a programmed process running on processing circuitry. The processing circuitry can take the form of numerous combinations of processors and operating systems, or a stand-alone device. The process can be implemented as instructions executed by such hardware, hardware alone, or any combination thereof. The software may be stored on a program storage device readable by a machine. 
   In addition, those of ordinary skill in the art will recognize that devices of a less general purpose nature, such as hardwired devices, field programmable logic devices (FPLDs), including field programmable gate arrays (FPGAs) and complex programmable logic devices (CPLDs), application specific integrated circuits (ASICs), or the like, may also be used without departing from the scope and spirit of the inventive concepts disclosed herein. 
   In accordance with one embodiment of the present invention, the method may be implemented on a data processing computer such as a personal computer, workstation computer, mainframe computer, or high performance server running an OS such as Solaris® available from Sun Microsystems, Inc. of Santa Clara, Calif., Microsoft® Windows® XP and Windows® 2000, available from Microsoft Corporation of Redmond, Wash., or various versions of the Unix operating system such as Linux available from a number of vendors. The method may also be implemented on a multiple-processor system, or in a computing environment including various peripherals such as input devices, output devices, displays, pointing devices, memories, storage devices, media interfaces for transferring data to and from the processor(s), and the like. In addition, such a computer system or computing environment may be networked locally, or over the Internet. 
   In the context of the present invention, the term “network” includes local area networks, wide area networks, the Internet, cable television systems, telephone systems, wireless telecommunications systems, fiber optic networks, ATM networks, frame relay networks, satellite communications systems, and the like. Such networks are well known in the art and consequently are not further described here. 
   In the context of the present invention, a hash function h is commutative if h(x,y)=h(y,x) for all x and y. In other words, the result of the hash function is independent of the argument order. 
   In the context of the present invention, the term “fingerprint” is defined as the result of a function that identifies or detects one or more changes in a byte sequence. By way of example, a fingerprint may comprise a non-commutative hash of an arbitrary byte sequence or a non-commutative hash of a sequence of one or more byte sequences. As a further example, a fingerprint may comprise a CRC (cyclic redundancy code), a message digest, or the like. Such functions are described in Knuth, D.  The Art of Computer Programming , Volume 2: Seminumerical Methods, Chapter 5. Addison Wesley, 1981. 
   In the context of the present invention, the term “authentication code” is defined as a digital signature, or a Message Authentication Code (MAC) using a block cipher. By way of example, an authentication code may be generated using the DES algorithm (Federal Information Processing Standards Publication 46-3,  Data Encryption Standard  ( DES ), Oct. 25, 1999; Federal Information Processing Standards Publication 197,  Advanced Encryption Standard  ( AES ), Nov. 26, 2001), the Rijndael algorithm (J. Daemen and V. Rijmen,  AES Proposal: Rijndael , AES Algorithm Submission, Sep. 3, 1999), or the like. An authentication code produced as a result of a keyed hash function is an example of an authentication code that is also a fingerprint. 
   In the context of the present invention, a keyed hash-based message authentication code (HMAC) is defined as a MAC that uses a cryptographic key in conjunction with a hash function. A HMAC is both a fingerprint and a MAC. 
   In the context of the present invention, the term “authenticated fingerprint” is defined as an authentication code based at least in part on a fingerprint. 
   In the context of the present invention, the term “authentication fingerprint” is defined as a fingerprint used to create an authenticated fingerprint. 
   In the context of the present invention, the term “session” or “user session” is defined as a period that begins when a user inserts a secure portable device such as a smart card or the like into a communications device such as a loading terminal or card acceptance device (CAD), and ends when the secure portable device is removed from the communications device. A “session ID” is used to describe an identifier that uniquely identifies such a session. One or more session ID may be used to uniquely identify the same session. 
   In the context of the present invention, the term “package-structured data” is defined as executable code using Java™-like naming conventions for references to external program units. By way of example, the Java™ naming convention for an external class includes a package name followed by the class name. 
   In the context of the present invention, the term “verification APDU” is defined as an APDU comprising a command and verification data. The verification data is located within the data field (reference numeral  240  of  FIG. 2 ) of the APDU. 
   In the context of the present invention, the term “link APDU” is defined as an APDU comprising a command and link data. The link data is located within the data field (reference numeral  240  of  FIG. 2 ) of the APDU. 
   In the context of the present invention, the term “program unit” is defined as an identifiable unit of program behavior. A higher-level program unit may include one or more lower-level program units. For example, a Java™ class may include one or more method. 
     FIG. 8  depicts a block diagram of a computer system  800  suitable for implementing aspects of the present invention. As shown in  FIG. 8 , computer system  800  includes a bus  802  which interconnects major subsystems such as a central processor  804 , a system memory  806  (typically RAM), an input/output (I/O) controller  808 , an external device such as a display screen  810  via display adapter  812 , serial ports  814  and  816 , a keyboard  818 , a fixed disk drive  820 , a floppy disk drive  822  operative to receive a floppy disk  824 , and a CD-ROM player  826  operative to receive a CD-ROM  828 . Many other devices can be connected, such as a pointing device  830  (e.g., a mouse) connected via serial port  814  and a modem  832  connected via serial port  816 . Modem  832  may provide a direct connection to a server via a telephone link or to the Internet via a POP (point of presence). Alternatively, a network interface adapter  834  may be used to interface to a local or wide area network using any network interface system known to those skilled in the art (e.g., Ethernet, xDSL, AppleTalk™). 
   Many other devices or subsystems (not shown) may be connected in a similar manner. Also, it is not necessary for all of the devices shown in  FIG. 8  to be present to practice the present invention, as discussed below. Furthermore, the devices and subsystems may be interconnected in different ways from that shown in  FIG. 8 . The operation of a computer system such as that shown in  FIG. 8  is readily known in the art and is not discussed in detail in this application, so as not to overcomplicate the present discussion. Code to implement the present invention may be operably disposed in system memory  806  or stored on storage media such as fixed disk  820 , floppy disk  824  or CD-ROM  828 . 
   Signature Protocol for Card Loading 
   Turning now to  FIG. 9 , a block diagram that illustrates a system for communicating program data between a host computer and a smart card in accordance with one embodiment of the present invention is presented. System  900  comprises a host computer  910 , a loading terminal  985  and a smart card  950 . Host computer  910  comprises an off-card installer  915  for augmenting a CAP file  980  comprising package-structured data  905  to create an augmented CAP file  920  comprising the package-structured data  925 , an authentication fingerprint  940 , one or more loading terminal authentication codes  930  and one or more target smart card authentication codes  935 . Augmented CAP file  920  may also comprise verification data  945  that verifies CAP file content. Authentication fingerprint  940  is computed over the payload portion of logical APDUs derived from the package-structured data  925 . Logical APDUs are illustrated in more detail below with reference to  FIG. 13 . As explained in more detail below, the similarity of the processes used by host computer  910 , loading terminal  985  and target smart card  950  to compute an authentication fingerprint guarantees that if the APDU payload remains the same, the same authentication fingerprint will be generated regardless of the entity performing the computation. Conversely, if the APDU payload changes between when each entity performs the computation, a different fingerprint will be generated, signaling a change in the payload. 
   According to one embodiment of the present invention, one or more of loading terminal authentication codes  930  and target smart card authentication codes  935  are based at least in part on authentication fingerprint  940 . According to another embodiment of the present invention, the authentication fingerprint  940  comprises a keyed hash-based message authentication code (HMAC). According to another embodiment of the present invention, one or more of loading terminal authentication codes  930  and target smart card authentication codes  935  comprise a digital signature computed over augmented CAP file  920 , without regard to logical APDUs. 
   According to embodiments of the present invention, a logical program unit APDU may be followed and/or preceded by one or more APDUs that provide verification information (verification APDU) and/or linking information (link APDU). The verification data may be embedded in the CAP file. Alternatively, the verification data may be computed by the loading terminal. If verification data is included in the CAP file, it may be used to compute an authentication fingerprint. Linking data may also be computed by the loading terminal. Linking data may be based on data obtained from the card, data obtained from the Web, data in the CAP file, or any combination thereof. 
   Still referring to  FIG. 9 , loading terminal  985  is configured to receive the augmented CAP file  920 , create one or more logical APDUs from package-structured data  925 , authenticate the CAP file based at least in part on the loading terminal authentication code  930 , create one or more APDUs comprising a selected target smart card authentication code  935  and the authentication fingerprint  940 , and communicate the one or more APDUs to target smart card  950 . 
   According to one embodiment of the present invention, host computer  910  communicates an augmented CAP file without verification data. According to another embodiment of the present invention, host computer  910  communicates an augmented CAP file having verification data. 
   According to one embodiment of the present invention, loading terminal  985  receives an augmented CAP file  920  without verification data, computes verification data and creates one or more verification APDUs. According to another embodiment of the present invention, loading terminal  985  receives an augmented CAP file  920  with verification data and creates one or more verification APDUs. According to another embodiment of the present invention, loading terminal  985  computes link data and creates one or more link APDUs. 
   According to one embodiment of the present invention, smart card  950  comprises a secure portable device such as a Java Card™ technology-enabled smart card, or the like. 
   According to one embodiment of the present invention, smart card  950  comprises a CDMA technology-enabled smart card. CDMA technology-enabled smart cards are described in  Smart Card Stage I Description , Version 1.1, CDMA Development Group—Smart Card Team Document (May 22, 1996). 
   According to another embodiment of the present invention, smart card  950  comprises a SIM (Subscriber Identity Module card) card. The term “SIM card” describes the smart card used in GSM (Global System for Mobile Communications) mobile telephones. The SIM includes the subscriber&#39;s personal cryptographic identity key and other information such as the current location of the phone and an address book of frequently called numbers. The SIM is described in  Digital cellular telecommunications system  ( phase  2+);  Specification of the Subscriber Identity Module—Mobile Equipment  ( SIM - ME )  interface , ETSI, GSM 11.11 version 7.4.0, Release 1998. 
   According to another embodiment of the present invention, smart card  950  comprises a WIM (Wireless Interface Module). A WIM is a smart card in a WAP (Wireless Application Protocol) phone. It is described in  Wireless Identity Module Part: Security , WAP-260-WIM-20010712-a, Wireless Application Protocol Forum, Jul. 12, 2001. 
   According to another embodiment of the present invention, smart card  950  comprises a USIM (Universal Subscriber Identity Module). A USIM is a smart card for a 3GPP (3 rd  Generation Partnership Project) mobile phone. It is described in 3 rd Generation Partnership Project; Technical Specification Terminals; USIM and IC card requirements , Release 4, 3GPP TS 21.111 V4.0.0 (2001-03). 
   According to another embodiment of the present invention, smart card  950  comprises a UIM (User Identity Module). A UIM is a smart card for a 3GPP Project 2 (3GPP2) mobile phone. The term “R-UIM” is used when the smart card is removable. A UIM is a super set of the SIM and allows CDMA (Code Division Multiple Access)-based cellular subscribers to roam across geographic and device boundaries. The R-UIM is described in a specification issued by the 3rd Generation Partnership Project 2 (3GPP2) and entitled 3rd Generation Partnership Project 2; Removable User Identity Module (R-UIM) for cdma2000 Spread Spectrum Systems, 3GPP2 C.S0023-0, Jun. 9, 2000. 
   The above description regarding various mobile phone technologies is not intended to be limiting in any way. Those of ordinary skill in the art will recognize that other user devices may be used. 
   Turning now to  FIG. 10 , a high level flow diagram that illustrates communicating program data from a host computer to a smart card in accordance with one embodiment of the present invention is presented. At  1020  an augmented CAP file is prepared. The augmented CAP file may comprise package-structured data and an authentication fingerprint computed over an APDU data stream comprising the package-structured data. Alternatively, the augmented CAP file may comprise package-structured data and at least one authentication code based at least in part on the authentication fingerprint. 
   According to one embodiment of the present invention, preparing an augmented CAP file ( 1020 ) is preceded by determining a loading order of program elements for optimized verification and linking ( 1015 ). The load order used in  1015  may be used in  1020  to determine the order of logical APDUs in the computation of the authentication fingerprint. In a Java™ environment, the loading order for one or more classes, methods in classes or fields in methods is determined. The program elements may be ordered based at least in part on a use graph of the program in the CAP file. The “use” of a method may comprise, by way of example, calling the method. The “use” of a field may comprise, by way of example, accessing the field. The program elements may also be ordered based at least in part on type map information defined for the program. Type maps are explained in more detail below with reference to  FIG. 14 . Ordering program elements is explained in more detail below with reference to  FIGS. 15A–15C . 
   Still referring to  FIG. 10 , at  1025  the augmented CAP file is communicated to a loading terminal. At  1030 , the loading terminal receives the augmented CAP file and initializes loading of an applet. At  1035 , authenticated applet code is loaded on a target smart card. At  1040 , applets are initialized. At  1045 , a proof of loading received from the target smart card is processed to determine and record whether the load was successful. 
   Still referring to  FIG. 10 , smart card  1050  receives a load request from the loading terminal. At  1055 , the smart card processes logical APDUs received from the loading terminal. The processing includes computing an authentication fingerprint over the APDU payload. At  1060 , initialization data received from the loading terminal is used to initialize the smart card. At  1065 , a proof of loading is sent to the loading terminal. 
   Turning now to  FIG. 11 , a low level flow diagram that illustrates communicating program data from a host computer to a smart card in accordance with one embodiment of the present invention.  FIG. 11  provides more detail for  FIG. 10 . More particularly, reference numerals  1106 – 1116 ,  1118 – 1136  and  1140 – 1150  of  FIG. 11  correspond with reference numerals  1020 – 1025 ,  1030 – 1045  and  1050 – 1065  of  FIG. 10 , respectively. At  1106 , a host computer disassembles a CAP file into logical data units, and the logical data units are partitioned into one or more APDUs. At  1108 , an authentication fingerprint is computed over the APDU data stream, as described below with reference to  FIGS. 20A and 20B . At  1110 , one or more loading terminal authentication codes are created. At  1112 , one or more target smart card authentication codes are created. At  1114 , the CAP file is augmented with the authentication codes, fingerprint, or both. At  1116 , the augmented CAP file is communicated to a loading terminal. 
   Still referring to  FIG. 11 , at  1118  the loading terminal receives a load request including the augmented CAP file, an applet ID (AID) or the like, initialization instructions and initialization data. The term “AID” is defined by International Standards Organization (ISO) Standard ISO-IEC 7816-3. At  1120 , loading of the applet is initiated. The initiating may include separating any authentication codes and fingerprint from the augmented CAP file and obtaining linking information. Optionally, at  1121  a loading order of program elements for optimized verification and linking is determined. The loading order of program elements may be determined as described with respect to reference numeral  1015  of  FIG. 10 . Alternatively, the order may be determined from an indicator stored in an augmented CAP file. At  1122 , the augmented CAP file is disassembled into one or more logical APDUs. At  1124 , the augmented CAP file is authenticated based on a loading terminal authentication code. At  1126 , a target authentication code is selected from the target smart card authentication codes in the augmented CAP file based upon the target smart card. At  1128 , one or more logical APDUs are communicated to the target smart card. At  1130 , the fingerprint or authentication code based on a fingerprint is sent to the smart card. At  1132 , the target smart card authentication code is sent to the smart card. At  1134 , initialization instructions and load data are sent to the target smart card. At  1136  a proof of loading is received from the target smart card. 
   According to embodiments of the present invention, processes  1122  and  1124  are performed before processes  1126 ,  1128  and  1130 . However, the order of processes  1126 ,  1128  and  1130  with respect to one another may be changed. 
   Still referring to  FIG. 11 , at  1140  the target smart card receives a load request from the loading terminal and performs load initialization. The load initialization may include receiving the fingerprint or authentication code based on a fingerprint that was sent at  1130 . At  1142 , logical APDUs received from the loading terminal are processed. The processing includes computing an authentication fingerprint over the logical APDU payload. The processing may also include receiving the fingerprint or authentication code based on a fingerprint that was sent at  1130 . At  1144 , the received content is authenticated based on the target smart card authentication code. The authenticating may include receiving the fingerprint or authentication code based on a fingerprint that was sent at  1130 . At  1146 , the received content is committed to memory on the smart card if the received fingerprint and the computed fingerprint matches, and if the received content is properly authenticated. At  1148 , initialization data received from the loading terminal is used to initialize the card. At  1150 , a proof of loading is sent to the loading terminal. 
   Alternatively, the processes illustrated in  FIGS. 10 and 111  may performed without using loading terminal authentication codes and/or target smart card authentication codes. The decision to use or not use authentication codes may be based at least in part on a level of trust in host computer  1100 , loading terminal  1105  and/or smart card  1110 . By way of example, if the loading terminal is trusted, the processes illustrated in  FIGS. 10 and 11  may be performed without a loading terminal authentication code. Thus if a card issuer uses its own terminals to update a card, a terminal authentication code is not needed since the card issuer can trust terminals which the issuer controls. But if a third party terminal at a point of sale remote from the card issuer is used to update the card and the card has been in the possession of a user, a terminal authentication code may be needed because the card issuer may have little if any control over the terminal. Similarly, if the target smart card is trusted, the processes illustrated in  FIGS. 10 and 11  may be performed without a target smart card authentication code. 
   Additionally, those of ordinary skill in the art will recognize that other mechanisms for creating a terminal authentication code may be used. 
   According to one embodiment of the present invention, the host computer  1100  and the loading terminal  1105  comprise the same device. 
   Host Computer 
   Turning now to  FIG. 12 , a flow diagram that illustrates a method for communicating program data from a host computer to a loading terminal from the perspective of a host computer in accordance with one embodiment of the present invention is presented.  FIG. 12  provides more detail for reference numerals  1015 – 1025  of  FIG. 10  and reference numerals  1106 – 1116  of  FIG. 11 . At  1200 , a CAP file is received. At  1205 , the CAP file is disassembled into one or more logical APDUs. At  1210 , an authentication fingerprint is computed over the APDU data stream. Alternatively, the authentication fingerprint may be computed upon creation of a logical APDU (i.e. as part of the CAP file disassembly process  1205 ). At  1215 , the CAP file is augmented to include the authentication fingerprint, at least one data authentication code based at least in part on the authentication fingerprint, or any combination thereof. At  1220 , the augmented CAP file is communicated to a loading terminal. 
   Turning now to  FIG. 13 , a block diagram that illustrates partitioning a CAP file into one or more logical APDUs in accordance with one embodiment of the present invention is presented.  FIG. 13  provides more detail for reference numeral  1205  of  FIG. 12 . CAP file  1300  is partitioned into one or more APDUs comprising package definition data  1305  for any package in the CAP file. Package definition data may comprise a package identifier. A class within a package is partitioned into one or more APDUs comprising class definition data  1310  for any class in the package. Class definition data may comprise, by way of example, a class identifier, a base class identifier and one or more interface identifiers. For any method in a class, the method is partitioned into one or more APDUs comprising method definition data  1315  and one or more APDUs comprising method code data  1320 . For any field in a class, the field is partitioned into one or more APDUs comprising field definition data  1325 . For static fields, the fields are also partitioned into one or more APDUs comprising field initialization data  1330 . 
   Method definition data  1315  may comprise, by way of example, a method identifier, a return type identifier, one or more parameter type identifiers and one or more throwable exception type identifiers. Method code data  1320  may comprise, by way of example, executable bytecodes. Field definition data  1325  may comprise, by way of example, a field count, and a field type identifier for each field included in the field count. Field initialization data  1330  may comprise, by way of example, data used to initialize constant data. 
   According to embodiments of the present invention, one or more APDUs comprising verification data may be associated with a program unit such a package, a class or a method, or the like. The verification information is computed off-card by a host computer or a loading terminal, and loaded onto the card for use at laod time, and possibly for use during program execution. The one or more verification APDUs may be inserted in the APDU data stream before the corresponding logical program unit APDUs. The one or more verification APDUs may also be inserted in the APDU data stream after the corresponding logical program unit APDUs. The verification data includes information for use in predicting program behavior during execution. Verification data may include, by way of example, primitive data type information such as bounds on values belonging to a particular data type. Verification data may also include program stack state information, such as the data type of entries on the program stack during simulated execution of the associated method code. The program stack state information may also include one or more reference to classes which are complex data types. 
   According to one embodiment of the present invention, class verification APDUs supplement verification data in the method verification APDUs for methods in a particular class. Such class verification APDUs may be used, by way of example, when a particular load order results in incomplete verification information availability when performing a per-method verification. 
   According to another embodiment of the present invention, package verification APDUs supplement verification data in the class verification APDUs for classes in a particular package. Such package verification APDUs may be used, by way of example, when a particular load order results in incomplete verification information availability when performing a per-class verification. 
   Type Map Information 
   According to another embodiment of the present invention, verification information is condensed using one or more type maps. The one or more type maps refer to sets of types that are relevant to a particular program unit. The one or more type maps refer to the data type of entries on an operand stack or in a register file during simulated execution of the corresponding code. The type maps allow optimization of verification by using relatively smaller numbers to refer to predefined sets of types as the types used in the corresponding code. This provides a relatively condensed representation of the types that need to be checked during verification of a program unit. This is explained in more detail below, with reference to  FIG. 14 . 
   Turning now to  FIG. 14 , a flow diagram that illustrates a method for using program unit type map information in accordance with one embodiment of the present invention is presented. At  1400 , a program unit is received. Using Java™ technology as an example, a method, class or package is received. At  1405 , the types used by the program unit are determined. At  1410 , a mapping for the types is created. At  1415 , the program unit mapping information is used in verification information for the program unit. 
   According to one embodiment of the present invention, program unit type map information is used to represent all type information in a program unit. According to another embodiment of the present invention, program unit type map information is used to represent a subset of type information in a program unit. By way of example, a type map may be used to represent the most-used types in the program unit. 
   According to one embodiment of the present invention, a type map comprises a bitmap, each bit of the type map representing a particular data type. By way of example, a 16-bit type map may be used to represent 16 types. 
   According to another embodiment of the present invention, type map information for a lower-level program unit is cumulative with respect to type map information for a higher-level program unit. By way of example, a package-level 4-bit type map may be used to represent the 16 most-used types in a package. A class-level 4-bit type map may be used to represent the 16 most-used types in a class, exclusive of the 16 types represented by the package-level type map. As a further example, a bitmapped package-level 4-bit type map may be used to represent the 4 most-used types in a package. A bitmapped class-level 4-bit type may be used to represent the 4 most-used types in a class, exclusive of the 4 types represented by the package level type map. 
   According to one embodiment of the present invention, a trailer APDU indicates the last APDU associated with a program unit. According to another embodiment of the present invention, a header APDU precedes one or more APDUs associated with a program unit and defines the expected sequence of logical program unit APDUs to follow. 
   Program Element Order 
     FIGS. 15A–17C  illustrate determining the order of program elements in a CAP file in accordance with one embodiment of the present invention.  FIGS. 15A–17C  provide more detail for reference numeral  1015  of  FIG. 10  and reference numeral  1121  of  FIG. 11 . FIG.  15 A illustrates a CAP file before ordering,  FIG. 15B  illustrates a use graph of the program elements in the CAP file of  FIG. 15A  and  FIG. 15C  illustrates the ordering of program elements in the original CAP file based at least in part on the use graph of  FIG. 15B . According to one embodiment of the present invention, the original CAP file is ordered based at least in part on the corresponding use graph. The ordered file is communicated to the target device. According to another embodiment of the present invention, the original CAP file is modified to include an order indicator that indicates the load order for the CAP file content. The modified CAP file is communicated to the target device. According to another embodiment of the present invention, the original CAP file and an order indicator that indicates the load order for the CAP file content are communicated to the target device. 
   Turning now to  FIG. 16 , a flow diagram that illustrates a method for ordering program units for optimized verification and linking in accordance with one embodiment of the present invention is presented. At  1600 , a program including multiple program units targeted to a device such as a smart card or the like is received. At  1605 , a use graph of the program is obtained. At  1610 , the program units are ordered to create an ordered program. The ordering is based at least in part on the use graph obtained at  1605 . At  1615 , the ordered program is communicated to the device. 
   According to one embodiment of the present invention, a “depth-first” approach for ordering program elements is followed. Using  FIGS. 15A–15C  as an example, method A.B.C ( 1540 ) is the main method and it calls method A.B.A ( 1542 ). Method A.B.A ( 1542 ) calls method A.B.B ( 1544 ) first and method A.A.B ( 1546 ) second. Neither method A.B.B ( 1544 ) nor method A.A.B ( 1546 ) calls other methods. Method A.B.C ( 1540 ) also calls method A.A.A ( 1548 ), followed by method A.A.C ( 1550 ). Following the use graph of  FIG. 15B , and proceeding in a depth-first, left-to-right manner, the resulting order is: A.B.B ( 1544 ), A.A.B ( 1546 ), A.B.A ( 1542 ), A.A.A ( 1548 ), A.A.C ( 1550 ), A.B.C ( 1540 ). This is the order reflected in the ordered package illustrated in  FIG. 15C . 
     FIGS. 17A–17C  illustrate determining the order CAP file content based on a use diagram to create a more flattened ordered CAP file.  FIGS. 17A–17C  are similar to  FIGS. 15A–15C  except that the ordered CAP file  1502  of  FIG. 15C  retains the class structure of the original CAP file  1500 , whereas the ordered CAP file  1702  of  FIG. 17C  has been flattened and thus does not retain the original class structure in the CAP file  1700 .  FIG. 17A  illustrates a CAP file comprising package-structured data.  FIG. 17B  illustrates a use diagram corresponding to the program within the CAP file of  FIG. 17A .  FIG. 17C  illustrates the CAP file of  FIG. 17A  ordered based upon the use diagram of  FIG. 17B  in accordance with one embodiment of the present invention. 
   As shown in  FIG. 17C , the first-used method is method A.B.B  1754 . The use of method A.B.B  1754  requires class A.B data  1724  and class A.B fields  1726 , so this information is placed before method A.B.B  1728  in the ordered CAP file  1702 . The next-used method is method A.A.B  1756 . The use of method A.A.B  1756  requires class A.A data  1730  and class A.A fields  1733 . Since the required class and field data does not occur earlier in the ordered CAP file, the required class and field data is placed before method A.A.B  1734  in the ordered CAP file  1702 . Placement of succeeding methods in the ordered CAP file  1702  proceeds according to the order of use, without regard to which class a method belongs to. In the present example, no further class or field data needs to be loaded because class and field data for the only two classes present in the original CAP file  1700  has already been placed in the ordered CAP file  1702 . 
   The program elements and use graph shown in  FIGS. 15A–17C  are for purposes of illustration only. Those of ordinary skill in the art will recognize a use graph may be used to represent the use of other portions of a program. By way of example, a use graph may also represent the use of fields or other program constructs. Additionally, portions of a program from different packages may be ordered in a fashion similar to that shown in  FIG. 17C , with package data for a particular package being positioned in the resulting file before any program units of the package. Also, those of ordinary skill in the art will recognize that many combinations of program elements and calling relationships between those program elements are possible. 
   According to another embodiment of the present invention, APDUs are arbitrarily ordered, with each APDU including context information. By way of example, an APDU may include information identifying the APDU contents as the fourth method of the second class. Including context information in an APDU facilitates loading all static data first (all the fields, classes and names) and then loading all the methods, ensuring information used by the methods for use in verification and linking is available first. 
   According to one embodiment of the present invention, a host computer inserts an ordering indicator in an augmented CAP file containing program data. A loading terminal uses the ordering indicator to determine the ordering of APDUs created as a result of the CAP file disassembly process. According to one embodiment of the present invention, the ordering indicator is based at least in part on a use graph of the program. By way of example, type map information may be loaded relatively late in the loading process, thus minimizing the amount of memory required. Alternatively, type map information may be loaded relatively early in the loading process, thus increasing the probability that the type information will be resident on the card when the types are referenced. 
   According to one embodiment of the present invention, one or more field definition APDUs  1325  and field initialization APDUs  1330  corresponding to a particular class are processed before any corresponding method definition APDU  1315  or method code APDU  1320  of the class. 
   CAP File Disassembly 
     FIGS. 18 and 19  are flow diagrams that illustrate disassembling a CAP file into logical APDUs from the perspective of a host computer in accordance with embodiments of the present invention.  FIG. 18  illustrates disassembling a CAP file that does not include verification data and  FIG. 19  illustrates disassembling a CAP file that includes verification data. 
   Turning now to  FIG. 18 , a flow diagram that illustrates a method for disassembling a CAP file into logical APDUs in accordance with one embodiment of the present invention is presented. The process illustrated within box  1800  is performed per package. At  1805 , one or more package definition APDUs comprising package definition data are created for a package. The process illustrated within box  1810  is performed per class. At  1815 , one or more class definition APDUs comprising class definition data are created for a class. At  1820 , one or more field definition APDUs comprising field definition data are created for the class. The process illustrated within box  1825  is performed per method. At  1835 , one or more method definition APDUs comprising method definition data are created for a method. At  1840 , one or more code APDUs comprising the method code are created for the method. At  1830 , one or more data initialization APDUs are created. 
   According to embodiments of the present invention, verification data may be created for program units. The verification data may be created for program units such as packages, classes, methods, or the like, or any combination thereof. As mentioned previously, the verification data for a program unit may be inserted in an APDU stream before the corresponding program unit code APDU or program unit definition APDU. In one embodiment, the verification data is inserted immediately before the corresponding program unit code APDU or program unit definition APDU. Alternatively, the verification data for a program unit may be inserted in an APDU stream after the corresponding program unit code APDU or program unit definition APDU. In one embodiment, the verification data is inserted immediately after the corresponding program unit code APDU or program unit definition APDU. This is explained in more detail below with reference to  FIG. 19 . 
   Turning now to  FIG. 19 , a flow diagram that illustrates a method for disassembling a CAP file into logical APDUs including APDUs comprising verification data in accordance with one embodiment of the present invention is presented.  FIG. 19  is similar to  FIG. 18 , except that verification data is included in  FIG. 19  at reference numerals  1940 ,  1945  and  1955 . The process illustrated within box  1900  is performed per package. At  1905 , one or more package definition APDUs comprising package definition data are created for a package. The process illustrated within box  1910  is performed per class. At  1915 , one or more class definition APDUs comprising class definition data are created for a class. At  1920 , one or more field definition APDUs comprising field definition data are created for the class. The process illustrated within box  1925  is performed per method. At  1930 , one or more method definition APDUs comprising method definition data are created for a method. At  1935 , one or more code APDUs comprising the method code are created for the method. At  1940 , one or more method verification APDUs comprising method verification data are created for a method. At  1945 , one or more class verification APDUs comprising class verification data are created for a class. At  1950 , one or more data initialization APDUs are created. At  1955 , one or more package verification APDUs comprising package verification data are created for a package. 
   According to embodiments of the present invention, one or more verification APDUs are inserted into the APDU stream before and/or after the corresponding one or more code or definition APDUs. Using  FIG. 19  as an example, one or more package verification APDUs may be inserted into the APDU stream ( 1955 ) after inserting the corresponding one or more package definition APDUs ( 1905 ). Alternatively, one or more package verification APDUs may be inserted into the APDU stream before inserting the corresponding one or more package definition APDUs. Similarly, one or more class verification APDUs may be inserted into the APDU stream ( 1945 ) after inserting the corresponding one or more class definition APDUs ( 1915 ). Alternatively, one or more class verification APDUs may be inserted into the APDU stream before inserting the corresponding one or more class definition APDUs. As a further example, one or more method verification APDUs may be inserted into the APDU stream ( 1940 ) after inserting the corresponding one or more method definition APDUs ( 1930 ). Alternatively, one or more method verification APDUs may be inserted into the APDU stream before inserting the corresponding one or more method definition APDUs. A verification APDU that precedes or succeeds the corresponding one or more code or definition APDUs may comprise, by way of example, one or more type maps. 
     FIGS. 20A and 20B  are flow diagrams that illustrate methods for computing an authentication fingerprint over an APDU data stream in accordance with embodiments of the present invention.  FIGS. 20A and 20B  provide more detail for reference numeral  1108  of  FIG. 11 .  FIG. 20A  illustrates computing an authentication fingerprint when verification APDUs are used to determine the authentication fingerprint.  FIG. 20B  illustrates computing an authentication fingerprint when verification APDUs are not used to determine the authentication fingerprint. The process illustrated by  FIGS. 20A and 20B  are the same processes used by a loading terminal (reference numerals  1128  and  1130  of  FIG. 11 ) and by a target smart card (reference numeral  1142  of  FIG. 11 ) to compute an authentication fingerprint, as described below. 
   Turning now to  FIG. 20 , a flow diagram that illustrates a method for computing an authentication fingerprint over an APDU data stream in accordance with one embodiment of the present invention is presented. Referring to  FIG. 20A , at  200  an authentication fingerprint is initialized. At  2005 , a logical APDU is received. At  2010 , the fingerprint is computed over the logical APDU payload. The fingerprint computation uses the result of the previously computed fingerprint. At  2015 , a determination is made regarding whether another logical APDU remains to be processed. Processing of additional APDUs continues at  2005 . 
   Referring to  FIG. 20B , at  2020  an authentication fingerprint is initialized. At  2025 , a logical APDU is received. At  2030 , a determination is made regarding whether the APDU is a verification APDU. If the APDU is not a verification APDU, the fingerprint is computed over the logical APDU payload at  2035 . The fingerprint computation uses the result of the previously computed fingerprint. At  2040 , a determination is made regarding whether another logical APDU remains to be processed. Processing of additional APDUs continues at  2025 . 
   Loading Terminal 
   Turning now to  FIG. 21 , a flow diagram that illustrates a method for communicating program data from a host computer to a loading terminal from the perspective of a loading terminal in accordance with one embodiment of the present invention is presented.  FIG. 21  provides additional detail for reference numerals  1030 – 1045  of  FIG. 10  and reference numerals  1118 – 1136  of  FIG. 11 . At  2100 , an augmented CAP file is received. At  2105 , any authentication codes and fingerprints are separated from the augmented CAP file. At  2110 , linking information is obtained. The linking information comprises information needed to link methods, such as the card&#39;s present callable routines and how to reference them. The linking information may be obtained from an external source. By way of example, a loading terminal may communicate via the Web with a central repository having knowledge of a particular target smart card&#39;s linking information. As a further example of obtaining linking information from an external source, a loading terminal may obtain the information from the target smart card itself. 
   Still referring to  FIG. 21 , at  2115  the augmented CAP file is disassembled into one or more logical APDUs. At  2120 , the one or more logical APDUs are communicated to a smart card and an authentication fingerprint is computed over the APDU payload. The process in  2115  and  2120  is similar to processes  1205  and  1210  of  FIG. 12  performed by the host computer as described above, as well as the processes  2905  of  FIGS. 29 and 3005  of  FIG. 30  performed by the target smart card as described below. The similarity of the processes guarantees that if the APDU payload remains the same, the same authentication fingerprint will be generated regardless of the entity performing the computation. Conversely, if the APDU payload changes between when each entity performs the computation, a different fingerprint will be generated, signaling a change in the payload. 
   Still referring to  FIG. 21 , process  2125  applies when a CAP file optionally includes an authentication fingerprint. If the CAP file includes an authentication fingerprint, a determination is made regarding whether the fingerprint extracted from the augmented CAP file in  2105  matches the fingerprint computed at  2120 . If the fingerprints match, at  2130  a target smart card authentication code appropriate for the particular target smart card is extracted from the CAP file. At  2135 , the fingerprint, authentication code, or both, are sent to the target smart card. At  2140 , initialization instructions are performed and the resultant data is loaded. At  2145 , a proof of loading is received from the smart card. According to one embodiment of the present invention, the proof of loading comprises the storage commitment fingerprint. 
   As illustrated in  FIG. 21 , the loading terminal disassembles an augmented CAP file into logical APDUs ( 2115 ) and then computes an authentication fingerprint over the logical APDU payload upon transmitting the logical APDUs to the target smart card ( 2120 ). Alternatively, the computation of the authentication fingerprint may be interleaved with the disassembly process ( 2115 ). As a further alternative, both the transmission of APDUs to the target smart card and the computation of the authentication fingerprint may be interleaved with the disassembly process ( 2115 ). 
   As mentioned previously, the augmented CAP file received by a loading terminal may include verification data. The loading terminal may also receive a CAP file without verification data, compute verification data, create one or more APDUs containing the data and send the one or more APDUs to the target smart card. The determination regarding whether to include verification data in the authentication fingerprint computation is based on whether the CAP file received by the loading terminal includes verification data, and on whether the target smart card requires verification data. If the received CAP file includes verification data, the authentication fingerprint is additionally computed over the verification data. If the received CAP file does not include verification data, the authentication fingerprint is not computed over verification data, regardless of whether the loading terminal produces verification data that is sent to the target smart card. 
   The loading terminal may also receive a CAP file, compute link data, create one or more APDUs containing the data and send the one or more APDUs to the target smart card.  FIGS. 22–27  illustrate methods for disassembling an augmented CAP file into one or more logical APDUs from the perspective of a loading terminal in accordance with embodiments of the present invention.  FIGS. 22–27  provide more detail for reference numeral  2115  of  FIG. 21 . As mentioned previously, the program elements of the CAP file to be disassembled may be ordered for optimized verification and linking (reference numeral  1121  of  FIG. 11 ) prior to the disassembling processes illustrated in  FIGS. 22–27 .  FIG. 22  illustrates disassembling an augmented CAP file into one or more logical APDUs.  FIG. 23  illustrates disassembling an augmented CAP file including verification data into one or more logical APDUs including APDUs comprising verification data.  FIG. 24  illustrates disassembling an augmented CAP file not including verification data into one or more logical APDUs including APDUs comprising verification data.  FIG. 25  illustrates disassembling an augmented CAP file into one or more logical APDUs including APDUs comprising link data.  FIG. 26  illustrates disassembling an augmented CAP file including verification data into one or more logical APDUs including APDUs comprising verification data and APDUs comprising link data.  FIG. 27  illustrates disassembling an augmented CAP file not including verification data into one or more logical APDUs including APDUs comprising verification data and APDUs comprising link data. 
   Turning now to  FIG. 22 , a flow diagram that illustrates a method for disassembling an augmented CAP file into one or more logical APDUs in accordance with one embodiment of the present invention is presented.  FIG. 22  is similar to the process performed by the host computer as illustrated in  FIG. 18 . The process illustrated within box  2200  is performed per package. At  2205 , one or more package definition APDUs comprising package definition data are created for a package. The process illustrated within box  2210  is performed per class. At  2215 , one or more class definition APDUs comprising class definition data are created for a class. At  2220 , one or more field definition APDUs comprising field definition data are created for the class. The process illustrated within box  2225  is performed per method. At  2230 , one or more method definition APDUs comprising method definition data are created for a method. At  2235 , one or more code APDUs comprising the method code are created for the method. At  2240 , one or more data initialization APDUs are created. 
   Turning now to  FIG. 23 , a flow diagram that illustrates a method for disassembling an augmented CAP file including verification data into one or more logical APDUs including APDUs comprising verification data in accordance with one embodiment of the present invention is presented.  FIG. 23  is similar to the process performed by the host computer as illustrated in  FIG. 19 . The process illustrated within box  2300  is performed per package. At  2305 , one or more package definition APDUs comprising package definition data are created for a package. The process illustrated within box  2310  is performed per class. At  2315 , one or more class definition APDUs comprising class definition data are created for a class. At  2320 , one or more field definition APDUs comprising field definition data are created for the class. The process illustrated within box  2325  is performed per method. At  2330 , one or more method definition APDUs comprising method definition data are created for a method. At  2335 , one or more code APDUs comprising the method code are created for the method. At  2340 , one or more method verification APDUs comprising method verification data are created for a method. At  2345 , one or more class verification APDUs comprising class verification data are created for a class. At  2350 , one or more data initialization APDUs are created. At  2355 , one or more package verification APDUs comprising package verification data are created for a package. 
   Turning now to  FIG. 24 , a flow diagram that illustrates a method for disassembling an augmented CAP file not including verification data into one or more logical APDUs including APDUs comprising verification data in accordance with one embodiment of the present invention is presented.  FIG. 24  is similar to  FIG. 23 , except that in  FIG. 24 , verification data is computed ( 2440 ,  2445 ,  2455 ), whereas in  FIG. 23 , verification data used to create one or more verification APDUs ( 2340 ,  2345 ,  2355 ) is extracted from the augmented CAP file. The process illustrated within box  2400  is performed per package. At  2405 , one or more package definition APDUs comprising package definition data are created for a package. The process illustrated within box  2410  is performed per class. At  2415 , one or more class definition APDUs comprising class definition data are created for a class. At  2420 , one or more field definition APDUs comprising field definition data are created for the class. The process illustrated within box  2425  is performed per method. At  2430 , one or more method definition APDUs comprising method definition data are created for a method. At  2435 , one or more code APDUs comprising the method code are created for the method. At  2440 , method verification data is computed and one or more method verification APDUs comprising method verification data are created for a method. At  2445 , class verification data is computed and one or more class verification APDUs comprising class verification data are created for a class. At  2450 , one or more data initialization APDUs are created. At  2455 , package verification data is computed and one or more package verification APDUs comprising package verification data are created for a package. 
   Turning now to  FIG. 25 , a flow diagram that illustrates a method for disassembling an augmented CAP file into logical one or more APDUs including APDUs comprising link data in accordance with one embodiment of the present invention is presented.  FIG. 25  is similar to  FIG. 22 , except that per-method link APDUs are created ( 2540 ) in  FIG. 25 . The process illustrated within box  2500  is performed per package. At  2505 , one or more package definition APDUs comprising package definition data are created for a package. The process illustrated within box  2510  is performed per class. At  2515 , one or more class definition APDUs comprising class definition data are created for a class. At  2520 , one or more field definition APDUs comprising field definition data are created for the class. The process illustrated within box  2525  is performed per method. At  2530 , one or more method definition A PDUs comprising method definition data are created for a method. At  2535 , one or more code APDUs comprising the method code are created for the method. At  2540 , per-method link APDUs are created. At  2545 , one or more data initialization APDUs are created. 
   Turning now to  FIG. 26 , a flow diagram that illustrates a method for disassembling an augmented CAP file including verification data into one or more logical APDUs including APDUs comprising verification data and APDUs comprising link data in accordance with one embodiment of the present invention is presented.  FIG. 26  represents the combination of  FIGS. 23 and 25 . The process illustrated within box  2600  is performed per package. At  2605 , one or more package definition APDUs comprising package definition data are created for a package. The process illustrated within box  2610  is performed per class. At  2615 , one or more class definition APDUs comprising class definition data are created for a class. At  2620 , one or more field definition APDUs comprising field definition data are created for the class. The process illustrated within box  2625  is performed per method. At  2630 , one or more method definition APDUs comprising method definition data are created for a method. At  2635 , one or more code APDUs comprising the method code are created for the method. At  2640 , one or more method verification APDUs comprising method verification data are created for a method. At  2645 , per-method link APDUs are created. At  2650 , one or more class verification APDUs comprising class verification data are created for a class. At  2655 , one or more data initialization APDUs are created. At  2660 , one or more package verification APDUs comprising package verification data are created for a package. 
   Turning now to  FIG. 27 , a flow diagram that illustrates a method for disassembling an augmented CAP file not including verification data into one or more logical APDUs including APDUs comprising verification data and APDUs comprising link data in accordance with one embodiment of the present invention is presented.  FIG. 27  represents the combination of  FIGS. 24 and 25 . The process illustrated within box  2700  is performed per package. At  2705 , one or more package definition APDUs comprising package definition data are created for a package. The process illustrated within box  2710  is performed per class. At  2715 , one or more class definition APDUs comprising class definition data are created for a class. At  2720 , one or more field definition APDUs comprising field definition data are created for the class. The process illustrated within box  2725  is performed per method. At  2730 , one or more method definition APDUs comprising method definition data are created for a method. At  2735 , one or more code APDUs comprising the method code are created for the method. At  2740 , method verification data is computed and one or more method verification APDUs comprising method verification data are created for a method. At  2745 , per-method link APDUs are created. At  2750 , class verification data is computed and one or more class verification APDUs comprising class verification data are created for a class. At  2755 , one or more data initialization APDUs are created. At  2760 , package verification data is computed and one or more package verification APDUs comprising package verification data are created for a package. 
   Turning now to  FIG. 28 , a flow diagram that illustrates a method for creating one or more method link APDUs in accordance with one embodiment of the present invention is presented.  FIG. 28  provides more detail for reference numeral  2540  of  FIG. 25 , reference numeral  2645  of  FIG. 26  and reference numeral  2745  of  FIG. 27 . At  2800 , verifiable linking instructions are computed based on logical memory layout and information from the card. The loading terminal may have previously obtained this information as described above with respect to reference numeral  2110  of  FIG. 21 . At  2805 , a link APDU that includes the verifiable linking instructions is created. 
   Smart Card 
   Turning now to  FIG. 29 , a flow diagram that illustrates a method for communicating program data from a loading terminal to a smart card from the perspective of a smart card in accordance with one embodiment of the present invention is presented.  FIG. 29  provides additional detail for reference numerals  1050 – 1065  of  FIG. 10  and reference numerals  1140 – 1150  of  FIG. 11 . At  2900 , load initialization is performed. At  2905 , one or more logical APDUs are processed to prepare the data and their data fields for loading. The processing comprises computing an authentication fingerprint. At  2910 , an authentication fingerprint APDU is received. Alternatively, the authentication fingerprint may be received as part of load initialization ( 2600 ), or as part of processing APDUs ( 2605 ). 
   Still referring to  FIG. 29 , at  2915  a determination is made regarding whether the received authentication fingerprint matches the authentication fingerprint computed at  2905 . If the received authentication fingerprint does not match the computed authentication fingerprint, a failure indication is made at  2945 . If the received authentication fingerprint matches the computed authentication fingerprint, a target smart card authentication code is received at  2920  and authentication is performed based on the target smart card authentication code at  2925 . At  2930 , a determination is made regarding whether the authentication was successful. If the authentication was unsuccessful, a failure indication is made at  2945 . If the authentication was successful, the program data is committed to the smart card memory at  2935  and a loading proof is provided at  2940 . The program data may be committed to the smart card memory by associating the program data with a storage commitment fingerprint computed over the finally stored program data. According to one embodiment of the present invention, the loading proof comprises the storage commitment fingerprint. According to another embodiment of the present invention, the loading proof comprises an authentication code based at least in part on the storage commitment fingerprint. 
   Turning now to  FIG. 30 , a flow diagram that illustrates a method for communicating program data from a loading terminal to a smart card from the perspective of a smart card using an authentication fingerprint that is a HMAC in accordance with one embodiment of the present invention is presented.  FIG. 30  is similar to  FIG. 29 , except that determinations  2930  and  2915  in  FIG. 29  are equivalent to determination  3015  in  FIG. 30 . Since a HMAC is both a fingerprint and a message authentication code, the program data may be committed to the smart card memory when the received authentication fingerprint matches the computed authentication fingerprint. At  3000 , load initialization is performed. At  3005 , one or more logical APDUs are processed to prepare the data in their data fields for loading. The processing comprises computing an authentication fingerprint. At  3010 , an authentication fingerprint APDU is received. Alternatively, the authentication fingerprint may be received as part of load initialization ( 2600 ), or as part of processing APDUs ( 2605 ). 
   Still referring to  FIG. 30 , at  3015  a determination is made regarding whether the received authentication fingerprint matches the authentication fingerprint computed at  3005 . If the received authentication fingerprint does not match the computed authentication fingerprint, a failure indication is made at  3030 . If the received authentication fingerprint matches the computed authentication fingerprint, the program data is committed to the smart card memory at  3020  and a loading proof is provided at  3025 . The program data may be committed to the smart card memory by associating the program data with a storage commitment fingerprint computed over the finally stored program data. According to one embodiment of the present invention, the loading proof comprises the storage commitment fingerprint. According to another embodiment of the present invention, the loading proof comprises an authentication code based at least in part on the storage commitment fingerprint. 
   Turning now to  FIG. 31 , a flow diagram that illustrates a method for performing load initialization in accordance with one embodiment of the present invention is presented. FIG.  31  provides more detail for reference numeral  2900  of  FIG. 29  and reference numeral  3000  of  FIG. 30 . At  3100 , a request for loading is received. At  3105 , the request is authenticated to determine whether the loading process should proceed. At  3110 , a determination is made regarding whether the authentication in  3105  was successful. If the authentication was not successful, the process ends with failure at  3130 . If the authentication was successful, at  3115  load parameters are checked to determine whether the load is capable of succeeding, based on known characteristics of the card and the program data to be loaded. By way of example, if the card has less memory than what is required by the program data to be loaded, an indication that the load will fail is made. Additionally, if the program data to be loaded requires classes that are not presently on the card and are not part of the program data to be loaded, an indication that the load will fail is made. At  3120 , a determination is made regarding whether the load is capable of succeeding based upon the result of process  3115 . If the load is capable of succeeding, preparations for loading are made at  3125 . Exemplary preparations include initializing one or more authentication fingerprints and one or more storage commitment fingerprints. If the load is not capable of succeeding, the loading process ends with failure at  3130 . 
   Alternatively, the order of processes  3105  and  3115  may be switched so that process  3115  is performed before process  3105 . However, load initialization ends with failure  3130  if either of processes  3105  and  3115  fails. 
   Turning now to  FIG. 32 , a flow diagram that illustrates a method for processing an APDU stream in accordance with one embodiment of the present invention is presented.  FIG. 32  provides more detail for reference numeral  2905  of  FIG. 29  and reference numeral  3005  of  FIG. 30 . At  3200 , a logical APDU is received. At  3205 , the logical APDU is pre-processed. The pre-processing may include, by way of example, finalizing processing of the previous program unit if the current APDU is the first APDU of another program unit. The pre-processing may also include, by way of example, decryption. The result of the pre-processing is an indication of whether the logical APDU is valid. At  3210 , a determination is made regarding whether the logical APDU is valid. If the logical APDU is invalid, loading is aborted at  3215 . If the logical APDU is valid, an authentication fingerprint is computed at  3210  and the received logical APDU is processed at  3225  to prepare the data in the logical APDU data field for storage. The processing may include, by way of example, resolving references to other program units. At  3230 , a determination is made regarding whether a stored result is required. Some APDUs may not require persistent storage. By way of example, an APDU that merely includes information about a preceding or succeeding APDU may not require persistent storage. If a stored result is required, the result is stored at  3225 . At  3240 , a storage commitment fingerprint is computed over the stored result using the result of the previously computed storage commitment fingerprint. 
   Turning now to  FIG. 33 , a flow diagram that illustrates a method for computing an authentication fingerprint in accordance with one embodiment of the present invention is presented.  FIG. 33  provides more detail for reference numeral  3220  of  FIG. 32 . At  3300 , a determination is made regarding whether the APDU is a link APDU. If the APDU is not a link APDU, at  3305  a determination is made regarding whether the APDU is a verification APDU. If the APDU is a verification APDU, at  3310  a determination is made regarding whether verification APDUs are part of the authentication fingerprint. If the APDU is not a link APDU or a verification APDU, or if the APDU is a verification APDU and verification APDUs are part of the authentication fingerprint, at  3315  the authentication fingerprint is computed over the logical APDU payload using the result of the previously computed authentication fingerprint. 
   As illustrated in  FIG. 32 , the receipt of logical APDUs ( 3200 ) is interleaved with the computation of an authentication fingerprint ( 3220 ) and computation of a storage commitment fingerprint ( 3240 ). Alternatively, the smart card may receive one or more logical APDUs and then compute an authentication fingerprint and storage commitment fingerprint over the one or more received APDUs. 
   Turning now to  FIG. 34 , a flow diagram that illustrates a method for processing a logical APDU in accordance with one embodiment of the present invention is presented.  FIG. 34  provides more detail for reference numeral  3225  of  FIG. 32 . At  3400 , verification information is accepted. At  3405 , the verification information is used to verify a logical APDU. At  3410 , a determination is made regarding whether the logical APDU was successfully verified. If the logical APDU was successfully verified, linking information is accepted at  3415  and at  3420 , the linking information is used to link. 
   Virtual Method Jump Table 
   The data structures as described with respect to  FIG. 7  illustrate linking to static methods, or methods having a single call address. Object-oriented languages such as the Java™ language support virtual methods, or methods that may have multiple copies. In the Java™ language, a virtual method may be declared in a class and a subclass of the class may override or replace the virtual method with its own instance of the virtual method. An instance of the subclass will reference the version of the method overridden in the subclass, while an instance of the class will reference the virtual method declared in the class. 
   According to one embodiment of the present invention, the capability to link virtual methods is provided by creating a jump table for each virtual method that is overridden at least once. The jump table includes the address of each instance of a virtual method. Object constructors are rewritten to accept a “type” parameter, constructor calls are rewritten to provide type information, and virtual method program calls are rewritten to include an indication of the current type of the called object. The indication of the current type is used as an index into the corresponding virtual method jump table, where the address of the appropriate virtual method code is obtained. This is explained in more detail below with reference to  FIGS. 35–37 . 
   Turning now to  FIG. 35 , data structures for linking a program including virtual methods in accordance with one embodiment of the present invention is presented. As shown in  FIG. 35 , subclass N ( 3505 ) extends class M ( 3500 ) and does not override method A ( 3525 ) or B ( 3530 ). Subclass O ( 3510 ) extends class M ( 3500 ) and overrides method A ( 3525 ). Any calls to method O.A ( 3550 ) actually calls method O.A ( 3550 ), not method M.A ( 3525 ). Jump table  3320  is indexed by a value of a type identifier in the class instance data. Each entry of jump table  3520  includes the address of the virtual method instance corresponding to the index, for each virtual method in a class having at least one instance. Every call to method M.A ( 3525 ) that has been overridden includes a type identifier. The type identifier is used as an index in the jump table  3320  to obtain the address of the code corresponding to the virtual method instance. The calls in subclass N ( 3505 ) and subclass O ( 3510 ) are rewritten to call with the type identifier. The calls may be rewritten by a host computer or a loading terminal before loading the program on a smart card, such as when an augmented CAP file is produced. Alternatively, the calls may be rewritten by a loading terminal. The target smart card may also rewrite the calls after the program data has been loaded. The type identifier is obtained from a “current type of the object” field  3345  in the called object  3515 . 
   Searching for the appropriate virtual method instance is thus made more deterministic by giving each subtype and each method a type identifier. Using the example illustrated in  FIG. 35 , when class “M” ( 3500 ) or class “N” ( 3505 ) objects are instantiated, both objects are instantiated with the type identifier having a value of zero. When the “O” ( 3510 ) object is instantiated, the type identifier associated with the instance is the value one. When object “O” ( 3510 ) calls the virtual method, the type identifier is used as an index into the jump table  3520  to determine which virtual method instance to call, thus obviating the need to perform an exhaustive search for the appropriate virtual method instance. 
   Turning now to  FIG. 36 , a block diagram that illustrates modifying a stored program having link data to resolve dynamic references in accordance with one embodiment of the present invention is presented.  FIG. 36  is similar to  FIG. 7 , except that  FIG. 36  includes a jump table ( 3676 ,  3680 ,  3682 ) for each virtual method having at least one virtual method instance. Referring to card memory  3600 , code for methods A1A ( 3602 ), A2A ( 3612 ) and B2A ( 3628 ) include calls to virtual methods A1C ( 3608 ), B1A ( 3620 ) and B1D ( 3626 ), respectively. Referring to modified card memory  3650 , code for methods A1A ( 3652 ), A2A ( 3660 ) and B2A ( 3674 ) has been modified to refer to the jump table associated with the called virtual method ( 3676 ,  3680 ,  3682 ) and a type indicator of the called object. 
   Turning now to  FIG. 37 , a flow diagram that illustrates modifying a stored program having link data to resolve dynamic references in accordance with one embodiment of the present invention is presented. At  3700 , a program is received. At  3705 , classes in the program are enumerated. Box  3710  is performed per class. At  3720 , object constructor calls are rewritten to provide type information. At  3725 , object constructors are rewritten to accept a “type” parameter. Box  3715  is performed per virtual method in a class. At  3720 , a determination is made regarding whether the virtual method has been overridden with an instance of the virtual method. If the virtual method has been overridden, at  3725  a virtual method jump table for the virtual method having at least one virtual method instance is created. At  3730 , program calls to the virtual method are rewritten to refer to the jump table associated with the called virtual method and a type indicator of the called object. If the virtual method has not been overridden, the virtual method may be linked in the same manner as a static method. 
   According to another embodiment of the present invention, a call to a virtual method that has been overridden at least once is replaced with a call instruction that uses the type indicator of the called object as an index into a table positioned in the instruction stream inline with the call instruction. 
   Program Unit Storage Commitment Fingerprint 
   According to embodiments of the present invention, a program unit storage commitment fingerprint is associated with a program unit. The program unit storage commitment fingerprint may be used to indicate commitment of the program unit. In other words, the program unit storage commitment fingerprint may be used to indicate the program unit has been finally loaded onto the target smart card. The program unit storage commitment fingerprint may also be used to indicate whether the program unit data has been tampered with or is otherwise unfit for execution. The program unit storage commitment fingerprint is computed over the program unit data and associated with the program unit at the time the program unit is finally stored in a persistent mutable memory and ready for use. The program unit storage commitment fingerprint may be stored in an area of memory contiguous with the associated program data. Alternatively, a reference to the program unit commitment fingerprint may be stored with the associated program data. As a further alternative, program units may be stored in a tabular form, with each entry including a storage unit and the corresponding fingerprint. Those of ordinary skill in the art will recognize other techniques for associating program units with commitment fingerprints are possible. 
   Upon use of the program unit, the program unit storage commitment fingerprint initially associated with the program unit is matched against the result of computing a storage commitment fingerprint over the program unit data. A mismatch indicates the program unit data has been tampered with or is otherwise unfit for execution. 
   A program unit may comprise any logical program structure. Using Java™ technology as an example, a program unit may comprise a package, a class, a method or any combination thereof. Additionally, a program unit may be stored in noncontiguous memory. 
   According to one embodiment of the present invention, “use” of a program unit comprises executing the program unit. According to another embodiment of the present invention, “use” of a program unit comprises creating an instantiation of another program unit based at least in part on the program unit. Using Java™ technology as an example, “use” of a program unit may comprise object instantiation. According to another embodiment of the present invention, “use” of a program unit comprises reading the program unit data. 
   Hierarchical Program Unit Storage Commitment Fingerprint 
   According to embodiments of the present invention, a storage commitment fingerprint of a higher level program unit may be based at least in part on at least one storage commitment fingerprint of a lower level program unit. This is illustrated below with respect to  FIG. 38 . 
   Turning now to  FIG. 38 , a block diagram that illustrates a hierarchy of program unit storage commitment fingerprints in accordance with one embodiment of the present invention is presented. Reference numerals  3800 – 3808  represent classes, reference numerals  3810 – 3812  represent packages and reference numeral  3814  represents a load comprising one or more packages. Class storage commitment fingerprints  3818 – 3826  are formed by computing a fingerprint over class-level data in classes  3800 – 3808 , respectively, and the collection of method storage commitment fingerprints in classes  3800 – 3808 , respectively. Package storage commitment fingerprints  3828 – 3830  are formed by computing a fingerprint over package-level data in packages  3810 – 3812 , respectively, and the collection of class storage commitment fingerprints in packages  3810 – 3812 , respectively. Load storage commitment fingerprint  3816  is formed by computing a fingerprint over the collection of package storage commitment fingerprints in load  3814 . 
   Alternatively, one or more storage commitment fingerprints of a higher level program unit may be based on the data of a lower level program unit. Using Java™ technology as an example, a class storage commitment fingerprint may be based over class-level data and method-level data for methods belonging to the class. 
   Turning now to  FIG. 39 , a block diagram that illustrates a data structure including program code and program unit storage commitment fingerprints in accordance with one embodiment of the present invention is presented. Card memory  3900  comprises a storage area for a load unit  3902  that comprises package “A”  3904  and package “B”  3906 . Packages  3904  and  3906  comprise classes  3908 – 3910  and  3912 – 3914 , respectively. Classes  3908 ,  3910 ,  3912  and  3914  comprise methods  3916 – 3922 ,  3924 – 3926 ,  3928 – 3934  and  3936 – 3938 , respectively. Method storage commitment fingerprints  3940 – 3964  are computed over method code  3916 – 3938 , respectively. Class storage commitment fingerprints  3966 ,  3968 ,  3970  and  3972  are computed over method storage commitment fingerprints  3940 – 3946 ,  3948 – 3950 ,  3954 – 3960  and  3962 – 3964 , respectively. Class storage commitment fingerprints  3966 ,  3968 ,  3970  and  3972  may also be computed over any field definitions and initialized static data that is part of the respective class. Package storage commitment fingerprints  3974  and  3976  are computed over class storage commitment fingerprints  3966 – 3968  and  3970 – 3972 , respectively. Load unit storage commitment fingerprint  3978  is computed over package storage commitment fingerprints  3974  and  3976 . 
   Turning now to  FIG. 40 , a block diagram that illustrates a data structure including program code and a load storage commitment fingerprint in accordance with one embodiment of the present invention is presented.  FIG. 40  is similar to  FIG. 39 , except  FIG. 40  does not include class storage commitment fingerprints or package storage commitment fingerprints. Load unit storage commitment fingerprint  4042  is computed over stored method code  4016 – 3840  in packages “A”  4004  and package “B”  4006 . 
   Runtime Integrity Checks 
   According to embodiments of the present invention, a program unit commitment fingerprint is used to check the integrity of a program unit at runtime.  FIGS. 41 and 42  illustrate the general case for this runtime integrity checking.  FIGS. 43 and 44  illustrate embodiments of the present invention that use a dispatching mechanism to implement runtime integrity checking. 
     FIG. 41  is a flow diagram that illustrates a method for using a program unit commitment fingerprint to determine whether a program unit may be used, in accordance with one embodiment of the present invention. At  4100 , a request for use of a program unit is received. According to one embodiment of the present invention, the “use” comprises creating an instantiation based at least in part on the program unit. According to another embodiment of the present invention, the “use” comprises executing the program unit code. According to another embodiment of the present invention, the “use” comprises reading the program unit data. 
   According to embodiments of the present invention, a program unit may be a program, a package, a class, a method an instance variable or a class variable. However, the illustration of a program unit with respect to Java™ technology is not intended to be limiting in any way. Those of ordinary skill in the art will recognize that a program may be partitioned in many ways. 
   Still referring to  FIG. 41 , at  4105  a determination is made regarding whether it is the first time the program unit use request has been received in the current session. If it is not the first time the program unit use request has been received in the current session, a stored determination of program unit data validity is used at  4130 . If this is the first time the program unit use request has been received in the current session, at  4135  an indication that the program unit has been used in the current session is made. At  4110 , a determination is made regarding whether the stored program unit data is valid. The result of this determination is checked at  4115 . If the stored program unit data is not valid, a failure indication is made at  4120 . If the stored program unit data is valid, the program unit is used at  4125 . 
   According to another embodiment of the present invention, the validity of a stored program unit is determined upon receiving a request for use of the program unit, without regard to whether a previous use request for the same program unit was received in the current session. 
   According to one embodiment of the present invention, a fingerprint device is configured to compute authentication fingerprints, program storage commitment fingerprints, or both. According to another embodiment of the present invention, a fingerprint device comprises a computation unit that computes the storage commitment fingerprint. The computation unit is linked to memory dedicated to storing committed data. The computation unit may be integrated with a memory device comprising the memory. Alternatively, the computation unit may be a standalone device in communication with a memory device comprising the memory. According to one embodiment of the present invention, the computation unit is configured to automatically and incrementally compute the fingerprint for the memory upon detecting a write operation to the memory. 
   According to another embodiment of the present invention, the computation unit is configured to automatically and incrementally compute the fingerprint for the memory before use of data in the memory, such as upon detecting a read operation for the memory. By way of example, upon receiving a read request for data stored at memory addresses specified by a memory range, the computation unit computes a fingerprint over the data stored at the memory addresses specified by the memory range. 
   Turning now to  FIG. 42 , a flow diagram that illustrates a method for determining whether stored program unit data is valid in accordance with one embodiment of the present invention is presented.  FIG. 42  provides more detail for reference numeral  4110  of  FIG. 41 . At  4200 , a fingerprint is computed over the program unit data. At  4205 , a determination is made regarding whether the computed fingerprint matches a stored fingerprint. If the computed fingerprint does not match the stored fingerprint, at  4210  an indication that the stored program unit data is invalid is made. If the computed fingerprint matches the stored fingerprint, at  4215  an indication that the stored program unit data is valid is made. 
   Dispatch Table 
   In the context of the present invention, the term “gateway dispatcher” is defined as a program unit configured to determine whether the executable code of a called method is valid before calling the method. A gateway dispatcher may be part of a virtual machine or a lower level routine. 
   According to embodiments of the present invention, links to called routines may be hard-coded. According to alternative embodiments of the present invention, a dispatch table associated with a protection unit includes an entry for methods protected by the protection unit. A caller of a method in a protection unit calls the method by referring to the protection unit and an index in the table. The reference determines whether the executable code of a called method is valid (has been verified) before calling the method. A gateway dispatcher verifies the protection unit if the protection unit dispatch table has been loaded but the protection unit has not been verified. The gateway dispatcher loads the dispatch table and verifies the protection unit if the protection unit dispatch table has not been loaded. This is explained in more detail below with reference to  FIGS. 43 and 44 . 
   Turning now to  FIG. 43 , a block diagram that illustrates a smart card configured to ensure a called method has been verified prior to execution in accordance with one embodiment of the present invention is presented.  FIG. 43  illustrates a data structure for implementing the “use program unit” process discussed previously with respect to reference numeral  4125  of  FIG. 41 . According to one embodiment of the present invention, entry points to a class or package are precomputed at load time. The entry points trigger a test to determine whether the method being called has been verified. Calls are linked to those entry points by rewriting code containing calls to the methods. 
   As shown in  FIG. 43 , there is a dispatch table entry for every callable routine in a protection unit. Each entry includes a check bit and a routine address. Once initialized, methods or routines within a protection unit can call each other. Methods that call outside a protection unit do so via a dispatch table ( 4300 ,  4305 ,  4310 ). If the check bit of the dispatch table entry corresponding to the called routine indicates a checked status, the routine address of the dispatch table entry is used to call the routine. If check bit indicates an unchecked status, verification of the code is performed. Storing the dispatch tables ( 4300 ,  4305 ,  4310 ) in an impersistent mutable memory such as a RAM  4345  and associating the value zero with an unchecked status guarantees the check bit indicates an unchecked status upon initialization. In other words, verification of program code is guaranteed to be session-based because the contents of RAM  4345  are destroyed after each session and the next session will start with the check bit indicating an unchecked status. 
   Having one check bit per entry allows the tables to be contiguous; referencing an entry requires just the base address of the table and an offset. Additionally, each entry includes a check bit because the corresponding routine may be the first routine within a protection unit to be called. 
   According to one embodiment of the present invention, the check bit comprises the most significant bit and the method address comprises the least significant bits of a dispatch table entry. If the gateway dispatcher reads check bit value that indicates an unchecked status, the least-significant bits of the dispatch table entry are used to call the routine. This mechanism obviates the need for a second memory access to obtain the method address. 
   According to another embodiment of the present invention, each table has a per-table check bit that indicates whether the table has been validly initialized. Each table entry comprises a method address. 
   According to one embodiment of the present invention, protection units are per package. According to another embodiment of the present invention, protection units are per class. According to another embodiment of the present invention, protection units are per method. 
   According to another embodiment of the present invention, the program units protected by a protection unit corresponds with the program units included in a storage commitment fingerprint. By way of example, if storage commitment fingerprints are computed over methods in a class, protection units are per class. As a further example, if storage commitment fingerprints are computed over classes in a package, protection units are per package. 
   The address of the next RAM-based dispatch table, as well as the current number and size of dispatch tables for other load units are examples of the type of information the card can provide for the link process mentioned above with respect to reference numeral  2110  of  FIG. 21 . 
   According to embodiments of the present invention, program code is rewritten to replace calls to routines outside a protection unit with calls to a gateway dispatcher. According to one embodiment of the present invention, the code is rewritten at conversion time, when a CAP file is created. According to another embodiment of the present invention, the code is rewritten at CAP file disassembly time. According to another embodiment of the present invention, the code is rewritten at load time, or at link time in the target smart card. 
   When a call is made to a routine outside a protection unit, it must be determined whether the called region is checked as well. The gateway dispatcher inspects the table that belongs to the called method to determine whether it may jump directly to the routine, or whether the called routine must be verified first. In the example illustrated in  FIG. 43 , a check bit value of zero is used to indicate an unchecked status. In this case, a value of zero may indicate the entry is corrupted. It may also indicate the entry is valid but that the code has not been verified. Thus, if the check bit has a value that indicates an unchecked status, the dispatch table template is obtained from a persistent mutable memory such as EEPROM, and the called routine is verified. This is shown in more detail below with reference to  FIG. 44 . 
   Turning now to  FIG. 44 , a flow diagram that illustrates a method for ensuring a called method has been verified prior to execution in accordance with one embodiment of the present invention is presented.  FIG. 44  presumes that program code has been rewritten such that calls between protection units have been replaced with calls to a gateway dispatcher.  FIG. 44  also presumes that a dispatch table template that points to the actual method for each of the entries is placed in EEPROM during the linking process.  FIG. 44  also presumes that upon reset or upon the first use of any entry in a dispatch table, the dispatch table template is copied to a preallocated space in an impersistent mutable memory such as RAM. 
   In the context of the present invention, a protection unit is collective if the unit of use is not the same as the unit of protection. By way of example, if the unit of use is a method and the unit of protection is a method, the protection unit is not collective. But if the unit of use is a method and the unit of protection is a class, the protection unit is collective. 
   Still referring to  FIG. 44 , at  4400  a determination is made regarding whether a calling method and a called method are within the same protection unit. This determination is made as part of the code rewriting process. If the two methods are within the same protection unit, the calling method calls the called method directly at  4405 . If the two methods are not within the same protection unit, the code rewriting process replaces the call to the called routine (B) with a call to the gateway dispatcher. If the code has been rewritten in this way, at  4410  the calling method calls a gateway dispatcher. At  4415 , the gateway dispatcher determines the dispatch table associated with the protection unit of the called method. At  4420 , a determination is made regarding whether protection unit has been checked. If the protection unit has not been checked, it is checked at  4425 . At  4430 , the dispatch table corresponding to the protection unit is obtained from a persistent mutable memory such as EEPROM and loaded into an impersistent mutable memory such as RAM. At  4435 , a determination is made regarding whether the protection unit is collective. If the protection unit is collective, at  4440  the check bits in the protection unit are made to indicate an unchecked status. Once the protection unit has been checked, at  4445  the dispatch table entry corresponding to the called method is examined. At  4450 , a determination is made regarding whether the check bit of the table entry has a value that indicates a checked status. If the check bit has a value that indicates a checked status, at  4465  the called method is called using the address in the table entry. If the check bit value indicates an unchecked status, verification of the protection unit comprising the method is performed at  4455  and the check bit of methods in the protection unit are made to indicate a checked status at  4460 . At  4465 , the called method is called using the address in the table entry. 
   The illustration of embodiments of the present invention with respect to Java Card™ technology is for purposes of illustration and is not intended to be limiting in any way. Any program file comprising program data may be used in place of a CAP file comprising structured program data. By way of example, an archive file such as a Java™ archive (JAR) file may be used. Additionally, any communication protocol that defines a protocol data unit may be used in place of the APDU protocol. Additionally, program data for programs written in languages other than the Java™ language may be used. Moreover, the target device need not be a smart card. The target device may be any device capable of receiving protocol data units and executing a program based at least in part on the received data. 
   While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art having the benefit of this disclosure that many more modifications than mentioned above are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims.