Abstract:
A system and method of operating a device connected to a host computer in a manner to preserve knowledge of logon authentication status to the host computer. Upon initialization of the device perform a pattern matching operation of an instruction sequence received by the second microcontroller. When the instruction sequence matches a prestored sequence indicative of performance of a logon process on the host computer tracking a logon state by the second microcontroller. Exchanging the logon state between the second and first microcontrollers such that when the second microcontroller resets, the second microcontroller may recover the logon state from the first microcontroller. Other systems and methods are disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to the following patent applications co-filed herewith: 
         [0000]    &lt;&lt;List of the other six applications to be added by amendment.&gt;&gt; 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to secure USB flash memory devices and more particularly to USB flash memory devices having both a microcontroller and a smart card. 
         [0003]    With the small physical size of computer memories having large address spaces, it has become possible to store relatively large quantities of data on small portable memory devices. This portability has made it possible for users to literally carry their important data in their pocket either for the purpose of sharing the data with other individuals or to have information available without carrying bulkier and less portable forms of data storage. 
         [0004]    USB flash drives are one example of such small portable devices that are becoming a very popular mechanism for storing computerized information and for physically moving the stored information from one computer to another. There are many popular uses; some common uses include personal data transport and data transfer. 
         [0005]    With the portability of data storage devices come security risks. There have been several highly publicized cases of private data being lost from misplaced or stolen laptop computers. Similar risks arise with the use of USB flash drives: being small, they are easily misplaced, often they are carried in a user&#39;s pocket and can then, like other small items carried in that fashion, inadvertently fall out of the pocket undetected. In the event of loss of the device, if the owner of the device has stored sensitive private information on it, that person would be more comfortable knowing that the private data could not be accessed without authorization, e.g., without being authenticated as the owner of the device. 
         [0006]    There is also a growing culture of using USB flash drives to move data to computers belonging to persons other than the owner of the USB flash drive. In that scenario the owner of the USB flash drive provides the USB flash drive to another person for connection to that persons computer via a USB port either for the purpose of receiving data files from the owner of the computer or vice versa. However, because the owner of the USB flash drive does not typically have control of the computer, the USB flash drive owner is subjected to having data moved, intentionally or unintentionally, from the USB flash drive to the computer to which it is being attached, or viewed by the owner of the computer. Furthermore, the owner of the computer could, again either with intent or inadvertently, cause information stored on the USB flash drive to be deleted or corrupted. 
         [0007]    Thus it is desirable to avoid the threat of being subjected to some form of attack from the computer to which the drive is attached. 
         [0008]    Encryption technology is available on many computers. Thus, one way to avoid some of the aforementioned problems is to use the encryption processing capabilities to encrypt and decrypt files stored on the USB flash memory device. While that solution may work to solve specific needs of particular users, it is not a good general solution to the data security problems that arise with USB flash memory devices. One problem is that multiple encryption standards exist. Thus, the encryption technology used to encrypt a file on one computer may not be available when the same file is to be decrypted on another computer. A more severe issue is that often a user would store the encryption key on the computer with which the USB flash memory device is most often used. Thus, the likelihood that the computer and USB flash memory device are lost together or stolen together is high and consequently a hacker may be able to find the encryption key for the USB flash memory device somewhere on the computer. 
         [0009]    To address the above-mentioned concerns, several manufacturers, including, Lexar Media, Inc. of Fremont, Calif. and Kingston Technology Company, Inc. of Fountain Valley, Calif., have introduced USB flash memory devices that provide encryption of a data zone having private data. The encryption and decryption is performed by the USB flash memory microcontroller and the encryption key is stored inside the microcontroller. While this solution provides a higher level of security than USB flash memory devices that have no security features and also improves security with respect to using a host computer for encryption and decryption, it is a solution that is vulnerable to certain attacks. For example, denial of service attacks may be launched against files in the private data zone by deleting files from that area of the device. As discovered by the smart card industry, hackers have developed many clever techniques for deducing the activity inside a microcontroller, for example, examining power consumption patterns, and can use those techniques for determining encryption keys. 
         [0010]    From the foregoing it will be apparent that there is still a need for a USB flash memory device that provides yet a higher level of data security to protect data stored on thereon. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a block diagram illustrating a use scenario of a USB flash memory device. 
           [0012]      FIG. 2  is a block diagram illustrating a high-level view of the architecture of a prior art USB flash memory device having a USB flash memory microcontroller and a NAND memory storage area. 
           [0013]      FIG. 3  is a block diagram illustrating a high-level view of the architecture of a USB flash drive incorporating a smart card circuit operating in cooperation with a USB microcontroller. 
           [0014]      FIG. 4  is a block diagram illustrating an exemplary layout of the addressable space of the memory of the flash memory of the USB flash drive of  FIG. 3 . 
           [0015]      FIG. 5  is a block diagram illustrating a high-level view of the architecture of a smart card module of  FIG. 3 . 
           [0016]      FIG. 6   a  is a schematic illustrating a user login on to a computer system. 
           [0017]      FIG. 6   b  is a schematic illustrating a user using a smart card to logon onto a computer system. 
           [0018]      FIGS. 7   a - b  are timing sequence diagrams illustrating the mechanism by which the USB flash drive microcontroller in conjunction with a smart card module of a USB flash drive having a smart card determines that an operating system logon operation has occurred. 
           [0019]      FIG. 8  is a timing sequence diagram illustrating the operation to provide the smart card module with the knowledge that the logon operation has already been performed. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    In the following detailed description, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. For example, a particular feature, structure, or characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the spirit and scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled. In the drawings, like numerals refer to the same or similar functionality throughout the several views. 
         [0021]    In an embodiment of the invention, a USB flash drive having a smart card module operating in conjunction with the USB flash drive microcontroller provides an hitherto unavailable level of security. Furthermore, the USB flash drive with a smart card provides a mechanism by which single-sign on operations are efficiently, flexibly, and securely provided for. 
         [0022]      FIG. 1  is a schematic diagram illustrating a typical use of a USB flash drive  101 . A user  111  operates a computer  103 . On that computer the user  111  has stored certain files (not shown). It is often the case that a computer user  111  needs to access these same files at other locations. For example, a user  111  may need to access a file, which was created on a work computer, using his home computer  103 . One way to transfer the file would be via a computer network or by sending the file via electronic mail. However, that may not always be practical. 
         [0023]    An alternative is to physically move a copy of the file on a storage medium. USB flash drives  101  is one such storage medium. In the example of  FIG. 1 , a USB flash drive  101   a  having a USB connector  105  is inserted into a USB port of the user&#39;s computer  103   a . The USB flash drive  101   a  then enumerates on the user&#39;s computer  103   a   1 .  1  Herein, letter suffixes are used in conjunction with reference numerals to designate specific instantiations of a class of objects having common generic features. The class is referred to using numerals only. Thus,  103   a  is a specific computer  103 . Any reference to a device solely by a numerical reference is meant to apply equally to all members of the class unless the context prohibits such an interpretation. 
         [0024]    USB enumeration process includes performing a reset operation of a USB flash drive  101  and the USB flash drive  101  is assigned a unique identifier. In the case of a USB mass storage device, like a USB flash drive  101 , a drive letter is assigned to the USB flash drive  101  so that a user  111  can access the USB flash drive  101  from his computer. Thus, at the conclusion of the enumeration process the USB flash drive  101  has been assigned a drive letter, e.g., “H:” or “K:”, by which the USB flash drive  101  is uniquely identified in the computer&#39;s operating system. 
         [0025]    After the user  111  has inserted the USB flash drive  101   a  into the computer  103   a  and the USB flash drive  101   a  has enumerated, the user  111  can copy files from the computer  103   a  to the USB flash drive  101   a . At this point, the files have become physically portable and the user  111  can move the files to another computer  103   b  by inserting the USB flash drive  101   a  into a USB port of that computer  103   b . The user  111  can now read the file using the file browser or application programs on that computer  103   b.    
         [0026]    Of course, as with other storage drives on a computer, a USB flash drive  101  may be used to create, read, delete and otherwise manipulate files as permitted by the operating system and application programs running on the computers to which it is connected  103 . 
         [0027]      FIG. 2  is a high-level block diagram illustrating the basic components of a prior art USB flash drive  101 . A USB flash drive  101  typically has a hard shell housing  201 , e.g., plastic or aluminum, to contain and protect the internal components of the USB flash drive  101 . At one end, the USB flash drive  101  has a connector for connecting the USB flash drive  101  to a host computer  103  and to provide a communications interface to the host computer  103  to which it is connected. 
         [0028]    A prior art USB flash drive  101  further contains a USB mass storage controller  203 . Flash memories are block-oriented and are subject to wear (a limit on the number of read-write cycles that a flash memory can handle). The USB mass storage controller  203  implements a USB host controller and provides a linear interface to block-oriented serial flash devices while hiding the complexities of block-orientation, block erasure, and wear leveling, or wear balancing. The controller contains a small RISC microprocessor  205  and a small amount of on-chip ROM  207  and RAM  209 . 
         [0029]    A USB flash drive  101  further contains a flash memory chip  211 , typically a NAND flash memory chip, for storing data, e.g., computer files. 
         [0030]    A USB flash drive  101  further contains a crystal oscillator for producing a clock signal, and may contain LEDs, write protect switches, and a myriad of non-electrical components for aesthetic or portability purposes. These are not important to the present discussion. 
         [0031]    As discussed hereinabove, the mainstream prior art USB flash drive  101  is extremely vulnerable to security threats. These devices provide no defense against the risk that the data stored thereon would come into the wrong hands if the device is stolen or lost. Furthermore, when inserted into a stranger&#39;s computer  103 , the data on a USB flash drive  101  may be either inadvertently or intentionally copied to that computer  103  or be deleted from the USB flash drive  101 . 
         [0032]    As further discussed hereinabove, there are prior art approaches to provide a certain level of security through the use of encryption services provided directly on the microcontroller  205 . An alternative, that provides yet higher security, using a smart card module for providing certain security features is presented here. 
         [0033]      FIG. 3  is a block diagram illustrating a high-level view of the architecture of a USB flash drive  101  incorporating a smart card module for providing security functionality, e.g., authentication and cryptographic services, to enhance the security of data stored on the USB flash drive  101  (referred to hereinafter as a USB flash drive SC). 
         [0034]    As with the prior art USB flash drive  101 , a USB flash drive SC  301  is constructed with a USB connector  105  at one end, and has a USB flash drive microcontroller  303  having a microprocessor  305 , a ROM  307 , and a RAM  309 , as well as a flash memory chip  311 . Additionally the USB flash drive SC  301  contains a smart card module  313  connected to the USB flash drive microcontroller  303 . 
         [0035]    In one embodiment, the smart card module  313  is used by the USB flash drive SC  301  to authenticate a user and to provide certain cryptographic capabilities. Thus, for example, when the USB flash drive SC  301  is inserted into a computer  103 , a logon screen may be presented to the user  111  requesting the user  111  to authenticate himself using a PIN or password. Authentication is then entirely a negotiation between the host computer  103  and the smart card module  313  with only the result presented to the USB flash drive microcontroller  303 . 
         [0036]    In one embodiment, the communication between the host the computer  103  and the USB flash drive SC  301  is performed using the USB mass storage protocol and the USB CCID (Chip Card Interface Device) protocol. 
         [0037]    Operations of the USB flash drive microcontroller  303  are according to instructions stored in a firmware control program  315  stored in the flash memory  311 . The firmware control program  315  contains start-up instructions executed on initialization of the USB flash drive SC  301 . Several of the start-up procedures are discussed in greater detail hereinbelow. 
         [0038]    As discussed hereinabove, USB enumeration is one function performed during startup. The USB flash drive SC  301  enumerates itself as a plurality of a USB mass storage drives and as a smart card interface device (akin to a USB smart card reader) to allow for communication using the CCID protocol. The firmware control program  315  contains the necessary instructions to act as a CCID device when the host computer  103  directs communication to the smart card module  313 . 
         [0039]      FIG. 4  is a block diagram illustrating an exemplary layout of the addressable space of the memory of the flash memory  311 . In one embodiment, the addressable space of the flash memory is partitioned into three partitions: a read only partition  401 , a private data partition  403 , and a public data partition  405 . 
         [0040]    The read only partition  401  contains the control program firmware  315  and a CCID module  407  for managing interaction with the host computer  103  over the CCID protocol. In alternative implementations, the communication with the smart card module  313  is carried over the USB Human Interface Device (HID) protocol, or any other suitable communications protocol. For such alternatives, the CCID module  407  would be replaced with communications modules appropriate for such protocols allowing the USB flash drive SC  301  to enumerate as such a device, e.g., as an HID device. 
         [0041]    The read only partition  401  also contains a host computer application program, the unlock application  409 . The unlock application  409  may be an autorun application that automatically launches on the host computer  103  or may appear as a launchable application when the read only partition  401  is browsed to using the host computer  103  operating system. 
         [0042]    The unlock application  409  may be used by a user  111  to perform several tasks associated with managing the USB flash drive SC  301 . The unlock application  409  may, for example, be used by the user  111  to authenticate to the USB flash drive SC  301 . 
         [0043]    The USB flash drive SC  301  enumerates as three USB mass storage partitions, one corresponding to the read only partition  401 , one as the private partition  403  and one as the public partition  405 . 
         [0044]    Upon initialization of the USB flash drive SC  301 , the private partition  403  enumerates as a drive without media, i.e., a user  111  would be able to see a drive letter designated for the drive, however, it would appear as an empty disk drive. 
         [0045]    Through the unlock application  409  the user  111  may unlock the private partition  403  to have access to files stored therein. In one embodiment, data in the private partition  403  is encrypted using an AES key (e.g., a 256 bit key). The AES key is stored in the smart card module  313 . When the user  111  has authenticated using the unlock application  409  the smart card module  313  encrypts the AES key in a manner in which the USB flash drive microcontroller  303  can decrypt. The USB flash drive microcontroller  303  then uses the decrypted AES key to decrypt information stored in the private drive. The USB flash drive microcontroller  303  stores the AES key only temporarily. Thus, when the USB flash drive SC  301  is removed from the host computer  103  the AES key is only stored in the smart card module  313 . 
         [0046]      FIG. 5  is a block diagram illustrating a high-level view of the architecture of a smart card module  313  used in the USB flash drive SC  301 . The smart card module  313  contains a central processing unit  501 , a RAM  503 , and a non-volatile memory  505 . These components are connected via a bus  507 . Also connected to the bus  507  is a communications interface  509  for providing a connection between the bus  507 , and consequently, the CPU  501 , RAM  503 , and non-volatile memory  505 , and the USB flash drive microcontroller  303 . 
         [0047]    In one embodiment communication between the USB flash drive microcontroller  303  and the smart card module  313  is over the ISO-7816 APDU protocol. Several special instructions are added to facilitate particular interactions required for coordinating the operations of the smart card module  313  and the USB flash drive microcontroller  303 . 
         [0048]    A useful application of smart cards is their ability to perform operating system logon. The traditional method of logging on to a computer system is illustrated in  FIG. 6   a  which is a schematic illustrating a user login on to a computer system. A user  111 , upon starting or restarting a computer  103 , is prompted by the operating system to enter a username and password. A higher level of security, so called two-factor authentication, is achieved by having a smart card participate in the logon procedure.  FIG. 6   b , which is a schematic illustrating a user  111  using a smart card to logon onto a computer system  103 , illustrates the latter scenario. 
         [0049]    In the context of USB flash drive SC  301  this presents a new challenge. It would be desirable to use the USB flash drive SC  301  to perform single sign on wherein if a user  111  authenticates herself to the USB flash drive SC  301 , she may be considered authenticated for a variety of services that the USB flash drive SC  301  provides authentication to. However, because the smart card module  313  is enumerated as a CCID device, or more accurately, because the USB flash drive microcontroller  303  enumerates as a series of USB mass storage devices and as a CCID device that is connected to the smart card module  313 , the interaction between the host computer  103  and the smart card module  313  is directed by the CCID driver of the host computer  103  operating system. Many operating systems demand, with relative frequency, that CCID devices reset themselves; much more frequently than USB mass storage devices. Accordingly, a situation occurs in which the USB flash drive microcontroller  303  remains running while the smart card module  313  has been forced into a reset. 
         [0050]    After such a forced reset, the smart card module  313  would be unable to know whether a logon to the operating system has taken place. The method described hereinbelow overcomes this issue by storing a login state in the USB flash drive microcontroller  303  and providing that logon state to the smart card module  313  after a reset operation of the smart card module  313 . 
         [0051]      FIGS. 7   a - b  are timing sequence diagrams illustrating the mechanism by which the USB flash drive microcontroller  303  determines that an operating system logon operation has occurred. When the smart card module  313  has concluded that an operating system logon has occurred, a logon counter, logon counter, is advanced  709 . The USB flash drive microcontroller  303  compares a logon counter, logon counter′, that it maintains, to the smart card module  313  maintained logon counter. If the smart card module  313  maintained logon counter is greater than the logon counter′ maintained by the USB flash drive microcontroller  303 , the USB flash drive microcontroller  303  concludes that a logon has occurred and stores that information in a state variable, LogonState. 
         [0052]    Generally speaking communication between the host computer  103  and the smart card module  313  is by way of USB CCID transactions to the USB flash drive microcontroller  303 , message  701 . The USB flash drive microcontroller  303  strips the USB headers, determines that the message is a CCID message and forwards the message as an APDU to the smart card module  313 , message  703 . The smart card module  313  responds to the USB flash drive microcontroller  303 , message  705 . 
         [0053]    A smart card assisted operating system logon (for example, to a Microsoft Windows operating system) consists of a predictable pattern of APDU operations. The smart card module  313  maintains a state machine to track whether the command stream is indicative that an operating system logon is occurring. A first state in that state machine may be that the very first command after a power up is an authentication, i.e., an attempt to authenticate a user to the smart card module  313 . Next, a sequence of cryptography operations occur. Finally, a deauthentication operation concludes the logon sequence. 
         [0054]    For each received command, the smart card module  313  determines if the received command matches a command that advances the current state in the pattern-matching state machine, step  705 . If so, the current state is advanced in the pattern-matching state machine, step  707 , until the pattern has finished, step  708 . When the pattern has finished, the smart card module  313  advances the logon counter  709 . 
         [0055]    Because the USB flash drive microcontroller  303  passes APDU commands for the smart card module  313 , USB flash drive microcontroller  303  can perform some analysis of those commands, for example, looking for commands of particular concern to the USB flash drive microcontroller  303 . One such command is the deauthenticate command. If an APDU instruction indicates that the host computer  103  is directing the smart card module  313  to deauthenticate, step  711 , the USB flash drive microcontroller  303  uses that instruction to trigger asking the smart card module  313  what the current logon count value is by issuing a GetWindowsLogonCount, step  713 , which is transmitted to the smart card module  313  as a message  703 . In this case, because the last command was deauthenticate, the smart card module  313  would not be in a login pattern matching state and would merely respond to the USB flash drive microcontroller  303 , step  705 . 
         [0056]    If a response from the smart card module  313  is to a GetWindowsLogonCount( ), step  715 , and the received count (logon count) is greater than the logon count maintained by the USB flash drive microcontroller  303  (logon count′), step  717 , then the USB flash drive microcontroller  303  concludes that a logon operation has been performed and, therefore, stores the new count in its logon count′ variable and sets the LogonState′ to True, step  719 . The USB flash drive microcontroller  303  then transmits a direction to the smart card module  313  to also set its logon state to true, message  721 , and consequently the smart card module  313 , in response, sets its LogonState to true, step  723 . 
         [0057]    As discussed above, the host computer  103  is prone to reset the smart card module  313  periodically. Such resets manifest themselves as a powerdown( ) command followed by a powerup( ) command. The USB flash drive microcontroller  303  detects the powerdown-powerup sequence and responds by transmitting to the smart card module  313  a direction to set the logon state to True, step  721 . 
         [0058]      FIG. 8  is a timing sequence diagram illustrating the operation to provide the smart card module  313  with the knowledge that the logon operation has already been performed and, therefore, to set the logon state to True. 
         [0059]    A reset is transmitted from the host computer  103  as a powerdown message  801  followed by a powerup message  803 . These messages, like all normal APDU messages, are passed on to the smart card module  313 , messages  805  and  807 . Because the sequence of power down followed by power up is indicative that the smart card module  313  has been reset, the USB flash drive microcontroller  303  then transmits a SetLoginState(T), step  809 , command to direct the smart card module  313  to set its logon state to True, which the smart card module  313  does, step  811 . 
         [0060]    The logon detection pattern should be expected to be operating system dependent and can change from operating system release-to-release. However, the patterns are easily determined from examining the instruction sequences transmitted to the smart card module  313  after a power up. Appendix A provides a code listing for detecting a logon operation for the Microsoft Windows XP operating system and may be considered an example implementation of the state machine method of detecting a logon operation presented hereinabove. 
         [0061]    From the foregoing it will be apparent that a USB flash drive SC  301  provides an efficient, flexible, and secure mechanism for maintaining a logon state persistent over a USB session of the USB flash drive microcontroller  303  even when the smart card module  313 , i.e., the device that is responsible for performing logon authentication has been reset. This provides a user with a great utility in that logon operations do not have to be repeated when the smart card module  313  has been reset thereby providing the possibility of a single logon. 
         [0062]    Although specific embodiments of the invention have been described and illustrated, the invention is not to be limited to the specific forms or arrangements of parts so described and illustrated. The invention is limited only by the claims.