Patent Publication Number: US-2009240958-A1

Title: System and method for generating a secure state indicator on a display

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of prior, and claims priority to, U.S. patent application Ser. No. 10/933,234, filed on Sep. 3, 2004, the entirety of which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to data protection, and more specifically to the protection of data on computing devices, including mobile devices for example. 
     BACKGROUND OF THE INVENTION 
     Confidential or otherwise sensitive data is commonly stored on computing devices. Such data may include the contents of e-mail messages, contact information, and scheduler information associated with a user, for example. For larger computing devices such as desktop computers, physical safeguards may be implemented to prevent unauthorized access to the computing devices themselves, and accordingly, the data therein. However, handheld or mobile devices may be considered less secure, since they are more likely to be lost or stolen by virtue of their relatively small size. As a result, it is often desirable to protect sensitive data on mobile devices in order to prevent unauthorized parties from accessing such information, particularly after the devices are lost or stolen. 
     Most mobile devices provide device-locking functionality to prevent unauthorized third party use. A mobile device lock may be initiated manually by a user, or automatically after a pre-determined timeout period or upon insertion of the mobile device into a holster, for example. When a mobile device is in a locked state, access to the device is prevented until the user is successfully authenticated, by entering an appropriate device access password, for example. 
     SUMMARY OF THE INVENTION 
     In accordance with one security scheme, when the device is in a locked state, the data stored on the device (or a subset of data that has been designated as sensitive, for example) is encrypted. This provides additional security in that sensitive data cannot be retrieved in unencrypted form, in the event that a memory store is removed from the device, for example. Furthermore, applications executing on the device are prevented from accessing sensitive data when the data is encrypted, affording even greater security. 
     While a computing device such as a mobile device is locked, the device may be more specifically considered to be in a secure state, if data on the device (either all of the data on the device, or all the data on the device that has been designated as sensitive, for example, as may be configured) is encrypted, such that applications which might wish to access the data cannot decrypt the data for use. Embodiments of the invention are generally directed to a system and method for generating a security indicator on a display of the device, to indicate when a locked device is in such a secure state. 
     In one broad aspect of the invention, there is provided a method of generating a security indicator on a display of a computing device, wherein secure data is stored on the computing device, wherein the secure data, when encrypted, can be decrypted using at least one encryption key in decrypted form, and wherein the method comprises the steps of: detecting when the computing device attains a locked state; determining if any of the secure data can be decrypted by any of one or more applications residing on the computing device, while the computing device is in the locked state; displaying a first indicator if it is determined at the determining step that at least some of the secure data can be decrypted by at least one of the one or more applications while the computing device is in the locked state; and displaying a second indicator if it is determined at the determining step that none of the secure data can be decrypted by any of the one or more applications on the computing device while the computing device is in the locked state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of embodiments of the invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: 
         FIG. 1  is a block diagram of a mobile device in one example implementation; 
         FIG. 2  is a block diagram of a communication subsystem component of the mobile device of  FIG. 1 ; 
         FIG. 3  is a block diagram of a node of a wireless network; 
         FIG. 4A  is a flowchart illustrating steps in a method of generating a security indicator on a display in an embodiment of the invention; and 
         FIG. 4B  is a flowchart illustrating steps in a method of generating a security indicator on a display in another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Some embodiments of the invention make use of a mobile station. A mobile station is a two-way communication device with advanced data communication capabilities having the capability to communicate with other computer systems, and is also referred to herein generally as a mobile device. A mobile device may also include the capability for voice communications. Depending on the functionality provided by a mobile device, it may be referred to as a data messaging device, a two-way pager, a cellular telephone with data messaging capabilities, a wireless Internet appliance, or a data communication device (with or without telephony capabilities). A mobile device communicates with other devices through a network of transceiver stations. 
     To aid the reader in understanding the structure of a mobile device and how it communicates with other devices, reference is made to  FIGS. 1 through 3 . 
     Referring first to  FIG. 1 , a block diagram of a mobile device in one example implementation is shown generally as  100 . Mobile device  100  comprises a number of components, the controlling component being microprocessor  102 . Microprocessor  102  controls the overall operation of mobile device  100 . Communication functions, including data and voice communications, are performed through communication subsystem  104 . Communication subsystem  104  receives messages from and sends messages to a wireless network  200 . In this example implementation of mobile device  100 , communication subsystem  104  is configured in accordance with the Global System for Mobile Communication (GSM) and General Packet Radio Services (GPRS) standards. The GSM/GPRS wireless network is used worldwide and it is expected that these standards will be superseded eventually by Enhanced Data GSM Environment (EDGE) and Universal Mobile Telecommunications Service (UMTS). New standards are still being defined, but it is believed that they will have similarities to the network behaviour described herein, and it will also be understood by persons skilled in the art that the invention is intended to use any other suitable standards that are developed in the future. The wireless link connecting communication subsystem  104  with network  200  represents one or more different Radio Frequency (RF) channels, operating according to defined protocols specified for GSM/GPRS communications. With newer network protocols, these channels are capable of supporting both circuit switched voice communications and packet switched data communications. 
     Although the wireless network associated with mobile device  100  is a GSM/GPRS wireless network in one example implementation of mobile device  100 , other wireless networks may also be associated with mobile device  100  in variant implementations. Different types of wireless networks that may be employed include, for example, data-centric wireless networks, voice-centric wireless networks, and dual-mode networks that can support both voice and data communications over the same physical base stations. Combined dual-mode networks include, but are not limited to, Code Division Multiple Access (CDMA) or CDMA2000 networks, GSM/GPRS networks (as mentioned above), and future third-generation (3G) networks like EDGE and UMTS. Some older examples of data-centric networks include the Mobitex™ Radio Network and the DataTAC™ Radio Network. Examples of older voice-centric data networks include Personal Communication Systems (PCS) networks like GSM and Time Division Multiple Access (TDMA) systems. 
     Microprocessor  102  also interacts with additional subsystems such as a Random Access Memory (RAM)  106 , flash memory  108 , display  110 , auxiliary input/output (I/O) subsystem  112 , serial port  114 , keyboard  116 , speaker  118 , microphone  120 , short-range communications  122  and other devices  124 . 
     Some of the subsystems of mobile device  100  perform communication-related functions, whereas other subsystems may provide “resident” or on-device functions. By way of example, display  110  and keyboard  116  may be used for both communication-related functions, such as entering a text message for transmission over network  200 , and device-resident functions such as a calculator or task list. Operating system software used by microprocessor  102  is typically stored in a persistent store such as flash memory  108 , which may alternatively be a read-only memory (ROM) or similar storage element (not shown). Those skilled in the art will appreciate that the operating system, specific device applications, or parts thereof, may be temporarily loaded into a volatile store such as RAM  106 . 
     Mobile device  100  may send and receive communication signals over network  200  after required network registration or activation procedures have been completed. Network access is associated with a subscriber or user of a mobile device  100 . To identify a subscriber, mobile device  100  requires a Subscriber Identity Module or “SIM” card  126  to be inserted in a SIM interface  128  in order to communicate with a network. SIM  126  is one type of a conventional “smart card” used to identify a subscriber of mobile device  100  and to personalize the mobile device  100 , among other things. Without SIM  126 , mobile device  100  is not fully operational for communication with network  200 . By inserting SIM  126  into SIM interface  128 , a subscriber can access all subscribed services. Services could include: web browsing and messaging such as e-mail, voice mail, Short Message Service (SMS), and Multimedia Messaging Services (MMS). More advanced services may include: point of sale, field service and sales force automation. SIM  126  includes a processor and memory for storing information. Once SIM  126  is inserted in SIM interface  128 , it is coupled to microprocessor  102 . In order to identify the subscriber, SIM  126  contains some user parameters such as an International Mobile Subscriber Identity (IMSI). An advantage of using SIM  126  is that a subscriber is not necessarily bound by any single physical mobile device. SIM  126  may store additional subscriber information for a mobile device as well, including datebook (or calendar) information and recent call information. 
     Mobile device  100  is a battery-powered device and includes a battery interface  132  for receiving one or more rechargeable batteries  130 . Battery interface  132  is coupled to a regulator (not shown), which assists battery  130  in providing power V+ to mobile device  100 . Although current technology makes use of a battery, future technologies such as micro fuel cells may provide the power to mobile device  100 . 
     Microprocessor  102 , in addition to its operating system functions, enables execution of software applications on mobile device  100 . A set of applications that control basic device operations, including data and voice communication applications, will normally be installed on mobile device  100  during its manufacture. Another application that may be loaded onto mobile device  100  would be a personal information manager (PIM). A PIM has functionality to organize and manage data items of interest to a subscriber, such as, but not limited to, e-mail, calendar events, voice mails, appointments, and task items. A PIM application has the ability to send and receive data items via wireless network  200 . PIM data items may be seamlessly integrated, synchronized, and updated via wireless network  200  with the mobile device subscriber&#39;s corresponding data items stored and/or associated with a host computer system. This functionality creates a mirrored host computer on mobile device  100  with respect to such items. This can be particularly advantageous where the host computer system is the mobile device subscriber&#39;s office computer system. 
     Additional applications may also be loaded onto mobile device  100  through network  200 , auxiliary I/O subsystem  112 , serial port  114 , short-range communications subsystem  122 , or any other suitable subsystem  124 . This flexibility in application installation increases the functionality of mobile device  100  and may provide enhanced on-device functions, communication-related functions, or both. For example, secure communication applications may enable electronic commerce functions and other such financial transactions to be performed using mobile device  100 . 
     Serial port  114  enables a subscriber to set preferences through an external device or software application and extends the capabilities of mobile device  100  by providing for information or software downloads to mobile device  100  other than through a wireless communication network. The alternate download path may, for example, be used to load an encryption key onto mobile device  100  through a direct and thus reliable and trusted connection to provide secure device communication. 
     Short-range communications subsystem  122  provides for communication between mobile device  100  and different systems or devices, without the use of network  200 . For example, subsystem  122  may include an infrared device and associated circuits and components for short-range communication. Examples of short range communication would include standards developed by the Infrared Data Association (IrDA), Bluetooth, and the 802.11 family of standards developed by IEEE. 
     In use, a received signal such as a text message, an e-mail message, or web page download will be processed by communication subsystem  104  and input to microprocessor  102 . Microprocessor  102  will then process the received signal for output to display  110  or alternatively to auxiliary I/O subsystem  112 . A subscriber may also compose data items, such as e-mail messages, for example, using keyboard  116  in conjunction with display  110  and possibly auxiliary I/O subsystem  112 . Auxiliary subsystem  112  may include devices such as: a touch screen, mouse, track ball, infrared fingerprint detector, or a roller wheel with dynamic button pressing capability. Keyboard  116  is an alphanumeric keyboard and/or telephone-type keypad. A composed item may be transmitted over network  200  through communication subsystem  104 . 
     For voice communications, the overall operation of mobile device  100  is substantially similar, except that the received signals would be output to speaker  118 , and signals for transmission would be generated by microphone  120 . Alternative voice or audio I/O subsystems, such as a voice message recording subsystem, may also be implemented on mobile device  100 . Although voice or audio signal output is accomplished primarily through speaker  118 , display  110  may also be used to provide additional information such as the identity of a calling party, duration of a voice call, or other voice call related information. 
     Referring now to  FIG. 2 , a block diagram of the communication subsystem component  104  of  FIG. 1  is shown. Communication subsystem  104  comprises a receiver  150 , a transmitter  152 , one or more embedded or internal antenna elements  154 ,  156 , Local Oscillators (LOs)  158 , and a processing module such as a Digital Signal Processor (DSP)  160 . 
     The particular design of communication subsystem  104  is dependent upon the network  200  in which mobile device  100  is intended to operate, thus it should be understood that the design illustrated in  FIG. 2  serves only as one example. Signals received by antenna  154  through network  200  are input to receiver  150 , which may perform such common receiver functions as signal amplification, frequency down conversion, filtering, channel selection, and analog-to-digital (A/D) conversion. A/D conversion of a received signal allows more complex communication functions such as demodulation and decoding to be performed in DSP  160 . In a similar manner, signals to be transmitted are processed, including modulation and encoding, by DSP  160 . These DSP-processed signals are input to transmitter  152  for digital-to-analog (D/A) conversion, frequency up conversion, filtering, amplification and transmission over network  200  via antenna  156 . DSP  160  not only processes communication signals, but also provides for receiver and transmitter control. For example, the gains applied to communication signals in receiver  150  and transmitter  152  may be adaptively controlled through automatic gain control algorithms implemented in DSP  160 . 
     The wireless link between mobile device  100  and a network  200  may contain one or more different channels, typically different RF channels, and associated protocols used between mobile device  100  and network  200 . A RF channel is a limited resource that must be conserved, typically due to limits in overall bandwidth and limited battery power of mobile device  100 . 
     When mobile device  100  is fully operational, transmitter  152  is typically keyed or turned on only when it is sending to network  200  and is otherwise turned off to conserve resources. Similarly, receiver  150  is periodically turned off to conserve power until it is needed to receive signals or information (if at all) during designated time periods. 
     Referring now to  FIG. 3 , a block diagram of a node of a wireless network is shown as  202 . In practice, network  200  comprises one or more nodes  202 . Mobile device  100  communicates with a node  202  within wireless network  200 . In the example implementation of  FIG. 3 , node  202  is configured in accordance with General Packet Radio Service (GPRS) and Global Systems for Mobile (GSM) technologies. Node  202  includes a base station controller (BSC)  204  with an associated tower station  206 , a Packet Control Unit (PCU)  208  added for GPRS support in GSM, a Mobile Switching Center (MSC)  210 , a Home Location Register (HLR)  212 , a Visitor Location Registry (VLR)  214 , a Serving GPRS Support Node (SGSN)  216 , a Gateway GPRS Support Node (GGSN)  218 , and a Dynamic Host Configuration Protocol (DHCP)  220 . This list of components is not meant to be an exhaustive list of the components of every node  202  within a GSM/GPRS network, but rather a list of components that are commonly used in communications through network  200 . 
     In a GSM network, MSC  210  is coupled to BSC  204  and to a landline network, such as a Public Switched Telephone Network (PSTN)  222  to satisfy circuit switched requirements. The connection through PCU  208 , SGSN  216  and GGSN  218  to the public or private network (Internet)  224  (also referred to herein generally as a shared network infrastructure) represents the data path for GPRS capable mobile devices. In a GSM network extended with GPRS capabilities, BSC  204  also contains a Packet Control Unit (PCU)  208  that connects to SGSN  216  to control segmentation, radio channel allocation and to satisfy packet switched requirements. To track mobile device location and availability for both circuit switched and packet switched management, HLR  212  is shared between MSC  210  and SGSN  216 . Access to VLR  214  is controlled by MSC  210 . 
     Station  206  is a fixed transceiver station. Station  206  and BSC  204  together form the fixed transceiver equipment. The fixed transceiver equipment provides wireless network coverage for a particular coverage area commonly referred to as a “cell”. The fixed transceiver equipment transmits communication signals to and receives communication signals from mobile devices within its cell via station  206 . The fixed transceiver equipment normally performs such functions as modulation and possibly encoding and/or encryption of signals to be transmitted to the mobile device in accordance with particular, usually predetermined, communication protocols and parameters, under control of its controller. The fixed transceiver equipment similarly demodulates and possibly decodes and decrypts, if necessary, any communication signals received from mobile device  100  within its cell. Communication protocols and parameters may vary between different nodes. For example, one node may employ a different modulation scheme and operate at different frequencies than other nodes. 
     For all mobile devices  100  registered with a specific network, permanent configuration data such as a user profile is stored in HLR  212 . HLR  212  also contains location information for each registered mobile device and can be queried to determine the current location of a mobile device. MSC  210  is responsible for a group of location areas and stores the data of the mobile devices currently in its area of responsibility in VLR  214 . Further VLR  214  also contains information on mobile devices that are visiting other networks. The information in VLR  214  includes part of the permanent mobile device data transmitted from HLR  212  to VLR  214  for faster access. By moving additional information from a remote HLR  212  node to VLR  214 , the amount of traffic between these nodes can be reduced so that voice and data services can be provided with faster response times and at the same time requiring less use of computing resources. 
     SGSN  216  and GGSN  218  are elements added for GPRS support; namely packet switched data support, within GSM. SGSN  216  and MSC  210  have similar responsibilities within wireless network  200  by keeping track of the location of each mobile device  100 . SGSN  216  also performs security functions and access control for data traffic on network  200 . GGSN  218  provides internetworking connections with external packet switched networks and connects to one or more SGSN&#39;s  216  via an Internet Protocol (IP) backbone network operated within the network  200 . During normal operations, a given mobile device  100  must perform a “GPRS Attach” to acquire an IP address and to access data services. This requirement is not present in circuit switched voice channels as Integrated Services Digital Network (ISDN) addresses are used for routing incoming and outgoing calls. Currently, all GPRS capable networks use private, dynamically assigned IP addresses, thus requiring a DHCP server  220  connected to the GGSN  218 . There are many mechanisms for dynamic IP assignment, including using a combination of a Remote Authentication Dial-In User Service (RADIUS) server and DHCP server. Once the GPRS Attach is complete, a logical connection is established from a mobile device  100 , through PCU  208 , and SGSN  216  to an Access Point Node (APN) within GGSN  218 . The APN represents a logical end of an IP tunnel that can either access direct Internet compatible services or private network connections. The APN also represents a security mechanism for network  200 , insofar as each mobile device  100  must be assigned to one or more APNs and mobile devices  100  cannot exchange data without first performing a GPRS Attach to an APN that it has been authorized to use. The APN may be considered to be similar to an Internet domain name such as “myconnection.wireless.com”. 
     Once the GPRS Attach is complete, a tunnel is created and all traffic is exchanged within standard IP packets using any protocol that can be supported in IP packets. This includes tunneling methods such as IP over IP as in the case with some IPSecurity (Ipsec) connections used with Virtual Private Networks (VPN). These tunnels are also referred to as Packet Data Protocol (PDP) Contexts and there are a limited number of these available in the network  200 . To maximize use of the PDP Contexts, network  200  will run an idle timer for each PDP Context to determine if there is a lack of activity. When a mobile device  100  is not using its PDP Context, the PDP Context can be deallocated and the IP address returned to the IP address pool managed by DHCP server  220 . 
     Embodiments of the invention relate generally to data protection, and more specifically to the protection of data on computing devices. While embodiments of the inventions are described herein with reference to a mobile device, at least some of these embodiments may be implemented on computing devices other than mobile devices. 
     In one example implementation, a mobile device (e.g. mobile device  100  of  FIG. 1 ) provides device-locking functionality to prevent unauthorized third party use. The mobile device lock may be initiated manually by a user, or it may be initiated automatically after a pre-determined timeout period or when the mobile device is inserted into a holster, for example. 
     In accordance with one security scheme, when mobile device  100  is in a locked state, data stored on the mobile device  100  (or a subset of data that has been designated as sensitive) is encrypted. This security scheme is applied by a data protection system residing on mobile device  100 , in this example implementation. The data protection system may be implemented as a software module, application or utility that resides and is executed (e.g. by microprocessor  102  of  FIG. 1 ) on mobile device  100 . In a variant implementation, the data protection system may be implemented in hardware. The data protection system described herein need not be implemented in a separate module, and some or all of its functions may be integrated with that of one or more other applications or modules residing on mobile device  100  in variant implementations. 
     In mobile device  100 , access to memory stores (e.g. in flash memory  108 ) is controlled by the data protection system. The data protection system encrypts data received for storage, stores encrypted data to memory, and decrypts stored data for components of mobile device  100 . In one example implementation, read and write operations to and from the memory stores initiated by components of mobile device  100  are performed via the data protection system. In a variant implementation, components of mobile device  100  have direct access to the memory stores, and will interact with the data protection system only when data is to be encrypted for storage or when encrypted data needs to be decrypted for use. 
     For ease of exposition, the following description makes reference to the encryption and decryption by the data protection system of data generally, where protection for the data is desired. However, it will be understood by persons skilled in the art, that not all data to be stored need be secured in this manner. For example, only data that is related specifically to a user of mobile device  100  may be secured. Alternatively, specific data items or specific types of data may be designated as sensitive, either by a user or automatically by an application executing on mobile device  100 , so that it may be secured in this manner. As a further example, only data stored in specified memory stores of mobile device  100  may be designated for protection. Other arrangements and configurations are possible in variant implementations. 
     In this example implementation, the data protection system may be enabled or disabled, such that data can only be encrypted and/or decrypted while the data protection system is enabled. Users may be permitted to enable and/or disable the data protection system. In a variant implementation, the data protection system may be enabled and/or disabled remotely, by an administrator for example, (and possibly in accordance with an information technology (IT) policy). 
     In operation, the data protection system accesses encryption keys in a key store residing in memory (e.g. flash memory  108  of  FIG. 1 ). In one example implementation, at least one symmetric key that is used for the encryption and decryption of data to be secured is stored in the key store. In order to protect the encryption keys from unauthorized use, the keys are stored in the key store in encrypted form. An encryption key may subsequently be decrypted, upon correct entry of a user&#39;s device password for example. A copy of the decrypted key may then be stored in the key store, or in another memory (e.g. RAM  106  of  FIG. 1 ) or cache so that it need not be decrypted each time it is needed. However, the decrypted symmetric key is subject to deletion when mobile device  100  is locked in this example implementation. The next time the mobile device  100  is unlocked (e.g. by a user entering the correct password), the encrypted symmetric key can then again be decrypted. 
     Furthermore, in accordance with the security scheme mentioned above, when mobile device  100  is in a locked state, the data to be secured (e.g. data that could be considered as sensitive) is encrypted. Since the mobile device lock can generally be initiated at any time, even when an application is in the process of performing an action that has not yet completed on certain data in a decrypted state (e.g. the sorting of secure data items), it may be desirable to allow such an application to complete the action in progress, rather than to have the data encrypted immediately upon the locking of the device so as to interrupt the action. 
     In order to facilitate such functionality, the data protection system of mobile device  100 , for example, may be further adapted to issue “tickets” to applications seeking access to secure data. When an application needs to perform an action that requires access to secure data, the application can request a ticket from the data protection system. If mobile device  100  is in an unlocked state, the data protection system will immediately issue a ticket to the application. On the other hand, if mobile device  100  is in a locked state, the data protection system will not issue a ticket to the application, preventing access by the application to the secure data. The request may either be denied, such that the application would be required to repeat the request for a ticket when mobile device  100  subsequently becomes unlocked; alternatively, the data protection system may defer the issuance of the ticket in response to the original request until mobile device  100  subsequently becomes unlocked, at which time the ticket is automatically issued to the application. 
     So long as an application holds a valid ticket, the application will be permitted access to the secure data. Even if mobile device  100  becomes subsequently locked, the application will continue to have access to the secure data until the application releases the ticket. Applications are expected to use tickets only for a short period of time in order to complete an action, and to subsequently release the tickets when the action has been completed. In a variant implementation, tickets may be considered to be valid only for a specified time interval, after which time the tickets may be deemed to have been released. 
     The data protection system is adapted to keep track of each application that has been issued a ticket, but which has not yet released its ticket. While there are outstanding tickets, the encryption key needed to decrypt the secure data remains in the clear even if mobile device  100  becomes locked, since an application with a ticket is still entitled to access the secure data. However, once the data protection system determines that all of the issued tickets have been released while mobile device  100  is in a locked state, the copy of the decrypted encryption key is deleted. Accordingly, the secure data stored in encrypted form can no longer be decrypted by applications in this state, and mobile device  100  may be considered to be in a secure state. 
     Embodiments of the invention are generally directed to a system and method for generating a security indicator on a display of a computing device, to indicate when a locked device is in a secure state. 
     Referring to  FIG. 4A , a flowchart illustrating steps in a method of generating a security indicator on a display in an embodiment of the invention is shown generally as  300 . This method facilitates user identification of when a computing device (e.g. mobile device  100  of  FIG. 1 ) is in a secure state when locked. 
     As described above with reference to mobile device  100 , in normal operation as shown at step  302 , tickets are issued (e.g. by a data protection system executing on mobile device  100 ) while the computing device is in an unlocked state, to applications requesting access to secure data in order to perform an action on the secure data. These tickets may then be released when the action is completed. 
     At step  310 , the data protection system detects when the computing device enters a locked state. The data protection system can continue to issue tickets (e.g. at step  302 ) so long as the computing device is in an unlocked state. 
     At step  320 , the data protection system determines whether all applications that were issued a ticket while the computing device was in an unlocked state have since released their tickets. If so, any encryption keys in decrypted form that can be used by applications to access secure data are deleted at step  328 , and a secure state indicator is displayed on the computing device at step  330 . 
     In one embodiment, the secure state indicator displayed at step  330  is an icon resembling a locked padlock. Other secure state indicators may be employed in variant embodiments. 
     The secure state indicator is displayed so that it is clearly visible to the user when the device is securely locked. For example, the secure state indicator may be displayed on a ribbon banner in the computing device display. 
     The secure state indicator displayed at step  330  shows that the computing device is not merely locked to prevent unauthorized user access, but is locked and in a secure state (i.e. “securely locked”), such that applications on the computing device cannot access secure data (e.g. data that has been designated as sensitive). The secure state indicator remains displayed until the computing device returns to an unlocked state, or until access to secure data by applications is otherwise permitted. 
     If at step  320 , the data protection system determines that not all applications that were issued a ticket while the computing device was in an unlocked state have released their tickets, an indicator indicating a non-secure state is displayed on the computing device at step  340 . 
     In one embodiment, the non-secure state indicator displayed at step  340  is an icon resembling an unlocked padlock. Other non-secure state indicators may be employed in variant embodiments. 
     The non-secure state indicator is displayed so that it is clearly visible to the user when the device is locked, but not securely locked. For example, the non-secure state indicator may be displayed on a ribbon banner in the computing device display. 
     This non-secure state indicator displayed at step  340  shows that although the computing device is in a locked state, the computing device is not in a secure state since at least one application still has access to secure data, and may be able to decrypt secure data. Furthermore, the computing device may not be considered to be secure since the encryption key used to decrypt the secure data may still exist in a memory store in a decrypted state, which an attacker could potentially retrieve and use to decrypt the secure data. The status of the outstanding tickets can be monitored by repeating step  320 , and the non-secure state indicator can remain displayed until a secure state on the computing device is detected, or alternatively until the computing device returns to an unlocked state or until access to secure data by applications is otherwise permitted. 
     Referring to  FIG. 4B , a flowchart illustrating steps in a method of generating a security indicator on a display in an embodiment of the invention is shown generally as  300   b . This method facilitates user identification of when a computing device (e.g. mobile device  100  of  FIG. 1 ) is in a secure state when locked. 
     Method  300   b  is similar to method  300 , except that method  300   b  may be applied in implementations where secure data, when decrypted, is marked as plaintext, for example. When an application requires access to secure data, the data protection system may decrypt the requisite secure data, store the decrypted data in memory, and mark the decrypted data as plaintext, as shown at step  304 . Moreover, for greater security, when the computing device becomes locked, the data marked as plaintext (referred to herein generally as plaintext objects) should be deleted, by the data protection system for example. If persistent storage of a plaintext object is required and the object is not already stored in encrypted form, it may be encrypted by the data protection system after the computing device becomes locked. Applications with tickets that have not yet been released may be permitted to hold some plaintext objects until they are no longer needed, at which time the plaintext objects may be released (e.g. for deletion). 
     In this embodiment of the invention, the computing device is not considered to be in a secure state until (1) all applications that were issued a ticket while the computing device was in an unlocked state have released their tickets, and (2) all plaintext objects have been released. Accordingly, at step  320   b , the data protection system determines whether both of these conditions are satisfied. If so, the secure state indicator is displayed at step  330 . If not, the non-secure state indicator is displayed at step  340 . 
     In a variant embodiment of the invention, criteria in addition to those described with reference to method  300  or method  300   b  may be established, in determining whether a computing device has attained a secure state. More than two states may also be defined and determined in variant embodiments. 
     In a variant embodiment of the invention, a third state indicator may be employed to denote a state where it is determined that (1) all applications that were issued a ticket while the computing device was in an unlocked state have released their tickets, and (2) all plaintext objects have not yet been released. In this embodiment, a tri-state icon denoting the three states (i.e. tickets exist and plaintext objects exist, no tickets exist but plaintext objects exist, neither tickets nor plaintext objects exist) may be employed, for example. 
     In a variant embodiment of the invention, the data protection system may be configurable to allow a secure state to be determined either in accordance with method  300  or with method  300   b  as may be configured at a particular time. The data protection system may be adapted to be configured (which may encompass modifications to an initial configuration) by a user, and/or by an administrator for example, possibly in accordance with an IT policy. 
     The steps of a method of generating a security indicator in embodiments of the invention may be provided as executable software instructions stored on computer-readable media, which may include transmission-type media. 
     The invention has been described with regard to a number of embodiments. However, it will be understood by persons skilled in the art that other variants and modifications may be made without departing from the scope of the invention as defined in the claims appended hereto.