Patent Publication Number: US-2013246547-A1

Title: Systems and methods for protecting header fields in a message

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 13/565,229, filed Aug. 2, 2012, which is a continuation of U.S. patent application Ser. No. 12/394,809, filed Feb. 27, 2009. U.S. patent application Ser. No. 12/394,809 issued to patent as U.S. Pat. No. 8,326,931 on Sep. 2, 2012. The entire contents of U.S. patent application Ser. No. 13/565,229, and U.S. application Ser. No. 12/394,809 are hereby incorporated by reference. 
    
    
     RELEVANT FIELD 
     Embodiments described herein relate generally to the processing of messages (e.g. electronic mail messages), and more specifically to the processing of encoded messages. 
     BACKGROUND 
     An electronic mail (“e-mail”) message may comprise one or more of the following: a message header, a message body, optionally one or more encoded attachments, one or more encrypted session keys (e.g. if the message is encrypted), and digital signature and signature-related information. The message header may comprise the following header fields, for example: “To”, “From”, “Cc”, “Bcc”, “Date”, “Reply-To”, and “Subject”. 
     Electronic mail messages may be generally encoded using one of a number of known protocols to facilitate secure message communication. Examples of known standards and protocols for facilitating secure message communication include the Secure Multiple Internet Mail Extensions (“S/MIME”) protocol and the Pretty Good Privacyl™ (PGP) protocol. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of embodiments of the systems and methods described herein, and to show more clearly how they may be carried into effect, reference will 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. 4  is a block diagram illustrating components of a host system in one example configuration; 
         FIG. 5  is a block diagram illustrating components of an example of an encoded message; 
         FIGS. 6A and 6B  are flowcharts illustrating acts of a method of transmitting an encoded message from a computing device (i.e. the message sender&#39;s device) to a message recipient at another computing device in accordance with at least one embodiment; 
         FIGS. 7A ,  7 B,  7 C and  7 D are flowcharts illustrating acts of a method of receiving an encoded message at a computing device (i.e. the message recipient&#39;s device) from a message sender at another computing device in accordance with at least one embodiment; 
         FIGS. 8A ,  8 B,  8 C,  8 D and  8 E are examples of messages from the perspective of the message sender&#39;s device, the message comprising a subject field to be protected, in accordance with at least one embodiment; and 
         FIGS. 9A and 9B  are examples of messages from the perspective of the message recipient&#39;s device, the message comprising the contents of a protected subject field inserted into the message body, in accordance with at least one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Some embodiments of the systems and methods described herein make reference to a mobile device. A mobile device may be a two-way communication device with advanced data communication capabilities having the capability to communicate with other computer systems. 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), for example. A mobile device may communicate 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, may be performed through communication subsystem  104 . Communication subsystem  104  may be configured to receive messages from and send messages to a wireless network  200 . In one example implementation of mobile device  100 , communication subsystem  104  may be 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 may be supplemented or superseded eventually by Enhanced Data GSM Environment (EDGE) and Universal Mobile Telecommunications Service (UMTS), and Ultra Mobile Broadband (UMB), etc. 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 embodiments of the present disclosure are 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. Other network communication technologies that may be employed include, for example, Integrated Digital Enhanced Network (iDENT™), Evolution-Data Optimized (EV-DO), and High Speed Packet Access (HSPA), etc. 
     Microprocessor  102  may also interact 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 subsystem  122  and other device subsystems  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 , as well as 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 network registration or activation procedures have been completed. Network access may be associated with a subscriber or user of a mobile device  100 . To identify a subscriber, mobile device  100  may provide for a Subscriber Identity Module (“SIM”) card  126  to be inserted in a SIM interface  128  in order to communicate with a network. SIM  126  may be one example 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  may not be fully operational for communication with network  200 . By inserting SIM  126  into SIM interface  128 , a subscriber may access all subscribed services. Services may include, without limitation: web browsing and messaging such as e-mail, voice mail, Short Message Service (SMS), and Multimedia Messaging Services (MMS). More advanced services may include, without limitation: point of sale, field service and sales force automation. SIM  126  may include a processor and memory for storing information. Once SIM  126  is inserted in SIM interface  128 , it may be coupled to microprocessor  102 . In order to identify the subscriber, SIM  126  may contain some user parameters such as an International Mobile Subscriber Identity (IMSI). By using SIM  126 , a subscriber may not necessarily be 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  may be a battery-powered device and may comprise a battery interface  132  for receiving one or more rechargeable batteries  130 . Battery interface  132  may be 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 power to mobile device  100 . In some embodiments, mobile device  100  may be solar-powered. 
     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, may be installed on mobile device  100  during its manufacture. Another application that may be loaded onto mobile device  100  is 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 may create 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 include standards developed by the Infrared Data Association (IrDA), Bluetooth®, and the 802.11 family of standards (Wi-Fi®) developed by IEEE. 
     In use, a received signal such as a text message, an e-mail message, or web page download is processed by communication subsystem  104  and input to microprocessor  102 . Microprocessor  102  then processes 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  may comprise an alphanumeric keyboard and/or telephone-type keypad, for example. A composed item may be transmitted over network  200  through communication subsystem  104 . 
     For voice communications, the overall operation of mobile device  100  may be substantially similar, except that the received signals may be processed and output to speaker  118 , and signals for transmission may 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  may comprise 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 generally a limited resource, typically due to limits in overall bandwidth and limited battery power of mobile device  100 . 
     When mobile device  100  is fully operational, transmitter  152  may be typically keyed or turned on only when it is sending to network  200  and may otherwise be turned off to conserve resources. Similarly, receiver  150  may be 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 GPRS and GSM technologies; however, in other embodiments, different standards may be implemented as discussed in more detail above. 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) server  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  may be a fixed transceiver station. Station  206  and BSC  204  together may 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 may be stored in HLR  212 . HLR  212  may also contain 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 while requiring less use of computing resources. 
     SGSN  216  and GGSN  218  are elements that may be 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 SGSNs  216  via an Internet Protocol (IP) backbone network operated within the network  200 . During normal operations, a given mobile device  100  performs a “GPRS Attach” to acquire an IP address and to access data services. This normally is not present in circuit switched voice channels as Integrated Services Digital Network (ISDN) addresses may be generally used for routing incoming and outgoing calls. Currently, GPRS capable networks may 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, for example. 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 , for example. 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 generally 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 . 
     Referring now to  FIG. 4 , a block diagram illustrating components of a host system in one example configuration is shown. Host system  250  will typically be a corporate office or other local area network (LAN), but may instead be a home office computer or some other private system, for example, in variant implementations. In this example shown in  FIG. 4 , host system  250  is depicted as a LAN of an organization to which a user of mobile device  100  belongs. 
     LAN  250  comprises a number of network components connected to each other by LAN connections  260 . For instance, a user&#39;s desktop computing device (“desktop computer”)  262   a  with an accompanying cradle  264  for the user&#39;s mobile device  100  may be situated on LAN  250 . Cradle  264  for mobile device  100  may be coupled to computer  262   a  by a serial or a Universal Serial Bus (USB) connection, for example. Other user computers  262   b  are also situated on LAN  250 , and each may or may not be equipped with an accompanying cradle  264  for a mobile device. Cradle  264  facilitates the loading of information (e.g. PIM data, private symmetric encryption keys to facilitate secure communications between mobile device  100  and LAN  250 ) from user computer  262   a  to mobile device  100 , and may be particularly useful for bulk information updates often performed in initializing mobile device  100  for use. The information downloaded to mobile device  100  may include S/MIME certificates or PGP keys used in the exchange of messages. 
     It will be understood by persons skilled in the art that user computers  262   a ,  262   b  will typically be also connected to other peripheral devices not explicitly shown in  FIG. 4 . Furthermore, only a subset of network components of LAN  250  are shown in  FIG. 4  for ease of exposition, and it will be understood by persons skilled in the art that LAN  250  will comprise additional components not explicitly shown in  FIG. 4 , for this example configuration. More generally, LAN  250  may represent a smaller part of a larger network [not shown] of the organization, and may comprise different components and/or be arranged in different topologies than that shown in the example of  FIG. 4 . 
     In this example, mobile device  100  communicates with LAN  250  through a node  202  of wireless network  200  and a shared network infrastructure  224  such as a service provider network or the public Internet. Access to LAN  250  may be provided through one or more routers [not shown], and computing devices of LAN  250  may operate from behind a firewall or proxy server  266 . 
     In a variant implementation, LAN  250  comprises a wireless VPN router [not shown] to facilitate data exchange between the LAN  250  and mobile device  100 . The concept of a wireless VPN router is new in the wireless industry and implies that a VPN connection can be established directly through a specific wireless network to mobile device  100 . The possibility of using a wireless VPN router has only recently been available and could be used when the new Internet Protocol (IP) Version 6 (IPV6) arrives into IP-based wireless networks. This new protocol will provide enough IP addresses to dedicate an IP address to every mobile device, making it possible to push information to a mobile device at any time. An advantage of using a wireless VPN router is that it could be an off-the-shelf VPN component, not requiring a separate wireless gateway and separate wireless infrastructure to be used. A VPN connection may include, for example, a Transmission Control Protocol (TCP)/IP or User Datagram Protocol (UDP)/IP connection to deliver the messages directly to mobile device  100  in this variant implementation. 
     Messages intended for a user of mobile device  100  are initially received by a message server  268  of LAN  250 . Such messages may originate from any of a number of sources. For instance, a message may have been sent by a sender from a computer  262   b  within LAN  250 , from a different mobile device [not shown] connected to wireless network  200  or to a different wireless network, or from a different computing device or other device capable of sending messages, via the shared network infrastructure  224 , and possibly through an application service provider (ASP) or Internet service provider (ISP), for example. 
     Message server  268  typically acts as the primary interface for the exchange of messages, particularly e-mail messages, within the organization and over the shared network infrastructure  224 . Each user in the organization that has been set up to send and receive messages is typically associated with a user account managed by message server  268 . One example of a message server  268  is a Microsoft Exchange™ Server. In some implementations, LAN  250  may comprise multiple message servers  268 . Message server  268  may also be adapted to provide additional functions beyond message management, including the management of data associated with calendars and task lists, for example. 
     When messages are received by message server  268 , they are typically stored in a message store [not explicitly shown], from which messages can be subsequently retrieved and delivered to users. For instance, an e-mail client application operating on a user&#39;s computer  262   a  may request the e-mail messages associated with that user&#39;s account stored on message server  268 . These messages may then typically be retrieved from message server  268  and stored locally on computer  262   a.    
     When operating mobile device  100 , the user may wish to have e-mail messages retrieved for delivery to the mobile device  100 . An e-mail client application operating on mobile device  100  may request messages associated with the user&#39;s account from message server  268 . The e-mail client may be configured (either by the user or by an administrator, possibly in accordance with an organization&#39;s information technology (IT) policy) to make this request at the direction of the user, at some pre-defined time interval, or upon the occurrence of some pre-defined event. In some implementations, mobile device  100  is assigned its own e-mail address, and messages addressed specifically to mobile device  100  may be automatically redirected to mobile device  100  as they are received by message server  268 . 
     To facilitate the wireless communication of messages and message-related data between mobile device  100  and components of LAN  250 , a number of wireless communications support components  270  may be provided. In this example implementation, wireless communications support components  270  may comprise a message management server  272 , for example. Message management server  272  may be used to specifically provide support for the management of messages, such as e-mail messages, that are to be handled by mobile devices. Generally, while messages are still stored on message server  268 , message management server  272  may be used to control when, if, and how messages should be sent to mobile device  100 . Message management server  272  also facilitates the handling of messages composed on mobile device  100 , which are sent to message server  268  for subsequent delivery. 
     For example, message management server  272  may: monitor the user&#39;s “mailbox” (e.g. the message store associated with the user&#39;s account on message server  268 ) for new e-mail messages; apply user-definable filters to new messages to determine if and how the messages will be relayed to the user&#39;s mobile device  100 ; compress and encrypt new messages (e.g. using an encryption technique such as Data Encryption Standard (DES) or Triple DES) and push them to mobile device  100  via the shared network infrastructure  224  and wireless network  200 ; and receive messages composed on mobile device  100  (e.g. encrypted using Triple DES), decrypt and decompress the composed messages, re-format the composed messages if desired so that they will appear to have originated from the user&#39;s computer  262   a , and re-route the composed messages to message server  268  for delivery. 
     Certain properties or restrictions associated with messages that are to be sent from and/or received by mobile device  100  can be defined (e.g. by an administrator in accordance with IT policy) and enforced by message management server  272 . These may include whether mobile device  100  may receive encrypted and/or signed messages, minimum encryption key sizes, whether outgoing messages must be encrypted and/or signed, and whether copies of all secure messages sent from mobile device  100  are to be sent to a pre-defined copy address, for example. 
     Message management server  272  may also be adapted to provide other control functions, such as only pushing certain message information or pre-defined portions (e.g. “blocks”) of a message stored on message server  268  to mobile device  100 . For example, when a message is initially retrieved by mobile device  100  from message server  268 , message management server  272  is adapted to push only the first part of a message to mobile device  100 , with the part being of a pre-defined size (e.g. 2 KB). The user can then request more of the message, to be delivered in similar-sized blocks by message management server  272  to mobile device  100 , possibly up to a maximum pre-defined message size. 
     Accordingly, message management server  272  facilitates better control over the type of data and the amount of data that is communicated to mobile device  100 , and can help to minimize potential waste of bandwidth or other resources. 
     It will be understood by persons skilled in the art that message management server  272  need not be implemented on a separate physical server in LAN  250  or other network. For example, some or all of the functions associated with message management server  272  may be integrated with message server  268 , or some other server in LAN  250 . Furthermore, LAN  250  may comprise multiple message management servers  272 , particularly in variant implementations where a large number of mobile devices are supported. 
     While Simple Mail Transfer Protocol (SMTP), RFC822 headers, and Multipurpose Internet Mail Extensions (MIME) body parts may be used to define the format of a typical e-mail message not requiring encoding, Secure/MIME (S/MIME), a version of the MIME protocol, may be used in the communication of encoded messages (i.e. in secure messaging applications). S/MIME enables end-to-end authentication and confidentiality, and provides data integrity and privacy from the time an originator of a message sends a message until it is decoded and read by the message recipient. Other standards and protocols may be employed to facilitate secure message communication, such as Pretty Good Privacy™ (PGP) and variants of PGP such as OpenPGP, for example. It will be understood that where reference is generally made to “PGP” herein, the term is intended to encompass any of a number of variant implementations based on the more general PGP scheme. 
     Secure messaging protocols such as S/MIME and PGP-based protocols rely on public and private encryption keys to provide confidentiality and integrity. Data encoded using a private key of a private key/public key pair can only be decoded using the corresponding public key of the pair, and data encoded using a public key of a private key/public key pair can only be decoded using the corresponding private key of the pair. It is intended that private key information never be made public, whereas public key information is shared. 
     For example, if a sender wishes to send message data to a recipient in encrypted form, the recipient&#39;s public key is used to encrypt the message data, which can then be decrypted only using the recipient&#39;s private key. Alternatively, in some encoding techniques, a one-time session key is generated and used to encrypt the message data, typically with a symmetric encryption technique (e.g. Triple DES). The session key is then encrypted using the recipient&#39;s public key (e.g. with a public key encryption algorithm such as RSA), which can then be decrypted only using the recipient&#39;s private key. The decrypted session key can then be used to decrypt the encrypted message data. The message header may comprise data specifying the particular encryption scheme that must be used to decrypt the encrypted message data. Other encryption techniques based on public key cryptography may be used in variant implementations. However, in each of these cases, only the recipient&#39;s private key may be used to facilitate successful decryption of the encrypted message data, and in this way, the confidentiality of that data can be maintained. 
     As a further example, a sender may sign message data using a digital signature. A digital signature generally comprises a digest of the message data being signed (e.g. a hash of the message data being signed) encoded using the sender&#39;s private key, which can then be appended to the outgoing message. To verify the digital signature when received, the recipient uses the same technique as the sender (e.g. using the same standard hash algorithm) to obtain a digest of the received message data. The recipient also uses the sender&#39;s public key to decode the digital signature, in order to obtain what should be a matching digest for the received message data, if the digests of the received message do not match, this suggests that either the message data was changed during transport and/or the message data did not originate from the sender whose public key was used for verification. Digital signature algorithms are designed in such a way that only someone with knowledge of the sender&#39;s private key should be able to encode a digital signature that the recipient will decode correctly using the sender&#39;s public key. Therefore, by verifying a digital signature in this way, authentication of the sender and message integrity can be maintained. 
     In the description of exemplary embodiments herein, the term “secure encoding” is used. When reference is made to the application of a secure encoding to message data, this means that the message data is encoded using an encoding technique. As noted above, an act of encoding message data may include either encrypting the message data or signing the message data. It will be understood that encoded message data may also be both encrypted and signed. As used in this disclosure, “signed and/or encrypted” means signed or encrypted or both. 
     In S/MIME, the authenticity of public keys used in these operations may be validated using certificates. A certificate is a digital document issued, for example, by a certificate authority (CA). Certificates are used to authenticate the association between users and their public keys, and essentially, provides a level of trust in the authenticity of the users&#39; public keys. Certificates contain information about the certificate holder, with certificate contents typically formatted in accordance with an accepted standard (e.g. X.509). The certificates are typically digitally signed by the certificate authority. 
     In PGP-based systems, a PGP key is used, which is like an S/MIME certificate in that it contains public information including a public key and information on the key holder or owner. Unlike S/MIME certificates, however, PGP keys are not generally issued by a certificate authority, and the level of trust in the authenticity of a PGP key typically requires verifying that a trusted individual has vouched for the authenticity of a given PGP key. 
     While the term “PGP key” may not be commonly used interchangeably with the term “certificate”, in the context of the embodiments described herein and for the purposes of the specification and in the claims, a “certificate” is deemed to include similar constructs of other secure messaging protocols such as a PGP key. 
     Standard e-mail security protocols typically facilitate secure message transmission between non-mobile computing devices (e.g. computers  262   a ,  262   b  of  FIG. 4 ; remote desktop devices). In order that signed messages received from senders may be read from mobile device  100  and that encrypted messages be sent from mobile device  100 , mobile device  100  may be adapted to store public keys (e.g. in S/MIME certificates, PGP keys) of other individuals. Keys stored on a user&#39;s computer  262   a  may be downloaded from computer  262   a  to mobile device  100  through cradle  264 , for example. 
     Mobile device  100  may also be adapted to store the private key of the public key/private key pair associated with the user, so that the user of mobile device  100  can sign outgoing messages composed on mobile device  100 , and decrypt messages sent to the user encrypted with the user&#39;s public key. The private key may be downloaded to mobile device  100  from the user&#39;s computer  262   a  through cradle  264 , for example. The private key may be exchanged between the computer  262   a  and mobile device  100  so that the user may share one identity and one method for accessing messages. 
     User computers  262   a ,  262   b  can obtain S/MIME certificates and PGP keys from a number of sources, for storage on computers  262   a ,  262   b  and/or mobile devices (e.g. mobile device  100 ) in a key store, for example. The sources of these certificates and keys may be private (e.g. dedicated for use within an organization) or public, may reside locally or remotely, and may be accessible from within an organization&#39;s private network or through the Internet, for example. In the example shown in  FIG. 4 , multiple public key infrastructure (PKI) servers  280  associated with the organization reside on LAN  250 . PKI servers  280  include a CA server  282  that may be used for issuing S/MIME certificates, a Lightweight Directory Access Protocol (LDAP) server  284  that may be used to search for and download S/MIME certificates and/or PGP keys (e.g. for individuals within the organization), and an Online Certificate Status Protocol (OCSP) server  286  that may be used to verify the revocation status of S/MIME certificates, for example. 
     Certificates and/or PGP keys may be retrieved from LDAP server  284  by a user computer  262   a , for example, to be downloaded to mobile device  100  via cradle  264 . However, in a variant implementation, LDAP server  284  may be accessed directly (i.e. “over the air” in this context) by mobile device  100 , and mobile device  100  may search for and retrieve individual certificates and PGP keys through a mobile data server  288 . Similarly, mobile data server  288  may be adapted to allow mobile device  100  to directly query OCSP server  286  to verify the revocation status of S/MIME certificates. 
     In variant implementations, only selected PKI servers  280  may be made accessible to mobile devices (e.g. allowing certificates to be downloaded only from a user&#39;s computer  262   a ,  262   b , while allowing the revocation status of certificates to be checked from mobile device  100 ). 
     In variant implementations, certain PKI servers  280  may be made accessible only to mobile devices registered to particular users, as specified by an IT administrator, possibly in accordance with an IT policy, for example. 
     Other sources of S/MIME certificates and PGP keys [not shown] may include a Windows certificate or key store, another secure certificate or key store on or outside LAN  250 , and smart cards, for example. 
     Referring now to  FIG. 5 , a block diagram illustrating components of one example of an encoded message, as may be received by a message server (e.g. message server  268  of  FIG. 4 ) and forwarded to a user (e.g. of mobile device  100 ), is shown generally as  350 . Encoded message  350  may comprise one or more of the following: a message header  352 , one or more encrypted session keys  358  (e.g. if the message is encrypted), a message body  354 , optionally one or more attachments  356  that may be encoded, digital signature and signature-related information  360 . For example, message header  352  for message  350  may comprise one or more header fields such as “To”, “From”, “Cc”, “Bcc”, “Date”, “Reply-To”, and “Subject”, and may also comprise message length indicators, and encryption and signature scheme identifiers, for example. Actual message content (“message data”) is normally included in the message body  354  and possibly in one or more attachments  356 , which may be encrypted by the sender, using a session key for example. If a session key is to be used, it is typically encrypted for each intended recipient using the respective public key for each recipient, and included in the message at  358 . If the message is signed, a digital signature and signature-related information  360  are included. 
     The format for an encoded message as shown in  FIG. 5  is provided by way of example only, and persons skilled in the art will understand that encoded messages may exist in other formats. For example, encrypted session keys  358  may be provided after message header  352  but before message body  354 . Depending on the specific secure messaging standard or protocol employed, components of an encoded message may appear in a different order than shown in  FIG. 5 , and an encoded message may include fewer, additional, or different components, which may depend on whether message data of the encoded message is encrypted, signed or both. 
     Under existing standards and protocols, the header fields of an encoded electronic mail message (e.g. message  350 ) are generally not secured (e.g. the contents of the header fields  352  are not encoded). Accordingly, a recipient of a message from a sender could change the contents of one or more header fields (e.g. the subject) in the message header and resend the message with the changed header to a second recipient without decoding the message body. After the message is resent, there is no way for the second recipient to confirm that the original contents in the header fields of the message header have not been tampered with. The digital signature of the message would still verify and/or the encrypted message body would still be decryptable, and it would appear as if the message came directly from the sender since typically only the message body, and not the message header, is encoded (e.g. signed and/or encrypted) under existing standards and protocols. As a further example, a third party may intercept a message in transit, and surreptitiously change the content of the subject field in the message header before it arrives at the recipient&#39;s device. The recipient would not know that the original content of the subject field in the message header has been changed. 
     In the above-described examples, the present inventors recognized that it may be desirable to preserve the integrity of the entire message, including the contents of the header fields in a message header. There may also be situations where confidentiality of the contents of the header fields (e.g. the subject) in a message header of a message may be desirable. 
     Embodiments of the systems and methods described herein generally facilitate the transmitting, receiving, and processing of encoded messages wherein one or more header fields in a message header of the message are protected. In one broad aspect, the contents of the one or more header fields to be protected are inserted into the message body by the message sender&#39;s device prior to encoding and transmitting the message to a message recipient, but typically after a user has finished composing the message and directed the device to send the message (e.g. by pressing a “send” button in a user interface provided on the sender&#39;s device). Subsequently, upon receipt of the message, the message recipient&#39;s device will process the encoded message such that the contents of the protected header fields can be extracted (e.g. viewed and/or verified). Accordingly, by inserting the contents of one or more header fields to be protected into the message body prior to transmission of the message from the sender&#39;s device to the recipient&#39;s device, the contents of these header fields can then be protected using existing standards and protocols for facilitating secure message communication, as the contents of these header fields are now contained within the message body. 
     In another broad aspect, there is provided a method and system for transmitting an encoded message from a computing device (i.e. the message sender&#39;s device) to a message recipient at another computing device, the message comprising a message header and a message body, the message header comprising a plurality of header fields, the method comprising: inserting content of one or more header fields to be protected of the plurality of header fields into the message body; encoding the message body; and transmitting the message after said encoding to the message recipient, such that when the message is processed by the message recipient, the content of the one or more header fields to be protected is extractable from the message body. In some embodiments, the one or more header fields to be protected comprises a subject field. 
     In another broad aspect, there is provided a method and system for receiving an encoded message at a computing device (i.e. the message recipient&#39;s device) from a message sender at another computing device, the message comprising a message header and a message body, the message header comprising one or more header fields, the method comprising: receiving the encoded message from the message sender, wherein the encoded message comprises an encoded message body, the encoded message body comprising content of one or more protected header fields inserted by the message sender&#39;s device therein; decoding the encoded message body; and extracting the content of the one or more protected header fields from the message body after said decoding. In some embodiments, the one or more protected header fields comprises a subject field. 
     In at least one example embodiment, the extracting comprises: searching the message body, after said decoding, for the content of the one or more protected header fields; and where said content is located by said searching, inserting the content of the one or more protected header fields located by said searching in a corresponding one or more header fields of the message header. 
     In example embodiments, the sender&#39;s device may be a mobile device  100  or some other computing device. Similarly, the recipient&#39;s device may be a mobile device  100  or some other computing device 
     These and other aspects and features of various embodiments will be described in greater detail below. It should be noted by persons skilled in the art that the embodiments described above are applicable to both signed and/or encrypted messages. 
     Referring first to  FIG. 6A , a flowchart illustrating acts of a method  600   a  of transmitting an encoded message (e.g. message  350  of  FIG. 5 ) from a computing device (i.e. the message sender&#39;s device) to a message recipient at another computing device, wherein one or more header fields are to be protected, is shown, in accordance with at least one embodiment. 
     In at least one embodiment, at least some of the acts of the method  600   a  are performed by a processor executing an application residing on a computing device, such as a mobile device (e.g. mobile device  100  of  FIG. 1 ). In variant embodiments, the application may reside on a computing device other than a mobile device. In at least one embodiment, the application is an e-mail application, although the acts of the method may be performed in the execution of one or more different applications in variant embodiments. 
     By way of illustration, references are made below to the parts of the example message as shown in  FIG. 5 . 
     At  610   a , a determination is made as to whether one or more header fields in the message header  352  are to be protected. The determination may be based on input from the sender of the message  350 , generally the user of the computing device, or based on a pre-set configuration setting, for example. 
     For example, the determination at  610   a  may be made based on user input provided via a user interface, in which the user may be presented with an option and be required to indicate whether one or more header fields are to be protected, and if so, which header fields are to be protected. This may be done on a message-by-message basis, after the user has finished composing the message  350  and directed the computing device to send the message  350  (e.g. by pressing a “send” button or similar option in the user interface), for example. Alternatively, this may be done while the user is still composing the message  350  (e.g. after the user has finished entering content into the message header  352 , but before or while the user is entering content into the message body  354 ), and before the user has directed the device to send the message  350  (e.g. by pressing a “send” button or similar option in the user interface). Another alternative is that the option may be presented to the user prior to the composition of message  350 , for example, upon installation of the application, or upon a powering on of the computing device. The user may be provided with the option of protecting selected header fields, on a message-by-message basis, for all messages, or for all messages meeting certain criteria (e.g. when the message is to be sent to one or more designated recipients). To be clear, all header fields may be protected or a selected subset of header fields may be protected as identified by a user. 
     In some other instances, there may be no option provided to the user at all. For example, the sender&#39;s device may be configured to automatically protect all header fields or certain header fields. The protection of header fields may be initiated by an administrator, for example, via an IT policy or other configuration settings in variant embodiments. 
     Notwithstanding that a user may have manually selected which header fields they would like to be protected at  610   a , it should be understood by persons skilled in the art that this selection can be overridden by the configuration settings as defined by the device or an administrator (e.g. via an IT policy), for example, in variant embodiments. 
     If it is not desired to protect any of the header fields, then the flow of method acts proceeds to  660   a  where the message  350  (specifically, at least the message body  354  and possibly message attachments  356 ) is securely encoded using one of a number of known standards and protocols for facilitating secure message communication, for subsequent transmission at  670   a  to the intended message recipient. 
     However, if it is desired to protect one or more header fields, then the flow of method acts proceeds to  630   a . At  630   a , the contents of the one or more header fields to be protected as determined at  610   a  are inserted into the message body  354 , for example, as one or more additional lines of text. In one example embodiment, the contents of the one or more header fields to be protected may be inserted into the message body  354  as one or more additional lines of text prefaced by a description, for example: “Secure &lt;name of header field&gt;: &lt;contents of header field” (e.g. “Secure subject: Do you want to go for lunch?”). The insertion of the header field contents into the message body  354  may be done after the user has finished composing the message and directed the device to send the message (e.g. by pressing a “send” button or similar option in a user interface). This insertion may be done automatically by the application, with no user intervention (i.e. not requiring the user to manually insert the contents of the one or more header fields to be protected into the message body  354 ), which may increase user convenience. 
     By inserting the contents of the one or more header fields into the message body  354 , the one or more header fields can then be automatically protected when the message  350  is encoded at  660   a  using existing standards and protocols for facilitating secure message communication, which typically encode the message body  354  of a message  350  but not the message header  352 . This may allow existing standards and protocols for encoding to be used and the recipient&#39;s device does not have to be specially configured to be able to decode the message  350  (e.g. a custom application specifically designed to process these types of messages  350  would not be required). 
     At  640   a , subsequent to the insertion of contents of the one or more header fields to be protected into the message body  354  at  630   a , the message header  352  can be optionally modified. In one embodiment, the original contents of the one or more header fields to be protected may be deleted, and the header fields left blank. Effectively, the combination of inserting the contents of the one or more header fields to be protected into the message body  354  at  630   a  and deleting the original contents of the one or more header fields to be protected at  640  results in the contents of the one or more header fields to be protected being moved into the message body  354 . 
     In another embodiment, the original contents of the one or more header fields to be protected may be modified to indicate that one or more of the header fields have been protected. By way of illustration, each of the header fields that have been protected may be modified to say, for example: “HEADER FIELD ENCRYPTED”, “HEADER FIELD ELIDED”, or “HEADER FIELD IN BODY”. By modifying the message header  352  as described above, this provides confidentiality of the contents of the header fields, while explicitly notifying recipients that the original contents can be retrieved. 
     In another embodiment, the contents of one or more header fields to be protected may not be deleted or modified at  640   a , but is instead retained in the message header  352  “as is” (i.e. unchanged from the original). This would allow for a message recipient to manually check (i.e. by visual comparison) if any of the header fields in the message header  352  have been tampered with, by comparing the contents of the header fields in the message header  352  as received with those as inserted into the message body  354  (after the message body is decoded, where necessary). Alternatively, this check may be performed automatically at the message recipient&#39;s device in a variant embodiment, as will be described in further detail below in accordance with methods  700   c  and  700   d  of  FIGS. 7C and 7D . 
     At  650   a , a disclaimer can be optionally inserted into the message body  354  to indicate that one or more header fields have been protected. The disclaimer may comprise text such as, for example: “One or more header fields in this electronic mail message have been protected by inserting the protected header fields into the message body.” By inserting a disclaimer, this allows message recipients at computing devices using messaging applications that do not support the automatic processing of messages that have been modified to protect the header field contents as described herein, to understand why the contents of one or more header fields have been inserted into the message body  354 . 
     At  660   a , the message  350  (specifically, at least the message body  354  and possibly message attachments  356 ), with the contents of the one or more header fields to be protected inserted therein at  630   a , is securely encoded by one of a number of known standards and protocols for facilitating secure message communication. 
     At  670   a , the message is then transmitted to the intended message recipient(s). 
       FIG. 6B  is a flowchart illustrating method  600   b , a specific variation of method  600   a  of  FIG. 6A . The flowchart in  FIG. 6B  is similar to the flowchart in  FIG. 6A  except that the one or more header fields to be protected specifically comprise a subject field. Each act,  610   b  to  670   b , is analogous to a corresponding act  610   a  to  670   a  of  FIG. 6A  respectively, and the reader is directed to the description of  FIG. 6A  for further details. 
     Referring next to  FIG. 7A , a flowchart illustrating acts of a method  700   a  of receiving an encoded message (e.g. message  350  of  FIG. 5 ) at a computing device (i.e. a message recipient&#39;s device) from a message sender at another computing device, wherein the contents of one or more protected header fields have been inserted into the message body (e.g. message body  354  of  FIG. 5 ), is shown, in accordance with at least one embodiment. 
     By way of illustration, references are made below to the parts of the example message as shown in  FIG. 5 . 
     In at least one embodiment, at least some of the acts of the method are performed by a processor executing an application residing on a computing device, such as a mobile device (e.g. mobile device  100  of  FIG. 1 ). In variant embodiments, the application may reside on a computing device other than a mobile device. In at least one embodiment, the application is an e-mail application, although the acts of the method may be performed in the execution of one or more different applications in variant embodiments. 
     At the recipient&#39;s computing device, an encoded message  350  (e.g. an encoded e-mail message) received from a message sender at  710   a  is processed by first decoding the encoded message  350  at  720   a  using one of a number of known standards and protocols for facilitating secure message communication. 
     At  725   a , the message body  354  of the decoded message  350  may optionally be checked for whether a disclaimer has been inserted therein (e.g. in accordance with act  650   a  of  FIG. 6A  as previously described) to indicate that one or more header fields have been protected. As previously described, the presence of a disclaimer allows message recipients at computing devices using messaging applications that do not support the automatic processing of messages that have been modified to protect header field contents, as described herein, to understand why the contents of one or more header fields have been inserted into the message body  354 . At  725   a , when a disclaimer is located in the message body  354 , the disclaimer may be automatically removed from or hidden in the message body  354 . 
     In one embodiment, the decoded message  350  can be automatically processed in accordance with subsequent acts of method  700   a  so that the contents of one or more protected header fields can be extracted (e.g. viewed and/or verified) from the message body  354 . In one example embodiment, the extracting comprises: searching the message body  354  of the decoded message  350  for the contents of the one or more protected header fields inserted therein, at  730   a ; and inserting the contents of the one or more protected header fields as located in the message body  354 , back in the message header  352  of the decoded message  350 , at  750   a . In some of these embodiments, the extracting may always occur. However, in other embodiments, the extracting may only occur if one or more header fields in the decoded message  350  had been modified (e.g. in accordance with  640   a  of  FIG. 6A  as previously described) to indicate that one or more of the header fields has been protected, with the respective header field stating for example: “HEADER FIELD ENCRYPTED”, “HEADER FIELD ELIDED”, or “HEADER FIELD IN BODY”. 
     However, for non-conforming legacy applications (i.e. applications that do not specifically support the processing of encoded messages wherein the header fields in the message header are protected in accordance with embodiments described herein), acts  730   a  and  750   a  may not be performed by the application, but may instead be performed manually by the message recipient. 
     Further details in respect of acts  730   a  and  750   a  are now provided. At  730   a , a determination may be optionally made as to whether the message body  354  of the decoded message  350  contains the contents of one or more protected header fields, inserted in accordance with act  630   a  ( FIG. 6A ) as previously described, for example. Message body  354  of the decoded message  350  may be searched for one or more protected header fields inserted therein. For example, as previously described, the contents of the one or more protected header fields may have been inserted into the message body  354  as one or more additional lines of text, for example, as one or more additional lines of text prefaced by a description: “Secure &lt;name of header field&gt;: &lt;contents of header field” (e.g. “Secure subject: Do you want to go for lunch?”). Accordingly, the message body  354  may be searched for the additional lines of text prefaced by a specific description, and the lines of text as containing the contents of a protected header field may be identified. 
     If the contents of one or more protected header fields are not located in the search of the message body  354  at  730   a , then this indicates that the header fields  352  of the message  350  have not been protected in accordance with method  600   a  described in  FIG. 6A  and the entirety of the message  350  as it is received may be displayed at  760   a  for the message recipient. 
     If, however, the contents of one or more protected header fields are located in the search of the message body  354  at  730   a , then this indicates that the header fields of the message  350  have been protected in accordance with method  600   a  described in  FIG. 6A . At  750   a , the header fields in the message header  352  may be reset by inserting contents of the one or more header fields as located in the message body  354  of the decoded message  350  at act  730   a  back into the message header  352  for display to the user. The resetting of the header fields in the message header  352  with the contents of header fields located in the message body  354  of the decoded message  350  ensures the integrity of the message header  352 , as it is typically only the message body  354  (and not the message header  352 ) which is encoded using existing standards and protocols for facilitating secure message communication. The resetting of the header fields at this stage (e.g. before the received message is made available to a user for display) may also allow for faster display and searching of the message  350  in a message list by a user for example, when the received message is subsequently retrieved. 
     Additionally, act  750   a  may further comprise deleting the contents of one or more header fields as located in the message body  354  of the received decoded message  350  on resetting the message header  352 . 
     In some embodiments, the resetting of one or more header fields at  750   a  need not be performed immediately subsequent to  730   a , but may instead be deferred until the opening of the message  350  is initiated by the message recipient. Resetting the header fields earlier may allow the message to be displayed more quickly when the user ultimately decides to view the message. On the other hand, processing power may be conserved by deferring the act of resetting the header fields, in the event that a particular message is never opened. 
     Subsequent to resetting the message header  352  with the one or more header fields to be protected located in the message body  354  of the decoded message  350  at  750   a , the message  350  may be displayed at  760   a  in a message listing. 
     In one example implementation, in addition to displaying the message header  352  and message body  354 , the display may comprise a bar, icon, highlighting, or other indicia, or a combination thereof, in a user interface that indicates to the message recipient that both the message header  352  and message body  354  have been protected, as illustrated in the examples provided in  FIGS. 9A and 9B  which will be described in more detail below. The indicia may indicate which of the one or more header fields have been protected. For example, the indicia may be a bar, wherein at least a part of the bar is displayed adjacent to the one or more protected header fields in the message header. As a further example, the indicia may be an icon. The icon may be displayed adjacent to the one or more protected header fields in the message header, for example. As another example, the indicia may be that the one or more protected header fields in the message header are highlighted and/or that data in the one or more protected header fields in the message header are highlighted. As another example, the indicia may comprise a combination of features. 
       FIG. 79  is a flowchart illustrating method  700   b , a specific variation of method  700   a  of  FIG. 7A . The flowchart in  FIG. 7B  is similar to the flowchart in  FIG. 7A  except that the one or more protected header fields specifically comprise a subject field. Each act,  710   b  to  760   b , is analogous to a corresponding act  710   a  to  760   a  of  FIG. 7A  respectively, and the reader is directed to the description of  FIG. 7A  for further details. 
     Reference is now made to  FIG. 7C , where a flowchart illustrating acts of a method  700   c  of receiving an encoded message at a computing device (i.e. a message recipient&#39;s device) from a message sender at another computing device, wherein the contents of one or more protected header fields have been inserted into the message body  354 , is shown in accordance with at least one embodiment. Each act  710   c  to  780   c  is analogous to a corresponding act  710   a  to  780   a  of  FIG. 7A  respectively, and the reader is directed to the description of  FIG. 7A  for further details. However, method  700   c  of  FIG. 7C  further differs from method  700   a  of  FIG. 7A  in that the flow of method acts does not proceed directly from searching the message body  354  of the decoded message  350  for the contents of one or more protected header fields inserted therein (i.e. act  730   c ) to resetting the message header  352  with the one or more protected header fields located in the message body  354  of the decoded message  350  (i.e. act  750   c ). Instead, method  700   c  assumes that the original contents of the header fields to be protected were left in the respective header fields. Method  700   c  additionally comprises performing a comparison of the contents of the one or more protected header fields located in the message body  354  of the decoded message  350  with the corresponding header fields of the message header  352 . 
     Accordingly, if it is determined, at  770   c , that the contents of the one or more protected header fields as located in the message body  354  do not match the corresponding header fields of the message header  352 , then this indicates that the header fields of the message  350  have been tampered with, and an indicia may optionally be provided to the message recipient to indicate so at  780   c . For example, a warning or an error message can be shown to the message recipient when the message  350  is opened for display at  760   c . The warning or error message may read, for example: “ALERT! One or more header fields in this electronic mail message have been tampered with during communication.” As a further example, an icon indicating that there is a mismatch may be displayed. As a further example, the indicia may be that the header fields of the message  350  are not displayed in the message list at  760   c.    
     Notwithstanding that the contents of the one or more protected header fields as located in the message body  354  do not match the corresponding header fields of the message header  352 , method  700   c  may optionally proceed to  750   c  where the header fields in the message header  352  may be reset with the one or more header fields located in the message body  354  of the decoded message  350 , as previously described with reference to  750   a  of  FIG. 7A . Alternatively, the flow of method acts may proceed directly to  760   c  from  780   c  (not explicitly shown in  FIG. 7C ). 
     On the other hand, if it is determined that the contents of the one or more protected header fields as located in the message body  354  match the corresponding header fields of the message header  352  at  770   c , the flow of method acts may proceed to  760   c.    
     At  760   c , the message  350  may be displayed in a message listing, as previously described with reference to  760   a  of  FIG. 7A . 
       FIG. 7D  is a flowchart illustrating method  700   d , a specific variation of method  700   c  of  FIG. 7C . The flowchart in  FIG. 7D  is similar to the flowchart in  FIG. 7C  except that the one or more protected header fields specifically comprise a subject field. Each act  710   d  to  780   d  is analogous to a corresponding act  710   c  to  780   c  of  FIG. 7C  respectively, and the reader is directed to the description of  FIGS. 7A to 7C  for further details. 
     To facilitate a better understanding of a number of features of the embodiments described herein, example messages  350  are provided in  FIGS. 8A to 9B , by way of illustration only. It will be understood that the general format and content of messages  350  displayed in a user interface may differ in variant implementations. 
     Referring first to  FIGS. 8A and 8B , examples of messages  350  from the perspective of a message sender are shown generally as  800   a  and  800   b .  FIG. 8A  shows an example of a message  350  with no message data in the message body  354 . Where there is no message data in the message body  354 , the subject field of the message  350  typically contains the entire content of the message  350 . Similarly,  FIG. 8B  shows an example of a message  350  with no message data in the message body  354  other than a signature (or tagline)  840   b , identifying the message sender, for example. A recipient of a message  350  that comprises only a signature (or tagline)  840   b  in the message body  354  might assume, possibly in error, that the message originates from the person identified in the signature and that the message has not been tampered with. 
     In these examples, a processor executing an application residing on a mobile device  100  processes the message  350  displayed in a display  110  of mobile device  100  after the user of the mobile device  100  has composed it. The message  350  may comprise some message header information  352  and, optionally, message data (not shown in  FIG. 8A ) in the message body  354 . In these examples, the message header  352  comprises a “To” field  810 , a “Cc” field  820 , and a “Subject” field  830   a . However, the message header  352  may optionally comprise additional header fields such as “Bcc”, “Date”, and “Reply-To”, as previously described, or different header fields. 
     In accordance with the example embodiment described with reference to method  600   b  and  FIG. 6B , it may be desired that the subject field  830   a  of the message  350  be protected (e.g. in the message illustrated in  FIG. 8A ). Accordingly, as illustrated in  FIGS. 8C ,  8 D and  8 E, the contents of the subject field  830   a  in the message header  352  may be inserted (see e.g. act  630   b  of method  600   b ) into the message body  354 , prior to encoding (see e.g. act  660   b  of method  600   b ) and transmitting (see e.g. act  670   b  of method  600   b ) the message  350  to a message recipient. Although not shown in the examples of  FIGS. 8C to 8E , persons skilled in the art will appreciate that the subject field  830   b  of the message  350  may also be protected by inserting the contents of the subject field  830   b  in the message header  352  into a message body  354  that only comprises a signature or tagline (see  FIG. 8B ) or into a message body  354  that contains additional and/or other message data, prior to encoding and transmitting the message  350  to a message recipient. 
       FIG. 8C  illustrates the content of a message where the subject field  830   c  in the message header  352  is not modified (e.g. act  640   b  of method  600   b  is not performed) and a disclaimer has not been inserted into the message body  354  (e.g. act  650   b  of method  600   b  is not performed). It will be understood by persons skilled in the art that the message  350  is shown herein for illustrative purposes only, and the message sender may not see the message  350  in this processing state (i.e. the user may not see the contents of the subject field to be protected  830   c  being inserted into the message body  354 ). 
     Alternatively,  FIGS. 8D and 8E  illustrate the contents of message  350  subsequent to the modification of the subject field  830   d  and  830   e  (see e.g. act  640   b  of method  600   b ) and the insertion of a disclaimer in the message body  354  (see e.g. act  650   b  of method  600   b ) in variant implementations. In  FIG. 8D , the original content of the subject field  830   d  is deleted. In  FIG. 8E  the original content of the subject field  830   e  is modified to say “&lt;subject encrypted” to indicate that the subject field has been protected. It will be understood by persons skilled in the art that the message  350  is shown herein for illustrative purposes only, and the message sender may not see the message  350  in this processing state (i.e. the user may not see changes made to the subject field, and/or the insertion of the disclaimer). 
     Referring next to  FIGS. 9A and 9B , examples of messages  350  from the perspective of a message recipient are shown generally as  900   a  and  900   b . In these two examples, a processor executing an application residing on a mobile device  100 , for example, processes the message  350  for display in a display  110  of mobile device  100  after the user of the mobile device  100  (i.e. the message recipient) has received it from the message sender. The messages  350  each comprise a subject that has been protected and inserted into the message body  354 . The portion of messages  350  include some message header information  352 , and, optionally, message data (not shown in the examples of  FIGS. 8A to 8E ) in the message body  354 . In these examples, the message header  352  comprises a “From” field  910 , a “Cc” field  920 , and a “Subject” field  930   a  and  930   b . However, the message header  352  may optionally comprise additional header fields such as “Bcc”, “Date”, and “Reply-To”, as previously described, or different header fields. In addition to displaying the message header  352  and message body  354 , the display  110  may comprise a bar  950 , for example, indicating that the message header  352  and the message body  354  have been protected. The bar  950  may be displayed adjacent to the one or more protected header fields in the message header to indicate which of the one or more header fields have been protected. 
       FIG. 9A  illustrates message  350  being displayed after the performance of method  700   b  on the message recipient&#39;s device. Here, subject field  930   a  in message header  352  has been reset with the protected subject as located in the message body  354   a.    
       FIG. 9B  illustrates message  350  being displayed after the performance of method  700   d  on the message recipient&#39;s device, where it was determined at  770   d  that the protected subject field located in the message body  354  did not match the subject field  930   b  as provided in the message header  352  of the message as received. Accordingly, a warning message  960  is shown to the message recipient to indicate that message  350  has been tampered with. 
     Typically the entire content of a header field will be inserted into the message body for protection, but in a variant embodiment, only a portion of the content of a given header field may be inserted into the message body for protection. 
     The acts of the method of transmitting an encoded message  350  from a computing device to a message recipient, and the acts of the method of receiving an encoded message  350  from a message sender at a computing device in any of the embodiments described herein may be provided as software instructions executable by a processor (e.g. microprocessor  102  of mobile device  100 ) stored on computer-readable storage media. 
     Although electronic mail messages are usually sent comprising data in the message body, sometimes messages may be sent comprising only data in a subject field of the message header  352  and without any data in the message body  354  (i.e. an empty message body  354 ). In at least some example embodiments described herein, the determination as to whether the subject field in the message header  352  is to be protected at  610   b  of method  600   b  of  FIG. 6B  may comprise a determination as to whether the message body  354  is empty (i.e. there is no data contained therein). This may have particular advantages since when the message body  354  of a message  350  is empty, this is usually because the content of the entire message is actually contained within the subject field in the message header  352  of the message  350 . 
     It will be understood by persons skilled in the art that in the case of signed only messages (i.e. the message is not encrypted), the content of the one or more protected header fields may be extracted from the message body (e.g. to be shown in a message list or to reset the one or more protected header fields) without the message data in the message body  354  having to be first decrypted. 
     In variant embodiments, the contents of the one or more protected header fields extracted from the message body may be stored in a memory (e.g. a non-volatile memory) of the computing device. It may be desirable to store the contents of the one or more protected header fields extracted from the message body  354  when the message body  354  is decrypted, independent of the message  350 , especially where the message body  354  may be subsequently re-encrypted for storage on the computing device. 
     Some computing devices may offer content protection capabilities. Generally, content protection provides for the automatic encryption of data that is stored on the computing device upon locking of the device, so that an attacker cannot access the data. This functionality may be particularly useful for securing potentially sensitive or personal data, including e-mail messages and addresses, calendar data, accessed web content and browser histories, and note or task data, for example. If content protection is enabled, then such data, when stored on the computing device, may be encrypted with a content protection key when the computing device is locked. In a variant embodiment, on a content protected computing device, the contents of one or more protected header fields may be extracted from the message body and stored along with the message (while not encrypted with the encryption key which typically protects that message body) so that the contents of the one or more protected header fields are always available when the computing device is unlocked (the content protection key provides security for the data when the computing device is locked), even if the body of the message is subsequently re-encrypted for storage on the computing device in encrypted form. 
     As used herein, the wording “and/or” is intended to represent an inclusive-or. That is, “X and/or Y” is intended to mean X or Y or both. Moreover, “X, Y, and/or Z” is intended to mean X or Y or Z or any combination thereof. 
     A number of embodiments have been described herein. 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 claimed embodiments appended hereto.