Abstract:
A method, system and computer program product for protecting access to a computer file are disclosed. In embodiments, the method comprises a user, employing a user computer, selecting a file, and creating a reference file to protect access to this selected file. When a requester uses a computer device to request access to the protected file, the reference file initiates a procedure to determine if the computing device is entitled to access the protected file by validating a series of computer components that uniquely identify the computing device. In embodiments, a set of specified computer configuration data is stored in a specified storage location; and the series of computer components that uniquely identify the computing device are validated by comparing this set of computer configuration data with the series of computer components that uniquely identify the computing device.

Description:
BACKGROUND 
     This invention generally relates to controlling access to files. More specifically, embodiments of the invention relate to assuring data privacy and to secure sharing across different devices. 
     Today, most people have sensitive data on their computers that should not be opened by unauthorized people. Even with known methods to protect data, data on a computer can be stolen in many ways by an unauthorized person improperly accessing the computer directly or remotely. 
     Despite the variety of methods for protecting or encrypting sensitive data, these solutions have important disadvantages or limitations. For example, a file stolen from a storage may often be easily opened on any machine by any person, and the file security is lost. Protection based on encryption may be lost if an unauthorized person, e.g., a hacker, obtains the decryption key. 
     SUMMARY 
     Embodiments of the invention provide a method, system and computer program product for protecting access to a computer file. In embodiments, the method comprises a user, employing a user computer, selecting a file on the user computer to be protected; and protecting access to the selected file. Protecting access to the selected file includes creating a reference file for the protected file; and using the reference file to control access to the protected file, including, when a requester uses a computer device to request access to the protected file, the reference file initiating a procedure to determine if the computing device is entitled to access the protected file by validating a series of computer components that uniquely identify the computing device. 
     In embodiments, the protecting access to the selected file includes storing a set of specified computer configuration data is a specified storage location; and the validating the series of computer components that uniquely identify the computing device includes comparing said set of specified computer configuration data with the series of computer components that uniquely identify the computing device. 
     In embodiments, the specified storage location is a data storage device remote from the user computer. 
     In embodiments, the set of specified configuration data identifies only the user computer, whereby access is granted to the protected file only when the attempt to access the protected file comes from the user computer. 
     In embodiments, the set of specified configuration data identifies a set of computers, whereby access to the protected file is granted when the attempt to access the protected file comes from any computer of, and only computers of, said set of computers. 
     In embodiments, the set of specified computer configuration data includes hardware configuration data and software configuration data. 
     In embodiments, the protecting access to the selected file includes storing the selected file in a specified location on the user computer. 
     In embodiments, the user computer has an operating system, and the protecting the selected file includes encapsulating the protected file on the user computer to restrict access to the protected file from said operating system. 
     In embodiments, the using the reference file to control access to the protected file includes giving the requester access to the protected file only when the reference file initiating the procedure to determine if the computing device is entitled to access the protected file by validating the series of computer components that uniquely identify the computing device. 
     In embodiments, when said procedure determines that the computing device is not entitled to access the protected file, requesting that said person provide a defined security token to have access granted to the protected file. 
     Embodiments of the invention provide a method and system in which files can be protected from non-authorized users by storing and linking computer-specific related information to a file, assuring that this data will only be accessible from the owner&#39;s computer or from devices with access granted by this owner. An administrative panel is available for users to select the files they want to protect. The selected files are hidden from the Operating System of the computer and stored internally into the protection system to be accessed only from the device where the selected files were originally protected or from any device authorized by the owner. 
     Embodiments of the invention provide a cloud-based method and system that verifies hardware and software information specific to a computer and only allows the file to be accessed if a request for access passes some validations testes, such as MAC Address, hardware items, IP address (to get the location) and Operating System information. The system may cross reference some or all of this information in order to uniquely identify the computer which has access granted to the file. 
     Embodiments of the invention create a reference file which represents protected data, which are encrypted and hidden. Access control is done via the reference file which checks if the device trying to access a protected file is entitled to do so, by validating a series of hardware and software components that uniquely identify that computer. 
     In embodiments of the invention, when a requester requests access to the protected file, the protected file calls the reference file, and the reference file invokes the method to determine if the request for access is from an authorized device. If the request is authorized, the reference file sends a message to the protected file indicating that the requested access can be given. 
     In embodiments of the invention, the protected file is only accessed once the computer credentials are verified, therefore before this process is complete, the protected data are totally inaccessible. The reference file contains the method to call the Web Service hosted in the cloud in order to verify if the requesting source is authorized to access the protected file. 
     Embodiments of the invention provide a number of important advantages. For instance, with embodiments of the invention, the file is protected and can only be accessed from authorized devices, and the owner of the file decides who can access the files. Further, even if the file is stolen, the file content is not accessible from non-authorized devices. Also, the user does not need programming skills to use the file protection application of embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a cloud computing node according to an embodiment of the present invention. 
         FIG. 2  depicts a cloud computing environment according to an embodiment of the present invention. 
         FIG. 3  depicts abstraction model layers according to an embodiment of the present invention. 
         FIG. 4  illustrates an embodiment of the invention that provides local storage protection. 
         FIG. 5  shows an embodiment of the invention that provides storage protection in a cloud sharing environment. 
     
    
    
     DETAILED DESCRIPTION 
     It is understood in advance that although this disclosure includes a detailed description on cloud computing, implementation of the teachings recited herein are not limited to a cloud computing environment. Rather, embodiments of the present invention are capable of being implemented in conjunction with any other type of computing environment now known or later developed. 
     Cloud computing is a model of service delivery for enabling convenient, on-demand network access to a shared pool of configurable computing resources (e.g. networks, network bandwidth, servers, processing, memory, storage, applications, virtual machines, and services) that can be rapidly provisioned and released with minimal management effort or interaction with a provider of the service. This cloud model may include at least five characteristics, at least three service models, and at least four deployment models. 
     Characteristics are as follows: 
     On-demand self-service: a cloud consumer can unilaterally provision computing capabilities, such as server time and network storage, as needed automatically without requiring human interaction with the service&#39;s provider. 
     Broad network access: capabilities are available over a network and accessed through standard mechanisms that promote use by heterogeneous thin or thick client platforms (e.g., mobile phones, laptops, and PDAs). 
     Resource pooling: the provider&#39;s computing resources are pooled to serve multiple consumers using a multi-tenant model, with different physical and virtual resources dynamically assigned and reassigned according to demand. There is a sense of location independence in that the consumer generally has no control or knowledge over the exact location of the provided resources but may be able to specify location at a higher level of abstraction (e.g., country, state, or datacenter). 
     Rapid elasticity: capabilities can be rapidly and elastically provisioned, in some cases automatically, to quickly scale out and rapidly released to quickly scale in. To the consumer, the capabilities available for provisioning often appear to be unlimited and can be purchased in any quantity at any time. 
     Measured service: cloud systems automatically control and optimize resource use by leveraging a metering capability at some level of abstraction appropriate to the type of service (e.g., storage, processing, bandwidth, and active user accounts). Resource usage can be monitored, controlled, and reported providing transparency for both the provider and consumer of the utilized service. 
     Service Models are as follows: 
     Software as a Service (SaaS): the capability provided to the consumer is to use the provider&#39;s applications running on a cloud infrastructure. The applications are accessible from various client devices through a thin client interface such as a web browser (e.g., web-based e-mail). The consumer does not manage or control the underlying cloud infrastructure including network, servers, operating systems, storage, or even individual application capabilities, with the possible exception of limited user-specific application configuration settings. 
     Platform as a Service (PaaS): the capability provided to the consumer is to deploy onto the cloud infrastructure consumer-created or acquired applications created using programming languages and tools supported by the provider. The consumer does not manage or control the underlying cloud infrastructure including networks, servers, operating systems, or storage, but has control over the deployed applications and possibly application hosting environment configurations. 
     Infrastructure as a Service (IaaS): the capability provided to the consumer is to provision processing, storage, networks, and other fundamental computing resources where the consumer is able to deploy and run arbitrary software, which can include operating systems and applications. The consumer does not manage or control the underlying cloud infrastructure but has control over operating systems, storage, deployed applications, and possibly limited control of select networking components (e.g., host firewalls). 
     Deployment Models are as follows: 
     Private cloud: the cloud infrastructure is operated solely for an organization. It may be managed by the organization or a third party and may exist on-premises or off-premises. 
     Community cloud: the cloud infrastructure is shared by several organizations and supports a specific community that has shared concerns (e.g., mission, security requirements, policy, and compliance considerations). It may be managed by the organizations or a third party and may exist on-premises or off-premises. 
     Public cloud: the cloud infrastructure is made available to the general public or a large industry group and is owned by an organization selling cloud services. 
     Hybrid cloud: the cloud infrastructure is a composition of two or more clouds (private, community, or public) that remain unique entities but are bound together by standardized or proprietary technology that enables data and application portability (e.g., cloud bursting for load-balancing between clouds). 
     A cloud computing environment is service oriented with a focus on statelessness, low coupling, modularity, and semantic interoperability. At the heart of cloud computing is an infrastructure comprising a network of interconnected nodes. 
     Referring now to  FIG. 1 , a schematic of an example of a cloud computing node is shown. Cloud computing node  10  is only one example of a suitable cloud computing node and is not intended to suggest any limitation as to the scope of use or functionality of embodiments of the invention described herein. Regardless, cloud computing node  10  is capable of being implemented and/or performing any of the functionality set forth hereinabove. 
     In cloud computing node  10  there is a computer system/server  12 , which is operational with numerous other general purpose or special purpose computing system environments or configurations. Examples of well-known computing systems, environments, and/or configurations that may be suitable for use with computer system/server  12  include, but are not limited to, personal computer systems, server computer systems, thin clients, thick clients, hand-held or laptop devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputer systems, mainframe computer systems, and distributed cloud computing environments that include any of the above systems or devices, and the like. 
     Computer system/server  12  may be described in the general context of computer system-executable instructions, such as program modules, being executed by a computer system. Generally, program modules may include routines, programs, objects, components, logic, data structures, and so on that perform particular tasks or implement particular abstract data types. Computer system/server  12  may be practiced in distributed cloud computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed cloud computing environment, program modules may be located in both local and remote computer system storage media including memory storage devices. 
     As shown in  FIG. 1 , computer system/server  12  in cloud computing node  10  is shown in the form of a general-purpose computing device. The components of computer system/server  12  may include, but are not limited to, one or more processors or processing units  16 , a system memory  28 , and a bus  18  that couples various system components including system memory  28  to processor  16 . 
     Bus  18  represents one or more of any of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, and a processor or local bus using any of a variety of bus architectures. By way of example, and not limitation, such architectures include Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnects (PCI) bus. 
     Computer system/server  12  typically includes a variety of computer system readable media. Such media may be any available media that is accessible by computer system/server  12 , and it includes both volatile and non-volatile media, removable and non-removable media. 
     System memory  28  can include computer system readable media in the form of volatile memory, such as random access memory (RAM)  30  and/or cache memory  32 . Computer system/server  12  may further include other removable/non-removable, volatile/non-volatile computer system storage media. By way of example only, storage system  34  can be provided for reading from and writing to a non-removable, non-volatile magnetic media (not shown and typically called a “hard drive”). Although not shown, a magnetic disk drive for reading from and writing to a removable, non-volatile magnetic disk (e.g., a “floppy disk”), and an optical disk drive for reading from or writing to a removable, non-volatile optical disk such as a CD-ROM, DVD-ROM or other optical media can be provided. In such instances, each can be connected to bus  18  by one or more data media interfaces. As will be further depicted and described below, memory  28  may include at least one program product having a set (e.g., at least one) of program modules that are configured to carry out the functions of embodiments of the invention. 
     Program/utility  40 , having a set (at least one) of program modules  42 , may be stored in memory  28  by way of example, and not limitation, as well as an operating system, one or more application programs, other program modules, and program data. Each of the operating system, one or more application programs, other program modules, and program data or some combination thereof, may include an implementation of a networking environment. Program modules  42  generally carry out the functions and/or methodologies of embodiments of the invention as described herein. 
     Computer system/server  12  may also communicate with one or more external devices  14  such as a keyboard, a pointing device, a display  24 , etc.; one or more devices that enable a user to interact with computer system/server  12 ; and/or any devices (e.g., network card, modem, etc.) that enable computer system/server  12  to communicate with one or more other computing devices. Such communication can occur via Input/Output (I/O) interfaces  22 . Still yet, computer system/server  12  can communicate with one or more networks such as a local area network (LAN), a general wide area network (WAN), and/or a public network (e.g., the Internet) via network adapter  20 . As depicted, network adapter  20  communicates with the other components of computer system/server  12  via bus  18 . It should be understood that although not shown, other hardware and/or software components could be used in conjunction with computer system/server  12 . Examples, include, but are not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data archival storage systems, etc. 
     Referring now to  FIG. 2 , illustrative cloud computing environment  50  is depicted. As shown, cloud computing environment  50  comprises one or more cloud computing nodes  10  with which local computing devices used by cloud consumers, such as, for example, personal digital assistant (PDA) or cellular telephone  54 A, desktop computer  54 B, laptop computer  54 C, and/or automobile computer system  54 N may communicate. Nodes  10  may communicate with one another. They may be grouped (not shown) physically or virtually, in one or more networks, such as Private, Community, Public, or Hybrid clouds as described hereinabove, or a combination thereof. This allows cloud computing environment  50  to offer infrastructure, platforms and/or software as services for which a cloud consumer does not need to maintain resources on a local computing device. It is understood that the types of computing devices  54 A-N shown in  FIG. 2  are intended to be illustrative only and that computing nodes  10  and cloud computing environment  50  can communicate with any type of computerized device over any type of network and/or network addressable connection (e.g., using a web browser). 
     Referring now to  FIG. 3 , a set of functional abstraction layers provided by cloud computing environment  50  ( FIG. 2 ) is shown. It should be understood in advance that the components, layers, and functions shown in  FIG. 3  are intended to be illustrative only and embodiments of the invention are not limited thereto. 
     As depicted, the following layers and corresponding functions are provided: 
     Hardware and software layer  60  includes hardware and software components. Examples of hardware components include mainframes  61 ; RISC (Reduced Instruction Set Computer) architecture based servers  62 ; servers  63 ; blade servers  64 ; storage devices  65 ; networks and networking components  66 . In some embodiments, software components include network application server software  67  and database software  68 . 
     Virtualization layer  70  provides an abstraction layer from which the following examples of virtual entities may be provided: virtual servers  71 ; virtual storage  72 ; virtual networks  73 , including virtual private networks; virtual applications and operating systems  74 ; and virtual clients  75 . 
     In one example, management layer  80  may provide the functions described below. Resource provisioning  81  provides dynamic procurement of computing resources and other resources that are utilized to perform tasks within the cloud computing environment. Metering and Pricing  82  provide cost tracking as resources are utilized within the cloud computing environment, and billing or invoicing for consumption of these resources. In one example, these resources may comprise application software licenses. Security provides identity verification for cloud consumers and tasks, as well as protection for data and other resources. User portal  83  provides access to the cloud computing environment for consumers and system administrators. Service level management  84  provides cloud computing resource allocation and management such that required service levels are met. Service Level Agreement (SLA) planning and fulfillment  85  provide pre-arrangement for, and procurement of, cloud computing resources for which a future requirement is anticipated in accordance with an SLA. 
     Workloads layer  90  provides examples of functionality for which the cloud computing environment may be utilized. Examples of workloads and functions which may be provided from this layer include: mapping and navigation  91 ; software development and lifecycle management  92 ; virtual classroom education delivery  93 ; data analytics processing  94 ; transaction processing  95 ; and avoiding file content reading using machine&#39;s information  96 . 
     Embodiments of the invention provide a cloud-based method and system that verifies hardware and software information specific to a computer and only allows the file to be accessed if a request for access passes some validations tests, such as MAC Address, items, IP address (to get the location) and Operating System information. The system may cross check some or all of this information in order to uniquely identify the computer which has access granted to the file. 
       FIG. 4  illustrates a method and system in accordance with an embodiment of the invention. The system provides an administrative console  102  operating on computer  104  so the user  106  can browse the files and select the ones  110  he wants to protect. Once the files are selected, they are encrypted  112  and an entry  114  is created in the Cloud  116  to store the computer related data such as hardware items, MAC address, IP (in order to determine the user&#39;s location) and Operating System information to uniquely identify that computer  104 , and a reference file  120  is generated containing a method which invokes a Web Service  122  hosted in the Cloud  116  to check for this information. 
     In the administrative console, the user can specify a security level for each file. These security levels can control both local access (from the computer  104  where the file is located), and remote access (file sharing). For example, the security levels for local access can include full access and read only mode. With full access, the file is fully accessible from the owner&#39;s computer and authorized devices only. In the read only mode, the files can be viewed but not edited nor copied to any other location. As another level of access, the file is accessible only by providing username and password every time to prevent unauthorized users that might have access to an authorized machine/device. 
     To allow remote access, the file owner  106  can send the reference file corresponding to protected data to another user  124  that the file owner wants to share the file with. With the reference file, an authorized user can access the original file content vie Cloud storage  116 . When a person  124  receives the file and tries to open the file for the first time, a prompt is shown asking for a token to grant access to this user. This token is only generated via the administrative console  102  from the file owner&#39;s  106  computer/device  104 . 
     The embodiment of  FIG. 4  provides local storage protection. The user  106  opens the Administrative Console  102  and selects the files  110  he wants to protect. For each file selected, the original file is encrypted  112  and hidden in Operating System level, a reference file  120  is generated and an entry is created in the Cloud  116  to store hardware configuration items, operating system information, mac address and ip address to uniquely identify that computer. The hiding of the protected file is done at the operating system level, and any suitable available hiding mechanism can be used to do this hiding. The purpose of the hiding is to hide the protected file from an invalid user on the operating system, to avoid access to an unauthorized user to the protected file. Additionally, the user can assign a password to this file for a higher level security. 
     The user then defines the access level to that file. If the user is sure that he is the only person who accesses the computer, he can specify a lower level security, which includes hardware, MAC and IP addresses and Operating System verification so this file can be easily accessed from his computer without being prompted to provide user credentials every time the file is accessed. By specifying this security level, if the file is stolen from his computer, the file cannot be accessed from any other computer as any request to access the file will fail the hardware and Operating System validations. 
     The reference file contains information such as hardware configuration items, operating system information, mac address and ip address to uniquely identify a computer. With the reference file, an authorized user can access the original file content via Cloud storage. Any request for access to the protected file requires data from the reference file. Thus, when the request is made to the protected file, the protected file checks for the data in the reference file. Even if the protected file is stolen, the thief would not have access to the reference file and thus would not be able to decrypt the encrypted protected file. 
     The reference file contains a method that invokes a Web Service  122  hosted in the Cloud that checks the hardware and software of each computer accessing the reference file. 
     If the reference file verifies that the computer  126  accessing the reference file is the computer where the file was created, then the access is granted locally to the original file  110 . However, in case the verification method identifies that the computer accessing the file is not the authorized computer, a security token is required to access the file, and this token can only be generated from the administrative console from where the file was created. An alert is sent to the creator of the file to inform him that someone is trying to access the file. 
     The security token can be generated from the Administrative Console  102  in case the user wants to share the file with another user or have the file accessible from another computer. 
     If the user specifies read only mode, the file can be accessible from the local computer, but cannot be edited (in the case of a text, spreadsheet or other documents) and cannot be copied or moved to another location. 
     If the file was marked to be accessible only by providing username and password, nothing can be done with the file unless the credentials are confirmed for each action (open, save, move, coy, etc.). 
     Generally, with the method illustrated in  FIG. 4 , the user open the Administrative Console and selects a file to be protected, hardware and software details captured from the computer are stored in the Cloud storage system, and a reference file is created. This reference file can invoke a remote method to verify if any computer trying to access the protected file is authorized to do so. 
       FIG. 5  shows a method and system in accordance with another embodiment of the invention. This embodiment provides secure file sharing via Cloud computing. In case the user  202  wants to share a secure file  204  with another person  206 , this can be done via Cloud  210 . The reference file  212  (which references the original file) contains a Web Service method which checks entries in Cloud storage  210  for all the devices certified to have access to the file. The user needs to enable sharing options to the file via Administrative console  214 . Once this is done, the protected file  204  is automatically uploaded to the Cloud  210 . The user  202  then can send the reference file  212  to any other user he wants to share the file  204  with. When the other user  206  first attempts to access the file, a prompt  214  is shown to this other user to request a security token. This security token is only generated from the Administrative Console installed in the computer  216  where the file was created. 
     The creator of the file receives a notification about this other user and specifications of the machine  220  of the other person trying to access the file. If the creator  202  wants to grant privileges to this other person, the file creator will then need to generate the security token from the Administrative Console  214  and share it with the other user. Once the other user  206  inputs this information, his hardware and Operating System details are captured and stored in the Cloud  210 , to assure that he is now an authorized user. 
     The access level of this user  206  depends on the file creator&#39;s preference. The access, for example, can be read only, full access without sharing, or full access with sharing options. With read only access, the user can see the file but not edit it. With full access without sharing, the user can edit the document but cannot share the document with other users. With full access with sharing options, the user can edit the document and share the document with others. In addition, for all these options, there is an alternative “Time limited option”, which is the same as the original option but for a limited time specified by the file creator. 
     Generally, with the method illustrated in  FIG. 5 , the user  202  who protected the file  204  shares the reference file  212  with another user  206 , and this other user tries to access the protected file (remote access via the Cloud). This other user is not yet authorized to access the file, and therefore a prompt  214  is shown to this user to request a security token. The creator of the file provides the other user with the security token, this other user inputs this information and is granted access to the protected file, and hardware and software information about the computer or computing device  220  used by this other user  206  is stored in the Cloud to enable him as an authenticated user. 
     Embodiments of the invention create a reference file which represents protected data, which is encrypted and hidden. The access control is done via the reference file which checks if a device trying to access the protected file is entitled to do so, by validating a series of hardware and software components that uniquely identify that device. The access restrictions can be applied locally as well, and the reference file allows easy and dynamic content sharing via the Cloud, as long as the owner of the protected files shares the security token that can be generated via Administrative Console and is used to authorize a different device. 
     Even behind an NAT Server, embodiments of the invention work in a similar way. Behind these servers, all the packages sent contain the global router IP (External IP) and in the source port, a number which was generated by NAT to identify this computer under the internal network. In that case, it does not matter whether the IP is dynamic or not, or even if the device is under an NAT Server. The goal is to have a reference of the source location with this information, and not using this information as a parameter that should precisely identify the device under an internal network. This way, this information can be stored in the administrative console and in the Cloud and would work as if it was a regular IP address. 
     Even though IP and MAC addresses can be cloned, they are just two of the parameters used to uniquely identify the computers, they are only part of the “key,” and a user who tries to steal or have unauthorized access to the files would need to know the MAC address and IP of the computes allowed to access the files in order to clone this information, and again, the MAC address and the IP of the computer are only part of the key. 
     In embodiments of the invention, the reference file contains information such as hardware configuration items, operating system information, mac address, and op address to uniquely identify a computer. With the reference file, an authorized user can access the original file content via cloud storage. 
     Any request for the access to the protected file requires data from the referenced file. Thus, when the request is made to the protected file, the protected file checks for the data in the referenced file. Even if the protected file is stolen, the thief would not have access to the reference file and thus would not be able to decrypt the encrypted protected file. 
     In embodiments of the invention, the protected file checks with the reference file if the access should be granted. There is a mapping between the protected file and the reference file. The protected file can have a file attribute that indicates the reference file. 
     In embodiments of the invention, the reference file contains a method that checks the hardware and software of each computer accessing the protected file. This method may be, for example, a method invocation using RMI, or web service, etc. There is communication that is happening between the reference file and the protected file that decides on the access. This communication can be through a remote method call, as an example. 
     In embodiments of the invention, the reference file contains a method which invokes a web services hosted in the cloud. The web service is hosted in the cloud, and the invocation of the web service happens from the reference file. 
     In embodiments of the invention, the protected file should only be accessed once the credentials are verified, therefore before the credentials are verified, the protected file is totally protected and inaccessible. Therefore, the reference file should contain the method to call the Web Service hosted in the cloud to verify the computer credentials. The method should be encapsulated in the reference file. 
     The description of the invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or to limit the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope of the invention. The embodiments were chosen and described in order to explain the principles and applications of the invention, and to enable others of ordinary skill in the art to understand the invention. The invention may be implemented in various embodiments with various modifications as are suited to a particular contemplated use.