Patent Publication Number: US-9906371-B2

Title: Secure connection certificate verification

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to secure socket layer connections, and more particularly to a review of certificates. 
     Transport Layer Security (TLS) and its predecessor, Secure Sockets Layer (SSL), are cryptographic protocols designed to provide communication security over the Internet. The term SSL often refers to different variations of TLS and SSL. SSL uses certificates and asymmetric cryptography to authenticate the counterparty and to exchange a symmetric key public or private session key. Data flowing between the parties is encrypted with a session key, which promotes data and message confidentiality. Additionally, the session key allows for message authentication codes for message integrity and as a by-product, message authentication. Several versions of the protocols are in widespread use in applications such as web browsing, electronic mail, Internet faxing, instant messaging, and voice-over-Internet-protocol (VoIP). A property in a SSL context is forward secrecy, so the short-term session key cannot be derived from the long-term asymmetric secret key. 
     SUMMARY 
     Embodiments of the present invention disclose a method, computer program product, and system for determining a policy action for a connection in which certificates are utilized in a secure network connection on one or more computing devices. One or more computer processors identify a first certificate that is used to establish a secure Internet connection. One or more computer processors identify a stored second certificate that shares at least one attribute with the first certificate. One or more computer processors determine a policy action based, at least in part, on a result of a comparison between an attribute of the first certificate and an attribute of the stored second certificate. In one embodiment, the method further includes executing the determined policy action on a client computing device. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a functional block diagram illustrating a distributed data processing environment, in accordance with an embodiment of the present invention; 
         FIG. 2  is a flowchart depicting operational steps of a program for operating on an in-line server computer to determine a policy for a SSL connection within the distributed data processing environment of  FIG. 1 , in accordance with an embodiment of the present invention; and 
         FIG. 3  depicts a block diagram of components of an in-line server computer, an intelligence source server, a web server, and client devices of  FIG. 1 , in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Secure Sockets Layers (SSL) are cryptographic protocols or encryption protocols used to provide secure connections over the Internet, and SSL, as used herein, refers to all protocols used to secure Internet connections, such as transport layer security (TLS). SSL utilizes X.509 certificates, certificate authorities, and a public key infrastructure to verify the relation between a certificate and its owner, as well as to generate, sign, and administer the validity of certificates. While certificate authorities are, in some scenarios, more beneficial than verifying the identities via a web of trust, embodiments of the invention recognize that certificate authorities are a weak point from a security standpoint, allowing man-in-the-middle attacks (MITM). 
     Implementation of embodiments of the invention may take a variety of forms, and exemplary implementation details are discussed subsequently with reference to the Figures. 
       FIG. 1  is a functional block diagram illustrating a distributed data processing environment, generally designated  100 , in accordance with one embodiment of the present invention.  FIG. 1  provides only an illustration of one implementation and does not imply any limitations with regard to the environments in which different embodiments may be implemented. Many modifications to the depicted environment may be made by those skilled in the art without departing from the scope of the invention as recited by the claims. 
     Distributed data processing environment  100  includes in-line server computer  102 , client computing devices  108 ,  110 , and  112 , web server  104 , domain name system (DNS) server  105 , and intelligence source server  106 , all interconnected over network  114 . Network  114  represents, for example, a telecommunications network, a local area network (LAN), a wide area network (WAN), such as the Internet, or a combination of the three, and includes wired, wireless, and/or fiber optic connections. Network  114  includes one or more wired and/or wireless networks that are capable of receiving and transmitting data, voice, and/or video signals, including multimedia signals that include voice, data, and video information. 
     In the depicted environment, in-line server computer  102  is one or more of a management server, a web server, or any other electronic device or computing system capable of receiving and sending data. In this embodiment, in-line server computer  102  is an in-line server which oversees contacts between client devices and outside devices as opposed to a proxy server which acts as an intermediary for requests from clients seeking resources from other servers or computers. In an example, in-line server computer  102  is a next generation intrusion prevention system or a next generation firewall. In other embodiments, in-line server computer  102  represents a server computing system utilizing multiple computers as a server system, such as in a cloud computing environment. In another embodiment, in-line server computer  102  represents a laptop computer, a tablet computer, a netbook computer, a personal computer (PC), a desktop computer, a personal digital assistant (PDA), a smart phone, or any programmable electronic device capable of communicating with client computing device  108 ,  110 ,  112 , web server  104 , DNS server  105 , and intelligence source server  106  via network  114 . In another embodiment, in-line server computer  102  represents a computing system utilizing clustered computers and components to act as a single pool of seamless resources. In an embodiment, in-line server computer  102  is used to identify certificates, determine policy, and regulate interactions between the client computers of an enterprise (e.g., client computing device  108 ,  110 ,  112 ) and web server  104 , via network  114 . In-line server computer  102  includes policy program  120  and database  130 . 
     In the depicted embodiment, database  130  resides on in-line server computer  102  and contains certificate  132 . In another embodiment, database  130  resides elsewhere in distributed data processing environment  100 . A database is an organized collection of data. Database  130  is implemented with any type of storage device capable of storing data that is accessed and utilized by in-line server computer  102 , intelligence source server  106 , web server  104 , DNS server  105 , and client computing devices  108 ,  110  and  112 , such as a database server, a hard disk drive, or a flash memory. In other embodiments, database  130  represents multiple storage devices within in-line server computer  102 . Database  130  stores certificates, such as certificate  132 , which are secure socket layer (SSL) certificates that correspond to possible certificates from web servers, such as web server  104 . Database  130  stores certificates from multiple web servers and intelligence sources for later comparison with a certificate utilized in an SSL connection. 
     In the depicted embodiment, database  130  stores certificates from past SSL connections. Database  130  also receives a certificate update, such as XML update  124 , from web server  104  and stores the updated certificates in database  130  to be referenced by policy program  120 . In one example, this connection is secure. In another embodiment, policy program  120  also accesses database  130  to send and receive certificates to and from an outside certificate source such as intelligence source server  106 . In one embodiment, database  130  is updated directly by a cloud-based intelligence source, such as through frequent updates with a local database or in real time calling out to the cloud via an API (application programing interface) to retrieve data for a particular domain. 
     In depicted distributed data processing environment  100 , policy program  120  resides on in-line server computer  102  and identifies and reviews certificates to determine a policy for a SSL connection. In one embodiment, policy program  120  receives updated and/or new certificates and stores the updated and/or new certificates in database  130 . In another embodiment, policy program  120  identifies the certificate that was utilized to establish the SSL connection and stores the certificate in database  130 . In an embodiment, policy program  120  identifies certificates with the same domain name or uniform resource locator (URL) and determines if the attributes of the certificates match by comparing the content of the attributes. In another embodiment, policy program  120  determines the policy to implement based upon the certificate utilized for the purposes of the SSL connection and any certificates that are similar to the utilized certificate. In an embodiment, policy program  120  enforces actions based on the determined policy and the corresponding predetermined user settings. Policy program  120  is depicted and described in further detail with respect to  FIG. 2 . 
     In the depicted embodiment, client computing devices  108 ,  110 , and  112  are each one or more of a desktop computer, a laptop computer, a tablet computer, a specialized computer server, a smart phone, or any programmable electronic device capable of communicating with in-line server computer  102  via network  114  and with various components and devices within distributed data processing environment  100 . In general, client computing devices  108 ,  110 , and  112  each represent any programmable electronic device or combination of programmable electronic devices capable of executing machine readable program instructions and communicating with other computing devices via a network, such as network  114 . In one embodiment, client computing devices  108 ,  110 , and  112  are connected to network  114  via in-line server computer  102 . In another embodiment, client computing devices  108 ,  110 , and  112  are connected directly to network  114 , but in-line server computer  102  still has access to client computing devices  108 ,  110 , and  112  and can implement policy and oversee connections to other computing devices. 
     User interface  122  is a program that provides an interface between a user of client computing device  108  and a plurality of applications (not shown) that reside on client computing device  108 . A user interface, such as user interface  122 , refers to the information (such as graphic, text, and sound) that a program presents to a user and the control sequences the user employs to control the program. There are many known types of user interfaces. In one embodiment, user interface  122  is a graphical user interface. A graphical user interface (GUI) is a type of user interface that allows users to interact with electronic devices, such as a computer keyboard and mouse, through graphical icons and visual indicators, such as secondary notation, as opposed to text-based interfaces, typed command labels, or text navigation. In computing, GUIs were introduced in reaction to the perceived steep learning curve of command-line interfaces which require commands to be typed on the keyboard. The actions in GUIs are often performed through direct manipulation of the graphical elements. 
     In the depicted environment, intelligence source server  106  is one or more of a management server, a web server, or any other electronic device or computing system capable of receiving and sending data. In other embodiments, intelligence source server  106  represents a server computing system utilizing multiple computers as a server system, such as in a cloud computing environment. In another embodiment, intelligence source server  106  represents one or more of a laptop computer, a tablet computer, a netbook computer, a personal computer (PC), a desktop computer, a personal digital assistant (PDA), a smart phone, or any programmable electronic device capable of communicating with client computing device  108 ,  110 , and  112 , in-line server computer  102 , DNS server  105 , and web server  104 , via network  114  In another embodiment, intelligence source server  106  represents a computing system utilizing clustered computers and components to act as a single pool of seamless resources. Intelligence source server  106  communicates with policy program  120 , and database  130 , located on in-line server computer  102 , to provide updated certificates and information regarding attributes of certificates. Intelligence source server  106  also receives information from in-line server computer  102  regarding new and/or updated certificates or new and/or updated attributes of certificates. 
     In depicted distributed data processing environment  100 , domain name system (DNS) server  105  represents one or more of a management server, a web server, or any other electronic device or computing system capable of receiving and sending data. In other embodiments, DNS server  105  represents a server computing system utilizing multiple computers as a server system, such as in a cloud computing environment. In another embodiment, DNS server  105  represents one or more of a laptop computer, a tablet computer, a netbook computer, a personal computer (PC), a desktop computer, a personal digital assistant (PDA), a smart phone, or any programmable electronic device capable of communicating with client computing device  108 ,  110 ,  112 , intelligence source server  106 , web server  104 , and in-line server computer  102 , via network  114 . In another embodiment, DNS server  105  represents a computing system utilizing clustered computers and components to act as a single pool of seamless resources. In an embodiment, DNS server  105  is a hierarchical distributed naming system for computing devices connected to the Internet. To further the embodiment, DNS server  105  translates domain names (which are easily memorized by users) into the numerical Internet protocol (IP) address needed for locating computer services and devices. 
     In depicted distributed data processing environment  100 , web server  104  represents one or more of a management server, a web server, or any other electronic device or computing system capable of receiving and sending data. In other embodiments, web server  104  represents a server computing system utilizing multiple computers as a server system, such as in a cloud computing environment. In another embodiment, web server  104  represents one or more of a laptop computer, a tablet computer, a netbook computer, a personal computer (PC), a desktop computer, a personal digital assistant (PDA), a smart phone, or any programmable electronic device capable of communicating with client computing device  108 ,  110 ,  112 , intelligence source server  106 , DNS server  105 , and in-line server computer  102 , via network  114 . In another embodiment, web server  104  represents a computing system utilizing clustered computers and components to act as a single pool of seamless resources. In an embodiment, web server  104  communicates with a client computing device (e.g., client computing device  108 ) and provides a certificate from a Certified Authority for the SSL connection. 
     In depicted distributed data processing environment  100 , extensible markup language (XML) update  124  resides on web server  104 . In one embodiment, XML update  124  contains information regarding certificates and keys. In various embodiments, web server  104  sends XML update  124  to either or both of intelligence source server  106  and database  130 . In an embodiment, XML update  124  is a file that database  130  receives from the domain through a trusted channel. In an example, a disc containing a XML formatted file is received from a business partner with whom this enterprise will interact. In another embodiment, XML update  124  may be any other update known in the art. 
       FIG. 2  is a flowchart depicting operational steps of policy program  120 , in accordance with an embodiment of the present invention. Policy program  120  operates on in-line server computer  102  to identify certificates to determine a policy for a SSL connection. Policy program  120  also reviews certificates to determine a policy for a SSL connection. In one embodiment, policy program  120  initiates in response to in-line server computer  102  receiving a certificate from another computing device (e.g., web server  104 ), such as during an SSL connection between a client computer under an in-line server and another computer or server not under the in-line server. In another embodiment, policy program  120  monitors connections between a computing device (e.g., client computing device  108 ) and another computing device (e.g., web server  104 ). In yet another embodiment, policy program  120  begins the steps of  FIG. 2  in response to a request of a user. For example, the user requests to monitor the connection between one computing device and another computing device. In an embodiment, policy program  120  begins the steps of  FIG. 2  in response to database  130  storing an update (e.g., XML update  124 ) or a new and/or updated certificate. 
     Policy program  120  identifies a network connection and verifies that it is a SSL connection (step  202 ). In one embodiment, policy program  120  monitors network connections between a client computing device, such as client computing device  108  and computing device not under in-line server computer  102 , such as web server  104 . Policy program  120  identifies a SSL connection between a client computing device, such as client computing device  108  and another computing device, such as web server  104 . In an example, a user of client computing device  108  requests a webpage provided by web server  104 . In this example, a connection is established between client computing device  108  and web server  104 . Policy program  120  identifies the connection and determines that the connection is a SSL connection. In this example, policy program  120  determines the connection is a SSL connection by identifying that a certificate has been utilized to establish the connection. In another embodiment, policy program  120  identifies all connections but does not verify that there is a SSL connection. In such an embodiment, policy program  120  proceeds to identify a certificate used in the connection (see step  204 ), and, if there is no certificate, policy program  120  aborts operations for that connection. In another embodiment, policy program  120  identifies a SSL connection during a server-to-server communication. 
     Policy program  120  identifies the certificate used in a SSL connection (step  204 ). In one embodiment, policy program  120  identifies the certificate, such as certificate  132 , which was utilized to establish the SSL connection. In this embodiment, certificate  132  was provided to a client computing device (e.g., client computing device  108 ) by web server  104  to establish the SSL connection between the two devices. In-line server computer  102  identifies the certificate, such as certificate  132 , which has been provided by web server  104  to establish the SSL connection to the webpage, web browser, or web server. In this embodiment, policy program  120  waits for a SSL connection to be established and the completion of a SSL connection establishment protocol before policy program  120  identifies the certificate utilized. In another embodiment, policy program  120  identifies the certificate before the establishment protocol is complete but waits until the establishment protocol is complete before proceeding with the next step. The establishment protocol includes certification that the domain name in the URL matches the name of the domain in the certificate, the certificate is signed by a trusted certified authority (CA) or trusted intermediate CA, and that the web server (e.g., web server  104 ) has access to the private key that matches the public key in the certificate. In another embodiment, the establishment protocol includes any other known protocol in the art. Once the SSL connection is established, policy program  120  proceeds to the next step. In one example, the establishment protocol for a SSL connection are not completed, and the connection is terminated. 
     In an embodiment, policy program  120  uses deep-packet inspection capabilities to capture the certificate that is utilized during the SSL connection. Deep-packet inspection is a form of computer network packet filtering that examines the data part and/or the header of a packet as the data passes an inspection point. Deep-packet inspection comprises searching for protocol non-compliance, viruses, spam, intrusions, and/or defined criteria to decide whether the packet may pass or if the packet needs to be routed to a different destination for the purpose of collecting statistical information. The captured certificate is stored in a database, such as database  130 . In another embodiment, policy program  120  uses any method of capturing a certificate known in the art. 
     Policy program  120  determines if the certificate is similar to a previous certificate (decision  206 ). In the depicted embodiment, policy program  120  searches database  130  for similar previous certificates, which takes place in real time or at any time after the SSL connection has been established. In the depicted embodiment, the previous certificates that policy program  120  searches for similarity are one or more of certificates that have been previously captured by policy program  120 , updates to certificates (e.g., XML update  124 ) that have been received from browsers or web servers, a trusted intelligence source (e.g., intelligence source server  106 ), or any other trusted source that has access to database  130 . In another embodiment, policy program  120  searches a trusted remote certificate source. In an example, this search is implemented if a local database is not used or as an additional location to search for a similar certificate. 
     By waiting for the SSL connection to be established, a man-in-the-middle attack is prevented. In an example in which the SSL connection is not established, an attacker creates a legitimate certificate for a webpage, redirects the victim&#39;s traffic from the intended webpage to a second webpage, and the second webpage delivers the certificate for the first webpage. By waiting for the SSL connection to be established before comparing certificates, redirect attacks or intercept traffic, such as DNS cache poisoning and man-in-the-middle attacks are detected. In an example, before a connection is trying to establish, the client computing device  108  asks the DNS server  105  for the IP address where the domain is hosted. Once the client computing device  108  has received that IP address, client computing device  108  tries to establish a connection to the received IP address. So, when the client is waiting for the SSL connection to be established, the IP address can&#39;t change. 
     Policy program  120  determines the similarities of the current certificate (e.g., certificate  132 ) as compared to a previous certificate by comparing multiple attributes from the previously stored certificates to those of the current certificate. In an example, policy program  120  searches for relevant certificates for comparison by searching for a common name attribute of the certificate, which contains the domain or subdomain. If the common name matches, then the certificate is identified as similar. In another example, policy program  120  determines that two certificates are similar if the CA serial number attribute of each certificate matches. In yet another embodiment, the search is more in depth and searches multiple attributes of a certificate to determine the similarity. In an example of searching multiple attributes, if 75 percent or more of the attributes from the previously stored certificate matches that of the current certificate, policy program  120  identifies the certificates as similar. In another embodiment, a user can set the threshold for similarity. In one embodiment, policy program  120  uses alterative search techniques as would be known and understood to one skilled in the art. 
     Policy program  120  compares identified similar certificates with the certificate from the current SSL connection. In the depicted embodiment, policy program  120  compares certificate  132  with other located certificates in database  130 . The attributes of certificate  132  are checked against previous certificates. In one example, each type of attribute has to match exactly for the attribute to be deemed the same. In another example, if the attribute is within a user preset threshold, such as 95 percent similar, the attribute would be deemed to match. Attributes of a certificate comprise: the version, the serial number, the algorithm ID, the issuer (which contains the name of the CA, the organization, the location, the state, the country), the validity, the subject (which contains many personal details, such as the common name), the subject public key information including public key algorithm and subject public key, the issuer unique identifier, the subject unique identifier, the extensions, the signature algorithm, and the certificate signature. In an embodiment, in an instance when policy program  120  finds no similar certificates to certificate  132 , policy program  120  goes to end (decision  206 , NO branch). In another instance, policy program  120  will continue to the next step but with no identified similar attributes. 
     If policy program  120  determines that the certificate is similar to a previous certificate (decision  206 , YES branch), then policy program  120  identifies policy actions based on the similarity of the certificates (step  208 ). In the depicted embodiment, policy program  120  identifies a policy action for certificate  132  based upon the similarity of attributes of a previously stored certificate. In an embodiment, policy actions are preset by the user. The policy actions are preset by a user of the client device, such as client computing device  108 , and are based upon which attributes match between the current certificate being utilized to establish the SSL connection (e.g., certificate  132 ) and a previously stored certificate in a local storage (e.g., database  130 ), a certificate stored in another non-depicted database, or a trusted source (e.g., intelligence source server  106 ). In an example, the user accesses policy program  120  and preselects from a list of certificate attributes to determine policy actions for policy program  120  to implement. In another example, in-line server computer  102  stores, for each client device, policy actions that are based on the risk aversion deemed appropriate by a user of the client device. In one embodiment, the preset policy actions are stored in database  130 . In another embodiment, the preset policy actions are stored on the client device. In another embodiment, policy program  120  queries the client device (e.g., client computing device  108 ) to determine the policy actions based upon the attributes of the certificate. 
     Some examples of policy actions include allow, block, or alert. These policy actions are triggered by policy program  120  comparing each of the attributes, or combinations of the attributes, of the current certificate to a similar certificate. In an example, if the country of the CA for certificate  132  does not match the country for the CA for the previously stored similar certificate, based upon the policy, action for policy program  120  is to block the connection. In another example, the certificate signature algorithm for certificate  132  has changed from a previously stored similar certificate, and the policy action for policy program  120  is to alert the user. 
     In one embodiment, policy program  120  sends a certificate to an outside source for analysis. In an example, policy program  120  does not find a previously stored certificate that is similar to certificate  132 , and, in response, sends certificate  132  to intelligence source server  106 . Intelligence source server  106  is an outside trusted source that reviews the certificate to determine the authenticity and sends back a recommendation, or a list of similarities and differences in attributes regarding the certificate utilized for the SSL connection, and a certificate in the trusted source for policy program  120  to determine which policy action to proceed with. In another example, if no similar certificate is located to certificate  132 , policy program  120  prompts the user to determine if certificate  132  should be sent to intelligence source server  106 . In one embodiment, a certificate (e.g., certificate  132 ) sent by policy program  120  is compared to certificates stored in a database located on intelligence source server  106  to determine if there is an exact match, in which case certificate  132  would be verified as a valid certificate. 
     Policy program  120  enforces an identified policy (step  210 ). In the depicted embodiment, policy program  120  enforces the identified policy for certificate  132  on a client computing device, such as client computing device  108 . In an example, policy program  120  allows the SSL connection to continue between client computing device and web server  104  but sends an alert to the user of client computing device  108  because no similar certificates to certificate  132  have been located. This action is taken because the presets for client computing device  108  indicate that there should only be an alert sent if no similar certificates are located. Various examples of alerts comprise visual (e.g., popups), tactile (e.g., vibrations), and/or sound (e.g., alarm). 
       FIG. 3  depicts a block diagram of components of computer  300 , which is representative of in-line server computer  102 , intelligence source server  106 , client computing devices  108 ,  110 ,  112 , and web server  104 , in accordance with an illustrative embodiment of the present invention. It should be appreciated that  FIG. 3  provides only an illustration of one implementation and does not imply any limitations with regard to the environments in which different embodiments may be implemented. Many modifications to the depicted environment may be made. 
     Computer  300  includes communications fabric  302 , which provides communications between computer processor(s)  304 , memory  306 , persistent storage  308 , communications unit  310 , and input/output (I/O) interface(s)  312 . Communications fabric  302  can be implemented with any architecture designed for passing data and/or control information between processors (such as microprocessors, communications, and network processors, etc.), system memory, peripheral devices, and any other hardware components within a system. For example, communications fabric  302  can be implemented with one or more buses. 
     Memory  306  and persistent storage  308  are computer readable storage media. In this embodiment, memory  306  includes random access memory (RAM)  314  and cache memory  316 . In general, memory  306  can include any suitable volatile or non-volatile computer readable storage media. Software and data  322  are stored in persistent storage  308  for access and/or execution by processor(s)  304  via one or more memories of memory  306 . With respect to in-line server computer  102 , software and data  322  represents policy program  120  and database  130 . 
     In this embodiment, persistent storage  308  includes a magnetic hard disk drive. Alternatively, or in addition to a magnetic hard disk drive, persistent storage  308  can include a solid-state hard drive, a semiconductor storage device, a read-only memory (ROM), an erasable programmable read-only memory (EPROM), a flash memory, or any other computer readable storage media that is capable of storing program instructions or digital information. 
     The media used by persistent storage  308  may also be removable. For example, a removable hard drive may be used for persistent storage  308 . Other examples include optical and magnetic disks, thumb drives, and smart cards that are inserted into a drive for transfer onto another computer readable storage medium that is also part of persistent storage  308 . 
     Communications unit  310 , in these examples, provides for communications with other data processing systems or devices. In these examples, communications unit  310  includes one or more network interface cards. Communications unit  310  may provide communications through the use of either or both physical and wireless communications links. Software and data  322  may be downloaded to persistent storage  308  through communications unit  310 . 
     I/O interface(s)  312  allows for input and output of data with other devices that may be connected to computer  300 . For example, I/O interface(s)  312  may provide a connection to external device(s)  318  such as a keyboard, a keypad, a touch screen, and/or some other suitable input device. External device(s)  318  can also include portable computer readable storage media such as, for example, thumb drives, portable optical or magnetic disks, and memory cards. Software and data  322  can be stored on such portable computer readable storage media and can be loaded onto persistent storage  308  via I/O interface(s)  312 . I/O interface(s)  312  also connect to a display  320 . 
     Display  320  provides a mechanism to display data to a user and may be, for example, a computer monitor. 
     The programs described herein are identified based upon the application for which they are implemented in a specific embodiment of the invention. However, it should be appreciated that any particular program nomenclature herein is used merely for convenience, and thus the invention should not be limited to use solely in any specific application identified and/or implied by such nomenclature. 
     The present invention may be a system, a method, and/or a computer program product. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present invention. 
     The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of the computer readable storage medium includes the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or raised structures in a groove having instructions recorded thereon, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire. 
     Computer readable program instructions described herein can be downloaded to respective computing/processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and/or a wireless network. The network may comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and/or edge servers. A network adapter card or network interface in each computing/processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing/processing device. 
     Computer readable program instructions for carrying out operations of the present invention may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++ or the like, and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The computer readable program instructions may execute entirely on the user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user&#39;s computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present invention. 
     Aspects of the present invention are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer readable program instructions. 
     These computer readable program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer readable program instructions may also be stored in a computer readable storage medium that can direct a computer, a programmable data processing apparatus, and/or other devices to function in a particular manner, such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function/act specified in the flowchart and/or block diagram block or blocks. 
     The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus or other device to produce a computer implemented process, such that the instructions which execute on the computer, other programmable apparatus, or other device implement the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions. 
     The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The terminology used herein was chosen to best explain the principles of the embodiment, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.