Patent Publication Number: US-9853943-B2

Title: Selectively performing man in the middle decryption

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of and claims priority to U.S. application Ser. No. 13/966,900, filed on Aug. 14, 2013 and issued as U.S. Pat. No. 9,009,461; and to U.S. application Ser. No. 14/682,703, filed on Apr. 9, 2015 and issued as U.S. Pat. No. 9,621,517. 
    
    
     TECHNICAL FIELD 
     The present document relates to computer networking. 
     BACKGROUND 
     A computer network is a collection of computers and other hardware interconnected by communication channels that allow sharing of resources and information. Communication protocols define the rules and data formats for exchanging information in a computer network. A gateway on a network is a node on the network equipped for interfacing with another network or networks. The gateway is often used for passing data between devices on different networks. Transport Layer Security (TLS) and Secure Socket Layer (SSL) are two examples of cryptographic communication protocols that provide communication security by allowing devices to exchange encrypted, as opposed to plaintext, messages. 
     SUMMARY 
     In one aspect, a method is performed by data processing apparatus. The method includes receiving, from a first device within the network, a Hypertext Transfer Protocol (HTTP) request addressed to a first resource on a second device outside the network. The method further includes redirecting the HTTP request to a third device within the network. The method further includes establishing a first encrypted connection between the first device and the third device, and a second encrypted connection between the third device and the second device. The method further includes retrieving, by the third device, the first resource from the second device. The method further includes modifying the first resource to change pointers within the first resource to point to location in a domain associated with the third device within the network. The method further includes serving, by the third device to the first device, the second resource. 
     Implementations can include any, all, or none of the following features. The method including selecting the third device from a plurality of available devices within the network. The third device is selected based on a comparison of the first resource with a rule defining destinations associated with encrypted communication traffic. The third device is selected based on hardware performance. The method includes receiving, from a fourth device within the network, a second HTTP request addressed to an address of a second resource on a fifth device outside the network; routing the HTTP request to the address of the third resource. The method includes modifying the first resource to conform with the security policy. The method includes modifying the first resource includes replacing the resource with a different resource. The method includes modifying the first resource includes replacing HTTP links in the resource with different HTTP links. The method includes modifying the first resource includes replacing the resource with an HTTP status code object. The method includes determining that a security policy of the network identifies the first resource for inspection upon entry to the network. 
     In one aspect, a computer storage media is encoded with computer program instructions that, when executed by one or more processors, cause a computer device to perform operations. The operations include receiving, from a first device within the network, a Hypertext Transfer Protocol (HTTP) request addressed to a first resource on a second device outside the network. The operations further include redirecting the HTTP request to a third device within the network. The operations further include establishing a first encrypted connection between the first device and the third device, and a second encrypted connection between the third device and the second device. The operations further include retrieving, by the third device, the first resource from the second device. The operations further include modifying the first resource to change pointers within the first resource to point to location in a domain associated with the third device within the network. The operations further include serving, by the third device to the first device, the second resource. 
     Implementations can include any, all, or none of the following features. The operations further include selecting the third device from a plurality of available devices within the network. The third device is selected based on a comparison of the first resource with a rule defining destinations associated with encrypted communication traffic. The third device is selected based on hardware performance. The computer operations further include receiving, from a fourth device within the network, a second HTTP request addressed to an address of a second resource on a fifth device outside the network; routing the HTTP request to the address of the third resource. The operations further include modifying the first resource to conform with the security policy. The operations further include modifying the first resource includes replacing the resource with a different resource. The operations further include modifying the first resource includes replacing HTTP links in the resource with different HTTP links. The computer operations further include modifying the first resource includes replacing the resource with an HTTP status code object. The operations further include determining that a security policy of the network identifies the first resource for inspection upon entry to the network. 
     In one aspect, a system includes one or more processors configured to execute computer program instructions. The system further includes computer storage media encoded with computer program instructions that, when executed by one or more processors, cause a computer device to perform operations. The operations include receiving, from a first device within the network, a Hypertext Transfer Protocol (HTTP) request addressed to a first resource on a second device outside the network. The operations further include redirecting the HTTP request to a third device within the network. The operations further include establishing a first encrypted connection between the first device and the third device, and a second encrypted connection between the third device and the second device. The operations further include retrieving, by the third device, the first resource from the second device. The operations further include modifying the first resource to change pointers within the first resource to point to location in a domain associated with the third device within the network. The operations further include serving, by the third device to the first device, the second resource. 
     Implementations can include any, all, or none of the following features. The operations further include selecting the third device from a plurality of available devices within the network. The third device is selected based on a comparison of the first resource with a rule defining destinations associated with encrypted communication traffic. The third device is selected based on hardware performance. The computer operations further include receiving, from a fourth device within the network, a second HTTP request addressed to an address of a second resource on a fifth device outside the network; routing the HTTP request to the address of the third resource. The operations further include modifying the first resource to conform with the security policy. The operations further include modifying the first resource includes replacing the resource with a different resource. The operations further include modifying the first resource includes replacing HTTP links in the resource with different HTTP links. The computer operations further include modifying the first resource includes replacing the resource with an HTTP status code object. The operations further include determining that a security policy of the network identifies the first resource for inspection upon entry to the network. 
     The systems and processes described here may be used to provide a number of potential advantages. A gateway can decouple domains from shared Internet Protocol (IP) addresses and selectively choose to intercept SSL, TLS, etc requests. If spoofed IP addresses are another server on the network, performance issues may be alleviated as only selective requests are sent to man in the middle (MitM) gateways for decryption. Cryptographically protected traffic can be inspected at network egress and ingress, allowing a network administrator to enforce security policies consistently across both cryptographically protected traffic and plaintext traffic. By using standard communication protocols, browser devices (e.g. cell phones, tablets, laptops) can join the network with little or no special configuration. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a block diagram of a network with a network gateway and a man in the middle gateway. 
         FIG. 1B  is a diagram of a webpage that has been modified. 
         FIG. 2  is a block diagram of a network with a network gateway and a group of man in the middle gateways. 
         FIG. 3  is a swim-lane diagram of an example process for establishing a communication link through a man in the middle gateway. 
         FIG. 4  is a block diagram showing example users responsible for a gateway. 
         FIG. 5  is a schematic diagram that shows an example of a computing device and a mobile computing device. 
     
    
    
     Like reference symbols in the various drawings indicate like elements 
     DETAILED DESCRIPTION 
     When data on a network is encrypted (e.g., by SSL or TSL) the data can pose challenges to network security appliances and routines in that it makes it difficult to inspect the data as it is transferred between the end users and servers on the Internet. This can lead to problems such as viruses being transferred over secure connections and entering the network instead of being blocked because the gateway security appliances could not inspect the data. In addition, organizational policies cannot be applied since the data within the encrypted traffic is protected causing security functions to fail as they cannot inspect the data. 
     Described in this document is a use of man in the middle decryption based on rules indicating which destinations should be decrypted and which should be passed directly to the Internet destination. A network gateway maps specific spoofed IP addresses to correlated domain in order to, among other uses, determine which encrypted connections should by bypassed and sent directly to the Internet destination and which connections should be decrypted using a man in the middle technique. 
     A computer network typically has one or more gateways that allow communication between devices on the network and devices on other networks (e.g. the Internet). One such gateway can be a network gateway that routes plaintext (i.e., non-encrypted) traffic among devices within the network and devices outside of the network. One common type of plaintext traffic that is routed through a network gateway is a request message (e.g., Hypertext Transfer Protocol&#39;s GET and POST, Post Office Protocol&#39;s RETR), which is a request to a server for a resource on the server. 
     Instead of passing all request messages to the server, the network gateway can intercept some of the request messages if the network gateway determines that traffic between the network devices and the URLs or URIs will be encrypted. For these request messages, the network gateway can respond to the network device with the address or addresses of one or more man in the middle (MitM) gateways in the network. The MitM gateways may then act as man in the middle proxies for the resource at the URL or URI, allowing cryptographically secure communication that can be inspected when entering or exiting the network. 
       FIG. 1A  is a block diagram of a network  100  with a network gateway  102  and a MitM gateway  104 . Also shown in the network  100  is a browser device  106 , which represents any appropriate computing device capable of browsing resources outside of the network  100 . While not shown for clarity&#39;s sake, the network  100  can include other elements including, but not limited to, wireless and/or wired access points, file and/or application servers, routers, and network cables, as well as additional browser devices  106 , network gateways  102 , and/or MitM gateways  104 . 
     The network  100  can be configured to route some or all of the plaintext messages addressed outside the network to the network gateway  102 . The network gateway  102  can inspect the plaintext messages and, optionally, modify or drop some messages. For example, the network gateway  102  may be configured to prevent traffic from a particular class of application (e.g., chat, files sharing). The network gateway  102  may also be configured to intercept messages intended for a recipient outside of the network  100  and reply directly. This process is sometimes referred to as spoofing. 
     For example, the network gateway may intercept and examine a request message  108  from the browser device  106  that is addressed to a server  118 . Based on, for example, the URL or URI in the request message  108  and rules  103  indicating which destination should be decrypted and which should be passed directly to the Internet destination, the network gateway  102  may determine that, instead of passing the request message  108  to the server  118 , the network gateway  102  should respond to the request message with a MitM gateway address  112  in, for example, a redirect message to the browser device  106 . The network gateway  102  may be configured to make this determination so that encrypted communication from the browser device  106  first passes through the MitM gateway  104 , thereby allowing the gateway  104  to decrypt the communication and perform man in the middle data inspection before allowing the communication to pass out of the network  100 . The network gateway  102  may make the determining to pass encrypted communication through the MitM gateway  104  based on security policies or concerns as applied to the network  100 . While passing communication through the MitM  104  may provide some other benefits (e.g., caching of frequently visited resources to reduce bandwidth usages), the rules  103  may be configured to primarily or exclusively account for the security considerations of passing communications through the network gateway  102  or the MitM gateway  104 . 
     The browser device  106 , upon receiving the MitM gateway address  112 , can initialize a cryptographic connection  114  with the MitM gateway  104  at the MitM gateway address  112 . The cryptographic connection  114  may be an SSL, TLS, or any other appropriate cryptographic session. The MitM gateway  104  may then initialize another cryptographic connection  116  with the server  118  that hosts the resource identified by the URL or URI of the DNS request  108 . 
     Once the cryptographic connections  114  and  116  are established, the browser device  106  and the server  118  may communicate with each other. In this communication, the MitM gateway  104  may act as a proxy of the server  118  for the browser device  106  and as a proxy of the browser device  106  for the server  118 . The MitM gateway  104  is thus able to receive an encrypted message from the browser device  106 , decrypt the message, inspect the message, optionally alter or drop the message, encrypt the possibly altered message into a second encrypted form, and pass the message to the server  118 . The MitM gateway  104  may perform the same type of reception, decryption, inspection, alteration or drop, encryption, and passage with messages from the server  118  to the browser device  106 . The MitM gateway  104  may sometimes be referred to by other terms including, but not limited to, a reverse proxy, intercepting proxy, accelerator, accelerating proxy, and transparent proxy. 
     One type of alteration that may be made by the MitM gateway  104  is to alter the URLs and URIs of webpages served by the server  118 . For example, the server  118  may serve a webpage with a number of links to other webpages on the same website. The MitM gateway  104  may replace those URLs and URIs that are similar to the original URLs and URIs but which to the MitM gateway  104 . 
     For clarity of description, here and elsewhere, variable names are enclosed in square brackets. In one example, the server  118  may serve a webpage with the URL www.[exampleEncryptedPage].com, and this webpage may have links to www.[exampleEncryptedPage].com/medai.html and www.[exampleEncryptedPage].come/links.html. The MitM gateway  104  may replace those links with www.[MitMGateway].com/[exampleEncryptedPage]/media and with www.[MitMGateway].com/[exampleEncryptedPage]/links, or with [exampleEncryptedPage].[MitMGateway].com/media and [exampleEncryptedPage.MitMGateway].com/links. In this example, the ULR www.[MitMGateway].com can be configured to resolve to an IP address of the MitM Gateway  104 . For clarity of description, here and elsewhere, variable names are enclosed in square brackets. 
     The inspection, alteration, and dropping performed by the MitM gateway  104  can allow the MitM gateway  104  to ensure that encrypted communication into and out of the network conforms to any number of policies. For example, the network  100  may have a policy of inspecting incoming messages for computer viruses, malware, or other unwanted content. The network gateway  102 , handling plaintext messages, can inspect the payloads of the messages and drop any messages that match viral signatures, malware black-lists, etc. The MitM gateway  104  may apply the same policy, inspecting incoming messages in their decrypted state and drop any messages that fail the same tests as applied by the network gateway  102 . 
     In some examples, the request message  108  may transmitted be in the clear. That is, the request message  108  may be in a cleartext form conforming to the HTTP specification. The address of the MitM gateway  112  may specify a secure connection. That is, the address of the MitM gateway  112  may specify that the browser device  106  should connect by HTTP Secure (“HTTPS”). This may be beneficial, for example, for ensuring that all content requested and served from the server  118  is encrypted, even if the server  118  does not enforce an encrypted-only policy. 
       FIG. 1B  is a diagram of a webpage that has been modified. Original webpage  150  is a rendered webpage that may be served by, for example, the server  118 . The original webpage  150  can include pointers to other webpages such an image  152  with an embedded link, and a text link  154 . The original webpage is located at the URL  156  http://www.[exampleEncryptedPage.]com. 
     Modified webpage  158  is a rendered webpage that has been created by modifying the original webpage  150 . For example, the MitM gateway  104  may receive the original webpage  150  from the server  118  and modify the original webpage  150  to create the modified webpage  158 . 
     The modified webpage  158  contains an image  160  that corresponds to the image  152  and a text link  162  that corresponds to the text link  154 . However, the embedded link of image  160  and the text link  162  have been modified to address of a domain associated with the MitM gateway  104 . Similarly, the URL  164  of the webpage  158  has been modified from the URL  156 . With these substitutions, the webpage  158  may be rendered to include links to the [MitMGateway] domain instead of the [exampleEncryptedPage] domain. In some cases, in addition to updating the anchor property link, the text of the text link  162  may be updated to indicate the [MitMGateway]. In some cases, the text of the link  162  may be unmodified while the anchor property link may be updated to point to the [MitMGateway] 
     In this example, the browser displays a lock icon  166  and  168  with the original webpage  150  and the modified webpage  158 . A web browser may be configured, for example, to display lock icons  166  and  168  when a webpage with trusted encryption is being rendered. In the case of the original webpage  150 , the encrypted connection can be considered trusted if an encrypted connection to the server  118  is trusted. In the case of the modified webpage  158 , the encrypted connection can be considered trusted if an encrypted connection to the MitM gateway  104  is trusted. 
     As shown here, URLs and URIs are replaced in the modified webpage  158  by inserting “[MitMGatway].” before the top level domain portion of URLs and URIs in the original webpage  150 . However, other forms of address modification are possible. 
     For example, elements of addresses in the original webpage  150  may be used as parameters in addresses in the modified webpage  158 . In this example, the image  160  may have an embedded link to www.[MitMDomain].com/orig_url=“www.[exampleEncryptedPage].com/media”, and the text link  162  may be to www.[MitMDomain].com/orig_url=“www.[exampleEncryptedPage].com/links”. 
       FIG. 2  is a block diagram of a network  200  with a network gateway  202  and a group of MitM gateways  204 - 210 . The network  200  can be configured to route some or all of the plaintext messages addressed outside the network to the network gateway  202 . The network gateway  202  can inspect the plaintext messages and, optionally, modify or drop a message. The network gateway  202  may also be configured to intercept and examine a request message from browser devices  212  and  214  and respond directly with the address or addresses of one or more of the MitM gateways  204 - 210 , for example, in a HTTP redirect message. 
     In general, decryption and encryption of network data may be a computationally intensive task for network appliances such as gateways. To alleviate performance issues, and for other reasons, the network gateway  202  and the group of MitM gateways  204 - 210  may be used to share or balance the load of the MitM gateways  204 - 210 . The network gateway  202  may respond to a request message from a browser device  212  or  214  with address of all available MitM gateways  204 - 210  in the network  200 . The browser devices  212  or  214  may then initiate a cryptographic connection with one the MitM gateway  204 - 210  in order to attempt to reach the resource specified in the DNS request. 
     The network gateway  202  may be configured to provide the addresses of the MitM gateways  204 - 210  in any appropriate scheme, for example, in any way that is permitted by a redirect protocol. In one example, the network gateway  202  may always respond with the addresses in the same order. In another example, the network gateway  202  may rotate the order of addresses. The browser devices  212  and  214  may be configured to select one address from the group of returned addresses in any appropriate scheme, for example, in any way that is permitted by the redirect protocol. In one example, the browser devices  212  and  214  may pseudorandomly select one of the addresses. In another example, the browser devices  212  and  214  cache a ping time every time an address is connected with, and the browser devices  212  and  214  may select the returned address associated with the lowest ping time. 
     In some cases, the network gateway  202  and the group of MitM gateways  204 - 210  may be used to route different classes of traffic to different MitM gateways  204 - 210 . This may be desirable, for example, if policies of the network  200  specify that different policy tests should apply to different classes of encrypted traffic. 
     In one example, the MitM gateway  204  may be configured to handle encrypted traffic that is generally unrestricted. That is, the encrypted traffic may not be inspected, modified, or dropped at all, or may be only minimally inspected (e.g., encrypted VPN (Virtual Private Network) traffic to and from a network at a branch office). For another class of traffic, the network administrator may wish to inspect only incoming traffic for virus, malware, or other malicious code (e.g., encrypted traffic to banking or financial institutions). For a third class of traffic, the network administrator may wish to inspect outgoing traffic to make sure secret or proprietary data is not being transmitted and inspect incoming traffic for malicious code (e.g., social networking and hosted storage sites). For a fourth class of data, a hosted application provider may share the same IPs for some services that should be permitted and for some services that should be blocked (e.g., an application provider hosts email and document sharing, which should be allowed, as well as media streaming, which should be blocked). 
     In this example, the MitM gateways  204 - 210  can be configured as follows: 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 MitM gateway 204 
                 Perform no inspection of data. 
               
               
                   
                 MitM gateway 206 
                 Inspect and drop incoming data that 
               
               
                   
                   
                 contains malicious code. 
               
               
                   
                 MitM gateway 208 
                 Inspect and drop incoming data that 
               
               
                   
                   
                 contains malicious code. Inspect and drop 
               
               
                   
                   
                 outgoing data that contains secret or 
               
               
                   
                   
                 proprietary data. 
               
               
                   
                 MitM gateway 210 
                 Inspect and drop incoming data that 
               
               
                   
                   
                 contains malicious code. Determine which 
               
               
                   
                   
                 service the data is associated with, 
               
               
                   
                   
                 dropping any related to blocked services. 
               
               
                   
                   
               
            
           
         
       
     
     To route traffic from the browser devices  212  and  214 , the network gateway  202  may inspect received request message and determine which of the MitM gateways  204 - 210  should handle the encrypted traffic. For example, the network gateway  202  may have a list that maps URLs and URIs to categories based on the type of content available at the URL or URI. When the network gateway  202  receives a request message, the network gateway  202  can compare the URL or URI of the DNS request to the list. If the request&#39;s URL or URI is not on the list, the network gateway  202  can pass the request message to the specified server for resolution. If the URL or URI is on the list, the network gateway  202  can respond to the requesting browser device  212  or  214  with the address of one of the MitM gateways  204 - 210  configured to handle traffic associated with the category that the URL or URI falls under. 
     Two browser devices  212  and  214  are shown in  FIG. 2 , however, these browser devices and other browser devices can enter and exit the network  200  over time. For example, a worker may bring one or more of her employer&#39;s or her own devices (e.g., laptop, phone, tablet) into the network  200  at the start of the day and remove the devices at the end when she goes home. Other than the configurations need to join the network (e.g. Wi-Fi passwords, plugging in Ethernet cords), the network  200  need not require any special configuration to ensure that encrypted traffic is routed through the correct MitM gateways  204 - 210  due to the fact that all messages to and from the browser devices conform to standards that are commonly supported on many common hardware, operating system, and browser systems. 
       FIG. 3  is a swim-lane diagram of an example process  300  for establishing a communication link through a MitM gateway. The process  300  is described with reference to the components shown in  FIG. 1A . However, other components, including and not limited to the components shown in  FIG. 2 , can be used to perform the process  300  or a similar process. 
     The browser device  106  creates a request message for a resource ( 302 ). For example, a user may request to download, from a hosted storage system, a data object identified by a unique URI. The browser device can create a request message that includes the data object&#39;s URI and send the request message to the network gateway  102 . 
     The network gateway  102  receives the request and selects a gateway to be used for traffic associated with the website address ( 304 ). For example, the network gateway  102  can process a set of rules  103  that indicate which destination should be decrypted and which should be passed directly to the Internet destination. These rules  103  may include, for example, a list of URLs, URIs, domain names and IP address mapped to security policies, content classifications, or directions for handling of network traffic (e.g., specifying that the traffic should be decrypted and inspected). If the network gateway  102  selects the network gateway  102  for the traffic to pass directly to the Internet destination, the browser device  106  and the server  118  establish a connection through the network gateway  102  ( 306 ). For example, if the network gateway  102  determines that the browser device  106  is likely to start an unencrypted communication session with the hosted storage system, the network gateway  102  can pass the request message to the server  118  (see  FIG. 1A ) and permit the browser device  106  to create an unencrypted connection with the server  118 . 
     If the network gateway  102  selects the MitM gateway  104 , the network gateway  102  returns the address of the selected MitM gateway  104  ( 308 ). For example, the network gateway  102  may have a record of past connections with the hosted storage system and determine that the hosted storage system usually communicates through encrypted communication channels. In such a case, the network gateway  102  may select the MitM gateway  104  for the communication between the browser device  106  and the server  118  and thus may return a redirect to the network address of the MitM gateway  104  to the browser device  106  Many types of redirection are possible, including but not limited to server-side scripting, frame redirects, and Apache mod 13  rewrite. Regardless of the redirection used, the redirection can include sufficient information for the MitM gateway  104  to identify the originally requested content. 
     The browser device  106  requests an encrypted connection with the device at the received address, which is the MitM gateway  104  ( 310 ). For example, the browser device  106  may send to the MitM gateway  104  an SSL Hello or other encryption handshake message. In another example, the MitM gateway  104  may have multiple network addresses, each associated with known destination URLs. When a connection request is received at one of the multiple addresses, the MitM gateway  104  may look up the associated URL. The browser device  106  and the MitM gateway  104  establish a first encrypted connection ( 312 ). For example, the MitM gateway  104  may act as a proxy of the server  118 , mimicking the interface of the server  118  in communications with the browser device  106 . 
     The MitM gateway  104  requests an encrypted connection with the server  118  ( 314 ). For example, the MitM gateway  104  can request an encrypted connection on behalf of the browser device  106 . The MitM gateway  104  and the server  118  establish a second encrypted connection ( 316 ). For example, the MitM gateway  104  may act as a proxy of the browser device  106 , mimicking the interface of the browser device  106  in communications with the server  118 . The two encryption sessions may be of the same or different formats or types. 
     The browser device  106  generates traffic, encrypts the traffic into a first encrypted form, and passes the traffic to the MitM gateway  104  ( 318 ). For example, the browser device can create a HTTP Get request for the data object. The browser device can encrypt the HTTP Get request according to the requirements of the encrypted connection with the MitM gateway  104  and pass the encrypted HTTP Get request to the MitM gateway  104 . 
     The MitM gateway  104  receives the traffic, decrypts the traffic, inspects the traffic, encrypts the traffic into a second encrypted form, and passes the traffic to the server  118  ( 320 ). For example, the MitM gateway  104  can decrypt the encrypted message into plaintext and determine that the message is an HTTP Get request. The MitM gateway  104  can compare the HTTP Get request with the rules of any policies that apply to traffic out of the network  100 . If the HTTP Get request does not violate any policy, the MitM gateway  104  can encrypt the HTTP Get request according to the requirements of the encrypted connection with the server  118  and pass the encrypted HTTP Get request to the server  118 . If the HTTP Get request does violate a policy, the MitM gateway  104  can modify or drop the request, as specified by the policy. 
     The server  118  receives the traffic in the second encrypted form ( 322 ). For example, the server  118  may receive the encrypted HTTP Get request, decrypt the HTTP Get request, and determine that the user of the browser device  106  has authorization to access the requested data object. 
     The server  118  generates traffic, encrypts the traffic into a third encrypted form, and passes the traffic to the MitM gateway  104  ( 324 ). For example, the server  118  can access the requested data object, format the data object into HTML or other appropriate format, and add the HTML object to an HTTP reply. The server  118  can encrypt the HTTP reply according to the requirements of the encrypted connection with the MitM gateway  104  and pass the encrypted HTTP reply to the MitM gateway  104   
     The MitM gateway  104  receives the traffic, decrypts the traffic, inspects the traffic, encrypts the traffic into a fourth form, and passes the traffic to the browser device  106  ( 326 ). For example, the MitM gateway  104  can decrypt the encrypted message into plaintext and determine that the message is an HTTP reply. The MitM gateway  104  can compare the HTTP reply with the rules of any policies that apply to traffic into the network  100 . If the HTTP reply does not violate any policy, the MitM gateway  104  can modify the HTML object to replace addresses of the server with address of the MitM Gateway  104 , encrypt the HTTP reply according to the requirements of the encrypted connection with the browser device  106  and pass the encrypted HTTP reply to the browser device  106 . If the HTTP reply does violate a policy (e.g., contains malicious code, too large), the MitM gateway  104  can modify or drop the reply, as specified by the policy. 
     The browser device  106  receives the encrypted traffic ( 328 ). For example the browser device can decrypt the HTTP reply, extract the modified HTML object, and render the modified HTML object in a web browser. 
     Although a particular number, type, and order of operations are shown here, other numbers, types, and orders of operations are possible. For example, if there are multiple MitM gateways available, the network gateway  102  may select one or more and return the addresses of selected MitM gateways. In another example, the browser device  106  and the server  118  may create and pass encrypted traffic in the opposite order shown here or substantially at the same time. 
       FIG. 4  is a block diagram showing example users responsible for a gateway. The users will be described according to their responsibilities for manufacturing, selling, and administering a gateway. In some cases, each of the users shown corresponds to many users, and/or some users may be responsible for more than on task described. 
     A manufacturer  400  is responsible for designing, assembling, and installing software  408  on a gateway  406 . The installed software may have many configurable options, including options to configure the gateway  406  to behave as a network gateway  102  or  202  and/or as a MitM gateway  104  or  204 - 210 . 
     A vendor  402  is responsible for selling the gateway  406  to a customer. The vendor  402  may be able to configure the software  410  of the gateway  406  to behave as a network gateway  102  or  202  and/or as a MitM gateway  104  or  204 - 210 . In some cases, the vendor  402  may replace the software that the manufacturer  400  installed on the gateway  406  as part of configuring the gateway  406 . 
     An administrator  404  is responsible for administering the network  414 , which may include the gateway  406 . In some cases, the administrator  404  is able to configure the software  410  of the gateway  406  to behave as a network gateway  102  or  202  and/or as a MitM gateway  104  or  204 - 210 . In some cases, the administrator  404  may replace the software that the manufacturer  400  or vendor  402  installed on the gateway  406  as part of configuring the gateway  406 . 
       FIG. 5  shows an example of a computing device  500  and an example of a mobile computing device that can be used to implement the techniques described here. The computing device  500  is intended to represent various forms of digital computers, such as laptops, desktops, workstations, personal digital assistants, servers, blade servers, mainframes, and other appropriate computers. The mobile computing device is intended to represent various forms of mobile devices, such as personal digital assistants, cellular telephones, smart-phones, and other similar computing devices. The components shown here, their connections and relationships, and their functions, are meant to be exemplary only, and are not meant to limit implementations of the inventions described and/or claimed in this document. 
     The computing device  500  includes a processor  502 , a memory  504 , a storage device  506 , a high-speed interface  508  connecting to the memory  504  and multiple high-speed expansion ports  510 , and a low-speed interface  512  connecting to a low-speed expansion port  514  and the storage device  506 . Each of the processor  502 , the memory  504 , the storage device  506 , the high-speed interface  508 , the high-speed expansion ports  510 , and the low-speed interface  512 , are interconnected using various busses, and may be mounted on a common motherboard or in other manners as appropriate. The processor  502  can process instructions for execution within the computing device  500 , including instructions stored in the memory  504  or on the storage device  506  to display graphical information for a GUI on an external input/output device, such as a display  516  coupled to the high-speed interface  508 . In other implementations, multiple processors and/or multiple buses may be used, as appropriate, along with multiple memories and types of memory. Also, multiple computing devices may be connected, with each device providing portions of the necessary operations (e.g., as a server bank, a group of blade servers, or a multi-processor system). 
     The memory  504  stores information within the computing device  500 . In some implementations, the memory  504  is a volatile memory unit or units. In some implementations, the memory  504  is a non-volatile memory unit or units. The memory  504  may also be another form of computer-readable medium, such as a magnetic or optical disk. 
     The storage device  506  is capable of providing mass storage for the computing device  500 . In some implementations, the storage device  506  may be or contain a computer-readable medium, such as a floppy disk device, a hard disk device, an optical disk device, or a tape device, a flash memory or other similar solid state memory device, or an array of devices, including devices in a storage area network or other configurations. A computer program product can be tangibly embodied in an information carrier. The computer program product may also contain instructions that, when executed, perform one or more methods, such as those described above. The computer program product can also be tangibly embodied in a computer- or machine-readable medium, such as the memory  504 , the storage device  506 , or memory on the processor  502 . 
     The high-speed interface  508  manages bandwidth-intensive operations for the computing device  500 , while the low-speed interface  512  manages lower bandwidth-intensive operations. Such allocation of functions is exemplary only. In some implementations, the high-speed interface  508  is coupled to the memory  504 , the display  516  (e.g., through a graphics processor or accelerator), and to the high-speed expansion ports  510 , which may accept various expansion cards (not shown). In the implementation, the low-speed interface  512  is coupled to the storage device  506  and the low-speed expansion port  514 . The low-speed expansion port  514 , which may include various communication ports (e.g., USB, Bluetooth, Ethernet, wireless Ethernet) may be coupled to one or more input/output devices, such as a keyboard, a pointing device, a scanner, or a networking device such as a switch or router, e.g., through a network adapter. 
     The computing device  500  may be implemented in a number of different forms, as shown in the figure. For example, it may be implemented as a standard server  520 , or multiple times in a group of such servers. In addition, it may be implemented in a personal computer such as a laptop computer  522 . It may also be implemented as part of a rack server system  524 . Alternatively, components from the computing device  500  may be combined with other components in a mobile device (not shown), such as a mobile computing device  550 . Each of such devices may contain one or more of the computing device  500  and the mobile computing device  550 , and an entire system may be made up of multiple computing devices communicating with each other. 
     The mobile computing device  550  includes a processor  552 , a memory  564 , an input/output device such as a display  554 , a communication interface  566 , and a transceiver  568 , among other components. The mobile computing device  550  may also be provided with a storage device, such as a micro-drive or other device, to provide additional storage. Each of the processor  552 , the memory  564 , the display  554 , the communication interface  566 , and the transceiver  568 , are interconnected using various buses, and several of the components may be mounted on a common motherboard or in other manners as appropriate. 
     The processor  552  can execute instructions within the mobile computing device  550 , including instructions stored in the memory  564 . The processor  552  may be implemented as a chipset of chips that include separate and multiple analog and digital processors. The processor  552  may provide, for example, for coordination of the other components of the mobile computing device  550 , such as control of user interfaces, applications run by the mobile computing device  550 , and wireless communication by the mobile computing device  550 . 
     The processor  552  may communicate with a user through a control interface  558  and a display interface  556  coupled to the display  554 . The display  554  may be, for example, a TFT (Thin-Film-Transistor Liquid Crystal Display) display or an OLED (Organic Light Emitting Diode) display, or other appropriate display technology. The display interface  556  may comprise appropriate circuitry for driving the display  554  to present graphical and other information to a user. The control interface  558  may receive commands from a user and convert them for submission to the processor  552 . In addition, an external interface  562  may provide communication with the processor  552 , so as to enable near area communication of the mobile computing device  550  with other devices. The external interface  562  may provide, for example, for wired communication in some implementations, or for wireless communication in other implementations, and multiple interfaces may also be used. 
     The memory  564  stores information within the mobile computing device  550 . The memory  564  can be implemented as one or more of a computer-readable medium or media, a volatile memory unit or units, or a non-volatile memory unit or units. An expansion memory  574  may also be provided and connected to the mobile computing device  550  through an expansion interface  572 , which may include, for example, a SIMM (Single In Line Memory Module) card interface. The expansion memory  574  may provide extra storage space for the mobile computing device  550 , or may also store applications or other information for the mobile computing device  550 . Specifically, the expansion memory  574  may include instructions to carry out or supplement the processes described above, and may include secure information also. Thus, for example, the expansion memory  574  may be provide as a security module for the mobile computing device  550 , and may be programmed with instructions that permit secure use of the mobile computing device  550 . In addition, secure applications may be provided via the SIMM cards, along with additional information, such as placing identifying information on the SIMM card in a non-hackable manner. 
     The memory may include, for example, flash memory and/or NVRAM memory (non-volatile random access memory), as discussed below. In some implementations, a computer program product is tangibly embodied in an information carrier. The computer program product contains instructions that, when executed, perform one or more methods, such as those described above. The computer program product can be a computer- or machine-readable medium, such as the memory  564 , the expansion memory  574 , or memory on the processor  552 . In some implementations, the computer program product can be received in a propagated signal, for example, over the transceiver  568  or the external interface  562 . 
     The mobile computing device  550  may communicate wirelessly through the communication interface  566 , which may include digital signal processing circuitry where necessary. The communication interface  566  may provide for communications under various modes or protocols, such as GSM voice calls (Global System for Mobile communications), SMS (Short Message Service), EMS (Enhanced Messaging Service), or MMS messaging (Multimedia Messaging Service), CDMA (code division multiple access), TDMA (time division multiple access), PDC (Personal Digital Cellular), WCDMA (Wideband Code Division Multiple Access), CDMA2000, or GPRS (General Packet Radio Service), among others. Such communication may occur, for example, through the transceiver  568  using a radio-frequency. In addition, short-range communication may occur, such as using a Bluetooth, WiFi, or other such transceiver (not shown). In addition, a GPS (Global Positioning System) receiver module  570  may provide additional navigation- and location-related wireless data to the mobile computing device  550 , which may be used as appropriate by applications running on the mobile computing device  550 . 
     The mobile computing device  550  may also communicate audibly using an audio codec  560 , which may receive spoken information from a user and convert it to usable digital information. The audio codec  560  may likewise generate audible sound for a user, such as through a speaker, e.g., in a handset of the mobile computing device  550 . Such sound may include sound from voice telephone calls, may include recorded sound (e.g., voice messages, music files, etc.) and may also include sound generated by applications operating on the mobile computing device  550 . 
     The mobile computing device  550  may be implemented in a number of different forms, as shown in the figure. For example, it may be implemented as a cellular telephone  580 . It may also be implemented as part of a smart-phone  582 , personal digital assistant, or other similar mobile device. 
     Various implementations of the systems and techniques described here can be realized in digital electronic circuitry, integrated circuitry, specially designed ASICs (application specific integrated circuits), computer hardware, firmware, software, and/or combinations thereof. These various implementations can include implementation in one or more computer programs that are executable and/or interpretable on a programmable system including at least one programmable processor, which may be special or general purpose, coupled to receive data and instructions from, and to transmit data and instructions to, a storage system, at least one input device, and at least one output device. 
     These computer programs (also known as programs, software, software applications or code) include machine instructions for a programmable processor, and can be implemented in a high-level procedural and/or object-oriented programming language, and/or in assembly/machine language. As used herein, the terms machine-readable medium and computer-readable medium refer to any computer program product, apparatus and/or device (e.g., magnetic discs, optical disks, memory, Programmable Logic Devices (PLDs)) used to provide machine instructions and/or data to a programmable processor, including a machine-readable medium that receives machine instructions as a machine-readable signal. The term machine-readable signal refers to any signal used to provide machine instructions and/or data to a programmable processor. 
     To provide for interaction with a user, the systems and techniques described here can be implemented on a computer having a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to the user and a keyboard and a pointing device (e.g., a mouse or a trackball) by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user can be received in any form, including acoustic, speech, or tactile input. 
     The systems and techniques described here can be implemented in a computing system that includes a back end component (e.g., as a data server), or that includes a middleware component (e.g., an application server), or that includes a front end component (e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the systems and techniques described here), or any combination of such back end, middleware, or front end components. The components of the system can be interconnected by any form or medium of digital data communication (e.g., a communication network). Examples of communication networks include a local area network (LAN), a wide area network (WAN), and the Internet. 
     The computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other.