Patent Publication Number: US-9413785-B2

Title: System and method for interlocking a host and a gateway

Description:
RELATED APPLICATION 
     This Application is a continuation (and claims the benefit of priority under 35 U.S.C. §120) of U.S. application Ser. No. 13/437,900, filed Apr. 2, 2012, entitled “SYSTEM AND METHOD FOR INTERLOCKING A HOST AND A GATEWAY,” Inventors Geoffrey Howard Cooper, et al. The disclosure of the prior application is considered part of (and is incorporated by reference in) the disclosure of this application. 
    
    
     TECHNICAL FIELD 
     This disclosure relates in general to the field of network security, and more particularly, to a system and a method for interlocking a host and a gateway through information sharing. 
     BACKGROUND 
     The field of network security has become increasingly important in today&#39;s society. The Internet has enabled interconnection of different computer networks all over the world. However, the Internet has also presented many opportunities for malicious operators to exploit these networks. Once malicious software has infected a host computer, a malicious operator may issue commands from a remote computer to control the malicious software. The software can be instructed to perform any number of malicious actions, such as sending out spam or malicious emails from the host computer, stealing sensitive information from a business or individual associated with the host computer, propagating to other host computers, and/or assisting with distributed denial of service attacks. In addition, the malicious operator can sell or otherwise give access to other malicious operators, thereby escalating the exploitation of the host computers. Thus, the ability to effectively protect and maintain stable computers and systems continues to present significant challenges for component manufacturers, system designers, and network operators. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To provide a more complete understanding of the present disclosure and features and advantages thereof, reference is made to the following description, taken in conjunction with the accompanying figures, wherein like reference numerals represent like parts, in which: 
         FIG. 1  is a simplified block diagram illustrating an example embodiment of a network environment in which information may be shared between a host and a network gateway for network protection in accordance with this specification; 
         FIG. 2  is a simplified block diagram illustrating additional details associated with one potential embodiment of the network environment, in accordance with this specification; 
         FIG. 3  is a simplified block diagram illustrating example operations associated with one embodiment of a network environment in accordance with this specification; 
         FIG. 4  is a simplified block diagram illustrating example operations associated with another embodiment of a network environment in accordance with this specification; and 
         FIG. 5  is a simplified block diagram illustrating additional details that may be associated with other embodiments of a network environment in accordance with this specification; and 
         FIG. 6  is a simplified block diagram illustrating additional details that may be associated with yet other embodiments of a network environment in accordance with this specification. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Overview 
     A method is described in example embodiments below that include receiving a content tag associated with transferring a file over a network connection. A session descriptor may also be received. The session descriptor and the content tag may be correlated with a network policy, which may be applied to the network connection. In some embodiments, the content tag may be received with the session descriptor. The file may be tainted by another file in some embodiments, and the content tag may be associated with other file. 
     Example Embodiments 
     Turning to  FIG. 1 ,  FIG. 1  is a simplified block diagram of an example embodiment of a network environment  10  in which a host and a network gateway may be interlocked through information sharing. In the embodiment illustrated in  FIG. 1 , network environment  10  can include Internet  15 , a user host  20 , a network gateway  25 , a policy server  30 , a datacenter  35 , a network data loss protection (NDLP) server  40 , a mail server  45 , and a web server  50 . In general, user host  20  may be any type of termination point in a network connection, including but not limited to a desktop computer, a server, a laptop, a mobile telephone, or any other type of device that can receive or establish a connection with a remote node, such as mail server  45  or web server  50 . Gateway  25  may control communications between user host  20  and other network nodes attached to Internet  15 , and may be representative of or include a firewall, intrusion prevention system (IPS), or other security application to block unauthorized access while permitting authorized communications. Policy server  20  may be used to manage user hosts, including user host  20 , and to administer and distribute network policies. Thus, in this example embodiment, user host  20  may communicate with servers attached to Internet  15 , such as mail server  45  or web server  50 , only by establishing a connection through network gateway  25  if permitted by policies implemented in gateway  25 . Datacenter  35  is representative of any storage device or devices, or any virtualized storage device or devices, accessible to user host  20  over a network connection. NDLP  40  is representative of any server that can index content found at rest in network environment  10 . 
     Each of the elements of  FIG. 1  may couple to one another through simple interfaces or through any other suitable connection (wired or wireless), which provides a viable pathway for network communications. Additionally, any one or more of these elements may be combined or removed from the architecture based on particular configuration needs. Network environment  10  may include a configuration capable of transmission control protocol/Internet protocol (TCP/IP) communications for the transmission or reception of packets in a network. Network environment  10  may also operate in conjunction with a user datagram protocol/IP (UDP/IP) or any other suitable protocol where appropriate and based on particular needs. 
     For purposes of illustrating the techniques for providing network security in example embodiments, it is important to understand the activities occurring within a given network. The following foundational information may be viewed as a basis from which the present disclosure may be properly explained. Such information is offered earnestly for purposes of explanation only and, accordingly, should not be construed in any way to limit the broad scope of the present disclosure and its potential applications. 
     Typical network environments used in organizations and by individuals include the ability to communicate electronically with other networks using the Internet, for example, to access web pages hosted on servers connected to the Internet, to send or receive electronic mail (i.e., email) messages, or to exchange files. Malicious users are continuously developing new tactics for using the Internet to spread malware and to gain access to confidential information. Malware may subvert a host and use it for malicious activity, such as spamming or information theft. Of course, malware is not a prerequisite to information theft. Individuals can also be compromised and intentionally transmit (or attempt to transmit) information in violation of applicable laws and/or policies. Information may also be transmitted inadvertently in violation of such laws and policies. 
     In some instances, malware may be used to deceive a person by using a different network protocol exchange than the person expects. The malware may be packaged so as to convince the person to allow access to run it in some innocuous way, thus allowing it access to the network, which often may require passing through a firewall or other security measure. The malware may then exploit the access to engage in alternative or additional activities not contemplated by the person. For example, a game may send email messages or a word processor may open a web connection. At the same time, the malware may also use standard protocols to deceive the firewall into permitting the malware to establish remote connections. 
     Botnets, for example, use malware and are an increasing threat to computer security. In many cases they employ sophisticated attack schemes that include a combination of well-known and new vulnerabilities. Botnets generally use a client-server architecture where a type of malicious software (i.e., a bot) is placed on a host computer and communicates with a command and control (C&amp;C) server, which may be controlled by a malicious user (e.g., a botnet operator). Usually, a botnet is composed of a large number of bots that are controlled by the operator using a C&amp;C protocol through various channels, including Internet Relay Chat (IRC) and peer-to-peer (P2P) communication. The bot may receive commands from the C&amp;C server to perform particular malicious activities and, accordingly, may execute such commands. The bot may also send any results or pilfered information back to the C&amp;C server. A bot is often designed to initiate communication with the C&amp;C server and to masquerade as normal web browser traffic. For example, a bot may use a port typically used to communicate with a web server. Such bots, therefore, may not be detected by existing technologies without performing more detailed packet inspection of the web traffic. Moreover, once a bot is discovered, the botnet operator may simply find another way to masquerade network traffic by the bot to continue to present as normal web traffic. More recently, botnet operators have crafted bots to use encryption protocols such as, for example, secure socket layer (SSL), thereby encrypting malicious network traffic. Such encrypted traffic may use a Hypertext Transfer Protocol Secure (HTTPS) port such that only the endpoints involved in the encrypted session can decrypt the data. Thus, existing firewalls and other network intrusion prevention technologies may be unable to perform any meaningful inspection of the web traffic and bots continue to infect host computers within networks. 
     Other software security technology focused on preventing unauthorized program files from executing on a host computer may have undesirable side effects for end users or employees of a business or other organizational entity. Network or Information Technology (IT) administrators may be charged with crafting extensive policies relevant to all facets of the business entity to enable employees to exchange information with desirable and trusted network resources. Without extensive policies in place, employees may be prevented from downloading or sending data from network resources that are not specifically authorized, even if such software and other data facilitate legitimate and necessary business activities. Such systems may be so restrictive that if unauthorized software is found on a host computer, any host computer activities may be suspended pending network administrator intervention. Moreover, at the network level there may simply be too many applications to effectively track and incorporate into policies. Large whitelists or blacklists can be difficult to maintain and may degrade network performance, and some applications may not be susceptible to easy identification. 
     In accordance with one embodiment, network environment  10  can overcome these shortcomings (and others) by tagging files based on content and sharing content tags with a network gateway. In particular embodiments, data may be scanned and a classification policy may be applied to tag data based on content. The content tags may be shared with a network gateway, and the network gateway may filter network traffic based on the content tags. Session information may also be shared with the network gateway, which may further filter network traffic based on the session information. Information may be shared, for example, through an in-band or out-of-band protocol that allows a host agent to communicate with a network gateway to collectively and mutually achieve better security. 
     In some embodiments, a host agent may provide content tags to a network gateway, while in other embodiments content tags may be provided by an external source such as a data-at-rest (DAR) server. For example, in some embodiments, a DAR server such as NDLP  40  may periodically scan and index files in a datacenter, apply a classification policy to identify appropriate content tags for each files, and create a map between files and content tags. In other example embodiments, a host agent or DAR server may periodically scan and index files on a host, apply a classification policy, and map files to content tags. In still other embodiments, a host agent can scan a file as it is accessed to determine appropriate content tags. A gateway may receive content tags (e.g., from a DAR server, a host agent, or a content tag server) and filter a file transfer based on the content tag. A host agent or other server may also classify content associated with an in-bound transfer and provide a content tag to the gateway to filter in-bound transfers. 
     In another particular example, session descriptors may be shared along with content tags. Session descriptors generally include information about a host and an application associated with a given network session. For example, a session descriptor may include a UUID associated with the host and the user credentials of a process owner. Since a user can run separate processes with different user credentials, such information may be particularly advantageous for Citrix and terminal services. A session descriptor may additionally include a filename, pathname or other unique identifier of an application file (e.g., C:\ . . . \WINWORD.EXE) that is running the process attempting to establish a network connection. For example, in some embodiments the application may be identified by a hash function of the application&#39;s executable file, so as to make it more difficult for a malicious user to spoof the application name. A gateway may correlate this information with an application identifier or protocol to ensure that the application is performing as expected. 
     In some instances, a process may be attempting to transfer information in or out of the network, and a session description may also include a unique identifier associated with the information (e.g., a hash of a file). A session descriptor may also contain information about the host environment, such as software installed on the host and the current configuration and state of the software, permitting the gateway to act as a network access control device. For example, a session descriptor may indicate whether the local anti-virus system is up to date and running. If host-based data loss prevention (HDLP) software is available, a session descriptor may also include file typing information for file transfer. HDLP normally determines the type of file being transmitted out of the network (e.g., PDF, Word, etc.). The gateway may have additional policies about certain file types being transmitted over particular protocols, which may not be visible directly to an HDLP program. 
     The host agent may understand an application on the host as an executable file that is running a process with specific authentication, for example, while the network gateway may understand the application as a protocol in a TCP connection, which may also be correlated to a particular user authentication. The host agent may share session descriptors with the network gateway, and the network gateway may share network policy with the host agent as needed to correlate application activities with expected network behavior. Network policy may include elements of security policy as well as other network specific parameters, such as quality of service (QoS) and routing. A host agent may also be associated with a universally unique identifier (UUID), which can be used to correlate connections and activities originating behind network address translators. 
     A host agent may also notify the gateway of additional network connections to the host. If a host has both wireless and wired connections active simultaneously, for example, there may be a risk of data received on one connection being transmitted on the other, so it may be desirable to restrict access to sensitive data. A host agent may also notify the gateway if the connection is associated with a virtual machine. A host agent may also notify the gateway if the host has mountable read/write media, such as a USB stick attached. 
     Dynamic information sharing may be provided in network environment  10 . Communications between a user host and a network gateway may be encoded in routine network traffic (e.g., IP or TCP options fields, packet padding locations, or trailers on DNS packets), or transmitted in a separate network packet from the host to the network gateway as each connection starts. In some embodiments, a network gateway may send a UDP packet containing a randomly chosen sequence number or nonce to a user host on the user host&#39;s first egress. On each TCP open of a permitted connection, the user host agent may format a hash of the current nonce and sequence ID, place it in the packet along with other session descriptors. A hash of packet contents may also be included in certain embodiments. The network gateway may receive the UDP packet and save the session descriptors to use in applying network policy to the TCP stream. The network gateway may send a new nonce periodically to discourage replay attacks. 
     In some embodiments of network environment  10 , user host  20  may include multiple attachment points, causing it to have multiple IP addresses. In other embodiments, user host  20  may use the IP version 6 (IPv6), perhaps including Privacy Extensions (RFC4941), causing it to have one or more registered and known IPv6 addresses and one or more hidden or private IPv6 addresses. In these embodiments, gateway  25  may readily use dynamic information sharing to discover the user to host mapping for all the addresses on user host  20 . 
     This dynamic information sharing in network environment  10  may provide several benefits over conventional architectures. For example, by coordinating firewall policy with a host agent, a gateway can apply policy based on user identifier, content classification, application identifier, or any combination thereof. Moreover, only applications that need to be granularly controlled need to be controlled by the gateway. Thus, the gateway may control arbitrary or evasive applications, provide higher effective throughput, and control mobile-user traffic. In addition, traffic that does not need to be completely allowed or denied can be rate-limited. Arbitrary or evasive applications can also be rate-limited with process information available on a gateway, and differentiated services can be provided for managed and unmanaged hosts. 
     Turning to  FIG. 2 ,  FIG. 2  is a simplified block diagram illustrating additional details that may be associated with one potential embodiment of network environment  10 .  FIG. 2  includes Internet  15 , user host  20 , network gateway  25 , policy server  30 , datacenter  35 , NDLP  40 , and mail server  35 . Each of user host  20 , network gateway  25 , policy server  30 , datacenter  35 , and NDLP  40  may include a respective processor  50   a - 50   e  and a respective memory element  55   a - 5   e , and may additionally include various hardware, firmware, and/or software elements to facilitate operations described herein. More particularly, user host  20  may include a mail client  60 , a network stack  65 , a policy agent  70 , a firewall agent  75 , and an application  80 . Gateway  25  may include a firewall module  85 , and policy server  30  may include a firewall connector module  90 . Datacenter  35  may also store and provide access to documents, files, and other data, such as document  95 . NDLP  40  may include a scanning module  100 , a content tag map  105 , and a content tag server  110 . 
     In general, scanning module  100  can scan data found at rest in network environment  10 , particularly in datacenter  35 , apply a content tagging policy to identify content for tagging, and index the content and associated tags in a repository, such as content tag map  105 . A content tag may be any indicator reflective of content in a file, such as source code, trade secrets or other intellectual property, financial reports, or strategic business plans, for example. A “file” in this context refers broadly to any block of electronically stored data, including without limitation text documents, spreadsheets, images, databases, email messages, source code, and executable files. A content tag may additionally or alternatively be indicative of content sensitivity, such as public domain, confidential, proprietary, top secret, or export controlled, for example. Content tag server  110  is representative of any server that can process queries for content tags based on a hash or other unique identifier, retrieve the content tags from a content tag map, such as content tag map  105 , and return the results. In some embodiments, as in  FIG. 2 , scanning module  100  and content tag server  110  may be co-located in a single element, but may be distributed in other embodiments. 
     In one example implementation, user host  20 , network gateway  25 , policy server  30 , and/or NDLP  40  are network elements, which are meant to encompass network appliances, servers, routers, switches, gateways, bridges, loadbalancers, firewalls, processors, modules, or any other suitable device, component, element, or object operable to exchange information in a network environment. Network elements may include any suitable hardware, software, components, modules, interfaces, or objects that facilitate the operations thereof. This may be inclusive of appropriate algorithms and communication protocols that allow for the effective exchange of data or information. However, user host  20  may be distinguished from other network elements as it tends to serve as a terminal point for a network connection, in contrast to a gateway or router. 
     In regards to the internal structure associated with elements of network environment  10 , each of user host  20 , network gateway  25 , policy server  30 , datacenter  35 , and/or NDLP  40  can include memory elements (e.g., as shown in  FIG. 2 ) for storing information to be used in the operations outlined herein. Moreover, each element may include one or more interfaces, and such interfaces may also include appropriate memory elements. Each element may keep information in any suitable memory element (e.g., random access memory (RAM), read-only memory (ROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), application specific integrated circuit (ASIC), etc.), software, hardware, or in any other suitable component, device, element, or object where appropriate and based on particular needs. Any of the memory elements discussed herein should be construed as being encompassed within the broad term “memory element” or “memory.” Information being used, tracked, sent, or received could be provided in any database, register, queue, table, cache, control list, or other storage structure, all of which can be referenced at any suitable timeframe. Any such storage options may be included within the broad term “memory element” or “memory” as used herein. 
     In certain example implementations, the functions outlined herein may be implemented by logic encoded in one or more tangible media (e.g., embedded logic provided in an ASIC, digital signal processor (DSP) instructions, software (potentially inclusive of object code and source code) to be executed by a processor, or other similar machine, etc.), which may be inclusive of non-transitory media. In some of these instances, memory elements can store data used for the operations described herein. This includes the memory elements being able to store software, logic, code, or processor instructions that are executed to carry out the activities described herein. 
     In one example implementation, user host  20 , network gateway  25 , policy server  30 , datacenter  35 , and/or NDLP  40  may include firmware and/or software modules to achieve, or to foster, operations as outlined herein. In other embodiments, such operations may be carried out by hardware, implemented externally to these elements, or included in some other network device to achieve the intended functionality. Alternatively, these elements may include software (or reciprocating software) that can coordinate in order to achieve the operations, as outlined herein. In still other embodiments, one or all of these devices may include any suitable algorithms, hardware, firmware, software, components, modules, interfaces, or objects that facilitate the operations thereof. 
     Additionally, each of user host  20 , network gateway  25 , policy server  30 , datacenter  35 , and/or NDLP  40  may include one or more processors (or virtual processors) that can execute software or an algorithm to perform activities as discussed herein. A processor, virtual processor, logic unit, or other processing unit can execute any type of instructions associated with the data to achieve the operations detailed herein. In one example, a processor could transform an element or an article (e.g., data) from one state or thing to another state or thing. In another example, the activities outlined herein may be implemented with fixed logic or programmable logic (e.g., software/computer instructions executed by a processor) and the elements identified herein could be some type of a programmable processor, programmable digital logic (e.g., a field programmable gate array (FPGA), an EPROM, an EEPROM) or an ASIC that includes digital logic, software, code, electronic instructions, or any suitable combination thereof. Any of the potential processing elements, modules, and machines described herein should be construed as being encompassed within the broad term “processor.” 
       FIG. 3  is a simplified block diagram illustrating example operations associated with one embodiment of network environment  10  that can use content tags and session information to filter traffic. As a preliminary matter or periodically, NDLP  40  may scan servers in datacenter  35  at  302  and apply classification policy to classify content in datacenter  35 , including document  95 . For example, NDLP  40  may scan data for keywords or other criteria to determine an appropriate content tag or tags. NDLP  40  may further calculate a hash for such data and link, map, relate, or otherwise associate content tags with hashes, for example in content tag map  105 . Also preliminarily or periodically, firewall module  85  may request a key from firewall connector module  90  in policy server  30  at  304 . For this particular example, user host  20  also retrieves document  95  from datacenter  35  at  306 . At  308 , firewall connector module  90  can generate a key, and send it to firewall module  85  and to all hosts, including policy agent  70  on user host  20 . 
     At  310 , an application such as mail client  60  may initiate a connection to a remote server such as mail server  45 . Thus, for example, mail client  60  may attach document  95  to an e-mail message at  312  and initiate a connection to mail server  45  using simple mail transfer protocol (SMTP). Network stack  65  may then route the traffic through firewall module  85 . At  314 , firewall module  85  can then send a HELLO packet to firewall agent  75  on user host  20  as a request for a session descriptor. A HELLO packet may include, for example, a KEY value, a SEQNUM, and a HASH value. The SEQNUM may be used both as a nonce and a sequence number. The HASH value is generally a suitable crypto hash, such as SHA-1, on data in the message. Firewall agent  75  may then decrypt the request from firewall module  85 , obtain information from network stack  65 , and send a sequenced, hashed, encrypted packet containing a session descriptor to firewall module  80  at  316 . For example, if a user has been authenticated with an identification of “auser” and is using Microsoft Outlook as a mail client, then the session descriptor may contain: auser, Outlook, session info. This may be encrypted and transmitted along with a sequence number and has, as Enc[KEY](SEQNUM++, session descriptor, HASH). 
     In the example embodiment of  FIG. 3 , firewall module  85  may analyze the connection and determine that it includes a document transfer, calculate a hash for document  95 , and query NDLP  40  at  318  for a content tag based on the hash. Gateway  25  may also query a reputation service (not shown) that can provide a reputation score for the address of mail server  45 , and possibly the location of mail server  45  based on its address. The document may be buffered until a response is received, or only the last bit may be held, for example. In other example embodiments, though, an agent on user host  20  (e.g., policy agent  70  or firewall agent  75 ) may calculate the hash and query NDLP  40 . Firewall module  85  may apply network policies at  320 , based on the session description, content tag(s) associated with document  95 , reputation of mail server  45 , and/or the country associated with the IP address of mail server  45 , for example, to determine if the connection to mail server  45  should be allowed. Additional session descriptor packets may be sent at  322  without the need for firewall module  85  to send a HELLO packet, as in  314 . 
       FIG. 4  is a simplified block diagram illustrating example operations associated with another embodiment of network environment  10 . In  FIG. 4 , network environment  10  includes hosts  402   a - 402   b , a network address translator  404 , an intrusion prevention system (IPS)  406 , and Internet  15 . Host  402   a  is associated with a first UUID (UUID 1 ) and host  402   b  is associated with a second UUID (UUID 2 ). A session descriptor may be transmitted out-of-band or in-band through network address translator  404 , or alternatively, a session identifier may be transmitted in-band, while a session descriptor is transmitted out-of-band. In such an embodiment, the session descriptor can also include the session identifier for correlating the in-band and out-of-band communication. Although network address translator  404  may alter the IP addresses of hosts  402   a - 402   b , IPS  406  may use the UUIDs of hosts  402   a - 402   b  to correlate traffic so that network policy can be applied to a host based on all network addresses associated with the host. 
     Note further that host  402   a  may be used concurrently by multiple users in certain embodiments, as in a timesharing system, Microsoft Windows “Switch Users” capability, Citrix, or Microsoft Terminal Services. Firewall module  85  may use information in the session descriptor to pair each network connection with the user that established it, permitting policy to be implemented differently by user rather than singly for all users of host  402   a.    
       FIG. 5  is a simplified block diagram illustrating additional details that may be associated with other embodiments of network environment  10 . As a preliminary matter or periodically, NDLP  40  may scan servers in datacenter  35  at  502  and apply classification policy to classify (i.e., identify appropriate content tags) data in datacenter  35 , including document  95 . NDLP  40  may further calculate a hash for such data and map classifications with hashes, for example in content tag map  105 . At  504 , user host  20  may retrieve document  95  from datacenter  35 . A agent running on user host  20 , such as firewall agent  75 , can detect the transfer of document  95  to user host  20  and calculate a hash of document  95  at  506 , and query NDLP  40  at  508  for content tags associated with document  95  based on the hash. Modifications to document  95  may be monitored at  510 . A transfer of the modified document  95  may be initiated at  512 . In the example of  FIG. 5 , a transfer is initiated using a web distributed authoring and versioning (WebDAV) protocol, but any other suitable protocol may be used, including SMTP, a file transfer protocol (FTP), or a hypertext transfer protocol (HTTP), for example. 
     Firewall module  85  may exchange a session descriptor substantially as described above with reference to  FIG. 3 . Although a modified document  95  should no longer match a hash in hash classification map  105 , modified document  95  is a “tainted” version of original document  95  and thus retains the same content tags. A tainted file generally includes modified versions of any file having a content tag, and it may also include any other files that are modified, copied, encrypted, transferred, or otherwise used during the same session in which a tagged file is opened, read, accessed, or otherwise used. The host agent (e.g., firewall agent  75 ) can detect the transfer of the tainted file and transfer the content tags associated with document  95  to gateway  25  at  514 . In some embodiments, the content tags may be combined with the session descriptor. In  FIG. 5 , for instance, firewall module  85  may receive a session descriptor from user host  20  that identifies “Alice” as the user and WebDAV as the application, and may receive a content sensitivity tag of “Business_Confidential” for document  95  from firewall agent  75 . Firewall module  85  further queries a reputation service (not shown) that indicates the WebDAV server is located in Switzerland (i.e., CZ) and has a reputation score of 35. 
     Firewall module  85  may apply network policies at  516 , based on the session description, content tag associated with document  95 , reputation of the WebDAV server, and/or the country associated with the IP address of the target, for example, to determine if the transfer should be allowed at  518 . 
       FIG. 6  is a simplified block diagram illustrating additional details that may be associated with yet other embodiments of network environment  10 . As a preliminary matter or periodically, NDLP  40  may scan servers in datacenter  35  at  602  and apply classification policy to identify appropriate content tags for data in datacenter  35 , including document  95 . NDLP  40  may further calculate a hash for such data and map classifications with hashes, for example in content tag map  105 . At  604 , user host  20  may retrieve document  95  from datacenter  35 . A agent running on user host  20 , such as firewall agent  75 , can detect the transfer of document  95  to user host  20  and calculate a hash of document  95  at  606 , and query NDLP  40  at  608  for content tags associated with document  95  based on the hash. Files tainted by document  95  may be monitored at  610   a - 610   d . For example, application  80  may modify document  95  and save it as a document  95   a  on a file system  612 , which may be monitored at  610   a . An encryption application  614  may encrypt document  95   a  and save it as document  95   b , which can be monitored at  610   b . Yet another application, such as a secure copy program (SCP)  616  can then load document  95   b , which may be monitored at  610   c . This application (e.g., secure copy program  616 ) can initiate a transfer of document  95   b  over an encrypted connection at  618 . Although the document being transferred is both a modified and encrypted version of document  95 , it is a tainted version and firewall agent  75  can enforce the same classification (i.e., apply the same content tags). The host agent (e.g., firewall agent  75 ) can detect the transfer at  610   d  and transfer the content tags associated with document  95  to gateway  25  at  620 . Firewall module  85  may apply network policies at  622 , based on the session description, content tags associated with document  95 , reputation of the target or destination server, or the country associated with the IP address of the target, for example, to determine if the document extrusion should be allowed at  624 . 
     Note that with the examples provided above, as well as numerous other potential examples, interaction may be described in terms of two, three, or four network elements. However, this has been done for purposes of clarity and example only. In certain cases, it may be easier to describe one or more of the functionalities of a given set of operations by only referencing a limited number of network elements. It should be appreciated that network environment  10  is readily scalable and can accommodate a large number of components, as well as more complicated/sophisticated arrangements and configurations. Accordingly, the examples provided should not limit the scope or inhibit the broad teachings of network environment  10  as potentially applied to a myriad of other architectures. Additionally, although described with reference to particular scenarios, where a particular module, such as an analyzer module, is provided within a network element, these modules can be provided externally, or consolidated and/or combined in any suitable fashion. In certain instances, such modules may be provided in a single proprietary unit. 
     It is also important to note that the steps in the appended diagrams illustrate only some of the possible scenarios and patterns that may be executed by, or within, network environment  10 . Some of these steps may be deleted or removed where appropriate, or these steps may be modified or changed considerably without departing from the scope of teachings provided herein. In addition, a number of these operations have been described as being executed concurrently with, or in parallel to, one or more additional operations. However, the timing of these operations may be altered considerably. The preceding operational flows have been offered for purposes of example and discussion. Substantial flexibility is provided by network environment  10  in that any suitable arrangements, chronologies, configurations, and timing mechanisms may be provided without departing from the teachings provided herein. 
     Numerous other changes, substitutions, variations, alterations, and modifications may be ascertained to one skilled in the art and it is intended that the present disclosure encompass all such changes, substitutions, variations, alterations, and modifications as falling within the scope of the appended claims. In order to assist the United States Patent and Trademark Office (USPTO) and, additionally, any readers of any patent issued on this application in interpreting the claims appended hereto, Applicant wishes to note that the Applicant: (a) does not intend any of the appended claims to invoke paragraph six (6) of 35 U.S.C. section 112 as it exists on the date of the filing hereof unless the words “means for” or “step for” are specifically used in the particular claims; and (b) does not intend, by any statement in the specification, to limit this disclosure in any way that is not otherwise reflected in the appended claims.