Abstract:
A document accessible over a network can be registered. A registered document, and the content contained therein, cannot be transmitted undetected over and off of the network. In one embodiment, the invention includes maintaining a plurality of stored signatures, each signature being associated with one of a plurality of registered documents, intercepting an object being transmitted over a network, calculating a set of signatures associated with the intercepted object, and comparing the set of signatures with the plurality of stored signatures. In one embodiment, the invention can further include detecting registered content from the registered document being contained in the intercepted object, if the comparison results in a match of at least one of the signatures in the set of signatures with one or more of the plurality of stored signatures.

Description:
PRIORITY AND RELATED APPLICATIONS 
       [0001]    This application is a continuation (and claims the benefit of priority under 35 U.S.C. §120) of U.S. application Ser. No. 10/815,239, filed Mar. 30, 2004, entitled “DOCUMENT REGISTRATION,” Inventor(s) Ratinder Paul Singh Ahuja, et al. The disclosure of the prior application is considered part of (and is incorporated by reference in) the disclosure of this application. 
         [0002]    This patent application is related to, incorporates by reference, and claims the priority benefit of U.S. Provisional Application 60/528,631, entitled “DOCUMENT REGISTRATION”, filed Dec. 10, 2003. 
     
    
     FIELD OF THE INVENTION 
       [0003]    The present invention relates to computer networks, and in particular, to registering documents in a computer network. 
       BACKGROUND 
       [0004]    Computer networks and systems have become indispensable tools for modern business. Modern enterprises use such networks for communications and for storage. The information and data stored on the network of a business enterprise is often a highly valuable asset. Modern enterprises use numerous tools to keep outsiders, intruders, and unauthorized personnel from accessing valuable information stored on the network. These tools include firewalls, intrusion detection systems, and packet sniffer devices. However, once an intruder has gained access to sensitive content, there is no network device that can prevent the electronic transmission of the content from the network to outside the network. Similarly, there is no network device that can analyze the data leaving the network to monitor for policy violations, and make it possible to track down information leaks. What is needed is a comprehensive system to capture, store, and analyze all data communicated using the enterprise&#39;s network. 
       SUMMARY OF THE INVENTION 
       [0005]    A document accessible over a network can be registered. A registered document, and the content contained therein, cannot be transmitted undetected over and off of the network. In one embodiment, the invention includes maintaining a plurality of stored signatures, each signature being associated with one of a plurality of registered documents, intercepting an object being transmitted over a network, calculating a set of signatures associated with the intercepted object, and comparing the set of signatures with the plurality of stored signatures. In one embodiment, the invention can further include detecting registered content from the registered document being contained in the intercepted object, if the comparison results in a match of at least one of the signatures in the set of signatures with one or more of the plurality of stored signatures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements and in which: 
           [0007]      FIG. 1  is a block diagram illustrating a computer network connected to the Internet; 
           [0008]      FIG. 2  is a block diagram illustrating one configuration of a capture system according to one embodiment of the present invention; 
           [0009]      FIG. 3  is a block diagram illustrating the capture system according to one embodiment of the present invention; 
           [0010]      FIG. 4  is a block diagram illustrating an object assembly module according to one embodiment of the present invention; 
           [0011]      FIG. 5  is a block diagram illustrating an object store module according to one embodiment of the present invention; 
           [0012]      FIG. 6  is a block diagram illustrating an example hardware architecture for a capture system according to one embodiment of the present invention; 
           [0013]      FIG. 7  is a block diagram illustrating a document registration system according to one embodiment of the present invention; 
           [0014]      FIG. 8  is a block diagram illustrating registration module according to one embodiment of the present invention; and 
           [0015]      FIG. 9  is a flow diagram illustrating object capture processing according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Although the present system will be discussed with reference to various illustrated examples, these examples should not be read to limit the broader spirit and scope of the present invention. Some portions of the detailed description that follows are presented in terms of algorithms and symbolic representations of operations on data within a computer memory. These algorithmic descriptions and representations are the means used by those skilled in the computer science arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared and otherwise manipulated. 
         [0017]    It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers or the like. It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise, it will be appreciated that throughout the description of the present invention, use of terms such as “processing”, “computing”, “calculating”, determining”, “displaying” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system&#39;s registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. 
         [0018]    As indicated above, one embodiment of the present invention is instantiated in computer software, that is, computer readable instructions, which, when executed by one or more computer processors/systems, instruct the processors/systems to perform the designated actions. Such computer software may be resident in one or more computer readable media, such as hard drives, CD-ROMs, DVD-ROMs, read-only memory, read-write memory and so on. Such software may be distributed on one or more of these media, or may be made available for download across one or more computer networks (e.g., the Internet). Regardless of the format, the computer programming, rendering and processing techniques discussed herein are simply examples of the types of programming, rendering and processing techniques that may be used to implement aspects of the present invention. These examples should in no way limit the present invention, which is best understood with reference to the claims that follow this description. 
         [0019]    Networks 
         [0020]      FIG. 1  illustrates a simple prior art configuration of a local area network (LAN)  10  connected to the Internet  12 . Connected to the LAN  10  are various components, such as servers  14 , clients  16 , and switch  18 . There are numerous other known networking components and computing devices that can be connected to the LAN  10 . The LAN  10  can be implemented using various wireline or wireless technologies, such as Ethernet and 802.11b. The LAN  10  may be much more complex than the simplified diagram in  FIG. 1 , and may be connected to other LANs as well. 
         [0021]    In  FIG. 1 , the LAN  10  is connected to the Internet  12  via a router  20 . This router  20  can be used to implement a firewall, which are widely used to give users of the LAN  10  secure access to the Internet  12  as well as to separate a company&#39;s public Web server (can be one of the servers  14 ) from its internal network, i.e., LAN  10 . In one embodiment, any data leaving the LAN  10  towards the Internet  12  must pass through the router  20 . However, there the router  20  merely forwards packets to the Internet  12 . The router  20  cannot capture, analyze, and store, in a searchable manner, the content contained in the forwarded packets. 
         [0022]    One embodiment of the present invention is now illustrated with reference to  FIG. 2 .  FIG. 2  shows the same simplified configuration of connecting the LAN  10  to the Internet  12  via the router  20 . However, in  FIG. 2 , the router  20  is also connected to a capture system  22 . In one embodiment, the router  20  splits the outgoing data stream, and forwards one copy to the Internet  12  and the other copy to the capture system  22 . 
         [0023]    There are various other possible configurations. For example, the router  20  can also forward a copy of all incoming data to the capture system  22  as well. Furthermore, the capture system  22  can be configured sequentially in front of, or behind the router  20 , however this makes the capture system  22  a critical component in connecting to the Internet  12 . In systems where a router  20  is not used at all, the capture system can be interposed directly between the LAN  10  and the Internet  12 . In one embodiment, the capture system  22  has a user interface accessible from a LAN-attached device, such as a client  16 . 
         [0024]    In one embodiment, the capture system  22  intercepts all data leaving the network. In other embodiments, the capture system can also intercept all data being communicated inside the network  10 . In one embodiment, the capture system  22  reconstructs the documents leaving the network  10 , and stores them in a searchable fashion. The capture system  22  can then be used to search and sort through all documents that have left the network  10 . There are many reasons such documents may be of interest, including network security reasons, intellectual property concerns, corporate governance regulations, and other corporate policy concerns. 
         [0025]    Capture System 
         [0026]    One embodiment of the present invention is now described with reference to  FIG. 3 .  FIG. 3  shows one embodiment of the capture system  22  in more detail. The capture system  22  is also sometimes referred to as a content analyzer, content or data analysis system, and other similar names. In one embodiment, the capture system  22  includes a network interface module  24  to receive the data from the network  10  or the router  20 . In one embodiment, the network interface module  24  is implemented using one or more network interface cards (NIC), e.g., Ethernet cards. In one embodiment, the router  20  delivers all data leaving the network to the network interface module  24 . 
         [0027]    The captured raw data is then passed to a packet capture module  26 . In one embodiment, the packet capture module  26  extracts data packets from the data stream received from the network interface module  24 . In one embodiment, the packet capture module  26  reconstructs Ethernet packets from multiple sources to multiple destinations for the raw data stream. 
         [0028]    In one embodiment, the packets are then provided the object assembly module  28 . The object assembly module  28  reconstructs the objects being transmitted by the packets. For example, when a document is transmitted, e.g. as an email attachment, it is broken down into packets according to various data transfer protocols such as Transmission Control Protocol/Internet Protocol (TCP/IP) and Ethernet. The object assembly module  28  can reconstruct the document from the captured packets. 
         [0029]    One embodiment of the object assembly module  28  is now described in more detail with reference to  FIG. 4 . When packets first enter the object assembly module, they are first provided to a reassembler  36 . In one embodiment, the reassembler  36  groups—assembles—the packets into unique flows. For example, a flow can be defined as packets with identical Source IP and Destination IP addresses as well as identical TCP Source and Destination Ports. That is, the reassembler  36  can organize a packet stream by sender and recipient. 
         [0030]    In one embodiment, the reassembler  36  begins a new flow upon the observation of a starting packet defined by the data transfer protocol. For a TCP/IP embodiment, the starting packet is generally referred to as the “SYN” packet. The flow can terminate upon observation of a finishing packet, e.g., a “Reset” or “FIN” packet in TCP/IP. If now finishing packet is observed by the reassembler  36  within some time constraint, it can terminate the flow via a timeout mechanism. In an embodiment using the TCP protocol, a TCP flow contains an ordered sequence of packets that can be assembled into a contiguous data stream by the reassembler  36 . Thus, in one embodiment, a flow is an ordered data stream of a single communication between a source and a destination. 
         [0031]    The flow assembled by the reassembler  36  can then be provided to a protocol demultiplexer (demux)  38 . In one embodiment, the protocol demux  38  sorts assembled flows using the TCP Ports. This can include performing a speculative classification of the flow contents based on the association of well-known port numbers with specified protocols. For example, Web Hyper Text Transfer Protocol (HTTP) packets—i.e., Web traffic—are typically associated with port  80 , File Transfer Protocol (FTP) packets with port  20 , Kerberos authentication packets with port  88 , and so on. Thus in one embodiment, the protocol demux  38  separates all the different protocols in one flow. 
         [0032]    In one embodiment, a protocol classifier  40  also sorts the flows in addition to the protocol demux  38 . In one embodiment, the protocol classifier  40 —operating either in parallel or in sequence with the protocol demux  38 —applies signature filters to the flows to attempt to identify the protocol based solely on the transported data. Furthermore, the protocol demux  38  can make a classification decision based on port number which is subsequently overridden by protocol classifier  40 . For example, if an individual or program attempted to masquerade an illicit communication (such as file sharing) using an apparently benign port such as port  80  (commonly used for HTTP Web browsing), the protocol classifier  40  would use protocol signatures, i.e., the characteristic data sequences of defined protocols, to verify the speculative classification performed by protocol demux  38 . 
         [0033]    In one embodiment, the object assembly module  28  outputs each flow organized by protocol, which represent the underlying objects. Referring again to  FIG. 3 , these objects can then be handed over to the object classification module  30  (sometimes also referred to as the “content classifier”) for classification based on content. A classified flow may still contain multiple content objects depending on the protocol used. For example, protocols such as HTTP (Internet Web Surfing) may contain over 100 objects of any number of content types in a single flow. To deconstruct the flow, each object contained in the flow is individually extracted, and decoded, if necessary, by the object classification module  30 . 
         [0034]    The object classification module  30  uses the inherent properties and signatures of various documents to determine the content type of each object. For example, a Word document has a signature that is distinct from a PowerPoint document, or an Email document. The object classification module  30  can extract out each individual object and sort them out by such content types. Such classification renders the present invention immune from cases where a malicious user has altered a file extension or other property in an attempt to avoid detection of illicit activity. 
         [0035]    In one embodiment, the object classification module  30  determines whether each object should be stored or discarded. In one embodiment, this determination is based on a various capture rules. For example, a capture rule can indicate that Web Traffic should be discarded. Another capture rule can indicate that all PowerPoint documents should be stored, except for ones originating from the CEO&#39;s IP address. Such capture rules can be implemented as regular expressions, or by other similar means. 
         [0036]    In one embodiment, the capture rules are authored by users of the capture system  22 . The capture system  22  is made accessible to any network-connected machine through the network interface module  24  and user interface  34 . In one embodiment, the user interface  34  is a graphical user interface providing the user with friendly access to the various features of the capture system  22 . For example, the user interface  34  can provide a capture rule authoring tool that allows users to write and implement any capture rule desired, which are then applied by the object classification module  30  when determining whether each object should be stored. The user interface  34  can also provide pre-configured capture rules that the user can select from along with an explanation of the operation of such standard included capture rules. In one embodiment, the default capture rule implemented by the object classification module  30  captures all objects leaving the network  10 . 
         [0037]    If the capture of an object is mandated by the capture rules, the object classification module  30  can also determine where in the object store module  32  the captured object should be stored. With reference to  FIG. 5 , in one embodiment, the objects are stored in a content store  44  memory block. Within the content store  44  are files  46  divided up by content type. Thus, for example, if the object classification module determines that an object is a Word document that should be stored, it can store it in the file  46  reserved for Word documents. In one embodiment, the object store module  32  is integrally included in the capture system  22 . In other embodiments, the object store module can be external—entirely or in part—using, for example, some network storage technique such as network attached storage (NAS) and storage area network (SAN). 
         [0038]    In one embodiment, the content store is a canonical storage location, simply a place to deposit the captured objects. The indexing of the objects stored in the content store  44  is accomplished using a tag database  42 . In one embodiment, the tag database  42  is a database data structure in which each record is a “tag” that indexes an object in the content store  44 , and contains relevant information about the stored object. An example of a tag record in the tag database  42  that indexes an objected stored in the content store  44  is set forth in Table 1: 
         [0000]    
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Field Name 
                 Definition 
               
               
                   
               
             
             
               
                 MAC Address 
                 Ethernet controller MAC address unique to each 
               
               
                   
                 capture system 
               
               
                 Source IP 
                 Source Ethernet IP Address of object 
               
               
                 Destination IP 
                 Destination Ethernet IP Address of object 
               
               
                 Source Port 
                 Source TCP/IP Port number of object 
               
               
                 Destination Port 
                 Destination TCP/IP Port number of the object 
               
               
                 Protocol 
                 IP Protocol that carried the object 
               
               
                 Instance 
                 Canonical count identifying object within a protocol 
               
               
                   
                 capable of carrying multiple data within a single 
               
               
                   
                 TCP/IP connection 
               
               
                 Content 
                 Content type of the object 
               
               
                 Encoding 
                 Encoding used by the protocol carrying object 
               
               
                 Size 
                 Size of object 
               
               
                 Timestamp 
                 Time that the object was captured 
               
               
                 Owner 
                 User requesting the capture of object (rule author) 
               
               
                 Configuration 
                 Capture rule directing the capture of object 
               
               
                 Signature 
                 Hash signature of object 
               
               
                 Tag Signature 
                 Hash signature of all preceding tag fields 
               
               
                   
               
             
          
         
       
     
         [0039]    There are various other possible tag fields, and some embodiments can omit numerous tag fields listed in Table 1. In other embodiments, the tag database  42  need not be implemented as a database; other data structures can be used. The mapping of tags to objects can, in one embodiment, be obtained by using unique combinations of tag fields to construct an object&#39;s name. For example, one such possible combination is an ordered list of the Source IP, Destination IP, Source Port, Destination Port, Instance and Timestamp. Many other such combinations including both shorter and longer names are possible. In another embodiment, the tag can contain a pointer to the storage location where the indexed object is stored. 
         [0040]    Referring again to  FIG. 3 , in one embodiment, the objects and tags stored in the object store module  32  can be interactively queried by a user via the user interface  34 . In one embodiment the user interface can interact with a web server (not shown) to provide the user with Web-based access to the capture system  22 . The objects in the content store module  32  can thus be searched for specific textual or graphical content using exact matches, patterns, keywords, and various other advanced attributes. 
         [0041]    For example, the user interface  34  can provide a query-authoring tool (not shown) to enable users to create complex searches of the object store module  32 . These search queries can be provided to a data mining engine (not shown) that parses the queries, scans the tag database  42 , and retrieves the found object from the content store  44 . Then, these objects that matched the specific search criteria in the user-authored query can be counted and displayed to the user by the user interface  34 . 
         [0042]    Searches can also be scheduled to occur at specific times or at regular intervals, that is, the user interface  34  can provide access to a scheduler (not shown) that can periodically execute specific queries. Reports containing the results of these searches can be made available to the user at a later time, mailed to the administrator electronically, or used to generate an alarm in the form of an e-mail message, page, syslog or other notification format. 
         [0043]    In several embodiments, the capture system  22  has been described above as a stand-alone device. However, the capture system of the present invention can be implemented on any appliance capable of capturing and analyzing data from a network. For example, the capture system  22  described above could be implemented on one or more of the servers  14  or clients  16  shown in  FIG. 1 . The capture system  22  can interface with the network  10  in any number of ways, including wirelessly. 
         [0044]    In one embodiment, the capture system  22  is an appliance constructed using commonly available computing equipment and storage systems capable of supporting the software requirements. In one embodiment, illustrated by  FIG. 6 , the hardware consists of a capture entity  46 , a processing complex  48  made up of one or more processors, a memory complex  50  made up of one or more memory elements such as RAM and ROM, and storage complex  52 , such as a set of one or more hard drives or other digital or analog storage means. In another embodiment, the storage complex  52  is external to the capture system  22 , as explained above. In one embodiment, the memory complex stored software consisting of an operating system for the capture system device  22 , a capture program, and classification program, a database, a filestore, an analysis engine and a graphical user interface. 
         [0045]    Document Registration 
         [0046]    The capture system  22  described above can also be used to implement a document registration scheme. In one embodiment, the user can register a document with the system  22 , which can then alert the user if all or part of the content in the registered document is leaving the network. Thus, one embodiment of the present invention aims to prevent un-authorized documents of various formats (e.g., Microsoft Word, Excel, PowerPoint, source code of any kind, text) from leaving an enterprise. There are great benefits to any enterprise that can keep its intellectual property, or other critical, confidential, or otherwise private and proprietary content from being mishandled. 
         [0047]    In one embodiment of the present invention, sensitive documents are registered with the capture system  22 , although data registration can be implemented using a separate device in other embodiments. One embodiment of implementing registration capability in the capture system  22  is now described with reference to  FIG. 7 . For descriptive purposes, the capture system  22  is renamed the capture/registration system  22  in  FIG. 7 , and is also sometimes referred to as the registration system  22  in the description herein. The capture/registration system  22  has components similar or identical to the capture system  22  shown in  FIG. 3 , including the network interface module  24 , the object store module  32 , the user interface  34 , and the packet capture  26 , object assembly  28 , and object classification  30  modules, which are grouped together as object capture modules  31  in  FIG. 7 . 
         [0048]    In one embodiment, the capture/registration system  22  also includes a registration module  54  interacting with a signature database  56  to facilitate a registration scheme. In one embodiment, the user can register a document via the user interface  34 . There are numerous ways to register documents. For example, a document can be electrically mailed (e-mailed), or uploaded to the registration system  22 . The registration system  22  can also periodically scan a file server (registration server) for documents to be registered. The registration process can be integrated with the enterprise&#39;s document management systems. Document registration can also be automated and transparent based on registration rules, such as “register all documents,” or “register all documents by specific author or IP address,” and so on. 
         [0049]    After being received, in one embodiment, a document to be registered is passed to the registration module  54 . The registration module  54  calculates a signature of the document, or a set of signatures. The set of signatures associated with the document can be calculated in various ways. For example, the signatures can be made up of hashes over various portions of the document, such as selected or all pages, paragraphs, tables and sentences. Other possible signatures include, but are not limited to, hashes over embedded content, indices, headers or footers, formatting information or font utilization. The signatures can also include computations and meta-data other than hash digests, such as Word Relative Frequency Methods (RFM)—Statistical, Karp-Rabin Greedy-String-Tiling-Transposition, vector space models, and diagrammatic structure analysis. 
         [0050]    The set of signatures is then stored in the signature database  56 . The signature database  56  need not be implemented as a database; the signatures can be maintained using any appropriate data structure. In one embodiment, the signature database  56  is part of the storage complex  52  in  FIG. 6 . 
         [0051]    In one embodiment, the registered document is also stored as an object in the object store module  32 . In one embodiment, the document is only stored in the content store  44  with no associated tag, since many tag fields do not apply to registered documents. In one embodiment, one file of files  46  is a “Registered Documents” file. 
         [0052]    In one embodiment, the document received from the user is now registered. As set forth above, in one embodiment, the object capture modules  31  continue to extract objects leaving the network, and store various objects based on capture rules. In one embodiment, all extracted objects—whether subject to a capture rule or not—are also passed to the registration module for a determination whether each object is, or includes part of, a registered document. 
         [0053]    In one embodiment, the registration module  54  calculates the set of signatures of an object received from the object capture modules  31  in the same manner as of a document received from the user interface  34  to be registered. This set of signatures is then compared against all signatures in the signature database  56 . In other embodiment, parts of the signature database can be excluded from this search to save time. 
         [0054]    In one embodiment, an unauthorized transmission is detected if any one or more signatures in the set of signatures of an extracted object matches one or more signatures in the signature database  56  associated with a registered document. Other detection tolerances can be configured for different embodiment, e.g. at least two signatures must match. Also, special rules can be implemented that make the transmission authorized, e.g., if the source address is authorized to transmit any documents off the network. 
         [0055]    One embodiment of the registration module  54  is now described with reference to  FIG. 8 . A discussed above, a document to be registered  68  arrives via the user interface  34 . The registration engine  58  generates signatures  60  for the document  68  and forwards the document  68  to the content store  44  and the signatures  60  to the signature database  54 . The signatures  60  are associated with the document, e.g., by including a pointer to the document  68 , or to some attribute from which the document  68  can be identified. 
         [0056]    A captured object  70  arrives via the object capture modules  31 . The registration engine calculates the signatures  62  of the captured object, and forwards them to the search engine  64 . The search engine  64  queries the signature database  54  to compare the signatures  62  to the signatures stored in the signature database  54 . Assuming for the purposes of illustration, that the captured object  70  is a Word document that contains a pasted paragraph from registered PowerPoint document  68 , at least one signature of signatures  62  will match a signature of signatures  60 . Such an event can be referred to as the detection of an unauthorized transfer, a registered content transfer, or other similarly descriptive terms. 
         [0057]    In one embodiment, when a registered content transfer is detected, the transmission can be halted with or without warning to the sender. In one embodiment, in the event of a detected registered content transfer, the search engine  64  activates the notification module  66 , which sends an alert  72  to the user via the user interface  34 . In one embodiment, the notification module  66  sends different alerts—including different user options—based on the user preference associated with the registration, and the capabilities of the registration system  22 . 
         [0058]    In one embodiment, the alert  72  can simply indicate that the registered content, i.e., the captured object  70 , has been transferred off the network. In addition, the alert  72  can provide information regarding the transfer, such as source IP, destination IP, any other information contained in the tag of the captured object, or some other derived information, such as the name of the person who transferred the document off the network. The alert  72  can be provided to one or more users via e-mail, instant message (IM), page, or any other notification method. In one embodiment, the alert  72  is only sent to the entity or user who requested registration of the document  68 . 
         [0059]    In another embodiment, the delivery of the captured object  70  is halted—the transfer is not completed—unless the user who registered the document  68  consents. In such an embodiment, the alert  72  can contain all information described above, and in addition, contain a selection mechanism, such as one or two buttons—to allow the user to indicate whether the transfer of the captured object  70  may be completed. If the user elects to allow the transfer, for example because he is aware that someone is emailing a part of a registered document  68  (e.g., a boss asking his secretary to send an email), the transfer is executed and the object  70  is allowed to leave the network. 
         [0060]    If the user disallows the transfer, the captured object  70  is not allowed off the network, and delivery is permanently halted. In one embodiment, halting delivery can be accomplished by implementing an intercept technique by having the registration system  22  proxy the connection between the network and the outside. In other embodiments, delivery can be halted using a black hole technique—discarding the packets without notice if the transfer is disallowed—or a poison technique—inserting additional packets onto the network to cause the sender&#39;s connection to fail. 
         [0061]      FIG. 9  provides a flow chart to further illustrate object capture/intercept processing according to one embodiment of the present invention. All blocks of  FIG. 9  have already been discussed herein. The example object capture processing shown in  FIG. 9  assumes that various documents have already been registered with the registration system  22 . The process shown in  FIG. 9  can be repeated for all objects captured by the system  22 . 
         [0062]    Thus, a capture system and a document/content registration system have been described. In the foregoing description, various specific values were given names, such as “objects,” and various specific modules, such as the “registration module” and “signature database” have been described. However, these names are merely to describe and illustrate various aspects of the present invention, and in no way limit the scope of the present invention. Furthermore, various modules, such as the search engine  64  and the notification module  66  in  FIG. 8 , can be implemented as software or hardware modules, or without dividing their functionalities into modules at all. The present invention is not limited to any modular architectures either in software or in hardware, whether described above or not.