United States Patent [19J
`Touboul
`
`[54] SYSTEM AND METHOD FOR PROTECTING
`A COMPUTER AND A NETWORK FROM
`HOSTILE DOWNLOADABLES
`
`[75]
`
`Inventor: Shlomo Touboul, Kefar-Haim, Israel
`
`[73]
`[ * l
`
`Assignee: Finjan Software, Ltd., Netanya, Israel
`
`Notice:
`
`This patent issued on a continued pros(cid:173)
`ecution application filed under 37 CFR
`1.53( d), and is subject to the twenty year
`patent term provisions of 35 U.S.C.
`154(a)(2).
`
`[21] Appl. No.: 08/964,388
`
`[22] Filed:
`
`Nov. 6, 1997
`
`Related U.S. Application Data
`[60] Provisional application No. 60/030,639, Nov. 8, 1996.
`
`[51]
`
`Int. Cl? ........................................................ H04L l/00
`
`[52] U.S. Cl. .............................................................. 713/200
`
`[58] Field of Search ............................... 395/187.01, 186;
`713/200, 201, 202; 714/38, 704; 709/229
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`5,077,677 12/1991 Murphy et a!. ........................... 395/10
`5,361,359 11/1994 Tajalli et a!. ............................ 395/700
`1!1996 Gupta et a!. ............................ 395/186
`5,485,409
`1!1996 Chess eta!. ....................... 395/183.14
`5,485,575
`5,572,643 11/1996 Judson .................................... 395/793
`.............................. 395/187.01
`4/1997 Ji et a!.
`5,623,600
`5,638,446
`6/1997 Rubin ........................................ 380/25
`5,692,047 11/1997 McManis .................................... 380/4
`5,692,124 11/1997 Holden et a!. ..................... 395/187.01
`5,720,033
`2/1998 Deo ......................................... 395/186
`5,724,425
`3/1998 Chang eta!. ............................. 380/25
`5,740,248
`4/1998 Fieres eta!. .............................. 380/25
`6/1998 van Hoff eta!. .................. 395/200.53
`5,761,421
`5,765,205
`6/1998 Breslau eta!. .......................... 711!203
`7/1998 Devarakonda eta!. .................... 380/4
`5,784,459
`5,796,952
`8/1998 Davis eta!. ....................... 395/200.54
`...................... 395/200.32
`9/1998 Cohen et a!.
`5,805,829
`5,832,208 11/1998 Chen et a!.
`........................ 395/187.01
`5,850,559 12/1998 Angelo et a!. ..................... 395!750.03
`
`111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US006092194A
`[11] Patent Number:
`[45] Date of Patent:
`
`6,092,194
`*Jul. 18, 2000
`
`5,864,683
`5,892,904
`
`1!1999 Boebert eta!. .................... 395/200.79
`4/1999 Atkinson et a!. .................. 395/187.01
`
`OTHER PUBLICATIONS
`
`http://iel.ihs.com:80/cgi-bin/iel_
`page:
`Web
`cgi?se ... 2ehts%26ViewTemplate%3ddocvie%5fb%2ehts,
`Okamato, E. et al., "ID-Based Authentication System For
`Computer Virus Detection", IEEE/IEE Electronic Library
`online, Electronics Letters, vol. 26, Issue 15, ISSN
`0013-5194, Jul. 19, 1990, Abstract and pp. 1169-1170.
`
`(List continued on next page.)
`
`Primary Examiner-Robert W. Beausoliel, Jr.
`Assistant Examiner-Christopher Revak
`Attorney, Agent, or Firm--Graham & James LLP
`
`[57]
`
`ABSTRACT
`
`A system protects a computer from suspicious Download(cid:173)
`abies. The system comprises a security policy, an interface
`for receiving a Downloadable, and a comparator, coupled to
`the interface, for applying the security policy to the Down(cid:173)
`loadable to determine if the security policy has been vio(cid:173)
`lated. The Downloadable may include a Java™ applet, an
`ActiveX™ control, a JavaScript™ script, or a Visual Basic
`script. The security policy may include a default security
`policy to be applied regardless of the client to whom the
`Downloadable is addressed, or a specific security policy to
`be applied based on the client or the group to which the
`client belongs. The system uses an ID generator to compute
`a Downloadable ID identifying the Downloadable,
`preferably, by fetching all components of the Downloadable
`and performing a hashing function on the Downloadable
`including the fetched components. Further, the security
`policy may indicate several tests to perform, including (1) a
`comparison with known hostile and non-hostile Download(cid:173)
`abies; (2) a comparison with Downloadables to be blocked
`or allowed per administrative override; (3) a comparison of
`the Downloadable security profile data against access con(cid:173)
`trol lists; ( 4) a comparison of a certificate embodied in the
`Downloadable against trusted certificates; and (5) a com(cid:173)
`parison of the URL from which the Downloadable origi(cid:173)
`nated against trusted and untrusted URLs. Based on these
`tests, a logical engine can determine whether to allow or
`block the Downloadable.
`
`68 Claims, 10 Drawing Sheets
`
`655
`
`~
`
`f
`
`--:68
`~
`ob
`
`Blue Coat Systems - Exhibit 1086
`
`

`
`6,092,194
`Page 2
`
`01HER PUBLICATIONS
`
`"Finjan Announces a Personal Java TM Firewall For Web
`Browsers-the SurfinShield™ 1.6", Press Release of Finjan
`Releases SurfinShield, Oct. 21, 1996, 2 pages.
`"Finjan Software Releases SurfinBoard, Industry's First
`JAVA Security Product For the World Wide Web", Article
`published on the Internet by Finjan Software, Ltd., Jul. 29,
`1996, 1 page.
`"Powerful PC Security for the New World of Java™ and
`Downloadables, Surfin Shield™"Article published on the
`Internet by Finjan Software Ltd., 1996, 2 Pages.
`"Company Profile Finjan-Safe Surfing, The Java Security
`Solutions Provider" Article published on the Internet by
`Finjan Software Ltd., Oct. 31, 1996, 3 pages.
`"Finjan Announces Major Power Boost and New Features
`for SurfinShield™ 2.0" Las Vegas Convention Center/Pa(cid:173)
`villion 5 P5551, Nov. 18, 1996, 3 pages.
`
`"Java Security: Issues & Solutions" Article published on the
`Internet by Finjan Software Ltd., 1996, 8 pages.
`"Products" Article published on the Internet, 7 pages.
`Mark LaDue, "Online Business Consultant" Article pub(cid:173)
`lished on the Internet, Home Page, Inc. 1996, 4 pages.
`
`Jim K. Omura, "Novel Applications of Cryptography in
`Digital Communications", IEEE Communications Maga(cid:173)
`zine, p 27, May 1990.
`Norvin Leach et al, "IE 3.0 applets will earn certification",
`PC Week, v13, n29, p1(2), Jul. 1996.
`
`Microsoft Authenticode Technology, "Ensuring Account(cid:173)
`ability and Authenticity for Software Components on the
`Internet", Microsoft Corporation, Oct. 1996.
`
`Frequently Asked Questions About Authenticode, Microsoft
`Corporation, Feb. 1997.
`
`

`
`U.S. Patent
`
`Jul. 18, 2000
`
`Sheet 1 of 10
`
`6,092,194
`
`100
`~
`
`125
`
`110
`
`Internal Network
`Security System
`
`130
`
`115
`
`Internal Computer Network
`
`135
`
`120
`
`Security
`Management
`Console
`
`FIG. 1
`
`

`
`From
`External Computer
`Network 105
`
`External
`Communications
`Interface
`
`205 ;
`
`CPU
`
`225 ;
`
`Internal
`Communications
`Interface
`
`130 v
`
`To
`External Computer
`Network 115
`
`230 ;
`
`Data Storage
`Device
`
`Security
`Database
`
`I Events Log
`
`I
`
`Users
`
`240
`v-___./
`245
`
`r--;60
`r__/
`
`d •
`\Jl
`•
`
`110
`
`~
`
`215 ;
`
`1/0 Interfaces
`
`220
`
`!
`235 ;
`
`RAM
`
`Security
`Program
`
`Operating
`System
`
`255
`/___./
`
`250
`
`v__/
`
`FIG. 2
`
`

`
`Security Database
`
`307
`
`309
`
`I
`I 240
`I
`~
`
`300
`
`d •
`\Jl
`•
`
`305
`
`Security Policies
`
`315
`
`317
`
`320
`
`Path 1
`-----+-
`
`Path 2 - .
`
`ACL
`
`330
`
`325
`
`Code
`Scanner
`
`ID
`Generator
`
`Policy
`Finder
`
`r-
`1
`I
`I
`User ID, 1
`URL I
`Received :
`Downloadable 1
`I
`
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`335
`I
`350
`I
`------------------------------------------------------------1
`FIG. 3
`
`Scanner
`
`340
`
`Path 4
`-----+-
`URL
`Comparator
`
`Record
`keeping
`En
`
`I
`I
`I
`I
`I
`I Nonsuspicious
`: Downloadable
`I
`I
`
`245
`
`

`
`U.S. Patent
`
`Jul. 18, 2000
`
`Sheet 4 of 10
`
`6,092,194
`
`Security Policies
`305
`
`~
`
`405
`
`410
`
`415
`
`420
`
`Policy Selectors
`
`Access Control
`Lists
`
`Trusted
`Certificate Lists
`
`URL Rule Bases
`
`Lists of Downloadables
`to Allow or Block per
`Administrative Override
`
`FIG. 4
`
`

`
`U.S. Patent
`
`Jul. 18, 2000
`
`Sheet 5 of 10
`
`6,092,194
`
`120
`
`~
`
`To/From
`Internal Computer
`Network
`
`~5
`
`505
`~.
`
`Security
`Policy Editor
`
`FIG. 5
`
`510
`
`515
`~
`
`Event Log
`Analysts
`Engine
`
`User
`Notification
`Engine
`
`

`
`U.S. Patent
`
`Jul. 18, 2000
`
`Sheet 6 of 10
`
`6,092,194
`
`600
`
`~
`
`602
`
`Receive Downloadable
`
`Generate Downloadable ID
`
`606
`
`No
`
`612
`
`Send results to
`Logical Engine
`
`FIG. 6A
`
`

`
`U.S. Patent
`
`Jul. 18, 2000
`
`Sheet 7 of 10
`
`6,092,194
`
`606
`
`~
`
`No
`
`Yes
`
`Fetch the generic
`security policy for
`User 10
`
`652
`
`654
`
`Fetch the policy
`for
`User 10 and
`Downloadable
`
`FIG. 68
`
`

`
`U.S. Patent
`
`Jul. 18, 2000
`
`Sheet 8 of 10
`
`6,092,194
`
`655
`
`~
`
`Receive Results from First
`Comparator, ACL
`Comparator, Certificate
`Comparator and URL
`Comparator
`
`Compare Results with
`Security Policies
`
`660
`
`662
`
`664
`
`Yes
`
`666
`
`670
`
`Pass Downloadable
`
`Stop Downloadable
`
`Record Findings
`
`End
`
`Send Substitute
`Downloadble to
`Inform The User
`
`668
`
`FIG. 6C
`
`

`
`U.S. Patent
`
`Jul. 18, 2000
`
`Sheet 9 of 10
`
`6,092,194
`
`628
`
`705
`
`710
`
`715
`
`720
`
`Start
`
`Disassemble the Machine
`Code
`
`Resolve a Respective
`Command in The Code
`
`Decode and Register The
`Command and The
`Command Parameters as
`DSP Data
`
`No
`
`FIG. 7
`
`

`
`U.S. Patent
`
`Jul. 18, 2000
`
`Sheet 10 of 10
`
`6,092,194
`
`800
`
`~
`
`Start
`
`Receive a Downloadable vJ
`
`81 0
`
`Fetch Downloadable vJ
`
`Components
`
`8 20
`
`Include Fetched Components in vJ
`
`The Downloadable
`
`8 30
`
`Perform a Hashing Function on ~
`
`the Downloadable to Generate
`a Downloadable ID
`
`8 40
`
`Store the Downloadable ID vJ
`
`8 50
`
`End
`
`FIG. 8
`
`

`
`6,092,194
`
`1
`SYSTEM AND METHOD FOR PROTECTING
`A COMPUTER AND A NETWORK FROM
`HOSTILE DOWNLOADABLES
`
`INCORPORATION BY REFERENCE TO
`RELATED APPLICATION
`
`This application hereby incorporates by reference related
`U.S. patent application Ser. No. 08/790,097, entitled "Sys(cid:173)
`tem and Method for Protecting a Client from Hostile
`Downloadables," filed on Jan. 29, 1997, by inventor Shlomo
`Touboul.
`
`PRIORITY REFERENCE TO PROVISIONAL
`APPLICATION
`
`This application claims benefit of and hereby incorporates
`by reference provisional application Ser. No. 60/030,639,
`entitled "System and Method for Protecting a Computer
`from Hostile Downloadables," filed on Nov. 8, 1996, by
`inventor Shlomo Touboul.
`
`BACKGROUND OF THE INVENTION
`
`10
`
`2
`security policy may include a default security policy to be
`applied regardless of the client to whom the Downloadable
`is addressed, a specific security policy to be applied based on
`the client or the group to which the client belongs, or a
`5 specific policy to be applied based on the client/group and on
`the particular Downloadable received. The system uses an
`ID generator to compute a Downloadable ID identifying the
`Downloadable, preferably, by fetching all components of the
`Downloadable and performing a hashing function on the
`Downloadable including the fetched components.
`Further, the security policy may indicate several tests to
`perform, including (1) a comparison with known hostile and
`non-hostile Downloadables; (2) a comparison with Down(cid:173)
`loadables to be blocked or allowed per administrative over(cid:173)
`ride; (3) a comparison of the Downloadable security profile
`15 data against access control lists; ( 4) a comparison of a
`certificate embodied in the Downloadable against trusted
`certificates; and (5) a comparison of the URL from which the
`Downloadable originated against trusted and untrusted
`URLs. Based on these tests, a logical engine can determine
`20 whether to allow or block the Downloadable.
`The present invention further provides a method for
`protecting a computer from suspicious Downloadables. The
`method comprises the steps of receiving a Downloadable,
`comparing the Downloadable against a security policy to
`determine if the security policy has been violated, and
`discarding the Downloadable if the security policy has been
`violated.
`It will be appreciated that the system and method of the
`present invention may provide computer protection from
`known hostile Downloadables. The system and method of
`the present invention may identify Downloadables that
`perform operations deemed suspicious. The system and
`method of the present invention may examine the Down-
`loadable code to determine whether the code contains any
`suspicious operations, and thus may allow or block the
`Downloadable accordingly.
`
`25
`
`1. Field of the Invention
`This invention relates generally to computer networks,
`and more particularly provides a system and method for
`protecting a computer and a network from hostile Down(cid:173)
`loadables.
`2. Description of the Background Art
`The Internet is currently a collection of over 100,000 30
`individual computer networks owned by governments,
`universities, nonprofit groups and companies, and is expand(cid:173)
`ing at an accelerating rate. Because the Internet is public, the
`Internet has become a major source of many system dam(cid:173)
`aging and system fatal application programs, commonly 35
`referred to as "viruses."
`Accordingly, programmers continue to design computer
`and computer network security systems for blocking these
`viruses from attacking both individual and network com(cid:173)
`puters. On the most part, these security systems have been 40
`relatively successful. However, these security systems are
`not configured to recognize computer viruses which have
`been attached to or configured as Downloadable application
`programs, commonly referred to as "Downloadables." A
`Downloadable is an executable application program, which 45
`is downloaded from a source computer and run on the
`destination computer. Downloadable is typically requested
`by an ongoing process such as by an Internet browser or web
`engine. Examples of Downloadables include Java™ applets
`designed for use in the Java™ distributing environment 50
`developed by Sun Microsystems, Inc., JavaScript scripts
`also developed by Sun Microsystems, Inc., ActiveX™ con(cid:173)
`trols designed for use in the ActiveX™ distributing envi(cid:173)
`ronment developed by the Microsoft Corporation, and
`Visual Basic also developed by the Microsoft Corporation. 55
`Therefore, a system and method are needed to protect a
`network from hostile Downloadables.
`
`SUMMARY OF THE INVENTION
`The present invention provides a system for protecting a 60
`network from suspicious Downloadables. The system com(cid:173)
`prises a security policy, an interface for receiving a
`Downloadable, and a comparator, coupled to the interface,
`for applying the security policy to the Downloadable to
`determine if the security policy has been violated. The 65
`Downloadable may include a Java™ applet, an ActiveX™
`control, a JavaScript™ script, or a Visual Basic script. The
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a block diagram illustrating a network system,
`in accordance with the present invention;
`FIG. 2 is a block diagram illustrating details of the
`internal network security system of FIG. 1;
`FIG. 3 is a block diagram illustrating details of the
`security program and the security database of FIG. 2;
`FIG. 4 is a block diagram illustrating details of the
`security policies of FIG. 3;
`FIG. 5 is a block diagram illustrating details of the
`security management console of FIG. 1;
`FIG. 6Ais a flowchart illustrating a method of examining
`for suspicious Downloadables, in accordance with the
`present invention;
`FIG. 6B is a flowchart illustrating details of the step for
`finding the appropriate security policy of FIG. 6A;
`FIG. 6C is a flowchart illustrating a method for determin(cid:173)
`ing whether an incoming Downloadable is to be deemed
`suspicious;
`FIG. 7 is a flowchart illustrating details of the FIG. 6 step
`of decomposing a Downloadable; and
`FIG. 8 is a flowchart illustrating a method 800 for
`generating a Downloadable ID for identifying a Download(cid:173)
`able.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`FIG. 1 is a block diagram illustrating a network system
`100, in accordance with the present invention. The network
`
`

`
`6,092,194
`
`10
`
`3
`system 100 includes an external computer network 105,
`such as the Wide Area Network (WAN) commonly referred
`to as the Internet, coupled via a communications channel
`125 to an internal network security system 110. The network
`system 100 further includes an internal computer network
`115, such as a corporate Local Area Network (LAN),
`coupled via a communications channel 130 to the internal
`network computer system 110 and coupled via a communi(cid:173)
`cations channel135 to a security management console 120.
`The internal network security system 110 examines
`Downloadables received from external computer network
`105, and prevents Downloadables deemed suspicious from
`reaching the internal computer network 115. It will be
`further appreciated that a Downloadable is deemed suspi(cid:173)
`cious if it performs or may perform any undesirable 15
`operation, or if it threatens or may threaten the integrity of
`an internal computer network 115 component. It is to be
`understood that the term "suspicious" includes hostile,
`potentially hostile, undesirable, potentially undesirable, etc.
`Security management console 120 enables viewing, modi- 20
`fication and configuration of the internal network security
`system 110.
`FIG. 2 is a block diagram illustrating details of the
`internal network security system 110, which includes a
`Central Processing Unit (CPU) 205, such as an Intel Pen- 25
`tium® microprocessor or a Motorola Power PC®
`microprocessor, coupled to a signal bus 220. The internal
`network security system 110 further includes an external
`communications interface 210 coupled between the com(cid:173)
`munications channel125 and the signal bus 220 for receiv- 30
`ing Downloadables from external computer network 105,
`and an internal communications interface 225 coupled
`between the signal bus 220 and the communications channel
`130 for forwarding Downloadables not deemed suspicious
`to the internal computer network 115. The external commu- 35
`nications interface 210 and the internal communications
`interface 225 may be functional components of an integral
`communications interface (not shown) for both receiving
`Downloadables from the external computer network 105 and
`forwarding Downloadables to the internal computer network
`115.
`Internal network security system 110 further includes
`Input/Output (110) interfaces 215 (such as a keyboard,
`mouse and Cathode Ray Tube (CRT) display), a data storage
`device 230 such as a magnetic disk, and a Random-Access 45
`Memory (RAM) 235, each coupled to the signal bus 220.
`The data storage device 230 stores a security database 240,
`which includes security information for determining
`whether a received Downloadable is to be deemed suspi(cid:173)
`cious. The data storage device 230 further stores a users list 50
`260 identifying the users within the internal computer net(cid:173)
`work 115 who may receive Downloadables, and an event log
`245 which includes determination results for each Down(cid:173)
`loadable examined and runtime indications of the internal
`network security system 110. An operating system 250
`controls processing by CPU 205, and is typically stored in
`data storage device 230 and loaded into RAM 235 (as
`illustrated) for execution. A security program 255 controls
`examination of incoming Downloadables, and also may be
`stored in data storage device 230 and loaded into RAM 235
`(as illustrated) for execution by CPU 205.
`FIG. 3 is a block diagram illustrating details of the
`security program 255 and the security database 240. The
`security program 255 includes an ID generator 315, a policy
`finder 317 coupled to the ID generator 315, and a first
`comparator 320 coupled to the policy finder 317. The first
`comparator 320 is coupled to a logical engine 333 via four
`
`4
`separate paths, namely, via Path 1, via Path 2, via Path 3 and
`via Path 4. Path 1 includes a direct connection from the first
`comparator 320 to the logical engine 333. Path 2 includes a
`code scanner coupled to the first comparator 320, and an
`5 Access Control List (ACL) comparator 330 coupling the
`code scanner 325 to the logical engine 333. Path 3 includes
`a certificate scanner 340 coupled to the first comparator 320,
`and a certificate comparator 345 coupling the certificate
`scanner 340 to the logical engine 333. Path 4 includes a
`Uniform Resource Locator (URL) comparator 350 coupling
`the first comparator 320 to the logical engine 3330. A
`record-keeping engine 335 is coupled between the logical
`engine 333 and the event log 245.
`The security program 255 operates in conjunction with
`the security database 240, which includes security policies
`305, known Downloadables 307, known Certificates 309
`and Downloadable Security Profile (DSP) data 310 corre(cid:173)
`sponding to the known Downloadables 307. Security poli(cid:173)
`cies 305 includes policies specific to particular users 260 and
`default (or generic) policies for determining whether to
`allow or block an incoming Downloadable. These security
`policies 305 may identify specific Downloadables to block,
`specific Downloadables to allow, or necessary criteria for
`allowing an unknown Downloadable. Referring to FIG. 4,
`security policies 305 include policy selectors 405, access
`control lists 410, trusted certificate lists 415, URL rule bases
`420, and lists 425 of Downloadables to allow or to block per
`administrative override.
`Known Downloadables 307 include lists of Download(cid:173)
`abies which Original Equipment Manufacturers (OEMs)
`know to be hostile, of Downloadables which OEMs know to
`be non-hostile, and of Downloadables previously received
`by this security program 255. DSP data 310 includes the list
`of all potentially hostile or suspicious computer operations
`that may be attempted by each known Downloadable 307,
`and may also include the respective arguments of these
`operations. An identified argument of an operation is
`referred to as "resolved." An unidentified argument is
`referred to as "unresolved." DSP data 310 is described below
`40 with reference to the code scanner 325.
`The ID generator 315 receives a Downloadable (including
`the URL from which it came and the use riD of the intended
`recipient) from the external computer network 105 via the
`external communications interface 210, and generates a
`Downloadable ID for identifying each Downloadable. The
`Downloadable ID preferably includes a digital hash of the
`complete Downloadable code. The ID generator 315 pref(cid:173)
`erably prefetches all components embodied in or identified
`by the code for Downloadable ID generation. For example,
`the ID generator 315 may prefetch all classes embodied in
`or identified by the Java™ applet bytecode to generate the
`Downloadable ID. Similarly, the ID generator 315 may
`retrieve all components listed in the .INF file for an
`ActiveX™ control to compute a Downloadable ID.
`55 Accordingly, the Downloadable ID for the Downloadable
`will be the same each time the ID generator 315 receives the
`same Downloadable. The ID generator 315 adds the gener(cid:173)
`ated Downloadable ID to the list of known Downloadables
`307 (if it is not already listed). The ID generator 315 then
`60 forwards the Downloadable and Downloadable ID to the
`policy finder 317.
`The policy finder 317 uses the use riD of the intended user
`and the Downloadable ID to select the specific security
`policy 305 that shall be applied on the received Download-
`65 able. If there is a specific policy 305 that was defined for the
`user (or for one of its super groups) and the Downloadable,
`then the policy is selected. Otherwise the generic policy 305
`
`

`
`6,092,194
`
`5
`
`5
`that was defined for the user (or for one of its super groups)
`is selected. The policy finder 317 then sends the policy to the
`first comparator 320.
`The first comparator 320 receives the Downloadable, the
`Downloadable ID and the security policy 305 from the
`policy finder 317. The first comparator 320 examines the
`security policy 305 to determine which steps are needed for
`allowing the Downloadable. For example, the security
`policy 305 may indicate that, in order to allow this
`Downloadable, it must pass all four paths, Path 1, Path 2,
`Path 3 and Path 4. Alternatively, the security policy 305 may
`indicate that to allow the Downloadable, it must pass only
`one of the paths. The first comparator 320 responds by
`forwarding the proper information to the paths identified by
`the security policy 305.
`Path 1
`In path 1, the first comparator 320 checks the policy
`selector 405 of the security policy 305 that was received
`from the policy finder 317. If the policy selector 405 is either
`"Allowed" or "Blocked," then the first comparator 320
`forwards this result directly to the logical engine 333.
`Otherwise, the first comparator 320 invokes the comparisons
`in path 2 and/or path 3 and/or path 4 based on the contents
`of policy selector 405. It will be appreciated that the first
`comparator 320 itself compares the Downloadable ID
`against the lists of Downloadables to allow or block per
`administrative override 425. That is, the system security
`administrator can define specific Downloadables as
`"Allowed" or "Blocked."
`Alternatively, the logical engine 333 may receive the 30
`results of each of the paths and based on the policy selector
`405 may institute the final determination whether to allow or
`block the Downloadable. The first comparator 320 informs
`the logical engine 333 of the results of its comparison.
`Path 2
`In path 2, the first comparator 320 delivers the
`Downloadable, the Downloadable ID and the security policy
`305 to the code scanner 325. If the DSP data 310 of the
`received Downloadable is known, the code scanner 325
`retrieves and forwards the information to the ACL compara- 40
`tor 330. Otherwise, the code scanner 325 resolves the DSP
`data 310. That is, the code scanner 325 uses conventional
`parsing techniques to decompose the code (including all
`prefetched components) of the Downloadable into the DSP
`data 310. DSP data 310 includes the list of all potentially 45
`hostile or suspicious computer operations that may be
`attempted by a specific Downloadable 307, and may also
`include the respective arguments of these operations. For
`example, DSP data 310 may include a READ from a specific
`file, a SEND to an unresolved host, etc. The code scanner 50
`325 may generate the DSP data 310 as a list of all operations
`in the Downloadable code which could ever be deemed
`potentially hostile and a list of all files to be accessed by the
`Downloadable code. It will be appreciated that the code
`scanner 325 may search the code for any pattern, which is 55
`undesirable or suggests that the code was written by a
`hacker.
`An Example List of Operations Deemed Potentially Hostile
`File operations: READ a file, WRITE a file;
`Network operations: LISTEN on a socket, CONNECT to
`a socket, SEND data, RECEIVE data, VIEW INTRA(cid:173)
`NET;
`Registry operations: READ a registry item, WRITE a
`registry item;
`Operating system operations: EXIT WINDOWS, EXIT
`BROWSER, START PROCESS/THREAD, KILL
`
`6
`PROCESS/THREAD, CHANGE PROCESS/
`THREAD PRIORITY, DYNAMICALLY LOAD A
`CLASS/LIBRARY, etc.; and
`Resource usage thresholds: memory, CPU, graphics, etc.
`In the preferred embodiment, the code scanner 325 performs
`a full-content inspection. However, for improved speed but
`reduced security, the code scanner 325 may examine only a
`portion of the Downloadable such as the Downloadable
`header. The code scanner 325 then stores the DSP data into
`10 DSP data 310 (corresponding to its Downloadable ID), and
`sends the Downloadable, the DSP data to the ACL com(cid:173)
`parator 330 for comparison with the security policy 305.
`The ACL comparator 330 receives the Downloadable, the
`corresponding DSP data and the security policy 305 from the
`15 code scanner 325, and compares the DSP data against the
`security policy 305. That is, the ACL comparator 330
`compares the DSP data of the received Downloadable
`against the access control lists 410 in the received security
`policy 305. The access control list 410 contains criteria
`20 indicating whether to pass or fail the Downloadable. For
`example, an access control list may indicate that the Down(cid:173)
`loadable fails if the DSP data includes a WRITE command
`to a system file. The ACL comparator 330 sends its results
`to the logical engine 333.
`25 Path 3
`In path 3, the certificate scanner 340 determines whether
`the received Downloadable was signed by a certificate
`authority, such as VeriSign, Inc., and scans for a certificate
`embodied in the Downloadable. The certificate scanner 340
`forwards the found certificate to the certificate comparator
`345. The certificate comparator 345 retrieves known certifi(cid:173)
`cates 309 that were deemed trustworthy by the security
`administrator and compares the found certificate with the
`known certificates 309 to determine whether the Download-
`35 able was signed by a trusted certificate. The certificate
`comparator 345 sends the results to the logical engine 333.
`Path 4
`In path 4, the URL comparator 350 examines the URL
`identifying the source of the Downloadable against URLs
`stored in the URL rule base 420 to determine whether the
`Downloadable comes from a trusted source. Based on the
`security policy 305, the URL comparator 350 may deem the
`Downloadable suspicious if the Downloadable comes from
`an untrustworthy source or if the Downloadable did not
`come from a trusted source. For example, if the Download(cid:173)
`able comes from a known hacker, then the Downloadable
`may be deemed suspicious and presumed hostile. The URL
`comparator 350 sends its results to the logical engine 333.
`The logical engine 333 examines the results of each of the
`paths and the policy selector 405 in the security policy 305
`to determine whether to allow or block the Downloadable.
`The policy selector 405 includes a logical expression of the
`results received from each of the paths. For example, the
`logical engine 333 may block a Downloadable if it fails any
`one of the paths, i.e., if the Downloadable is known hostile
`(Path 1 ), if the Downloadable may request suspicious opera-
`tions (Path 2), if the Downloadable was not signed by a
`trusted certificate authority (Path 3), or if the Downloadable
`came from an untrustworthy source (Path 4). The logical
`engine 333 may apply other logical expressions according to
`the policy selector 405 embodied in the security policy 305.
`If the policy selector 405 indicates that the Downloadable
`may pass, then the logical engine 333 passes the Download(cid:173)
`able to its intended recipient. Otherwise, if the policy
`65 selector 405 indicates that the Downloadable should be
`blocked, then the logical engine 333 forwards a non-hostile
`Downloadable to the intended recipient to inform the user
`
`60
`
`

`
`6,092,194
`
`5
`
`45
`
`7
`that internal network security system 110 discarded the
`original Downloadable. Further, the logical engine 333
`forwards a status report to the record-keeping engine 335,
`which stores the reports in event log 245 in the data storage
`device 230 for subsequent review, for example, by the MIS
`director.
`FIG. 5 is a block diagram illustrating details of the
`security management console 120, which includes a security
`policy editor 505 coupled to the communications channel
`135, an event log analysis engine 510 coupled between
`communications channel135 and a user notification engine
`515, and a Downloadable database review engine 520
`coupled to the communications channel 135. The security
`management console 120 further includes computer com(cid:173)
`ponents similar to the computer components illustrated in
`FIG. 2.
`The security policy editor 505 uses an 1!0 interface
`similar to 1!0 interface 215 for enabling authorized user
`modification of the security policies 305. That is, the secu(cid:173)
`rity policy editor 505 enables the authorized user to modify 20
`specific security policies 305 corresponding to the users 260,
`the default or generic security policy 305, the Download(cid:173)
`abies to block per administrative override, the Download(cid:173)
`abies to allow per administrative override, the trusted cer(cid:173)
`tificate lists 415, the policy selectors 405, the access control 25
`lists 410, the URLs in the URL rule bases 420, etc. For
`example, if the authorized user learns of a new hostile
`Downloadable, then the user can add the Downloadable to
`the Downloadables to block per system override.
`The event log analysis engine 510 examines the status 30
`reports contained in the event log 245 stored in the data
`storage device 230. The event log analysis engine 510
`determin