Detecting malicious Java code using virtual machine auditing

Detecting Malicious Java Code Using Virtual Machine Auditing Sunil Soman Chandra Krintz Giovanni Vigna

Computer Science Department

University of California,Santa Barbara

{sunils,ckrintz,vigna}@https://www.wendangku.net/doc/0415385494.html,

Abstract

The Java Virtual Machine(JVM)is evolving as an infrastructure for the ef?cient execution of large-scale, network-based applications.To enable secure execu-tion in this environment,industrial and academic efforts have implemented extensive support for veri?cation of type-safety,authentication,and access control.However, JVMs continue to lack intrinsic support for intrusion de-tection.

Existing operating system auditing facilities and host-based intrusion detection systems operate at the process level,with the assumption that one application is mapped onto one process.However,in many cases,multiple Java applications are executed concurrently as threads within a single JVM process.As such,it is dif?cult to analyze the behavior of Java applications using the correspond-ing OS-level audit trail.In addition,the malicious ac-tions of a single Java application may trigger a response that disables an entire execution environment.To over-come these limitations,we have developed a thread-level auditing facility for the Java Virtual Machine and an in-trusion detection tool that uses audit data generated by this facility to detect attacks by malicious Java code.This paper describes the JVM auditing mechanisms,the in-trusion detection tool,and the quantitative evaluation of their performance.

1Introduction

Java technology[18]was initially used by web page de-signers to embed active content.As a result of the wide-spread success and popularity of Java,developers now use the language for implementation of a wide range of large-scale systems,e.g.,robust,mobile code sys-tems[36,19,33]and complex server systems[43,32]. In these systems,multiple applications and code compo-nents are uploaded by multiple(possibly untrusted)users for concurrent execution within a single Java Virtual Ma-chine(JVM)[38].The portability,?exibility,and secu-rity features of Java make it an ideal technology for the implementation of systems that support the execution of mobile code.

The use of Java enables portability because programs are encoded using an architecture-independent transfer for-mat that can be executed without modi?cation on any platform for which a JVM has been developed.Java supports?exibility by allowing applications to be up-graded and extended at run time through the use of dy-namic code loading.In addition,the Java type system and veri?cation mechanisms provide protection against some programming errors and malicious attacks.

The key areas that must be improved to enable continued wide-spread use of Java for Internet-scale server appli-cations are performance and security.Recent advances in Just-In-Time(JIT)compilation and optimization tech-niques[35,6,8]offer signi?cant improvements in Java program performance.Currently,to support security in server applications,Java provides mechanisms for au-thentication and access control[17,2].However,ad-ditional mechanisms are required to detect attacks that circumvent(or attempt to circumvent)the existing pro-tections or abuse legitimate access.

Host-based Intrusion Detection Systems(HIDSs)pro-vide a suitable solution to this problem[3,12].Ex-isting HIDSs use process-level execution events,col-lected by an auditing facility in the operating system,

to identify and respond to security threats and viola-tions[13,26,52].

Unfortunately,since a JVM executes as a single,multi-threaded user process,we must presume that all suspi-cious activity reported by the auditing facility for the JVM process ID,is caused by the JVM itself.However, the culprit may be one of the many applications running within the JVM process.As users increasingly demand higher availability and reliability from the servers exe-cuting their applications,an intrusion response mecha-nism that simply terminates the JVM process that is ex-ecuting malicious code becomes unacceptable.There-fore,novel auditing and intrusion detection techniques are needed,to provide?ner-grained threat identi?cation and response.

To this end,we have developed a JVM auditing facil-ity and an intrusion detection system that detects attacks that are initiated by malicious Java code.To implement our system,We leveraged two existing technologies:a high-performance,open-source,Java Virtual Machine, called JikesRVM[1];and an intrusion detection frame-work,called STAT,that we developed in prior work[50]. In this paper,we describe the JVM auditing mechanisms and the intrusion detection tool that we implemented,and provide a quantitative evaluation of the performance of our system.

In the next section,we place our work in the context of existing approaches to intrusion detection.In Section3, we present an overview of our approach.In Section4,we describe the JVM auditing system.Then,in Section5, we present the intrusion detection system.Section6dis-cusses the experimental evaluation of our system.Sec-tion7presents related work on Java security.Finally, Section8draws conclusions and outlines future work. 2Extant Approaches

to Intrusion Detection

Intrusion detection is performed by identifying the man-ifestation of a security violation in an input event stream. In host-based intrusion detection systems,the input event stream is usually represented by the audit records pro-duced by the auditing facility of an operating system, such as the Solaris Basic Security Module[47].Other possible input streams are system call traces and UNIX syslog messages.The detection process can be performed according to dif-ferent techniques.For example,it is possible to use sta-tistical measures to characterize the normal behavior of users and applications[13,23,29].Deviations from the established pro?les are assumed to be evidence of an at-tack.The problem with these approaches is the dif?culty to create a reliable model of the application behavior. An imprecise model may lead to both missed detections (called false negatives)and false alarms(called false pos-itives).

Other approaches rely on the formal speci?cation of the acceptable behavior of an application[34,54,52].An execution history that does not conform to this behav-ior is considered malicious.The advantage of this ap-proach is that the generation of false positives is greatly reduced.On the other hand,the generation of the speci?-cation requires access to the application source code and considerable effort,even when supported by tools.For this reason,these techniques are not in wide-spread use. The most commonly used approach relies on models of attacks to analyze the input event stream.Systems based on this approach[20,26,39]are equipped with a num-ber of attack signatures.These signatures are matched against the stream of audit data to identify the manifesta-tion of an attack.The advantage of this approach is that it supports very effective intrusion detection and produces few false positives.In addition,signatures are not limited to modeling attacks against an application.For example, it is possible to describe attacks that represent abuses of legitimate access to the system.The disadvantage is that the signature set must be updated continuously as new ways of attacking a system are found.

In the work we present herein,we describe the design and implementation of a signature-based intrusion de-tection system.The system is an extension of previous work[49]in which we developed an auditing facility and an intrusion detection system for a mobile agent system, called Aglets[36].This prior system detects malicious agent activity through the monitoring of the Aglets exe-cution environment.In that case,the Java server applica-tion that was responsible for transferring and executing the mobile agents was instrumented to produce agent-related information.

The development of this agent monitoring system sug-gested a far more general approach in which the JVM itself is extended to produce the necessary informa-tion.Therefore,we developed a mechanism that collects

Figure1:Architecture of the Java Virtual Machine auditing system and the STAT-based intrusion detection system

events that give information about the activity of threads within a JVM.The resulting auditing system can moni-tor the activity of any Java application,including various technologies supporting mobile code.We also developed an intrusion detection system that takes advantage of the ?ner-grained information produced by the JVM audit-ing system to detect attacks coming from malicious Java code.

To the best of our knowledge,no existing system per-forms auditing and threat detection at the Java thread level.

3System Overview

Figure1shows a high-level overview of our intrusion detection architecture.The auditing system monitors executing Java threads(possibly associated with multi-ple,independent applications)and produces an audit log composed of records related to thread activity.The log is converted to an event stream by an event provider.The event stream is subsequently analyzed by an intrusion detection system for possible security threats or attacks. More precisely,the intrusion system compares patterns in the event stream against known attack scenarios.A match indicates that an intrusion or threat is in progress and that a response should be initiated.To do so,the intrusion detection system contacts the JVM which im-mediately terminates all offending threads.The JVM au-diting system maps authenticated user IDs to threads so that malicious users can be identi?ed and their threads selectively terminated.

Our system implementation couples and extends two ex-isting frameworks:the JikesRVM,a high-performance Java virtual machine[30,1],and STAT[51,14],a gen-eral platform for the creation of intrusion detection sen-sors that we developed as part of prior work.The grayed boxes in the?gure identify our extensions to these sys-tems.In the sections that follow,we describe each of these components.

4An Auditing System

For A Java Virtual Machine

We implemented an auditing facility for the JikesRVM. The JikesRVM was designed with the goal of enabling high-performance Java server applications.As such,it represents the next generation of JVM technologies.The JikesRVM compiles Java bytecode programs into binary code(x86or Power PC)at run time.The system oper-ates at the method level and employs aggressive program

optimization.The JikesRVM implements extensive run-time services including,garbage collection(GC),thread scheduling,synchronization,name-space separation,and class?le veri?cation.We implemented the latter two features ourselves as part of other projects[55].Cur-rently,the JikesRVM enables over25%reduction in ex-ecution time over the Sun HotSpot JVM version1.3.1 for x86/Linux(This value refers to a number of standard benchmark programs that we also used in Section6of this paper to evaluate the overhead introduced by our au-diting facility).

All Java threads in the JikesRVM derive from a virtual machine thread(VM

Processor),which is the abstrac-tion of an underlying operating system thread.This im-plementation enables the JikesRVM to perform thread scheduling,independent to that performed by the oper-ating system.

To monitor any suspicious activity performed by applica-tions running in the JikesRVM,we extended the virtual machine with an event logging system.Each time an application or code component is uploaded into the exe-cuting JVM,a thread is created to execute the code.The thread is assigned a unique system identi?er(SID)and a user identi?er(UID).The SID enables the JikesRVM auditing system to identify a speci?c thread when log-ging execution events.UIDs associate users with individ-ual threads.Both SIDs and UIDs are inherited by every thread created by the initial thread.Strong authentica-tion mechanisms can be used to assign UIDs to threads, however,authentication and identi?cation are not imple-mented natively by the JikesRVM(we are investigating such mechanisms as part of our current research).

In this?rst prototype,we simply map IP addresses to user IDs;this implementation is suf?cient to effectively identify malicious threads.Since each application thread that executes in the system has an associated user ID,the threads of a user can be killed without affecting other user applications or the execution environment.

Figure2provides a graphic description of the JVM au-diting facility.The auditing facility consists of an event driver,an event queue,and an event logger.The event driver adds thread-level execution events to the event queue.The logger processes events that are contained in the queue and writes them to an external log.We next describe the event driver.The implementation of the log-

ger component is described in Section4.2.

4.1Event Driver

The event driver provides an interface for inserting events in the event queue.The security-relevant opera-tions in the JikesRVM are instrumented with calls to the event driver interface.For example,system calls invoked by the executing programs are instrumented in this way. We currently instrument operations that are of interest from a security perspective.However,any dynamic be-havior can be instrumented using our system.The events we monitor in our prototype are:class events,system call events,JNI events,and thread interaction events.

4.1.1Class Events

A class event occurs each time a thread loads a class.We instrumented the JikesRVM class loading code to record these events during execution.If a class is loaded from the network,the IP address of the code source is logged as part of the event.

We also record events associated with the creation of user-de?ned class loaders[37]and the classes that they https://www.wendangku.net/doc/0415385494.html,er-de?ned class loaders are a powerful feature of the Java language that allows programs to de?ne dy-namically the way in which a class can be loaded and created.However,this functionality might also allow malicious applications to load classes from untrusted lo-cations[41].To record these events,we instrument the class loading code in user components that extend the Java ClassLoader library class[28].

4.1.2System Call Events

System calls provide an interface through which an exe-cuting program can access operating system resources. For example,network communication,?le I/O,and memory allocation are all accessed via system calls.By intercepting system calls,we are able to monitor and con-trol such access.

The JikesRVM provides an abstraction of system calls via the VM system class.The system call routines in this class invoke the corresponding routines in the“Magic”(VM

VM

17:17:142002”>

15:30:272002”>

mode=”WRITE”/>

status=”FAILED”/>

15:31:022002”>

port=”25640”/>

status=”FAILED”/>

Figure3:XML Encoding of example JikesRVM events.

is an example of a system call event in which a thread with ID2,owned by a user with ID17attempts to open the/etc/passwd?le for writing and fails.The?-nal example in the?gure shows the encoding of a net-work event in which a thread,owned by user with ID11, tries to establish a connection to a host having IP address 128.111.68.170on port25640and the connection is re-fused.

The source element describes the thread(and hence, user)that initiates the operation;the thread ID(attribute id)and the user ID(attribute uid)are both attributes of the thread element.The action element describes the operation performed by the source.The type at-tribute of this action element describes the action be-ing recorded(for example,“JNI”to denote that a native method was invoked).The target element describes the target to which the action is being applied.The tar-get of an operation can be a?le,a server,a method,or a thread.Of these,the latter is described by the id at-tribute;others are described using the name attribute. The result element speci?es the outcome of the opera-tion.This element has two attributes,returncode and status,which are used to record return values,e.g., from system calls,and status values,e.g.,errno values. 5Detecting Malicious Java Code

The event stream produced by the JikesRVM event log-ger thread is used by an intrusion detection system to identify possible threats and attacks.The intrusion detec-tion system was developed leveraging the STAT frame-work[26,50].The STAT framework provides a generic signature-based intrusion detection engine that can be extended to match a speci?c environment through a well-de?ned process.

The?rst step of the extension process includes the de?-nition of a language extension module.This module ex-tends STATL[14],the domain-independent attack mod-eling language provided by the framework,with the event types that are speci?c of a particular target do-main.Therefore,we developed a language extension module that de?nes the event types that are produced by the JikesRVM auditing facility(e.g.,the JEvent type). By doing this,it was possible to use the JVM-speci?c events when writing STATL scenarios.These scenarios represent state-transition models of attacks.

An example of a scenario is shown in Figure4.The sce-nario models a two-step attack in which a malicious ap-plication uses the JNI to obtain a reference to another application’s thread,and then calls the“kill”method on that reference in an attempt to terminate the thread.This attack is detected by checking for a JNI method invoca-tion(transition

2).This and other scenarios are pre-sented in detail in Section5.1.

The second step of the framework extension process is the development of an event provider module.This mod-ule is responsible for collecting events from the envi-ronment and translating them in the format de?ned in the language extension module.We developed an event provider module that reads the events contained in the audit log produced by the JikesRVM event logger and generates events in the format speci?ed by the language extension described above.These events are matched by the STAT analysis engine against the available attack sce-

scenario jikesRVM

1(s0→s1)nonconsuming{ [JEvent m1]:m1.targetType==”method”&&

m1.actionString==”JNICALL”;

{

log(”JNI method%s invoked by thread%s”,

https://www.wendangku.net/doc/0415385494.html,,m1.source.id);

}

}

transition transition

alert from the intrusion detection tool.The alert repre-sents the attempt of an application to write to the privi-leged/etc/shadow?le,which stores users’password hashes(on many UNIX systems).

TIME:01/20/200313:44:04

ACTION:PRIVILEGED ACCESS

SOURCE UID:0

SOURCE THREAD ID:2

PRIVILEGED RESOURCE:/etc/shadow

ACCESS MODE:WRITE

MSG:Attempt to stat privileged file.

RESULT:FAILURE

SENSOR:jikesRVMstat@localhost

This scenario is an example of how the system can be used to detect malicious behavior even when an attack fails.

5.1.2Harmful Inter-Thread Communication

A reasonably enterprising intruder might disrupt the functioning of other application threads in the sys-tem[41].Consider the scenario in which an intruder has forged a legitimate user’s identity,e.g.,by stealing her user id,and has uploaded code using the stolen iden-tity.In addition,the legitimate user is authorized to in-voke native methods via the Java Native Interface(JNI). The intruder executes a native method that is designed to give her access to a thread object of another user.She then sends signals to that thread to terminate the thread. The system detects this scenario by detecting that a JNI invocation is performed followed by potentially harm-ful cross-thread communication between threads owned by two different users.The intrusion detection response module can communicate this information to the Java Virtual Machine,which can terminate the application up-loaded by the intruder.Following is an example of such a detection alert:

TIME:01/20/200320:44:04

ACTION:THREAD STOP after JNI Call.

SOURCE UID:0

SOURCE THREAD ID:2

TARGET UID:8

TARGET THREAD ID:1

MSG:JNI method"print"invoked by thread2(uid0).

Suspicious thread communication after

JNI method invocation!!

RESULT:SUCCESS

SENSOR:jikesRVMstat@localhost

This scenario shows that in some cases malicious behav-ior can be detected only by using features that are internal to the JVM.Alternately,the attacker might obtain ille-gal access to an application thread by ascending to the thread’s root thread group,and recursively descending through threads and thread groups below[41].The in-truder can then call Thread.stop()on the victim’s thread. This single-step attack and can be handled by monitoring Thread.stop()calls.

5.1.3Detecting Network Scans

With the next scenario,we show how the system can de-tect“bounce”attacks[24,41]on internal https://www.wendangku.net/doc/0415385494.html,-ing these well-known attacks,a malicious program may identify,manipulate,or discover vulnerabilities in hosts on an internal network.

In this scenario,the Java socket library is used by an at-tacker to perform network scans against hosts on a net-work behind a?rewall.We assume that the JVM server system has access to these internal hosts.A malicious user uploads code that performs ping scans against inter-nal subnets in an attempt to identify hosts that are alive. Similarly,the attacker can perform TCP and UDP scans to identify hosts with potentially vulnerable network ser-vices.To detect ping scans,we monitor the connection attempts made by an application to a range of hosts,or a range of ports on a host.Following is an example of an alert from the intrusion detection system that detects multiple connection attempts to a range of ports on host 128.111.68.170.The system identi?es the thread and the user who performed the scan.

TIME:01/23/200317:56:04

ACTION:MULTIPLE CONNECTS

SOURCE UID:0

SOURCE THREAD ID:2

SOURCE ADDR:128.111.68.169

TARGET ADDR:128.111.68.170

MSG:Connect attempts(1058)to multiple ports. RESULT:FAILURE

SENSOR:jikesRVMstat@localhost

This scenario shows that it is possible to precisely iden-tify the malicious code performing the attack using JVM-level audit data.

5.1.4Detecting Transfer of Privileged Information In the next scenario,we show how events that“leak”sen-sitive server information to the outside world[7]can be detected.The system is capable of detecting such events since we record system calls and network events.

Description Classes Methods Time(sec)

127.11

316.22 on the Purdue Compiler Construction Tool set315

java cup LALR parser generator:A parser is created

360.38

176 6.28 Computes solutions to rule based puzzles690

mpeg Spec JVM98audio?le decompression tool

55 5.84

ray tracing implementation180

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N o r m a l i z e d E x e c u t i o n T i m e

Figure 5:Execution times of our JikesRVM extension relative to the JikesRVM without auditing and response for a number of standard Java benchmarks.Full event logging implies that all system call,thread interaction,and JNI events are recorded.With partial event logging,we only log network use,?le I/O,thread interaction,and JNI invocation events.suite.

6.1

JikesRVM Auditing Overhead

To evaluate the ef?cacy of our system,we measured the overhead that the system imposes on the execution of programs for which no intrusions or threats are detected.Figure 5shows the relative slowdown for each bench-mark.The base case to which we are comparing is the JikesRVM without modi?cation.

The delay experienced by the user application due to event logging depends on the number of events.The left-hand bar in the graph shows the impact of full log-ging,i.e.,when all system calls,thread interaction,and JNI calls are logged.System call events generally dom-inate all other kinds of events,and applications with a large number of system calls incur in a substantial per-formance penalty.The right-hand bar,gives the perfor-mance of our system when partial logging is performed,that is when we only log events that we use in the attack scenarios presented in this paper,namely,network and ?le I/O,thread interaction,and JNI access.By reducing the number of events of interest,program performance improves.A user can con?gure our system to record any number of event types to manually adjust the trade-off between system performance and events audited.

The graph indicates that our logging introduces very lit-

Total Logging

Partial Logging

956

compress 190

1894

java cup 420

400

jess 10075

453

mtrt 474Average

3982

sysStat

sysReadByte

sysWriteBytes

Figure 6:Breakdown of events for partial logging.These events are only those that we use for the attack scenarios that we present in this paper.Note that partial logging implies that in case of system call events,only network and ?le I/O events are recorded.

types of events.The number of system call events of each type varies across the benchmarks.However,?le reads and writes are the most common in all cases.As part of future work,we plan to aggregate read and write system calls to reduce the overhead of instrumentation,so that events are generated only when a threshold is reached.

7Related Work

Our work is primarily related to and complements three different areas of research.The ?rst is extant intrusion detection research which we describe and contrast to our system in Section 2.Other related work includes al-ternate approaches to ensuring safe execution of mobile programs (including Java-based operating systems)and thread termination techniques.

The goal of much of the prior related research has been to develop operating systems and system manage-ment components using the Java language to enable re-source management and process protection through the use of Java type-safety and load-time veri?cation mech-anisms [5,31,40,22,46,48,11,21,27,4].Other related work has focused on mechanisms that ensure that the execution of mobile code will not unintention-ally or maliciously harm the underlying systems.Such techniques include stack inspection [16],proof-carrying

code [42,10,9],software fault isolation [53],and code replacement [7].

The system that we propose is not an alternative to these existing approaches to program protection and system security.Instead,it offers a complementary technique (thread-level intrusion detection)that can be used to identify suspicious events or activities that may not be caught or detected by these existing approaches.For ex-ample,our system can be used within secure execution environments and Java-based operating systems to de-tect threads that continuously allocate memory in an at-tempt to cause the system to fail due to memory exhaus-tion or threads that perform bounce attacks on internal machines.In addition,our system is easily extensible and as such,administrators can add event detection of previously unforeseen attacks that arise but that are not handled by the underlying system.

A second area of related work is thread termination [44,15].In [44],the authors provide a formal speci?ca-tion and implementation of a technique for thread cessa-tion called soft termination .Using this technique,a mo-bile code system can asynchronously and safely destroy the threads of a mobile program without termination of the execution environment.In our system,the response module receives messages from the STAT system when thread activity warrants its termination.The response module discontinues all threads in the system that were initiated by the user that spawned the ill-behaved thread.The module destroys non-running threads by removing them from the thread scheduling queue.

We could have implemented soft termination within the response module instead.Soft termination guarantees correct thread termination in the presence of all program and system activities,e.g.,blocking system calls.As such,it is more robust and complete than our termina-tion process.Since the JikesRVM currently only sup-ports non-blocking system calls,we selected our sim-pler implementation for our initial prototype.As the JikesRVM evolves to include blocking system calls,we plan to consider the use of soft termination within our response module as part of future work.

8Conclusions and Future work

Auditing at the Java Virtual Machine (JVM)level allows for ?ne-grained access to application execution events.

This information is necessary to perform effective in-trusion detection and response for next-generation JVM server technologies in which multiple applications are uploaded from multiple(possibly untrusted)sites and ex-ecute concurrently within a single JVM.To this end,we developed an auditing facility for the JikesRVM and a host-based intrusion detection system that employs this audit data.As a result,attacks that exploit features inter-nal to the JVM,such as the JNI,can now be detected.To our knowledge,this is the?rst system that performs au-diting and intrusion detection at the thread-level within a JVM.

We also evaluated both the effectiveness of the detec-tion process and the performance of the auditing systems. The results show that our approach introduces limited, adjustable,overhead while enabling many different at-tack scenarios to be detected.

Our future work will have two foci.First,we plan to extend and optimize the auditing system to handle addi-tional events and to reduce the overhead of instrumenta-tion.The extensions we plan include a publish-subscribe mechanism that allows intrusion detection systems to dy-namically con?gure the auditing facility so that only the events that actually are necessary to the detection pro-cess are logged.In addition,we will use the experience that we gained with the prototype described herein,to reduce the overhead of instrumentation and audit collec-tion within the JikesRVM.

As a second research direction,we plan to correlate traces collected at different abstraction levels to per-form more effective intrusion detection.In particular, we plan to analyze the JVM-level traces with respect to application-level and OS-level traces.This integrated, multi-level approach will allow for more focused mali-cious code detection and a clearer evaluation of the im-pact of an attack on the underlying operating system. Acknowledgments

We would like to thank the anonymous reviewers for pro-viding extensive and useful comments on this paper. Giovanni Vigna’s work was supported by the National Science Foundation under grant CCR-0209065.References

[1] B.Alpern,C.R.Attanasio,J.J.Barton,M.G.Burke,

P.Cheng,J.-D.Choi,A.Cocchi,S.J.Fink,D.Grove, M.Hind,S.F.Hummel,D.Lieber,V.Litvinov,M.F.

Mergen,T.Ngo,J.R.Russell,V.Sarkar,M.J.Serrano, J.C.Shepherd,S.E.Smith,V.C.Sreedhar,H.Srinivasan, and J.Whaley.The Jalape?n o Virtual Machine.IBM Sys-tems Journal,39(1):211–221,2000.

[2] A.Anderson.Java Access Control Mechanisms.Techni-

cal report,Sun Microsystems,March2002.

[3]https://www.wendangku.net/doc/0415385494.html,puter Security Threat Monitoring and

Surveillance.James P.Anderson Co.,Fort Washington, April1980.

[4]G.Back,P.Tullmann,L.Stoller,W.Hsieh,and J.Lep-

reau.Processes in KaffeOS:Isolation,Resource Manage-ment,and Sharing in Java.In Proceedings of the Fourth Symposium on Operating Systems Design and Implemen-tation,pages333–346,San Diego,CA,October2000. [5]G.Back,P.Tullmann,L.Stoller,W.Hsieh,and J.Lep-

reau.Techniques for the Design of Java Operating Sys-tems.In Proceedings of the2000USENIX Annual Tech-nical Conference,pages197–210,San Diego,CA,June 2000.

[6]M.Burke,J.Choi,S.Fink,D.Grove,M.Hind,V.Sarkar,

M.Serrano,V.Shreedhar,H.Srinivasan,and J.Whaley.

The Jalape?n o Dynamic Optimizing Compiler for Java.

In ACM Java Grande Conference,pages129–141,June 1999.

[7] A.Chander,J.Mitchell,and I.Shin.Mobile Code Se-

curity by Java Bytecode Instrumentation.In Proceedings of the2001DARPA Information Survivability Conference &Exposition(DISCEX II),pages1027–1040,Anaheim, CA,June2001.

[8]M.Cierniak,G.Lueh,and J.Stichnoth.Practicing JUDO:

Java Under Dynamic Optimizations.In Proceedings of the ACM SIGPLAN2000Conference on Programming Language Design and Implementation,pages13–26,June 2000.

[9] C.Colby,K.Crary,R.Harper,P.Lee,and F.Pfenning.

Automated Techniques for Provably Safe Mobile Code.

In Proceedings of the DARPA Information Survivability Conference and Exposition,volume1,pages406–419, Hilton Head,SC,January2000.IEEE Computer Society Press.

[10] C.Colby,P.Lee,G.Necula,F.Blan,M.Plesko,and

K.Cline.A Certifying Compiler for Java.In Proceed-ings of the ACM SIGPLAN2000Conference on Program-

ming Language Design and Implementation,pages95–107,Vancouver,British Columbia,Canada,June2000.

[11]G.Czajkowski and T.von Eicken.JRes:A Resource

Accounting Interface for Java.In ACM Conference on Object-Oriented Programming,Systems,Languages, and Applications(OOPSLA’98),pages21–35,Vancou-ver,Canada,October1998.

[12]H.Debar,M.Dacier,and A.Wespi.Towards a Tax-

onomy of Intrusion Detection https://www.wendangku.net/doc/0415385494.html,puter Net-works,31(8):805–822,1999.

[13] D.E.Denning.An Intrusion Detection Model.IEEE

Transactions on Software Engineering,13(2):222–232, February1987.

[14]S.T.Eckmann,G.Vigna,and R.A.Kemmerer.STATL:

An Attack Language for State-based Intrusion Detection.

Journal of Computer Security,10(1/2):71–104,2002. [15]M.Flatt,R.Findler,S Krishnamurthy,and M.Felleisen.

Programming Lanugages as Operating Systems(or Re-venge of the Son of the Lisp Machine).In Proceed-ings of the ACM International Conference on Functional Programming(ICFP’99),pages138–147,Paris,France, September1999.

[16] C.Fournet and A.D.Gordon.Stack Inspection:Theory

and Variants.In Proceedings of the29th ACM SIGPLAN-SIGACT symposium on Principles of programming lan-guages,pages307–318,Portland,Oregon,2002.ACM Press.

[17]L.Gong.Inside Java2Platform Security:Architecture,

API Design,and Implementation.Addison-Wesley,1999.

[18]J.Gosling,B.Joy,and G.Steele.The Java Language

Speci?cation.Addison-Wesley,1996.

[19]R.S.Gray,D.Kotz,G.Cybenko,and D.Rus.D’Agents:

Security in a Multiple-language,Mobile-agent System.

In G.Vigna,editor,Mobile Agents and Security,volume 1419of Lecture Notes in Computer Science,pages154–187.Springer-Verlag,1998.

[20]N.Habra,B.Le Charlier,A.Mounji,and I.Mathieu.

ASAX:Software Architecture and Rule-based Language for Universal Audit Trail Analysis.In Proceedings of European Symposium on Research in Computer Security (ESORICS),pages435–450,Toulouse,France,Novem-ber1992.

[21] C.Hawblitzel,C.Chang,G.Czajkowski,D.Hu,and

T.von Eicken.Implementing Multiple Protection Do-mains in Java.In Proceedings of the1998USENIX An-nual Technical Conference,pages259–270,New Orleans, LA,June1998.[22] C.Hawblitzel and T.von Eicken.Luna:A Flexible Java

Protection System.In Proceedings of the5th Sympo-sium on Operating Systems Design and Implementation, Boston,MA,December2002.

[23]P.Helman and G.Liepins.Statistical Foundations of Au-

dit Trail Analysis for the Detection of Computer Misuse.

In IEEE Transactions on Software Engineering,volume V ol19,No.9,pages886–901,1993.

[24]Hobbit.The FTP Bounce Attack.Bugtraq,

July1995.https://www.wendangku.net/doc/0415385494.html,/ SiliconValley/1947/Ftpbounc.htm.

[25]IBM Research.The Jikes Research Virtual Machine

User’s Guide.https://www.wendangku.net/doc/0415385494.html,/ developerworks/oss/jikesrvm/userguide/ HTML/userguide.html.

[26]K.Ilgun,R.A.Kemmerer,and P.A.Porras.State Transi-

tion Analysis:A Rule-Based Intrusion Detection System.

IEEE Transactions on Software Engineering,21(3):181–199,March1995.

[27]J.Hartman and L.Peterson and A.Bavier and P.Bigot

and P.Bridges and B.Montz and R.Piltz and T.Proeb-sting and O.Spatscheckti.Experiences Building a Communication-oriented JavaOS.Software–Practice and Experience,30(10),April2000.

[28]Java 1.2Library API.http://java.sun.

com/products/jdk/1.2/docs/api/

overview-summary.html.

[29]H.S.Javitz and A.Valdes.The NIDES Statistical Com-

ponent Description and Justi?cation.Technical report, SRI International,Menlo Park,CA,March1994. [30]JikesRVM.Project Home Page.http://www-124.

https://www.wendangku.net/doc/0415385494.html,/developerworks/oss/jikesrvm. [31]JOS Developer Team.JOS:An Open,Portable,and

Extensible Java Object Operating System.http:// https://www.wendangku.net/doc/0415385494.html,/archive/.

[32]JRun.Project Home Page.http://www.

https://www.wendangku.net/doc/0415385494.html,/jrun.

[33]Jumping Beans.Project home page.http://www.

https://www.wendangku.net/doc/0415385494.html,.

[34] C.Ko,M.Ruschitzka,and K.Levitt.Execution Monitor-

ing of Security-Critical Programs in Distributed Systems:

A Speci?cation-based Approach.In Proceedings of the

1997IEEE Symposium on Security and Privacy,pages 175–187,Oakland,CA,May1997.

[35] C.Krintz.Coupling On-Line and Off-Line Pro?le Infor-

mation to Improve Program Performance.In Proceedings of the International Symposium on Code Generation and

Optimization(CGO03),pages69–78,San Francisco,CA, March2003.

[36] https://www.wendangku.net/doc/0415385494.html,nge and M.Oshima.Programming and Deploy-

ing Java Mobile Agents with Aglets.Addison-Wesley Longman,1998.

[37]S.Liang and G.Bracha.Dynamic Class Loading in the

Java Virtual Machine.In ACM Conference on Object-Oriented Programming,Systems,Languages,and Ap-plications(OOPSLA),pages36–44,Vancouver,British Columbia,Canada,1998.

[38]T.Lindholm and F.Yellin.The Java Virtual Machine

Speci?cation.Addison-Wesley,1997.

[39]U.Lindqvist and P.A.Porras.Detecting Computer and

Network Misuse with the Production-Based Expert Sys-tem Toolset(P-BEST).In IEEE Symposium on Security and Privacy,pages146–161,Oakland,California,May 1999.

[40]M.Golm and M.Felser and C.Wawersich and J.Klein-

oder.The JX Operating System.In Proceedings of the USENIX Annual Technical Conference,pages45–58, Monterey,CA,June2002.

[41]G.McGraw and E.W.Felten.Securing Java:Getting

Down to Business with Mobile Code.John Wiley&Sons, 2nd edition,1999.

[42]G.Necula.Proof-Carrying Code.In Proceedings of

the24th Annual ACM SIGPLAN-SIGACT Symposium on Principles of Programming Languages(POPL97),pages 106–119,Paris,France,January1997.

[43]NonStop Server for Java Software.Project Home

Page.https://www.wendangku.net/doc/0415385494.html,/view.

asp?IO=NSJAVAPD01.

[44] A.Rudys and D.S.Wallach.Termination in Language-

based Systems.ACM Transactions on Information and System Security,5(2):138–168,2002.

[45]SpecJVM’98Benchmarks.http://www.spec.

org/osg/jvm98.

[46]T.Stack, E.Eide,and J.Lepreau.Bees:A Se-

cure,Resource-Controlled,Java-Based Execution Envi-ronment.In Proceedings of the IEEE Conference on Open Architectures and Network Programming,pages97–106, San Francisco,CA,April2003.

[47]Sun Microsystems,Inc.Installing,Administering,and

Using the Basic Security Module.2550Garcia Ave., Mountain View,CA94043,December1991.

[48]P.Tullmann and J.Lepreau.Nested Java Processes:OS

Structure for Mobile Code.In Proceedings of the Eighth

ACM SIGOPS European Workshop on Support for Com-posing Distributed Applications,pages111–117,Sintra, Portugal,1998.

[49]G.Vigna,B.Cassel,and D.Fayram.An Intrusion De-

tection System for Aglets.In Proceedings of the In-ternational Conference on Mobile Agents,pages64–77, Barcelona,Spain,October2002.

[50]G.Vigna,S.Eckmann,and R.Kemmerer.The STAT

Tool Suite.In Proceedings of DISCEX2000,pages1046–1055,Hilton Head,South Carolina,January2000.IEEE Computer Society Press.

[51]G.Vigna,R.A.Kemmerer,and P.Blix.Designing a Web

of Highly-Con?gurable Intrusion Detection Sensors.In W.Lee,L.M`e,and A.Wespi,editors,Proceedings of the4th International Symposiun on Recent Advances in Intrusion Detection(RAID2001),volume2212of LNCS, pages69–84,Davis,CA,October2001.Springer-Verlag.

[52] D.Wagner and D.Dean.Intrusion Detection via Static

Analysis.In Proceedings of the IEEE Symposium on Se-curity and Privacy,pages156–169,Oakland,CA,May 2001.IEEE Press.

[53]R.Wahbe,S.Lucco,T.Anderson,and S.Graham.Ef-

?cient Software-Based Fault Isolation.In Proceedings of the14th Symposium on Operating Systems Principles, pages203–216,New York,NY,USA,December1993.

ACM Press.

[54] C.Warrender,S.Forrest,and B.A.Pearlmutter.Detecting

Intrusions using System Calls:Alternative Data Models.

In IEEE Symposium on Security and Privacy,pages133–145,1999.

[55]L.Zhang and C.Krintz.An Investigation of Concurrent

Application Execution in the JikesRVM.Technical Re-port TR2003-02,https://www.wendangku.net/doc/0415385494.html,puter Science,UCSB,2003.

电子邮件试题及答案

《信息技术基础》（电子邮件部分） 强化练习 1．如果E-mail地址是wang@https://www.wendangku.net/doc/0415385494.html,，那么用该邮箱地址发送邮件范围：（）A．只能是云南 B．只能是中国 C．只能是教育部门 D．可以是全世界 2．某同学以myname为用户名在新浪网(https://www.wendangku.net/doc/0415385494.html,)注册的电箱地址应该是:（） A myname@https://www.wendangku.net/doc/0415385494.html, B．https://www.wendangku.net/doc/0415385494.html, C．myname.sina@com D．https://www.wendangku.net/doc/0415385494.html,@myname 3．使用WEB方式(直接在网站上)收发电子邮件时，以下描述错误的是:（） A．不用设置SMTP服务域名 B．不用设置POP3服务域名 C．不用输入账号和密码登录 D．可以在附件中插入图片文件 4．在撰写邮件时，在收件人对话框的“收件人”栏中:（） A．只能输入一个人的收件地址 B．只能输人多个人的收件地址 C．既可以输入一个人的收件地址又可以输人多个人的收件地址 D．只能输入收件人的姓名 5．要将一封电子邮件同时发送给几个人，可以在收件人栏中输入他们的地址，并用（）分隔。 （A）”（B）。（C），（D） / 6．关于发送电子邮件，下列说法中正确的是（）。 （A）你必须先接入Internet，别人才可以给你发送电子邮件 （B）你只有打开了自己的计算机，别人才可以给你发送电子邮件 （C）只要有E-Mail地址，别人就可以给你发送电子邮件 （D）别人只要接入了Internet，就可以给你发送电子邮件 7．要给某人发电子邮件，必须知道他的（）。 （A）电话号码（B）家庭地址（C）姓名（D）E-Mail地址 8．在发送电子邮件时，在邮件中（）。 （A）只能插入一个图形附件（B）只能插入一个声音附件 （C）只能插入一个文本附件（D）可以根据需要插入多个附件 9．电子邮件从本质上来说就是（）。 （A）浏览（B）电报（C）传真（D）文件 10．小明写了一份研究性学习结题报告电子文档，投稿前就稿子审阅修订问题需要与身在国外留学的叔叔进行较长时间的交流。你认为小明应该采用的较合理的信息交流方式是：（） (A)电报 (B)电话 (C)书信 (D)电子邮件 11．下列主要用于电子邮件收发和管理的软件是（） (A)FrontPage (B)Outlook Express (C)ACDSee (D)WinRAR 12．接收电子邮件的协议是（） (A)SMTP (B)HTTP (C)POP3 (D)TCP/IP 13．在电子邮件中所包含的信息（） (A)只能是文字信息 (B)只能是文字和图形图像信息 (C)只能是文字与声音信息 (D)可以是文字、声音和图形图像信息 14．把电子邮件发送到收件人的电子信箱中，所采用的邮件传输协议是（）

河北工业大学软件测试的期末复习资料

软件测试的重点 第一章 P4 软件缺陷：它是计算机系统或者程序中存在的任何一种破坏正常运行能力的问题，错误，或者隐藏的功能缺陷，瑕疵。注：软件缺陷出现最多的阶段是需求规格说明书。 P9软件测试的定义：软件测试为了发现程序中的错误而执行程序的过程。 {软件测试的目的：就在于在软件投入运行之前，尽可能多地发现软件中的错误。===测试的目的是发现程序中的错误，是为了证明程序有错，而不是证明程序无错。} 实现此目的的核心是测试用例的设计。判断软件测试的成功与失败：一个好的测试用例在于发现还未曾发现的错误，成功的测试是发现了错误的测试。 软件测试的目标是为了检验软件系统是否满足用户的需求。 调试和测试的区别：首先调试是由程序员编试的，且调试是在测试之前。/////调试是一个随机的、不可重复的过程，目的是寻找错误的原因和具体的位置，并修复错误。调试一般在测试前进行。 4.优秀的软件测试员应具备的素质: 1 软件测试人员是群探索者。 2 软件测试人员是故障排除员。 3 软件测试人员不放过任何蛛丝马迹。 4 软件测试人员具有创造性。 5 软件测试人员是群追求完美者。 6人员判断准确。 7 软件测试人员注重策略和外交。 8 软件测试人员善于说服。 5. P12软件测试的分类： 1.从是否需要执行被测软件的角度（程序是否运行的角度）：软件测试可分为静态测试和动态测试。其中静态测试可分为(1)代码检查法（2）静态结构分析法（3）代码度量质量法其中动态测试分为（1）黑盒测试和白盒测试

###二者的区别:静态测试不实际执行程序，而是利用人工手段及静态测试工具完成对程序的静态测试。主要目的是检查软件的表示与描述是否一致，没有冲突和歧义。而动态测试则是实际运行测试用例，以发现软件中的错误。 ### 静态测试和动态测试的时序关系： 一般可先进行静态测试，即代码检查法、静态结构分析法、代码质量度量法等进行测试；然后进行动态测试，即逻辑覆盖法、基本路径测试法、程序插桩等进行测试。 2.从软件测试用例设计方法的角度（从测试的策略）：可分为黑盒测试和白盒测试 （1）黑盒测试是一种从用户角度出发的测试，又称为功能测试，数据驱动测试和基于规格说明的测试。（2）白盒测试基于产品的内部结构来进行测试，检查内部操作是否按规定执行，软件各个部分功能是否得到充分利用，又称为结构测试，逻辑驱动测试和基于程序的测试，即根据被测程序的内部结构设计测试用例，测试者需要事先了解被测程序的结构。 3.按照软件的开发阶段分类:软件测试可分为单元测试，集成测试，确认测试，系统测试和验收测试。 4.按照实施测试的组织，可将测试分为Alpha测试、Beta测试及第三方测试。 （1）． Alpha测试 Alpha测试属于开发方进行，指软件开发组织公司内部人员模拟各类用户对即将交付的软件产品进行测试，以发现其中的错误并改正。 （2 ）.Beta测试 Beta测试是用户进行的测试，但通常不等同于验收测试，即决定是否接受软件并不是Beta测试的目的。 Beta测试的目的在于帮助开发方在正式发布软件产品前对其进行最后的改进。 （3 ）第三方测试 第三方测试是指由不同开发方和用户方的组织进行的测试。 6.软件测试技术的发展历史和现状 （1）软件测试技术的发展历史 ●20世纪50年代，英国，图灵给出了软件测试的原始定义。 ●1957年，测试是发现软件潜在错误和缺陷的活动。 ●1972年，北卡罗纳大学举行了首届软件测试正式会议。

苏科版信息技术下册第10课《收发电子邮件》教案

第10课收发电子邮件 ［教学目的与要求］ 1.学会进入自己的电子邮箱。 2.学会发电子邮件。 3.学会回复电子邮件。 4.通过发电子邮件的实践活动，让学生学会自主学习，能够协同合作、探索新知。 5.让学生养成遵守网络道德规范的良好习惯。 6.培养学生学习、使用因特网的兴趣和意识。 ［课时安排］ 建议安排1课时。 ［教学重点与难点］ 1．重点：登录电子邮箱的操作方法，如何编写、发送电子邮件。 2.难点：如何充分调动学生参与的积极性，使学生遵守网络道德规范的良好习惯。［教材分析与教法建议］ 1．教材的地位与作用 E-mail是因特网上重要的信息服务方式，它为世界各地的因特网用户提供了一种快速、便捷、经济的通信方式，由于这些优点, 因特网上数以亿计的用户都有自己的E-mail地址，E-mail也成为利用率最高的因特网应用。 本课是在前一课学习申请电子邮箱的基础上，让学生对电子邮箱和电子邮件有进一步的认识。 2．教学方法指导 培养学生良好的网络道德习惯和信息技术素养。从低层次探索入手，充分调动学生积极自主地探究新知识。让学生自主探索，主动构建知识。以学生为主体，凸现分层教学。让学生展示自己的新发现，体验成功的喜悦。同时也让学生学会与他人合作学习，营造一个相互学习，相互得益的氛围，调动每个学生的积极性。 （1）课前，教师可以布置学生注册两个以上电子邮箱账号，或批量注册一批账号以供备用，并及时地把自己的新邮箱地址通知同班好友，这样在课堂上可以有更多实践的机会。 （2）在备课时，教师可设计一些适合小学生心理特点的电子邮件内容，增加练习或模拟发电子邮件的趣味性，使学生尽快掌握收发电子邮件的技能。 （3）有条件的学校，可在本校的局域网上，利用Windows NT 的Microsoft 邮局系统，建立起局域网内部电子邮件系统，给每位学生设置账号账号和密码，然后设置好学生机上收

基于Java的图形图像处理软件的设计与实现

目录 引言 (4) 第一章绪论 (5) 1.1.1 计算机图形图像学的发展简史 (5) 1.1.2现有图形图像处理软件 (5) 1.2课题研究的目的及意义 (6) 第二章图形图像处理软件开发技术基础 (7) 2.1 Java Swing 简介 (7) 2.1.1 Swing的特性 (7) 2.1.2 Swing程序包和类 (8) 2.2 MVC体系结构 (9) 2.2.1 模型 (9) 2.2.2 视图 (9) 2.2.3 控制器 (10) 第三章图形图像软件的设计 (11) 3.1图形处理模块的设计 (11) 3.1.1结构设计 (11) 3.1.2功能描述 (11) 3.1.3图形处理模块结构图 (11) 3.1.4主要类设计.................................................................... 错误！未定义书签。 3.2 图像处理模块的设计 (12) 3.2.1结构设计 (12) 3.2.3结构图 (13) 4.1 绘图功能的详细设计与实现 (15) 4.1.1 菜单栏 (15) 4.1.2工具栏 (16) 4.1.3画图区 (16) 4.1.4状态栏 (17) 4.2 图像编辑的详细设计与实现 (18) 4.3滤镜处理的详细设计与实现 (19) 4.3.1 图像增强 (19) 4.3.2图像边缘检测 (21) 4.3.3 图像平滑处理 (23) 4.3.4 系统测试 (24) 结论 (26) 致谢 (27)

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