Home > Articles > Security > Network Security

This chapter is from the book

Using Zelix KlassMaster to Obfuscate a Chat Application

Even though each obfuscator has its own format of configuring the transformations, they all support a common set of features. The Chat application does not contain state-of-the-art algorithms or patent-pending inventions, but it is dear to our hearts so we are going to use Zelix KlassMaster to protect it from the prying eyes of hackers and thieves.

First, we obtain a copy of Zelix KlassMaster and install it on a local machine. Remember that we refer to the Chat application's home directory as CovertJava. Next, we copy ZKM.jar from KlassMaster's installation directory to our project lib directory so we can script against it. The easiest way to create the obfuscation script is with KlassMaster's GUI. Using the command

java -jar ZKM.jar

from the lib directory, we run the GUI. Then, in the initial helper dialog box that appears, we select the Set Classpath option. We now select the runtime libraries of the JDK we're using and, in the Open Classes dialog box that appears next, we select CovertJava/lib/chat.jar. After that, KlassMaster should load all the classes of the Chat application and we should be able to view the internal structure of the bytecode. The screen should look similar to Figure 3.1.

Figure 3.1Figure 3.1 Chat classes loaded into the KlassMaster GUI.

While working with the GUI, you can easily see just how flexible KlassMaster is. You can manually change the names of classes, methods, and fields; modify the visibility of classes or methods; make methods final; change text strings; and do other cool stuff. KlassMaster attempts to propagate the changes throughout the loaded code, so if other classes refer to a method and you change its name, the referring classes are updated to reflect the change. After making all your changes, you can save the classes as is or trim and obfuscate them first. Classes loaded into the GUI environment can be further modified after the obfuscation, even though I can't think of a reason why someone would need to do so. For details of KlassMaster's features and how to use it, please refer to its user manual.

A well-written Java application provides scripts to build it, so let's integrate obfuscation into our build script. We start by using KlassMaster's GUI to create the obfuscation script. Then, we update it manually to make it more flexible. It is entirely possible to write the script manually or copy and modify a sample script. We run the GUI and select ZKM Script Helper from the Tools menu. Then, we do the following:

  1. Read the instructions on the Introductory Page and click Next.

  2. On the Classpath Statement page, select rt.jar and click Next.

  3. On the Open Statement page, navigate to CovertJava/distrib/chat.jar and click > to select it for opening. We only need one file because all our application classes are packaged in it. Click Next.

  4. On the TrimExclude Statement page, the default exclusions are preset to exclude the cases where obfuscation is likely to result in an error. For example, renaming methods of an EJB implementation class makes it unusable, so EJBs are excluded by default.

  5. On the Trim Statement page, select the Delete Source File Attributes check box and the Delete Deprecated Attributes check box to get rid of the debug information; then click Next.

  6. In the Don't Change Main Class Name combo box on the Exclude Statement page, select covertjava.chat.ChatApplication to preserve its name. This keeps JAR manifest entries valid and enables users to continue invoking the chat using a human-readable name.

  7. On the Obfuscate Statement page, select Aggressive in the Obfuscate Control Flow combo box. Then select Aggressive in the Encrypt String Literals combo box, and select Scramble in the Line Number Tables combo box. This ensures adequate protection for the code but enables us to translate stack traces later. Make sure that Produce a Change Log File is checked and click Next.

  8. On the SaveAll Statement page, navigate to CovertJava/distrib and create a subdirectory called obfuscated. Select the newly created directory for output and click Next.

  9. The next page should show the script text and allow us to save it to a directory. Save it as obfuscate_script.txt in the CovertJava/build directory and exit the GUI.

The resulting script should look similar to Listing 3.4.

Listing 3.4 Obfuscation Script Generated by the GUI

/* Generated by Zelix KlassMaster 4.1.1 ZKM Script Helper 2003.08.13 17:03:43 */

classpath  "c:\java\jdk1.4\jre\lib\rt.jar"

open    "C:\Projects\CovertJava\distrib\chat.jar";

trim    deleteSourceFileAttributes=true

exclude   covertjava.chat.^ChatApplication^ public static main(java.lang.String[]);

obfuscate  changeLogFileIn=""

saveAll   archiveCompression=all "C:\Projects\CovertJava\distrib\obfuscated";

A good idea would be to replace the absolute file paths with the relative ones, so that instead of opening C:\Projects\CovertJava\distrib\chat.jar, the script opens distrib\chat.jar. Finally, we will integrate obfuscation into the build process by declaring a custom task and adding a target that calls it. KlassMaster is written in Java and can be called from any build script. Conveniently, it provides a wrapper class for Ant integration, so all we have to do is add the following to Chat's build.xml:

<!-- Define a task that will execute Zelix KlassMaster to obfuscate classes -->
<taskdef name="obfuscate" classname="ZKMTask" classpath="${basedir}/lib/ZKM.jar"/>
<!-- Define a target that produces obfuscated version of Chat -->
<target name="obfuscate" depends="release">
  <obfuscate scriptFileName="${basedir}/build/obfuscate_script.txt"

We can now run Ant on obfuscate target. If the build is successful, a new file (chat.jar) is created in CovertJava/distrib/obfuscated. This file contains the obfuscated version of Chat that can still be invoked using the java -jar chat.jar command. Take a few moments to look inside that JAR and try decompiling some of the classes.

Before we close the subject of using KlassMaster, I'd like to give a few more examples of script file syntax for excluding classes and class members from obfuscation. The format shown in Table 3.2 can be used for statements of obfuscation script that take in names as parameters. ZKM script language supports wildcards, such as * (any sequence of characters) and ? (any one character), and boolean operations, such as || (or) and ! (not). For a detailed explanation and full syntax, please refer to KlassMaster documentation.

Table 3.2 Commonly Used Name Patterns for KlassMaster


What It Matches


Package names package1 and package2. Other package names and children of package2 are not matched.


All package names in the application.


The name of the class Class1.


The name of Class1 in package package1 but not package1's name.


The names of Class1 and package1.

package1.^Class1^ method1()

The names of package1, Class1, and method1 with no parameters.

package1.^Class1^ method1(*)

The names of package1, Class1, and all overloaded versions of method1.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020