Home > Articles

Obfuscating Classes

This chapter is from the book

Potential Problems and Common Solutions

Obfuscation is a reasonably safe process that should preserve application functionality. However, in certain cases the transformations performed by obfuscators can inadvertently break code that used to work. The following sections look at the common problems and recommended solutions.

Dynamic Class Loading

The renaming of packages, classes, methods, and variables works fine as long as the name is changed consistently throughout the system. Obfuscators ensure that any static references within the bytecode are updated to reflect the new name. However, if the code performs dynamic class loading using Class.forName() or ClassLoader.loadClass() passing an original class name, a ClassNotFound exception can result. Modern obfuscators are pretty good with handling such cases, and they attempt to change the strings to reflect the new names. If the string is created at runtime or read from a properties file, though, the obfuscator is incapable of handling it. Good obfuscators produce a log file with warnings pointing out the code that has potential for runtime problems.

The simplest solution is to configure the obfuscator to preserve the names of dynamically loaded classes. The content of the class, such as the methods, variables, and code, can still be transformed.

Stories From the Trenches

The most innovative product from CreamTec is WebCream, which is available for a free download from the Web. The free edition is limited to five concurrent users; to get more users, you must buy a commercial license. Having grown up in the Ukraine, I knew many people who would prefer to crack the licensing to turn the free edition into an unlimited edition that would normally be worth thousands of dollars. At CreamTec, we used a simple, free obfuscator that didn't do much more than name mangling. We thought it was good enough until a friend of mine, who views limited-functionality commercial software as a personal insult, cracked our licensing code in less than 15 minutes. The message was clear enough, and we decided to purchase Zelix KlassMaster to protect the product as well as we could. After we used the aggressive control flow obfuscation with a few extra tricks, our friend has not been able to get to the licensing code with the same ease as before—and because he didn't want to spend days figuring it out, he has given up.

Reflection

Reflection requires compile-time knowledge of method and field names, so it is also affected by obfuscation. Be sure to use a good obfuscator and to review the log file for warnings. Just as with the dynamic class loading, if runtime errors are caused by obfuscation, you must exclude from obfuscation the method or field names that are referenced in Class.getMethod or Class.getField.

Serialization

Serialized Java objects include instance data and information about the class. If the version of the class or its structure changes, a deserialization exception can result. Obfuscated classes can be serialized and deserialized, but an attempt to deserialize an instance of a nonobfuscated class by an obfuscated class will fail. This is not a very common problem, and it can usually be solved by excluding the serializable classes from obfuscation or avoiding the mixing of serialized classes.

Naming Conventions Violation

The renaming of methods can violate design patterns such as Enterprise JavaBeans (EJB), where the bean developer is required to provide methods with certain names and signatures. EJB callback methods such as ejbCreate and ejbRemove are not defined by a super class or an interface. Providing these methods with a specific signature is a mere convention prescribed by EJB specification and enforced by the container. Changing callback method names violates the naming convention and makes the bean unusable. You should always be sure to exclude the names of such methods from obfuscation.

Maintenance Difficulties

Last, but not least, obfuscation makes maintaining and troubleshooting applications more difficult. Java exception handling is an effective way of isolating the faulty code, and looking at the stack trace can generally give you a good idea of what went wrong and where. Keeping the debugging information for source filenames and line numbers enables the runtime to report the exact location in code where the error occurred. If done carelessly, obfuscation can inhibit this feature and make debugging harder because the developer sees only the obfuscated class names instead of the real class names and line numbers.

You should preserve at least the line number information in the obfuscated code. Good obfuscators produce a log of the transformations, including the mapping between the original class names and methods and the obfuscated counterparts. The following is an excerpt from the log file generated by Zelix KlassMaster for the ChatServer class:

Class: public covertjava.chat.ChatServer    =>    covertjava.chat.d
    throw new Exception(a("\002)qUe7egDs1,rM6:*g@6  covertjava.chat.d
  Source: "ChatServer.java"
  FieldsOf: covertjava.chat.ChatServer
    hostName  =>  e
    protected static instance  =>  a
    messageListener  =>  d
    protected registry  =>  c
    protected registryPort  =>  b
    userName  =>  f
  MethodsOf: covertjava.chat.ChatServer
    public static getInstance()  =>  a
    public getRegistry(int)  =>  a
    public init()  =>  b
    public receiveMessage(java.lang.String, covertjava.chat.MessageInfo)
    _NameNotChanged
    public sendMessage(java.lang.String, java.lang.String)  =>  a
    public setMessageListener(covertjava.chat.MessageListener)  =>  a

So, if an exception stack trace shows the covertjava.chat.d.b method, you can use the log and find out that it was originally called "init" in a class that was originally called covertjava.chat.ChatServer. If the exception occurred in covertjava.chat.d.a, you would not know the original method name for sure because multiple mappings exist (witness the power of overloading). That's why line numbers are so important. By using the log file and the line number in the original source file, you can quickly locate the problem area in the application code.

Some obfuscators provide a utility that reconstructs the stack traces. This is a convenient way of getting the real stack trace for the obfuscated stack trace. The utility typically uses the same method as we used earlier, but it automates the job—so why not save ourselves some time? It also allows scrambling the line numbers for extra protection.

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.

Overview


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.

Surveys

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.

Newsletters

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.

Security


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

Children


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

Marketing


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.

Choice/Opt-out


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.

Links


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