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How does it work?
ClassGuard is a tool to
prevent Java decompiling and for
licensing Java applications.
The Java class files are encrypted using a 128Bit AES encryption. The AES key is generated
randomly every time you start the encryption tool. The decryption is done transparently by a custom
class loader. The main part of this class loader is written in C to prevent decompiling and other
tampering.
The current version additionally contains a license manager. The main part of the license
manager is also written in C. Java class files are only decrypted if a valid license is found.
How does Tomcat and Jboss support work?
As of Version 1.5, ClassGuard supports
Tomcat and
Jboss containers.
To use ClassGuard in combination with tomcat, you have to configure your web application for
using the ClassGuard tomcat class loader. This can be set in the context of the web
application.
To use ClassGuard in combination with Jboss, you have to include the ClassGuard Jboss service
JbossClassGuard.sar in your ear file. Note that Jboss support is still experimental.
Support for other J2EE containers may be implemented on request, please
ask.
Further links:
How secure is it really?
There is no way of cracking the used 128Bit
AES Encryption. As the main part of ClassGuard is written in C, the key can't be
extracted using a Java decompiler. However, there may be possibilities to crack the encryption
using a debugger on the assembler level. At the moment, no such attempt is known.
Some experts state, it would be possible to crack byte code encryption by hacking some class
files of the Java language itsself, e.g. defineClass() in java.lang.ClassLoader. Bytecode encrypted
by ClassGuard is passed through to the virtual machine on the native level. The bytecode never
appears in any Java class.
Is there a way of encrypting additional resources?
Since version 2.0, the encryption of addtional resources (e.g. property files or images) is
possible in a transparent way. Encrypted resources may be loaded by
getResource() or
getResourceAsStream().
Further links:
What platforms are supported?
The current version 2.5 supports Sun Java 5 and 6 for Windows and Linux on i386 and x86-64. More
platforms are planned for Version 3.0, including MacOS X and Solaris on x86-64. The release
planning for platforms is based on demand, more platforms may be available on request. Virtual
machines besides Sun Java may work, but are not supported.
When I debug my encrypted project, I get a java.lang.NoClassDefFoundError
Currently, there are three ways to implement a Java debugger or profiler:
- java.lang.instrument (-javaagent)
- jvmti (-agentlib/-agentpath)
- jvmpi (-Xrun)
It is possible to get Java bytecode by all of these ways. Therefor
ClassGuard detects Java debuggers and refuses to decrypt any classes in case of
any running debugger.
Can I combine ClassGuard and Code Obfuscation?
As ClassGuard works on the binary level of class files, it does not iterfere with Java code
obfuscation tools.
How can I check if my class encryption tool works reliably?
You may use our debugging agent to test your code encryption tool. Download JSecurityAgent.jar
and run your application with the additional parameter
-javaagent:JSecurityAgent.jar. The bytecode agent displays all classes of which it can get
the bytecode. If you see a line like
BytecodeAgent: Got bytecode of my/encrypted/class
your tool is vulnerable.
Further links:
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