Zelix KlassMaster - Documentation

Compatibility

What do you need to run Zelix KlassMaster™?

Zelix KlassMaster™ is written entirely in Java 8 (i.e. JDK 1.8) and technically should run on any platform that supports a Java 8 or better Virtual Machine. However, note that Zelix KlassMaster™ version 10 or better requires a recent version of a Java 8 JVM or better to run. If you use an Oracle JVM earlier than 1.8.0_152 then you may get a JVM crash due to HotSpot bugs. Also note that Zelix KlassMaster™ version 25 currently may not run successfully on older versions (e.g. pre-Aug 2020) of the Eclipse OpenJ9 JVM due to a JVM bug.

More generally, differences in the file systems and GUIs can also cause problems. Further, Zelix KlassMaster's flow obfuscation technology can expose bugs in some Just in Time (JIT) compilers.

Zelix KlassMaster™ has been tested on:
  • Windows 11™ 64bit using
    • java version "1.8.0_461" Java HotSpot(TM) 64-Bit Server VM (build 25.461-b11, mixed mode)
    • openjdk version "1.8.0_462" IBM Semeru Runtime Open Edition (build 1.8.0_462-b08) Eclipse OpenJ9 VM (build openj9-0.53.0, JRE 1.8.0 Windows 11 x86-32-Bit 20250723_1280 (JIT enabled, AOT enabled)
    • java version "11.0.28" 2025-07-15 LTS Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.28+12-LTS-279, mixed mode)
    • java version "21.0.8" 2025-07-15 LTS Java HotSpot(TM) 64-Bit Server VM (build 21.0.8+12-LTS-250, mixed mode, sharing)
    • openjdk version "21.0.8" 2025-07-15 LTS IBM Semeru Runtime Open Edition 21.0.8.0 (build 21.0.8+9-LTS) Eclipse OpenJ9 VM 21.0.8.0 (build openj9-0.53.0, JRE 21 Windows 11 amd64-64-Bit Compressed References 20250715_505 (JIT enabled, AOT enabled)
    • java version "24.0.2" 2025-07-15 Java HotSpot(TM) 64-Bit Server VM (build 24.0.2+12-54, mixed mode, sharing)
    • openjdk version "24.0.2" 2025-07-15 IBM Semeru Runtime Open Edition 24.0.2.0 (build 24.0.2+12) Eclipse OpenJ9 VM 24.0.2.0 (build openj9-0.54.0, JRE 24 Windows 11 amd64-64-Bit Compressed References 20250715_118 (JIT enabled, AOT enabled)
    • java version "24.0.2" 2025-07-15 Java HotSpot(TM) 64-Bit Server VM Oracle GraalVM 24.0.2+11.1 (build 24.0.2+11-jvmci-b01, mixed mode, sharing) but with errors (Warning: Systemic Graal compilation failure detected: 1 of 39 (2%) of compilations failed)
    • openjdk version "25" 2025-09-16 OpenJDK 64-Bit Server VM (build 25+36-3489, mixed mode, sharing)
  • Linux (Xubuntu 22.04) using
    • java version "1.8.0_461" Java HotSpot(TM) 64-Bit Server VM (build 25.461-b11, mixed mode)
    • openjdk version "1.8.0_442" IBM Semeru Runtime Open Edition (build 1.8.0_442-b06) Eclipse OpenJ9 VM (build openj9-0.49.0, JRE 1.8.0 Linux amd64-64-Bit Compressed References 20250205_1153 (JIT enabled, AOT enabled)
    • java version "11.0.28" 2025-07-15 LTS Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.28+12-LTS-279, mixed mode)
    • java version "17.0.16" 2025-07-15 LTS Java HotSpot(TM) 64-Bit Server VM (build 17.0.16+12-LTS-247, mixed mode, sharing)
    • java version "21.0.8" 2025-07-15 LTS Java HotSpot(TM) 64-Bit Server VM (build 21.0.8+12-LTS-250, mixed mode, sharing)
    • openjdk version "21.0.8" 2025-07-15 LTS IBM Semeru Runtime Open Edition 21.0.8.0 (build 21.0.8+9-LTS) Eclipse OpenJ9 VM 21.0.8.0 (build openj9-0.53.0, JRE 21 Linux amd64-64-Bit Compressed References 20250715_547 (JIT enabled, AOT enabled)
    • java version "24.0.2" 2025-07-15 Java HotSpot(TM) 64-Bit Server VM (build 24.0.2+12-54, mixed mode, sharing)
    • openjdk version "24.0.2" 2025-07-15 IBM Semeru Runtime Open Edition 24.0.2.0 (build 24.0.2+12) Eclipse OpenJ9 VM 24.0.2.0 (build openj9-0.54.0, JRE 24 Linux amd64-64-Bit Compressed References 20250715_136 (JIT enabled, AOT enabled)
    • openjdk version "25" 2025-09-16 OpenJDK 64-Bit Server VM (build 25+36-3489, mixed mode, sharing)
  • MacOS (Monterey 12.7.6) using
    • java version "1.8.0_461" Java HotSpot(TM) 64-Bit Server VM (build 25.461-b11, mixed mode)
    • openjdk version "1.8.0_462" IBM Semeru Runtime Open Edition (build 1.8.0_462-b08) Eclipse OpenJ9 VM (build openj9-0.53.0, JRE 1.8.0 Mac OS X amd64-64-Bit Compressed References 20250722_1319 (JIT enabled, AOT enabled)
    • java version "21.0.8" 2025-07-15 LTS Java HotSpot(TM) 64-Bit Server VM (build 21.0.8+12-LTS-250, mixed mode, sharing)
    • java version "24.0.2" 2025-07-15 Java HotSpot(TM) 64-Bit Server VM (build 24.0.2+12-54, mixed mode, sharing)
    • openjdk version "25" 2025-09-16 OpenJDK 64-Bit Server VM (build 25+36-3489, mixed mode, sharing)

What can Zelix KlassMaster™ process?

Zelix KlassMaster™ can process bytecode compiled for Java 9 through to 25 including modules.

Of course, it can also process bytecode compiled for JDK 1.1.x, 1.2.x, 1.3.x, 1.4.x, 1.5.0, 1.6.0, 1.7.0 and 1.8.0 JVMs. However, it is highly recommended that you always set the internal classpath used by Zelix KlassMaster™ (i.e. the ZKM Script classpath statement) to point to the bootstrap classes corresponding to the classes you are obfuscating. For Java 2 through to Java 8 that is the corresponding rt.jar. For Java 9 to Java 25 it is the corresponding lib\jrt-fs.jar file system.

Note that if you use the Reference Obfuscation functionality on bytecode which is at the Java 8 level then your obfuscated bytecode will require a newer Java 8 or better JVM to run. For example, if you use an Oracle JVM earlier than 1.8.0_152 then you may get a JVM crash due to HotSpot bugs.
 
Documentation Table of Contents
Zelix KlassMaster - Java Obfuscator
 
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