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 26 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_481" Java HotSpot(TM) 64-Bit Server VM (build 25.481-b10, mixed mode)
    • openjdk version "1.8.0_482" IBM Semeru Runtime Open Edition (build 1.8.0_482-b08) Eclipse OpenJ9 VM (build 1.8.0_482-b08-openj9-0.57.0, JRE 1.8.0 Windows 11 x86-32-Bit 20260225_1444) (JIT enabled, AOT enabled)
    • java version "11.0.30" 2026-01-20 LTS Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.30+7-LTS-282, mixed mode)
    • java version "17.0.18" 2026-01-20 LTS Java HotSpot(TM) 64-Bit Server VM (build 17.0.18+8-LTS-264, mixed mode, sharing)
    • java version "21.0.10" 2026-01-20 LTS Java HotSpot(TM) 64-Bit Server VM (build 21.0.10+8-LTS-217, mixed mode, sharing)
    • openjdk version "21.0.10" 2026-01-20 LTS IBM Semeru Runtime Open Edition 21.0.10.1 (build 21.0.10+7-LTS) Eclipse OpenJ9 VM 21.0.10.1 (build 21.0.10+7-openj9-0.57.0) (JIT enabled, AOT enabled)
    • java version "25.0.2" 2026-01-20 LTS Java HotSpot(TM) 64-Bit Server VM (build 25.0.2+10-LTS-69, mixed mode, sharing)
    • openjdk version "25.0.2" 2026-01-20 LTS IBM Semeru Runtime Open Edition 25.0.2.1 (build 25.0.2+10-LTS) Eclipse OpenJ9 VM 25.0.2.1 (build 25.0.2+10-openj9-0.57.0) (JIT enabled, AOT enabled)
    • openjdk version "26" 2026-03-17 OpenJDK 64-Bit Server VM (build 26+35-2893, mixed mode, sharing)
  • Linux (Xubuntu 22.04) using
    • java version "1.8.0_481" Java HotSpot(TM) 64-Bit Server VM (build 25.481-b10, mixed mode)
    • openjdk version "1.8.0_482" IBM Semeru Runtime Open Edition (build 1.8.0_482-b08) Eclipse OpenJ9 VM (build 1.8.0_482-b08-openj9-0.57.0) (JIT enabled, AOT enabled)
    • java version "11.0.30" 2026-01-20 LTS Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.30+7-LTS-282, mixed mode)
    • openjdk version "21.0.10" 2026-01-20 LTS IBM Semeru Runtime Open Edition 21.0.10.1 (build 21.0.10+7-LTS) Eclipse OpenJ9 VM 21.0.10.1 (build 21.0.10+7-openj9-0.57.0) (JIT enabled, AOT enabled)
    • java version "25.0.2" 2026-01-20 LTS Java HotSpot(TM) 64-Bit Server VM (build 25.0.2+10-LTS-69, mixed mode, sharing)
    • openjdk version "25.0.2" 2026-01-20 LTS IBM Semeru Runtime Open Edition 25.0.2.1 (build 25.0.2+10-LTS) Eclipse OpenJ9 VM 25.0.2.1 (build 25.0.2+10-openj9-0.57.0) (JIT enabled, AOT enabled)
    • openjdk version "26" 2026-03-17 OpenJDK 64-Bit Server VM (build 26+35-2893, mixed mode, sharing)
  • MacOS (Tahoe 26.3.1) using
    • java version "1.8.0_481" Java HotSpot(TM) 64-Bit Server VM (build 25.481-b10, mixed mode)
    • java version "11.0.30" 2026-01-20 LTS Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11.0.30+7-LTS-282, mixed mode)
    • java version "21.0.10" 2026-01-20 LTS Java HotSpot(TM) 64-Bit Server VM (build 21.0.10+8-LTS-217, mixed mode, sharing)
    • java version "25.0.2" 2026-01-20 LTS Java HotSpot(TM) 64-Bit Server VM (build 25.0.2+10-LTS-69, mixed mode, sharing)
    • openjdk version "25.0.2" 2026-01-20 LTS IBM Semeru Runtime Open Edition (build 25.0.2+10-LTS) Eclipse OpenJ9 VM 25.0.2.1 (build 25.0.2+10-openj9-0.57.0) (JIT enabled, AOT enabled)
    • openjdk version "26" 2026-03-17 OpenJDK 64-Bit Server VM (build 26+35-2893, mixed mode, sharing)

What can Zelix KlassMaster™ process?

Zelix KlassMaster™ can process bytecode compiled for Java 9 through to 26 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 26 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
 
Copyright © 2026 Zelix Pty Ltd (A.B.N. 47 078 740 093) All rights reserved.
Privacy Refunds Terms of Use