jhoja

The Java disassembler for Jasmin, Decompile protection tool for JD

Last update 24 Mar 2018

What is jhoja?

jhoja is a disassembler for Java class files.
It converts Java class files into Jasmin assembly source code.
It can also insert decompilation protection code using the -g option.
It is a command-line tool.
No graphical user interface is provided.
Based on SWAG javap2 Ver 1.02.
forked from SWAG javap2. http://www.swag.uwaterloo.ca/javap2/

Known limitations

Reassembly supports ASCII-only source files.
(Without comments.)
Other character encodings are not supported.
jhoja can output UTF-8 strings.
However, Jasmin does not support UTF-8.
Converting the UTF-8 source to a local character encoding may allow it to work on that system.
However, cross-platform compatibility may be lost.
The decompilation protection function is intended for the JD-GUI decompiler.
It does not support the Jad decompiler.

Download

Download jhoja Ver 1.01 for Windows. (including source patch.)
Download from GitHub. (including patched source.)

How does jhoja differ from javap and SWAG javap2?

jhoja supports Jasmin assembly source output.
It also provides a decompilation protection function.
These features are not supported by Oracle javap or SWAG javap2.
jhoja outputs UTF-8 text.
SWAG javap2 does not support UTF-8.

Decompilation protection

The decompilation protection function is intended for the JD-GUI decompiler.
It does not support the Jad decompiler.
The protection does not affect execution speed.
However, the resulting class file is larger than usual.
Additional protection code is inserted.
Requires Jasmin (Java assembler) and a JRE or JDK.
This protection is not strong.
The protection can be bypassed relatively easily with jhoja and Jasmin.

Examples: Decompile jhoja decompile protection class file by JD-GUI Decompiler.

Decompile jhoja decompile protection file by JD-GUI

Debug information

Debug information can be read in the source comments.
However, reassembling the file causes the debug information in the class file to be lost.

Supported operating systems

The provided binary runs on Microsoft Windows.
Compiled with C++ Builder XE8.
Written in C++, but mostly C-style code.
It may work on other operating systems if recompiled.
The Windows version may run on GNU/Linux (Intel/AMD) using Wine.

Binary License

Apache v2 license
(follow the SWAG's license.)

jhoja ver 1.01 Source patch License

Apache v2 license
(follow the SWAG's license.)
chenged 2-clause BSD license to Apache v2 licence.
(C) Masaki Oba
admin@nabeta.tk
http://www.nabeta.tk

Example: excerpt of disassembled code


.field	hizuke_str Ljava/lang/String;

.field	moto_gatsu I

.field	moto_nen I

.field	static properties Ljava/util/Properties;

.field	static menubarheight I



.method	private static resizeframe(II)V



    .limit stack 6

    .limit locals 20



    getstatic	asucalendar/menubarheight I

    istore 18 

    iload_0

    iconst_2

    iadd

    istore 16 

    iload_0

    iload_1

    if_icmple	Z18

    iload_1

    istore 16 

    ;.line 101

Z18:

    iload 16 

    i2f

    f2d

    ldc2_w	0.200000

    dmul

    d2i

    istore 17 

    iload 17 

    bipush	40

    if_icmplt	Z43

    iload_0

    sipush	300

    if_icmpge	Z47

    ;.line 103

Z43:

    bipush	40

    istore 17 

    ;.line 106

Z47:

    getstatic	asucalendar/bbb Ljavax/swing/JPanel;

    iconst_0

    iload 18 

    iload_0

    iconst_1

    isub

    iload 17 

    iload 18 

    iadd

    iconst_1

    isub

    invokevirtual	javax/swing/JPanel/setBounds(IIII)V

    getstatic	asucalendar/tugi Ljavax/swing/JButton;

    iload_0

    iconst_1

    isub

    bipush	65

    isub

    iconst_1

    bipush	30

    bipush	19

    invokevirtual	javax/swing/JButton/setBounds(IIII)V

    getstatic	asucalendar/tugi_nen Ljavax/swing/JButton;

    iload_0

    iconst_1

    isub

    bipush	30

    isub

    iconst_1

    bipush	30

    bipush	19

    invokevirtual	javax/swing/JButton/setBounds(IIII)V

    getstatic	asucalendar/lb Ljavax/swing/JLabel;

    iconst_1

    bipush	12

    iload_0

    iconst_1

    isub

    iload 17 

    iconst_1

    isub

    invokevirtual	javax/swing/JLabel/setBounds(IIII)V

    getstatic	asucalendar/dp Ljavax/swing/JPanel;

    iconst_0

    iload 18 

    iload 17 

    iadd

    iload_0

    iconst_1

    iadd

    iload_1

    iload 18 

    isub

    iload 17 

    isub

    iconst_1

    iadd

    invokevirtual	javax/swing/JPanel/setBounds(IIII)V

    iload 17 

    bipush	40

    if_icmpgt	Z164

    iload 17 

    bipush	20

    isub

    i2f

    f2d

    ldc2_w	0.700000

    dmul

    d2i

    istore 10 

    goto Z178

    ;.line 115

Z164:

    iload 17 

    bipush	20

    isub

    i2f

    f2d

    ldc2_w	0.600000

    dmul

Usage

Usage: jhoja [-g] [-h] xxx.class > xxx.j
-g: Insert decompile protection code.
-h: show help.

Examples:


jhoja -g xxx.class > xxx.j

jhoja xxx.class > xxx.j

jhoja xxx.class | more

Examples using Jasmin

Without decompilation protection:


jhoja xxx.class > xxx.j

java -jar jasmin.jar  xxx.j

With decompilation protection:


jhoja -g xxx.class > xxx.j

java -jar jasmin.jar  xxx.j

Example: batch file to protect multiple class files

Windows batch file.
Requires Jasmin (Java assembler) and a JRE or JDK.


C:\>zenbu *.class

zenbu.bat


@echo off

for %%f in (%*) do (

  jhoja -g %%f > %%f.j

  java -jar jasmin.jar  %%f.j

)

History

12 Mar 2018 jhoja for Windows Ver 1.0 (binary and source patch)
13 Mar 2018 fixed a HTML file in ZIP file
14 Mar 2018 fixed HTML files in ZIP file
24 Mar 2018 ver 1.01

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