The other day I downloaded ICQ java, because I wanted to decompile
it(Imagine the possibilities!)
I tried decompiling with Mocha, but unfortunately it didn't
work(Mocha is a Beta version,and always will be, as sadly, the author 
died)
Searching for other de-compilers I came accross WingDis
The output is only slightly inferrior to Mocha, but it can decompile
all java programs I have come across, and it is being continually 
updated
The program has a 5 day limit though!
In this essay I will show how I patched WingDis.

                                
Search for the text "trial" in all the class files in the wingdis
directory.
The only file you will find containing the text is, ClassReader.class,
so this is our immediate target.
Obviously the first thing to try is to use Wingdis on itself to
decompile ClassReader.

"Sorry, WingDis is not allowed to decompile itself."

Oh good! Another thing to crack! Time Cracks are always boring, so
lets crack this first!

Mocha doesn't work, so load up ClassReader.class in IDA, and search 
for the "trial" again.


021 004         iload var020_4
006             iconst_3
159 000 076     if_icmpeq met020_355	:If Good jump away
042             aload_0 # var020_0
180 001 027     getfield 283
018 096         ldc1 "javadis"
182 000 201     invokevirtual int
		java.lang.String.indexOf(java.lang.String)
156 000 027     ifge met020_318		:If Bad jump to Error
042             aload_0 # var020_0
180 001 027     getfield 283
018 095         ldc1 "WingSoft"
182 000 201     invokevirtual int
		java.lang.String.indexOf(java.lang.String)
156 000 015     ifge met020_318		:If Bad jump to Error
042             aload_0 # var020_0
180 001 027     getfield 283
018 094         ldc1 "wingsoft"
182 000 201     invokevirtual int
		java.lang.String.indexOf(java.lang.String)
155 000 040     iflt met020_355		:If Good Jump away
met020_318:Bad Guy
042             aload_0
187 000 131     new java.lang.StringBuffer
089             dup
183 000 130     invokenonvirtual void java.lang.StringBuffer.()
178 000 121     getstatic java.lang.String NEWLINE
182 000 129     invokevirtual java.lang.StringBuffer
		java.lang.StringBuffer.append(java.lang.String)
018 093         ldc1 "Sorry, WingDis is not"
{Unimportant code}
met020_355:Good Guy
{Unimportant code}


(Make sure you have told IDA to display op codes)

Simple crack! Just change the third statement to always jump 
to good guy.

Look through the code until you find a "goto" operation, 
and write down the opcode

It's 167, or 0xA7
Then just search for the relavant bytes, and change the 
159(0x9F) to 0xA7.

Then try de-compiling Wingdis, and it works!

Run WingDis on itself, and search the source code until you 
find the date check:


Long long13	= new Long(string11);
long14		= long13.longValue();
date3		= new Date();
long16		= date3.getTime() - long14;
if ((long16 <(long)0)) { throw new IOException("Sorry, the trial version has expired"); } if (((long16 / long8)>= 5L))
{
   throw new IOException("Sorry, the trial version has expired");
}
if ((boolea1 == false))
{                
	.......
}


All we have to do is change the first if, to always jump to 
the third if.
Search in IDA for "sorry", and we get to here:



182 000 147     invokevirtual long java.util.Date.getTime()
022 014         lload var083_14
101             lsub
055 016         lstore var083_16
022 016         lload var083_16
009             lconst_0
148             lcmp
156 000 013     ifge met083_241		//if ((long16 <(long)0))
187 000 146     new java.io.IOException
089             dup
018 010         ldc1 "Sorry, the trial version has expired"
183 000 145     invokenonvirtual void
java.io.IOException.(java.lang.String)
191             athrow
met083_241:	//if (((long16 / long8) >= 5L))
022 016         lload var083_16
022 008         lload var083_8
109             ldiv
020 000 160     ldc2w 5
148             lcmp
155 000 013     iflt met083_263
187 000 146     new java.io.IOException
089             dup
018 010         ldc1 "Sorry, the trial version has expired"
183 000 145     invokenonvirtual void
java.io.IOException.(java.lang.String)
191             athrow
met083_263:	//if ((boolea1 == false))


Ok, lets change 156 000 013     ifge met083_241 to
make it always jump to met083_263.

The Offset for the goto instrcution is calculated by the 
front of the goto instruction to the front of the instruction 
jumped to.
By adding the bytes listed above, you will see we need to 
jump 35 bytes.
We do this by changing:
156 000 013 ifge jump 13 bytes
to
167 000 035 jump 35 bytes

As usual, Date crack was so simple it could make you cry!
When will programmers learn?

At the start of each disassembled file, there is a comment:

// This program is generated by WingDis 2.12 Trial Version, 
                                    a product from WingSoft
// For more information about WingSoft, please visit 
                                    http://www.wingsoft.com

I wanted to keep a comment there(So I can know what I have written, 
and what I have decompiled), but I don't like being bothered about 
irrelevant things.

This is simple to fix, just hex edit ClassReader.class, and 
change the text (Nice of the programmers to put the entire protection 
inside one file for us!) To make things easier, don't change the length 
of the comments, just change them to something like:

// This source code was decompiled using WingDis 2.12 ALT-F4_HCU Version
//**********************************************************************




Appendix A:Java Opcodes
Here is a quick list of some of Java Opcodes I got just from looking
at the source code.

Cmnd	Opcode		Hex
ifge	156 xxx xxx	:9c
iflt	155 xxx xxx	:9b
Goto	167 xxx xxx	:a7
ifieq	159 xxx xxx	:9f
Call	182 xxx xxx	:b6

For a more complete source, go to 
http://www.palenaka.com/~palenaka/que/quebooks/sej2e/36javafi.htm


 (c) +Alt-F4 9 Jan 1998 All rights reversed.