[CTF Writeups] InCTF 2014 Round 2 Reverse[2] 50

Download the file and extract it.
Check the file details using the command 'file'

#file two
two: compiled Java class data, version 51.0

Executing it won't help and so we will move on to de-compile it. I used an online decompiler available in this link
Upload the class file, decompile it and download the source, it will look like this.

import java.io.*;  
 public class challenge {  
 public challenge() { }   
public static void main(string args[]) throws ioexception 
{ 
byte abyte[] = 
{ byte.valueOf((byte)106), byte.valueOf((byte)97), byte.valueOf((byte)50), byte.valueOf((byte)37), byte.valueOf((byte)36), byte.valueOf((byte)103), byte.valueOf((byte)94), byte.valueOf((byte)115), byte.valueOf((byte)94), byte.valueOf((byte)92), byte.valueOf((byte)96), byte.valueOf((byte)101), byte.valueOf((byte)94), byte.valueOf((byte)105), byte.valueOf((byte)105), byte.valueOf((byte)98), byte.valueOf((byte)107), byte.valueOf((byte)100), byte.valueOf((byte)98), byte.valueOf((byte)112), byte.valueOf((byte)92), byte.valueOf((byte)94), byte.valueOf((byte)111), byte.valueOf((byte)98), byte.valueOf((byte)92), byte.valueOf((byte)112), byte.valueOf((byte)113), byte.valueOf((byte)102), byte.valueOf((byte)105), byte.valueOf((byte)105), byte.valueOf((byte)92), byte.valueOf((byte)98), byte.valueOf((byte)94), byte.valueOf((byte)112), byte.valueOf((byte)118), byte.valueOf((byte)36), byte.valueOf((byte)38) 
}; 
string s = "";
 byte abyte1[] = abyte;
 int i = abyte1.length;
 for(int j = 0; j < i; j++) 
{
 byte byte0 = abyte1[j].byteValue(); s = (new StringBuilder()).append(s).append((char)(byte0 + 3)).toString(); 
}  
 bufferedreader bufferedreader = new bufferedreader(new inputstreamreader(system.in));
 bufferedreader.readLine();
 system.exit(0);
 system.out.println(s); }
 }

For a quick look through in the code you can figure out that the key is stored in variable 's' and also before the statement that print out the variable 's' there is an 'exit' statement ' system.exit(0)'.
So remove that line and remove the ' bufferedreader.readLine()' also.
Compile the new code and execute it.
The output will be
md5('java_challenges_are_still_easy')
Find the md5 of the text and it will be the flag.