java环境下的base64解码程序设计

标签：java   base64   ctf   

  最近遇到一个ctf题，要求求解一个字符串经过几次base64解码可以恢复成正常的字符串。原题的字符串如下：

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

  上面这个字符串是经过多次base64编码后形成的，一个比较笨的办法是把这个字符串放到base64的解码网站上面，多次解码，是可以解决问题的，但比较浪费时间，考虑了一下，可以用一段简单的java程序解决这个问题。

  用到的java环境是：jdk1.8.0_112。开发环境是：Eclipse luna,需要安装javabase64-1.3.1的包。

 思路很简单，把字符串读进来，然后用一个循环多次解码，当发现异常时停止循环，停止的地方即为解码成功的字符串。

 具体的java代码如下：

package it.sauronsoftware.base64;
import java.io.*;

public class MyDecode extends Base64 {
	public void f_decode(String str){
		int i=0;
		int j=i;
		String str1="";
		System.out.println("解密结果:");
		try{do{
			
			
			str=Base64.decode(str);
			i++;
			System.out.println(i+":"+str);
			str1=Base64.encode(str);
			j=i-1;
		}while(i<30);}
		catch (RuntimeException e) {
			System.out.println("最终字符串:");
			System.out.println(str1);
			System.out.println(j);
	        
	    }  
		
	}

	public static void main(String args[]) throws IOException{
	BufferedReader br = new BufferedReader(new
                InputStreamReader(System.in));
	String str=br.readLine();
	System.out.println("原始字符串:");
	System.out.println(str);
	
	MyDecode m=new MyDecode();
    m.f_decode(str);
		   }
}

运行成功后，解码后的字符串是：

key is jkljdkl232jkljkdl2389

运行次数是20次。

本文出自 “梦9无双” 博客，转载请与作者联系！

java环境下的base64解码程序设计

标签：java   base64   ctf   

原文地址：http://meng9wushuang.blog.51cto.com/12428568/1884791