Programming of Base64 decoding in Java environment

Recently encountered a CTF problem that requires solving a string after several Base64 decoding can revert to a normal string. The string for the original question is as follows:

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The above string is a number of Base64 encoded after the formation of a more stupid way is to put this string on the Base64 decoding site, multiple decoding, can solve the problem, but a waste of time, consider a bit, you can use a simple Java program to solve the problem.

The Java environment used is: jdk1.8.0_112. The development environment is: Eclipse Luna, which needs to install javabase64-1.3.1 packages.

The idea is simple, read the string in, and then use a loop to decode multiple times, when the exception is found to stop the loop, where the stop is the decoding of the successful string.

The specific Java code is as follows:

package it.sauronsoftware.base64;import java.io.*;p ublic class mydecode extends  Base64 {public void f_decode (STRING&NBSP;STR) {int i=0;int j=i; String str1= ""; System.out.println ("Decryption result:"); 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 ("final string:"); 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 ("original string:"); System.out.println (str); Mydecode m=new mydecode ();     m.f_decode (str);    }} 

After successful operation, the decoded string is:

Key is jkljdkl232jkljkdl2389

The number of runs is 20 times.

This article from "Dream 9 matchless" blog, reproduced please contact the author!

Programming of Base64 decoding in Java environment