BackdoorCTF 2016 / Dtune_Misc

June 5, 2016

today i will explain how i solve a task in backdoorctf

first we have a simple wav file

the sound look like someone typing his password in old phone, so its DTMF Tones

convert the wav to phone number we get this

84433033355524044477770777744225606663330337222344994462222779

as in the ctf the hint said that the flag is a capital alphabet

so this is not the final flag

as this number used to write some text in the phone so we need to use T9

using a t9 emulator online or a simple code we can get the final flag

my code used to solve this is

import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;

public class t9 {
        public static void main(String[] args) 
        {  BufferedReader inputReader=new java.io.BufferedReader(new InputStreamReader(System.in));
           String inputCode="";
           System.out.println("T9 SMS MODE Decoder");
           System.out.println("\nEnter the Value You Want to Press ");
           try 
           {
                inputCode=inputReader.readLine();
           }
           catch(IOException e)
           {
                System.out.println("IO Exception");
           }

           System.out.println(t9.decode(inputCode));        
         }
    
         private static char [][] keyPadCharSet= 
         {
            {' '},
            {'.',',','\'','?','!','\"','-','(',')'},
            {'a','b','c'},
            {'d','e','f'},
            {'g','h','i'},
            {'j','k','l'},
            {'m','n','o'},
            {'p','q','r','s'},
            {'t','u','v'},
            {'w','x','y','z'},
          };
    
          public static String decode(String inputCode)
          {
                StringBuilder outputString=new StringBuilder("");
                char[] inputCodeCharArray=inputCode.toCharArray();
                int len=inputCodeCharArray.length;
                int count=0;

                for(int i=0;i<len;i++) {
                char currentChar=inputCodeCharArray[i];
                char nextChar;

                if((i+1)!=len)  
                    nextChar=inputCodeCharArray[i+1];
                else
                    nextChar='\0';

                if(currentChar==nextChar)
                    count++;    
                else 
                {
                
                     if(currentChar!=' ') 
                     {  if(Character.isDigit(currentChar)) 
                        {    
                            int temp=Integer.parseInt(String.valueOf(currentChar)); 
                            count=count%keyPadCharSet[temp].length; 
                            char outputChar=keyPadCharSet[temp][count]; 
                            outputString.append(outputChar);    
                         }
                         else 
                         {   outputString=new StringBuilder("Please Enter Numerical value Only");
                              break;  
                         }
                      }
                      count=0; 
                  }
        }
        return outputString.toString(); 
    }
    
}

so the output is

the flag is shbjm of EPCDHXHMCAQW

As in this ctf all the flag should be converted to sha256 before submit so the final text is

the flag is sha256 of EPCDHXHMCAQW

and the flag is : 39551506faa3c2b1c1ee082adf79938da826910bf953665df882dd62b579759e

thanks