BCACTF WRITEUP

Challenge -->>> Large-Data

In this challange we upto 2700 text file in 27 different folder so we have to do some analysis technique to extract the flag.

As we can see in above challenge they given a link to download that files for analysis. and they clearly told that flag is 27 character long.

At first i have open file from a folder and get some random characters. that are in every files.then i decided to do something with the characters to extract the flag. so i'm doing trial on one file i have design a solver for one file that read data from file then make sum of each characters ASCII value and finally take average by from counting character emmmmmm... the equation like

flagChar = SUM_OF_ALL_CHARACTER(ASCII_CODE)/TOTAL_CHARACTERS_OF_FILE

by doing this i got flags characters like bcactf{.............. then i have created a solver that do this stuff in each file and folder..

SOLVER.py

---

import os
f = []
root = os.getcwd()
i=0
for filename in os.listdir(os.getcwd()):
    f.append(filename)

f.pop()
f1=[]
for i in range(0, len(f)): 
    f[i] = int(f[i])
f.sort()
flag=[]

st = ""
for i in f:
      os.chdir(os.getcwd()+"\\"+str(i))
      filelist = os.listdir(os.getcwd())
      cntch=0
      charcode=0
      i=0
      
      for j in range(0, len(filelist)): 
          filelist[j] = int(filelist[j])
      filelist.sort()
  
      for afile in filelist:
          if(i<100):
              #print(afile)
              fp = open(str(afile),"r")
              for filedata in fp:
                    for ch in filedata:
                          charcode += ord(ch)
                          cntch = cntch + 1 
              st += (chr(int(charcode/cntch)))
              cntch=0
              charcode=0
          i+=1
  
  flag.append(st)
  os.chdir(root)
  st=""

k=0
l=0
flags=""
for i in range(0,100):
    for j in range(0,27):
           flags += flag[k][l]
           k=k+1
    l=l+1
 
    print(flags)
    flags=""
    k=0

By running this solver we got 100 Flags--->

100 flags link --> https://raw.githubusercontent.com/dhavz/BCACTF-WRITEUP/master/flags

So after that i have found a flag from that list that have good meaningful words like a FLAGGG!!!!!!!!!!!!

bcactf{crunch1ng_num5_c00l}

c001_dh@/7_