cybergrabs2022-rev

CUSTOM CIPHER  

Solution

We are provided a .pyc file which is a compiled python file we can't read it in plain text but there is an amazing tool online 

https://www.toolnb.com/tools-lang-en/pyc.html

Using this website I found the python code behind the file 

So, encryption function:

def encode_secret(secret):

    rotate_const = 37

    encoded = ''

    for c in secret:

        index = alphabet.find(c)

        original_index = (index + rotate_const) % len(alphabet)

        encoded = encoded + alphabet[original_index]

    return encoded

We need to decrypt this so I wrote a small decryption function

You can even try it by yourselves 

code:

for i in encoded_flag:

  temp=alphabet.index(i)-37

  while(temp<0):

    temp+=len(alphabet)

  print(alphabet[temp],end='')

FLAG: cybergrabs{yOU_FounD_7H3_SHIfT_c1PheR}