Cryptography,  Cryptography,  CTF,  ShellCTF

shellCTF – Algoric Shift (Cryptography)

Tiens (Verniel) competed in the shellCTF this past weekend and here’s the first solution to the flag for the first Cryptography challenge.

The challenge was called “Algoric-Shift” and we were given the below:

Download the script.py to decrypt the above ciphered text. To view the code please watch the video below for this challenge as I do not want to share it since it is not my code.

In short there is a text variable containing a string ‘flag{…}’, the program contains 3 lists and checks the length of the text variable. It then does a modulus on each and appends each character to a list.

I pasted the ciphered text into the text variable and ran the Python program. I could then see is shifted the characters. I took the output and added that to the text variable and ran the program again which then produced the flag after the 2nd run.