ångstromCTF 2019 | Classy Cipher

#angstromCTF2019

https://ctftime.org/task/8336

Every CTF starts off with a Caesar cipher, but we're more classy.

from secret import flag, shift


def encrypt(d, s):
    e = ""
    for c in d:
        e += chr((ord(c) + s) % 0xFF)
    return e


assert encrypt(flag, shift) == ":<M?TLH8<A:KFBG@V"

何をやっても求まる。シフト数を求めるよりも全探索するほうが頭を使わない

def encrypt(d, s):
    e = ""
    for c in d:
        e += chr((ord(c) + s) % 0xFF)
    return e


ciphertext = ":<M?TLH8<A:KFBG@V"
for shift in range(256):
    print(encrypt(ciphertext, shift))

$ python3 solve.py | grep actf -a
actf{so_charming}