Sonic

Gotta go fast

URL: nc chal.tuctf.com 30100

Recon

Shift cipher, just gotta code it. Turns out, not really needed, only one challenge is given.

Code

words_dictionary.json is from here.

from pwn import *
import sys
import json
import string

# Copy-paste from https://eddmann.com/posts/implementing-rot13-and-rot-n-caesar-ciphers-in-python/
def rot_alpha(n):
    from string import ascii_lowercase as lc, ascii_uppercase as uc
    lookup = string.maketrans(lc + uc, lc[n:] + lc[:n] + uc[n:] + uc[:n])
    return lambda s: s.translate(lookup)

with open('words_dictionary.json', 'r') as fs:
    words = json.load(fs)

rots = { k: rot_alpha(k) for k in range(26) }

def solve(s):
    for i in range(26):
        x = rots[i](s)
        print(x)
        # deal with plurals and shit.
        if x.lower() in words or x.lower() + 's' in words:
            return x
    return None


c = remote("chal.tuctf.com", 30100)

while True:
    r = c.readuntil("\n")

    if "Hey, decode this:" in r:
        s = r.strip("\n").split(": ")[1]

    if not r.startswith("Hey, decode"):
        print("< " + r)
        continue

    o = solve(s)
    print("LINE: " + r)
    print("GOT: " + o)

    c.send(o + "\n")

c.interactive()