One True Problem

Two of my friends were arguing about which CTF category is the best, but they encrypted it because they didn't want anyone to see. Lucky for us, they reused the same key; can you recover it?

Here are the ciphertexts: 213c234c2322282057730b32492e720b35732b2124553d354c22352224237f1826283d7b0651 3b3b463829225b3632630b542623767f39674431343b353435412223243b7f162028397a103e

Recon

The key is probably the flag, we know it starts with utflag{. With that we did a plain text attack (xor against the ciphertext) and could figure out the flag/key.

Code

Code to decode the ciphertext:

import string

text1 = "213c234c2322282057730b32492e720b35732b2124553d354c22352224237f1826283d7b0651".decode("hex")
text2 = "3b3b463829225b3632630b542623767f39674431343b353435412223243b7f162028397a103e".decode("hex")

flag = "utflag{tw0_tim3_p4ds}"

out1 = ""
out2 = ""
for i in range(len(text1)):
    out1 += chr(ord(flag[i %len(flag)]) ^ ord(text1[i]))
    out2 += chr(ord(flag[i %len(flag)]) ^ ord(text2[i]))

print flag
print out1
print out2

Running it:

utflag{tw0_tim3_p4ds}
THE BEST CTF CATEGORY IS CRYPTOGRAPHY!
NO THE BEST ONE IS BINARY EXPLOITATION

Flag

utflag{tw0_tim3_p4ds}