NozZyS0uS_l3s_r4d4r
Contents
Midnight Flag 2024 - S0uS_l3s_r4d4r
Category
Steganography
Description
By memory
Recover the hidden flag
Format : MCTF{flag{XXXXXXXXX}}
Files
Difficulty
- Author: kuorashi
Write up
Aperisolve does not give anything interesting at first sight. But if you scroll into the strings, you’ll find something interesting.
Push the thing a way further, doing this:
strings -n 8 Gorille_wallpaper.jpg
...
@wzJPB))v
,U#=b0t`
{La[!dm7
qB)P',W18b
import string; alph = string.ascii_letters;flag_enc = "109 115 104 110 { 130 111 131 104 111 132 108 122 123 145 104 122 149 121 118 119 149 118 123 }"
def decode_flag(flag):
lst = flag.split(" ")
new_flag = ""
for item in lst:
if item != '{' and item != '}':
new_flag += alph[int(item) % 25]
else:
new_flag += item
print(new_flag)
def encode_flag(flag):
text = ""
for i in flag:
if i not in alph:
text += i + " "
else:
text += f"{alph.index(i) + int(flag_enc.split(' ')[2])} + "
print(text)
decode_flag(flag_enc)
1s;iWC)7buckd
GhQEgPh1
Ddl00wHX7
...
There is some python code:
import string
alph = string.ascii_letters
flag_enc = "109 115 104 110 { 130 111 131 104 111 132 108 122 123 145 104 122 149 121 118 119 149 118 123 }"
def decode_flag(flag):
lst = flag.split(" ")
new_flag = ""
for item in lst:
if item != '{' and item != '}':
new_flag += alph[int(item) % 25]
else:
new_flag += item
print(new_flag)
def encode_flag(flag):
text = ""
for i in flag:
if i not in alph:
text += i + " "
else:
text += f"{alph.index(i) + int(flag_enc.split(' ')[2])} + "
print(text)
decode_flag(flag_enc)
SO the given code… decodes the flag?
jpek{flgelhiwxuewyvstysx}
Nope, that doesn’t work. Even with ROT, thats dioes not work properly.
So, instead of thinking how to reverse this simple code, let’s create every encoded character, and reconstruct the flag:
import string
alph = string.ascii_letters
flag_enc = "109 115 104 110 { 130 111 131 104 111 132 108 122 123 145 104 122 149 121 118 119 149 118 123 }"
def encode_flag(flag):
text = ""
for i in flag:
if i not in alph:
text += i + " "
else:
text += f"{alph.index(i) + int(flag_enc.split(' ')[2])}"
return text
encoded_chars = {}
for a in alph:
encoded_chars.update({encode_flag(a): a})
flag = ""
for c in flag_enc.split():
try:
flag += encoded_chars.get(c)
except:
flag += c
print(flag)
# flag{AhBahCestPasTropTot}
Flag
🚩
MCTF{flag{AhBahCestPasTropTot}}