This is a crypto challenge i created for the hackthissite discord.
I have a working exploit, so I'm somewhat confident that everything works fine - still,
if you run into any issues, feel free ping Alaska#4736
.
(Yes, the flag is already viewable. I'm not hosting an instance of this. If you create your own flag, make it about equal in length)
Last active
September 7, 2022 21:30
-
-
Save simonwuelker/01eba191efed0faa352b338bdbaa0d1a to your computer and use it in GitHub Desktop.
Crypto CTF challenge
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum. |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
#!/usr/bin/env python3 | |
from Crypto.Cipher import AES | |
from Crypto.Random import get_random_bytes, random | |
from Crypto.Util import Counter | |
import binascii | |
used_nonces = set() | |
MAX_NONCE = 100000 | |
def get_random_nonce(): | |
global used_nonces | |
if len(used_nonces) == MAX_NONCE: | |
print("""Error: Nonce space is exhausted, continuing would compromise security. | |
Installing a new key will allow nonces to be reused safely, go do that :^)""") | |
exit(0) | |
while True: | |
nonce = random.randint(0, MAX_NONCE) | |
if nonce not in used_nonces: | |
used_nonces.add(nonce) | |
return nonce | |
def encrypt(data): | |
nonce = get_random_nonce() | |
counter = Counter.new(nbits=128, initial_value=nonce) | |
cipher = AES.new(key, AES.MODE_CTR, counter=counter) | |
ciphertext = cipher.encrypt(data) | |
return nonce, binascii.hexlify(ciphertext).decode("ascii") | |
key = get_random_bytes(16) | |
print("""Welcome to Alaska's super duper mega encryption system. | |
We encrypt our data with state of the art AES-CTR mode - which is | |
mathematically unbreakable since it involves a one time pad. | |
You'll never be able to get the flag!""") | |
while True: | |
print("""Enter a number between [1-3]: | |
1. Get encrypted flag.txt | |
2. Encrypt your own data | |
3. Quit""") | |
choice = input(">") | |
if choice == "1": | |
with open("flag.txt", "rb") as infile: | |
data = infile.read() | |
nonce, ciphertext = encrypt(data) | |
print("nonce:", nonce) | |
print("ct:", ciphertext) | |
elif choice == "2": | |
print("Please give me the data to encrypt (as hex):") | |
data = binascii.unhexlify(input(">")) | |
if len(data) > 256: | |
print("data must not be larger than 256 bytes") | |
continue | |
nonce, ciphertext = encrypt(data) | |
print("nonce:", nonce) | |
print("ct:", ciphertext) | |
elif choice == "3": | |
break | |
else: | |
print(f"Invalid input '{choice}', try again:") | |
print() | |
print("Bye!") | |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
pycryptodome==3.15.0 |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment