Squ1rrel Lottery

Welcome to the squ1rrel lottery! 9 winning numbers will be selected, and if any of your tickets share 3 numbers with the winning ticket you’ll win a flag!

Hint: This is a math challenge

nc 34.132.166.199 11112

squ1rrel-lottery.py

Short (essentially a cheese) writeup.

Here’s the source:

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import random
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# user version
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def input_lines():
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    lines = []
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    print("Welcome to the squ1rrel lottery! 9 winning numbers will be selected, and if any of your tickets share 3 numbers with the winning ticket you'll win! Win 1000 times in a row to win a flag")
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    for i in range(1, 41):
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        while True:
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            line = input(f"Ticket {i}: ").strip()
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            numbers = line.split()
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            if len(numbers) != 9:
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                print("Please enter 9 numbers")
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                continue
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            try:
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                numbers = [int(num) for num in numbers]
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                if not all(1 <= num <= 60 for num in numbers):
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                    print("Numbers must be between 1 and 60")
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                    continue
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                lines.append(set(numbers))
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                break
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            except ValueError:
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                print("Please enter only integers.")
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    return lines
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user_tickets = input_lines()
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wincount = 0
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for j in range(1000):
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    winning_ticket = random.sample(range(1, 61), 9)
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    win = False
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    for i in user_tickets:
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        if len(i.intersection(set(winning_ticket))) >= 3:
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            print(f'Win {j}!')
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            win = True
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            wincount += 1
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            break
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    if not win:
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        print("99 percent of gamblers quit just before they hit it big")
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        break
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if wincount == 1000:
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    print("squ1rrelctf{test_flag}")

So, essentially the gist of the problem is that we’re allowed to input 40 tickets, 9 numbers each between 1 and 60, inclusive. 1000 times in a row, we need at least one of our tickets to share at least 3 of the same numbers as the winning ticket.

I believe the intended solution was some pigeonhole principle logic that involved actual math and thinking, but, I figured why not try to just evenly distribute the numbers?

There are 40*9 = 360 inputs, so I put 6 of each number across the 40 tickets, ensuring that no one number is in the same ticket twice.

My ticket generation fails like 70% of the time, but whenever it works it gets the flag so good enough ¯\_(ツ)_/¯

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from pwn import *
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from random import *
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sets = [[] for i in range(40)]
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space = [9 for i in range(40)]
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curr_indices = set()
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for i in range(40):
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    curr_indices.add(i)
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next_indices = []
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for i in range(1, 61):
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    # print(space)
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    indices = sample(list(curr_indices), 6 - len(next_indices)) + next_indices
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    for j in indices:
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        sets[j].append(i)
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        space[j]-=1
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        curr_indices.remove(j)
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    for i in next_indices:
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        curr_indices.add(i)
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    next_indices = []
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    if len(curr_indices) <= 6:
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        for i in curr_indices:
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            next_indices.append(i)
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        for i in range(40):
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            if space[i] > 0 and i not in next_indices: curr_indices.add(i)
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# print('\n'.join(map(str, sets)))
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for i in sets:
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    assert len(set(i)) == len(i)
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    assert len(i) == 9
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# exit()
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p = remote('34.132.166.199', 11112)
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for i in range(40):
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    # print(' '.join(map(str, sets[i])).split())
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    p.sendlineafter(b': ', ' '.join(map(str, sets[i])).encode())
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p.interactive()

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squ1rrelctf{your_prize_is_519225_squ1rrel_bucks}