[Misc] Rock Paper Scissors Sh**t

We’re given an IP and a port to connect to - 45.77.20.199:6969
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We tried connecting to it and it’s a rock paper scissor game. We tried poking around with it and we discovered that each iteration, the winning sequence is the same. We built a python code to interface with the input and output. The idea is as follows:

  1. Send the known correct winning sequence. It will stop on an iteration number where no known winning move is reached.
  2. Set the current iteration number.
  3. Send input: rock, paper, and scissors. If the input is losing, return to step 1 to try the next input until a winning move is accepted.
  4. Save the current iteration number along the winning input adding it to the known winning sequence.
  5. Repeat until step 1000


The following code is used to do this automatically: 

from pwn import *
import json

winning_sequence = {
    0 : b"paper",
    1 : b"scissors",
    2 : b"rock",
    3 : b"paper"
}

def guess_winning_move(curr_round):

    choices = [b"rock", b"paper", b"scissors"]

    for c in choices:

        r = remote('45.77.20.199', 6969)

        x = list([ v for k,v in winning_sequence.items()])

        r.sendline(b"\n".join(x))

        for j in range(len(x)+1):
            print(r.recvuntil(b"move: "))
        
        print("Sending {}...".format(c))
        r.sendline(c)

        res = r.recvuntil(b"move: ")

        print(res)

        if b"You won!" in res:

            print("{} is winning on round {}".format(str(c), curr_round+1))
            r.close()
            return (curr_round, c)

        r.close()

def save_winning_sequence():

    with open("winning_sequence.txt", "w") as wf:
        wf.write(str(winning_sequence))

wins = 0


for i in range (4,1001):
    print("Guess winning move of rnd {}...".format(i+1))
    curr_round, winning_move = guess_winning_move(i)
    winning_sequence[curr_round] = winning_move
    print(str(winning_sequence))
    save_winning_sequence()


We found the sequence and therefore the flag:
lol it didn't load