条件反射的にブルートフォースしてしまったが。。。
Here's a program that plays rock, paper, scissors against you. I hear something good happens if you win 5 times in a row.
問題
ソースコード
game-redacted.c
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <sys/time.h>
#include <sys/types.h>
#define WAIT 60
static const char* flag = "[REDACTED]";
char* hands[3] = {"rock", "paper", "scissors"};
char* loses[3] = {"paper", "scissors", "rock"};
int wins = 0;
int tgetinput(char *input, unsigned int l)
{
fd_set input_set;
struct timeval timeout;
int ready_for_reading = 0;
int read_bytes = 0;
if( l <= 0 )
{
printf("'l' for tgetinput must be greater than 0\n");
return -2;
}
/* Empty the FD Set */
FD_ZERO(&input_set );
/* Listen to the input descriptor */
FD_SET(STDIN_FILENO, &input_set);
/* Waiting for some seconds */
timeout.tv_sec = WAIT; // WAIT seconds
timeout.tv_usec = 0; // 0 milliseconds
/* Listening for input stream for any activity */
ready_for_reading = select(1, &input_set, NULL, NULL, &timeout);
/* Here, first parameter is number of FDs in the set,
* second is our FD set for reading,
* third is the FD set in which any write activity needs to updated,
* which is not required in this case.
* Fourth is timeout
*/
if (ready_for_reading == -1) {
/* Some error has occured in input */
printf("Unable to read your input\n");
return -1;
}
if (ready_for_reading) {
read_bytes = read(0, input, l-1);
if(input[read_bytes-1]=='\n'){
--read_bytes;
input[read_bytes]='\0';
}
if(read_bytes==0){
printf("No data given.\n");
return -4;
} else {
return 0;
}
} else {
printf("Timed out waiting for user input. Press Ctrl-C to disconnect\n");
return -3;
}
return 0;
}
bool play () {
char player_turn[100];
srand(time(0));
int r;
printf("Please make your selection (rock/paper/scissors):\n");
r = tgetinput(player_turn, 100);
// Timeout on user input
if(r == -3)
{
printf("Goodbye!\n");
exit(0);
}
int computer_turn = rand() % 3;
printf("You played: %s\n", player_turn);
printf("The computer played: %s\n", hands[computer_turn]);
if (strstr(player_turn, loses[computer_turn])) {
puts("You win! Play again?");
return true;
} else {
puts("Seems like you didn't win this time. Play again?");
return false;
}
}
int main () {
char input[3] = {'\0'};
int command;
int r;
puts("Welcome challenger to the game of Rock, Paper, Scissors");
puts("For anyone that beats me 5 times in a row, I will offer up a flag I found");
puts("Are you ready?");
while (true) {
puts("Type '1' to play a game");
puts("Type '2' to exit the program");
r = tgetinput(input, 3);
// Timeout on user input
if(r == -3)
{
printf("Goodbye!\n");
exit(0);
}
if ((command = strtol(input, NULL, 10)) == 0) {
puts("Please put in a valid number");
} else if (command == 1) {
printf("\n\n");
if (play()) {
wins++;
} else {
wins = 0;
}
if (wins >= 5) {
puts("Congrats, here's the flag!");
puts(flag);
}
} else if (command == 2) {
return 0;
} else {
puts("Please type either 1 or 2");
}
}
return 0;
}
じゃんけんで5回連続で勝てば, flag がとれそうだ。
動きの確認
$ nc saturn.picoctf.net 51420
Welcome challenger to the game of Rock, Paper, Scissors
For anyone that beats me 5 times in a row, I will offer up a flag I found
Are you ready?
Type '1' to play a game
Type '2' to exit the program
じゃんけんするので, 1 を入力
1
1
Please make your selection (rock/paper/scissors):
ここでグーを出す。
rock
rock
You played: rock
The computer played: rock
Seems like you didn't win this time. Play again?
Type '1' to play a game
Type '2' to exit the program
勝てなかった。
次
1
1
Please make your selection (rock/paper/scissors):
scissors
scissors
You played: scissors
The computer played: paper
You win! Play again?
Type '1' to play a game
Type '2' to exit the program
勝った。
5連勝するまで,無限じゃんけんプログラム
仕様1
Type '2' to exit the program に対して 1 を入力する
仕様2
勝っても負けても結果表示の末尾は Play again? と出る
仕様3
勝った時は, You win! が表示される
仕様4
5連勝したときフラグ picoCTF{xxxxxx} が表示される。
solver.py
# coding: UTF-8
# python 2.7
import socket
import string
import time
start = time.time()
def recvuntil(s, tail):
data = ''
while True:
if tail in data:
return data
data += s.recv(1)
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(('saturn.picoctf.net',51420))
win = 0
# ブルートフォース
while True:
# Type '2' to exit the programまでを受信,出力
data = recvuntil(s, 'to exit the program')
print(data)
# 1を送信
s.sendall('1\n')
# じゃんけんの準備
data = recvuntil(s, 'Please make your selection (rock/paper/scissors):')
print(data)
# グーを送信
s.sendall('rock\n')
# 終了判定 "You win! Play again?" か"Seems like you didn't win this time. Play again?" を受信したら
data = recvuntil(s, 'again?')
# 勝敗は?
if data.find('win!') > 0:
# 勝利数加算
win=win+1
else:
# 勝利数クリア
win=0
print(data)
# 5連勝ならフラグを受け取って終了
if win==5:
data = recvuntil(s, '}')
print(data)
break
elapsed_time = time.time() - start
print ("speed:{0}".format(elapsed_time) + "[sec]")
実行結果
(略)
Please make your selection (rock/paper/scissors):
rock
You played: rock
The computer played: scissors
You win! Play again?
Congrats, here's the flag!
picoCTF{50M3_3X7R3M3_1UCK_58F0F41B}
speed:171.631999969[sec]
もし,6連勝を求められていたら,この方法でフラグ取れただろうか?