2022 | SDCTF | MISC
Bishop Duel
题目¶
2 bishops on the chessboard.
Goal 1 (first flag)
Lose the game by letting your bishop be captured.
Goal 2 (second flag)
Win by capturing the other bishop.
Avoiding a draw is easy huh? But wait...
Connect via
nc bishop.sdc.tf 1337
main.rs
use std::io::{stdout, Write};
use std::process::exit;
use std::thread::sleep;
use std::time::Duration;
/*
* Can you tell this was my first rust program ever? lmao
*/
use crossterm::{cursor, execute, queue, style, terminal::{Clear, EnterAlternateScreen, LeaveAlternateScreen}};
use crossterm::terminal::ClearType;
use rand::{rngs, SeedableRng};
use rand::prelude::SliceRandom;
use text_io::read;
static TITLE_SCREEN: &str = "
o
(^)
-=H=- BISHOP DUEL
] [ -- press enter to start --
/___\\
";
// having to double escape these backslashes makes this astoundingly ugly
static BOARD: &str = "
\\__\\\\\\\\__\\\\\\\\__\\\\\\\\__\\\\\\\\ Q# - up left # spaces
\\\\\\\\__\\\\\\\\__\\\\\\\\__\\\\\\\\__\\ E# - up right # spaces
\\__\\\\\\\\__\\\\\\\\__\\\\\\\\__\\\\\\\\ Z# - down left # spaces
\\\\\\\\__\\\\\\\\__\\\\\\\\__\\\\\\\\__\\ C# - down right # spaces
\\__\\\\\\\\__\\\\\\\\__\\\\\\\\__\\\\\\\\
\\\\\\\\__\\\\\\\\__\\\\\\\\__\\\\\\\\__\\ D - offer draw
\\__\\\\\\\\__\\\\\\\\__\\\\\\\\__\\\\\\\\ R - resign
\\\\\\\\__\\\\\\\\__\\\\\\\\__\\\\\\\\__\\
";
enum Direction {
UpLeft, UpRight, DownLeft, DownRight
}
struct Bishop {
position: u16
}
impl Bishop {
fn get_xy(&self) -> (u16, u16) {
let rows = self.position / 8 + 1;
return ((self.position % 8) * 3 + rows, rows);
}
fn move_position(&mut self, dir: Direction, dist: u16) -> bool {
let position_multiplier: i32 = match dir {
Direction::UpRight => -7,
Direction::DownLeft => 7,
Direction::UpLeft => -9,
Direction::DownRight => 9,
};
let new_position = i32::from(self.position) + position_multiplier * i32::from(dist);
// make sure we don't exceed the bottom and top of the chessboard
if new_position < 0 || new_position > 64 { return false; }
// make sure we don't exceed the left and right edge of the chessboard
match dir {
Direction::UpLeft | Direction::DownLeft => {
if self.position % 8 < dist { return false; }
}
Direction::UpRight | Direction::DownRight => {
if dist + self.position % 8 > 8 { return false; }
}
}
self.position = u16::try_from(new_position).unwrap();
return true;
}
}
fn pause(msg: &str) -> String {
println!("{}", msg);
read!("{}\n")
}
fn main() {
let mut stdout = stdout();
let mut is_player_turn = true;
let mut white_bishop = Bishop { position: 5 };
let mut black_bishop = Bishop { position: 57 };
queue!(stdout, EnterAlternateScreen, Clear(ClearType::All), style::Print(TITLE_SCREEN)).unwrap();
stdout.flush().unwrap();
pause("");
loop {
let (bb_x, bb_y) = black_bishop.get_xy();
let (ww_x, ww_y) = white_bishop.get_xy();
queue!(
stdout,
Clear(ClearType::All),
cursor::MoveTo(0, 0),
style::Print(BOARD),
cursor::MoveTo(bb_x, bb_y),
style::Print("BB"),
cursor::MoveTo(ww_x, ww_y),
style::Print("WW"),
cursor::MoveTo(0, 10)
).unwrap();
stdout.flush().unwrap();
// this means SOMEBODY has been captured
if white_bishop.position == black_bishop.position {
if is_player_turn {
pause("You have been defeated! Your flag is REDACTED");
exit(0);
}
pause("You have claimed victory! Your flag is REDACTED");
exit(0);
}
if is_player_turn {
// if its the white bishop's turn
execute!(stdout, style::Print("You are the white bishop. Input move > ")).unwrap();
let command: String = read!("{}\n");
let mut command_chars = command.chars();
if let Some(c1) = command_chars.next() {
match c1 {
'r' | 'R' => {
pause("A brave bishop shall never resign!");
},
'd' | 'D' => {
execute!(stdout, style::Print("The black bishop is thinking.")).unwrap();
sleep(Duration::from_millis(1000));
execute!(stdout, style::Print(".")).unwrap();
sleep(Duration::from_millis(1000));
execute!(stdout, style::Print(".")).unwrap();
sleep(Duration::from_millis(1000));
pause("Accepted! The game is a draw!");
break;
},
_ => {
let direction: Direction = match c1 {
'e' | 'E' => Direction::UpRight,
'z' | 'Z' => Direction::DownLeft,
'q' | 'Q' => Direction::UpLeft,
'c' | 'C' => Direction::DownRight,
_ => continue
};
let distance = match command_chars.next() {
None => continue,
Some(c2) => match c2.to_digit(10) {
None => continue,
Some(d) => d as u16
}
};
let successful = white_bishop.move_position(direction, distance);
if successful {
// now its the black bishop's turn
is_player_turn = false;
}
}
}
}
} else {
// black bishop's turn
println!("The black bishop is thinking...");
sleep(Duration::from_millis(1000));
// get all black spaces and filter by currently accessible
let curr = i32::from(black_bishop.position);
let mut possible_positions =
(0..64).step_by(2)
.map(|i| if (i/8) % 2 == 0 { i } else { i+1 })
.filter(|i| (curr - i).abs() % 7 == 0 || (curr - i).abs() % 9 == 0).collect::<Vec<i32>>();
// if the white bishop is in our path, CRUSH THEM
if possible_positions.contains(&i32::from(white_bishop.position)) {
black_bishop.position = white_bishop.position;
is_player_turn = true;
continue;
}
// otherwise, let's filter out moves that would put us in the path of the white bishop
let white_curr = i32::from(white_bishop.position);
if white_curr % 2 == 0 {
possible_positions = possible_positions.into_iter()
.filter(|i| (white_curr - i) % 7 != 0 && (white_curr - i) % 9 != 0).collect::<Vec<i32>>();
}
// otherwise, randomly select a new move
let mut rng = rngs::StdRng::seed_from_u64(white_bishop.position as u64);
let new_position = possible_positions.choose(&mut rng).unwrap();
black_bishop.position = u16::try_from(*new_position).unwrap();
// now its the white bishop's turn
is_player_turn = true;
}
}
execute!(stdout, LeaveAlternateScreen).unwrap();
}
解题思路¶
-
使用
QEZC在棋盘范围内移动时，由于走的是对角线，黑白主教始终在对应类型（黑 / 白）的格子内移动，没有交集\__\\\\__\\\\__\WW\__\\\\ Q# - up left # spaces \\\\__\\\\__\\\\__\\\\__\ E# - up right # spaces \__\\\\__\\\\__\\\\__\\\\ Z# - down left # spaces \\\\__\\\\__\\\\__\\\\__\ C# - down right # spaces \__\\\\__\\\\__\\\\__\\\\ \\\\__\\\\__\\\\__\\\\__\ D - offer draw \__\\\\__\\\\__\\\\__\\\\ R - resign \\\\BB\\\\__\\\\__\\\\__\ -
想要抓到
black bishop或者被抓到，首先要移动到同一种类型的格子里 - 那么关键点就是函数
move_position了，因为移动并不是按照类似 \((x,y)\) 的坐标形式。实际上，每个格子的位置相当于按照光栅扫描的顺序编号，根据当前位置 + 对应方向的系数 * 移动格数取得下一个位置，然后判断移动是否有效- 新位置的值应在 \([0,64]\) 之间
- 如果移动方向为左上/左下，那么移动格数不大于当前位置的值模 \(8\)
- 如果移动方向为右上/右下，那么移动格数与当前位置值模 \(8\) 的和不大于 \(8\)
- 以初始位置 \(5\) 为例，上移一定导致位置值小于 \(0\)，所以只考虑下移
- 右下移动两格以内显然是可行的，但如果是 \(3\) 格呢？显然新位置的值不会超过 \(64(> 5+9\times 3)\)，而 \(3+5 \% 8\) 恰好等于 \(8\)，所以可以移动，并且会进入
black_bishop的移动范围 ΦωΦ - 左下方向正常可移动范围内的格子就有五个了，所以想要利用左下移动跳到另一种类型的格子是不可行的 —v—
- 右下移动两格以内显然是可行的，但如果是 \(3\) 格呢？显然新位置的值不会超过 \(64(> 5+9\times 3)\)，而 \(3+5 \% 8\) 恰好等于 \(8\)，所以可以移动，并且会进入
- 移动到同一种类型的格子之后，再玩玩游戏就能获得 Flag 啦 \(ΦωΦ ≡ ΦωΦ)/
Flag¶
Goal 1 (first flag)
sdctf{L0SiNG_y0uR_S0uRC3_C0d3_sUcKs}
Goal 2 (second flag)
sdctf{I_d1dnt_hAND_0u7_th3_s0urC3_c0D3_thIs_TIME}
最后更新:
2022年5月10日 21:35:00
Contributors: