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pub struct Rc4 {
    i: u8,
    j: u8,
    s: [u8; 256],
}

#[allow(clippy::needless_range_loop)]
impl Rc4 {
    pub fn new(key: &[u8]) -> Rc4 {
        assert!(!key.is_empty() && key.len() <= 256);

        let mut s = [0u8; 256];
        for i in 0..256 {
            s[i] = i as u8;
        }

        let mut j = 0u8;
        for i in 0..256 {
            j = j.wrapping_add(s[i]).wrapping_add(key[i % key.len()]);
            s.swap(i, j as usize);
        }

        Rc4 { i: 0, j: 0, s }
    }

    pub fn apply_keystream(&mut self, data: &mut [u8]) {
        for byte in data.iter_mut() {
            self.i = self.i.wrapping_add(1);
            self.j = self.j.wrapping_add(self.s[self.i as usize]);

            self.s.swap(self.i as usize, self.j as usize);

            let k =
                self.s[(self.s[self.i as usize].wrapping_add(self.s[self.j as usize])) as usize];
            *byte ^= k;
        }
    }
}

// Function to create a challenge response