rars_crypto/
rar13.rs

1use zeroize::ZeroizeOnDrop;
2
3#[derive(ZeroizeOnDrop)]
4pub struct Rar13Cipher {
5    key: [u8; 3],
6}
7
8pub struct Rar13DecryptReader<R> {
9    inner: R,
10    cipher: Rar13Cipher,
11}
12
13impl Rar13Cipher {
14    pub fn new(password: &[u8]) -> Self {
15        let mut key = [0u8; 3];
16        for &byte in password {
17            key[0] = key[0].wrapping_add(byte);
18            key[1] ^= byte;
19            key[2] = key[2].wrapping_add(byte).rotate_left(1);
20        }
21        Self { key }
22    }
23
24    pub fn new_comment() -> Self {
25        Self { key: [0, 7, 77] }
26    }
27
28    pub fn encrypt_in_place(mut self, data: &mut [u8]) {
29        for byte in data {
30            *byte = self.encrypt_byte(*byte);
31        }
32    }
33
34    pub fn decrypt_in_place(mut self, data: &mut [u8]) {
35        for byte in data {
36            *byte = self.decrypt_byte(*byte);
37        }
38    }
39
40    pub fn encrypt_byte(&mut self, byte: u8) -> u8 {
41        self.advance();
42        byte.wrapping_add(self.key[0])
43    }
44
45    pub fn decrypt_byte(&mut self, byte: u8) -> u8 {
46        self.advance();
47        byte.wrapping_sub(self.key[0])
48    }
49
50    fn advance(&mut self) {
51        self.key[1] = self.key[1].wrapping_add(self.key[2]);
52        self.key[0] = self.key[0].wrapping_add(self.key[1]);
53    }
54}
55
56impl<R> Rar13DecryptReader<R> {
57    pub fn new(inner: R, cipher: Rar13Cipher) -> Self {
58        Self { inner, cipher }
59    }
60}
61
62impl<R: std::io::Read> std::io::Read for Rar13DecryptReader<R> {
63    fn read(&mut self, out: &mut [u8]) -> std::io::Result<usize> {
64        let read = self.inner.read(out)?;
65        for byte in &mut out[..read] {
66            *byte = self.cipher.decrypt_byte(*byte);
67        }
68        Ok(read)
69    }
70}
71
72#[cfg(test)]
73mod tests {
74    use super::Rar13Cipher;
75
76    #[test]
77    fn rar13_cipher_matches_pinned_stream_vector() {
78        let mut data = *b"hello world";
79        Rar13Cipher::new(b"password").encrypt_in_place(&mut data);
80        assert_eq!(
81            data,
82            [0x37, 0xcd, 0xaa, 0xbd, 0x10, 0x4e, 0x6f, 0x6e, 0xb5, 0x30, 0xe6]
83        );
84
85        Rar13Cipher::new(b"password").decrypt_in_place(&mut data);
86        assert_eq!(&data, b"hello world");
87    }
88}
rars_crypto/rar13.rs

rars_crypto/
rar13.rs
