76 lines
2.1 KiB
Rust
76 lines
2.1 KiB
Rust
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use lazy_static::lazy_static;
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pub fn derive_table<const N: usize>(init: f64, step: f64) -> [usize; N] {
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debug_assert!(step > 0.0);
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debug_assert!(init > 0.0);
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let mut result = [0usize; N];
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let mut temp = init;
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let mut data = [0f64; N];
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for datum in data.iter_mut() {
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*datum = temp;
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temp = temp * step * (1.0 - temp);
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}
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let mut sorted = data;
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sorted.sort_unstable_by(|a, b| a.total_cmp(b));
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for (item, needle) in result.iter_mut().zip(data) {
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let idx = sorted
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.iter()
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.position(|&x| x == needle)
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.expect("could not find item");
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*item = idx;
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sorted[idx] = -f64::NAN; // values can not be negative, so...
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}
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result
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}
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lazy_static! {
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static ref TABLE_X2M: [usize; 0x400] = derive_table(0.615243, 3.837465);
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static ref TABLE_X3M: [usize; 0x400] = derive_table(0.726354, 3.948576);
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}
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pub enum FileType {
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X2M,
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X3M,
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}
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/// Decrypt the first 0x400 bytes.
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pub fn decrypt_android(version: FileType, buffer: &mut [u8; 0x400]) {
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let (content_key, scramble_table) = match version {
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FileType::X2M => (*b"xmlyxmlyxmlyxmlyxmlyxmlyxmlyxmly", &*TABLE_X2M),
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FileType::X3M => (*b"3989d111aad5613940f4fc44b639b292", &*TABLE_X3M),
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};
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let src = *buffer;
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for (i, hdr) in buffer.iter_mut().enumerate() {
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*hdr = src[scramble_table[i % scramble_table.len()]] ^ content_key[i % content_key.len()];
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_x2m() {
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let mut buffer = *include_bytes!("__fixture__/x2m_hdr.bin");
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let expected = *include_bytes!("__fixture__/x2m_hdr_plain.bin");
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let buffer_slice: &mut [u8] = &mut buffer;
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decrypt_android(FileType::X2M, buffer_slice.try_into().unwrap());
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assert_eq!(expected, buffer);
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}
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#[test]
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fn test_x3m() {
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let mut buffer = *include_bytes!("__fixture__/x3m_hdr.bin");
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let expected = *include_bytes!("__fixture__/x3m_hdr_plain.bin");
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let buffer_slice: &mut [u8] = &mut buffer;
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decrypt_android(FileType::X3M, buffer_slice.try_into().unwrap());
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assert_eq!(expected, buffer);
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}
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}
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