50 lines
1.5 KiB
Rust
50 lines
1.5 KiB
Rust
use crate::header::Header;
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use crate::KugouError;
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pub struct DecipherV3 {
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slot_key: [u8; 16],
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file_key: [u8; 17],
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}
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impl DecipherV3 {
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fn hash_key<T: AsRef<[u8]>>(data: T) -> [u8; 16] {
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let digest = umc_utils::md5(data);
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let mut result = [0u8; 16];
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for (result, digest) in result.rchunks_exact_mut(2).zip(digest.chunks_exact(2)) {
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result[0] = digest[0];
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result[1] = digest[1];
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}
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result
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}
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pub fn new(header: &Header, slot_key: &[u8]) -> Result<Self, KugouError> {
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let slot_key = Self::hash_key(slot_key);
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let mut file_key = [0x6b; 17];
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file_key[..16].copy_from_slice(&Self::hash_key(header.file_key));
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Ok(Self { slot_key, file_key })
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}
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fn offset_key(offset: usize) -> u8 {
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let offset_key = (offset as u32).to_ne_bytes();
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offset_key[0] ^ offset_key[1] ^ offset_key[2] ^ offset_key[3]
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}
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pub fn decrypt<T: AsMut<[u8]> + ?Sized>(&self, buffer: &mut T, offset: usize) {
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for (datum, offset) in buffer.as_mut().iter_mut().zip(offset..) {
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let offset_key = Self::offset_key(offset);
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let file_key = self.file_key[offset % self.file_key.len()];
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let slot_key = self.slot_key[offset % self.slot_key.len()];
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let mut temp = *datum;
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temp ^= file_key;
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temp ^= temp << 4;
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temp ^= slot_key;
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temp ^= offset_key;
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*datum = temp;
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}
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}
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}
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