49 lines
1.5 KiB
Rust
49 lines
1.5 KiB
Rust
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use crate::header::Header;
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use crate::{Decipher, 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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}
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impl Decipher for DecipherV3 {
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fn decrypt(&self, buffer: &mut [u8], offset: usize) {
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let slot_key_stream = self.slot_key.iter().cycle().skip(offset);
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let file_key_stream = self.file_key.iter().cycle().skip(offset);
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let mut offset = offset as u32;
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let key_stream = slot_key_stream.zip(file_key_stream);
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for (datum, (&slot_key, &file_key)) in buffer.iter_mut().zip(key_stream) {
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let mut temp = *datum;
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temp ^= file_key;
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temp ^= temp.wrapping_shl(4);
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temp ^= slot_key;
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temp ^= offset.to_ne_bytes().iter().fold(0, |acc, &x| acc ^ x);
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*datum = temp;
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offset = offset.wrapping_add(1);
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}
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}
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}
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