80 lines
2.4 KiB
Rust
80 lines
2.4 KiB
Rust
use anyhow::Result;
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use itertools::Itertools;
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use lazy_static::lazy_static;
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use std::ops::Mul;
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use tc_tea::TcTeaError;
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use thiserror::Error;
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use umc_utils::base64;
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/// Base64 encoded prefix: "QQMusic EncV2,Key:"
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const EKEY_V2_PREFIX: &[u8; 24] = b"UVFNdXNpYyBFbmNWMixLZXk6";
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const EKEY_V2_KEY1: [u8; 16] = [
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0x33, 0x38, 0x36, 0x5A, 0x4A, 0x59, 0x21, 0x40, 0x23, 0x2A, 0x24, 0x25, 0x5E, 0x26, 0x29, 0x28,
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];
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const EKEY_V2_KEY2: [u8; 16] = [
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0x2A, 0x2A, 0x23, 0x21, 0x28, 0x23, 0x24, 0x25, 0x26, 0x5E, 0x61, 0x31, 0x63, 0x5A, 0x2C, 0x54,
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];
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lazy_static! {
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static ref EKEY_SIMPLE_KEY: [u8; 8] = make_simple_key::<8>();
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}
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#[derive(Debug, PartialEq, Error)]
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pub enum EKeyDecryptError {
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#[error("EKey is too short for decryption")]
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EKeyTooShort,
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#[error("Error when decrypting ekey v1: {0}")]
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FailDecryptV1(TcTeaError),
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#[error("Error when decrypting ekey v2: {0}")]
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FailDecryptV2(TcTeaError),
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}
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fn make_simple_key<const N: usize>() -> [u8; N] {
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let mut result = [0u8; N];
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for (i, v) in result.iter_mut().enumerate() {
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let i = i as f32;
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let value = 106.0 + i * 0.1;
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let value = value.tan().abs().mul(100.0);
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*v = value as u8;
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}
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result
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}
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pub fn decrypt_v1(ekey: &[u8]) -> Result<Vec<u8>> {
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if ekey.len() < 12 {
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Err(EKeyDecryptError::EKeyTooShort)?;
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}
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let ekey = base64::decode(ekey)?;
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let (header, cipher) = ekey.split_at(8);
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// tea_key: interleave a byte from each stream
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let tea_key = EKEY_SIMPLE_KEY
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.iter()
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.zip(header)
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.flat_map(|(&simple_key_part, &header_part)| [simple_key_part, header_part])
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.collect_vec();
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let plaintext = tc_tea::decrypt(cipher, tea_key).map_err(EKeyDecryptError::FailDecryptV1)?;
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Ok([header, &plaintext].concat())
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}
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pub fn decrypt_v2(ekey: &[u8]) -> Result<Vec<u8>> {
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let ekey = base64::decode(ekey)?;
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let ekey = tc_tea::decrypt(ekey, EKEY_V2_KEY1).map_err(EKeyDecryptError::FailDecryptV2)?;
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let ekey = tc_tea::decrypt(ekey, EKEY_V2_KEY2).map_err(EKeyDecryptError::FailDecryptV2)?;
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let ekey = ekey.iter().take_while(|&&b| b != 0).copied().collect_vec();
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decrypt_v1(&ekey)
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}
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pub fn decrypt<T: AsRef<[u8]>>(ekey: T) -> Result<Vec<u8>> {
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let ekey = ekey.as_ref();
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match ekey.strip_prefix(EKEY_V2_PREFIX) {
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Some(v2_ekey) => decrypt_v2(v2_ekey),
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None => decrypt_v1(ekey),
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}
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}
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