From c4249226a2407f1962e5235c8f461803fd63a311 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E9=B2=81=E6=A0=91=E4=BA=BA?= <lu.shuren@um-react.app>
Date: Fri, 6 Sep 2024 00:51:56 +0100
Subject: [PATCH] feat: add ekey

---
 um_crypto/qmc/Cargo.toml  |  7 ++--
 um_crypto/qmc/src/ekey.rs | 73 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+), 3 deletions(-)
 create mode 100644 um_crypto/qmc/src/ekey.rs

diff --git a/um_crypto/qmc/Cargo.toml b/um_crypto/qmc/Cargo.toml
index a4fd420..e1fa004 100644
--- a/um_crypto/qmc/Cargo.toml
+++ b/um_crypto/qmc/Cargo.toml
@@ -4,8 +4,9 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
-base64 = "0.22.1"
-itertools = "0.13.0"
 anyhow = "1.0.86"
-thiserror = "1.0.63"
 byteorder = "1.5.0"
+itertools = "0.13.0"
+tc_tea = "0.1.4"
+thiserror = "1.0.63"
+umc_utils = { path = "../utils" }
\ No newline at end of file
diff --git a/um_crypto/qmc/src/ekey.rs b/um_crypto/qmc/src/ekey.rs
new file mode 100644
index 0000000..8d138fb
--- /dev/null
+++ b/um_crypto/qmc/src/ekey.rs
@@ -0,0 +1,73 @@
+use anyhow::Result;
+use itertools::Itertools;
+use std::ops::Mul;
+use thiserror::Error;
+use umc_utils::base64;
+
+/// Base64 encoded prefix: "QQMusic EncV2,Key:"
+const EKEY_V2_PREFIX: &[u8; 24] = b"UVFNdXNpYyBFbmNWMixLZXk6";
+const EKEY_V2_KEY1: [u8; 16] = [
+    0x33, 0x38, 0x36, 0x5A, 0x4A, 0x59, 0x21, 0x40, 0x23, 0x2A, 0x24, 0x25, 0x5E, 0x26, 0x29, 0x28,
+];
+const EKEY_V2_KEY2: [u8; 16] = [
+    0x2A, 0x2A, 0x23, 0x21, 0x28, 0x23, 0x24, 0x25, 0x26, 0x5E, 0x61, 0x31, 0x63, 0x5A, 0x2C, 0x54,
+];
+
+#[derive(Debug, Clone, PartialEq, Error)]
+pub enum EKeyDecryptError {
+    #[error("EKey is too short for decryption")]
+    EKeyTooShort,
+    #[error("Error when decrypting ekey v1")]
+    FailDecryptV1,
+    #[error("Error when decrypting ekey v2")]
+    FailDecryptV2,
+}
+
+fn make_simple_key<const N: usize>() -> [u8; N] {
+    let mut result = [0u8; N];
+
+    for (i, v) in result.iter_mut().enumerate() {
+        let i = i as f32;
+        let value = 106.0 + i * 0.1;
+        let value = value.tan().abs().mul(100.0);
+        *v = value as u8;
+    }
+
+    result
+}
+
+pub fn decrypt_v1(ekey: &[u8]) -> Result<Box<[u8]>> {
+    if ekey.len() < 12 {
+        Err(EKeyDecryptError::EKeyTooShort)?;
+    }
+
+    let ekey = base64::decode(ekey)?;
+    let (header, cipher) = ekey.split_at(8);
+
+    let simple_key = make_simple_key::<8>();
+    let tea_key = simple_key
+        .iter()
+        .zip(header)
+        .flat_map(|(&simple_part, &header_part)| [simple_part, header_part])
+        .collect::<Vec<_>>();
+
+    let plaintext = tc_tea::decrypt(cipher, tea_key).ok_or(EKeyDecryptError::FailDecryptV1)?;
+    Ok([header, &plaintext].concat().into())
+}
+
+pub fn decrypt_v2(ekey: &[u8]) -> Result<Box<[u8]>> {
+    let ekey = base64::decode(ekey)?;
+    let ekey = tc_tea::decrypt(ekey, EKEY_V2_KEY1).ok_or(EKeyDecryptError::FailDecryptV2)?;
+    let ekey = tc_tea::decrypt(ekey, EKEY_V2_KEY2).ok_or(EKeyDecryptError::FailDecryptV2)?;
+    let ekey = ekey.iter().take_while(|&&b| b != 0).copied().collect_vec();
+
+    decrypt_v1(&ekey)
+}
+
+pub fn decrypt<T: AsRef<[u8]>>(ekey: T) -> Result<Box<[u8]>> {
+    let ekey = ekey.as_ref();
+    match ekey.strip_prefix(EKEY_V2_PREFIX) {
+        Some(v2_ekey) => decrypt_v2(v2_ekey),
+        None => decrypt_v1(ekey),
+    }
+}