From 92a52c1565d35c34fa899798b6c44657da8dd45a 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: Sun, 15 Sep 2024 23:53:00 +0100
Subject: [PATCH] [kgm] feat: add decipher self-test on startup

---
 um_crypto/kgm/src/header.rs | 36 ++++++++++++++++++++++++++++++++++++
 um_crypto/kgm/src/lib.rs    |  6 ++++++
 2 files changed, 42 insertions(+)

diff --git a/um_crypto/kgm/src/header.rs b/um_crypto/kgm/src/header.rs
index 5526049..b1ef1eb 100644
--- a/um_crypto/kgm/src/header.rs
+++ b/um_crypto/kgm/src/header.rs
@@ -11,6 +11,8 @@ pub struct Header {
     pub key_slot: u32,
     pub decrypt_test_data: [u8; 0x10],
     pub file_key: [u8; 0x10],
+
+    challenge_data: [u8; 0x10],
 }
 
 impl Header {
@@ -25,6 +27,8 @@ impl Header {
 
         let mut magic = [0u8; 0x10];
         magic.copy_from_slice(&buffer[..0x10]);
+        let challenge_data = get_challenge_data(&magic)?;
+
         let offset_to_data = LE::read_u32(&buffer[0x10..0x14]) as usize;
         let crypto_version = LE::read_u32(&buffer[0x14..0x18]);
         let key_slot = LE::read_u32(&buffer[0x18..0x1C]);
@@ -40,6 +44,7 @@ impl Header {
             key_slot,
             decrypt_test_data,
             file_key,
+            challenge_data,
         })
     }
 
@@ -54,6 +59,37 @@ impl Header {
             3 => Box::from(DecipherV3::new(self, slot_key)?),
             version => Err(KugouError::UnsupportedCipherVersion(version))?,
         };
+
+        let mut test_data = self.decrypt_test_data;
+        decipher.decrypt(&mut test_data, 0);
+        if self.challenge_data != test_data {
+            Err(KugouError::SelfTestFailed)?;
+        }
+
         Ok(decipher)
     }
 }
+
+fn get_challenge_data(magic_header: &[u8; 0x10]) -> Result<[u8; 0x10], KugouError> {
+    match magic_header {
+        &KGM_HEADER => Ok(KGM_TEST_DATA),
+        &VPR_HEADER => Ok(VPR_TEST_DATA),
+        _ => Err(KugouError::NotKGMFile)?,
+    }
+}
+
+pub const KGM_HEADER: [u8; 16] = [
+    0x7C, 0xD5, 0x32, 0xEB, 0x86, 0x02, 0x7F, 0x4B, 0xA8, 0xAF, 0xA6, 0x8E, 0x0F, 0xFF, 0x99, 0x14,
+];
+
+pub const KGM_TEST_DATA: [u8; 16] = [
+    0x38, 0x85, 0xED, 0x92, 0x79, 0x5F, 0xF8, 0x4C, 0xB3, 0x03, 0x61, 0x41, 0x16, 0xA0, 0x1D, 0x47,
+];
+
+pub const VPR_HEADER: [u8; 16] = [
+    0x05, 0x28, 0xBC, 0x96, 0xE9, 0xE4, 0x5A, 0x43, 0x91, 0xAA, 0xBD, 0xD0, 0x7A, 0xF5, 0x36, 0x31,
+];
+
+pub const VPR_TEST_DATA: [u8; 16] = [
+    0x1D, 0x5A, 0x05, 0x34, 0x0C, 0x41, 0x8D, 0x42, 0x9C, 0x83, 0x92, 0x6C, 0xAE, 0x16, 0xFE, 0x56,
+];
diff --git a/um_crypto/kgm/src/lib.rs b/um_crypto/kgm/src/lib.rs
index 80ccaaa..7af6573 100644
--- a/um_crypto/kgm/src/lib.rs
+++ b/um_crypto/kgm/src/lib.rs
@@ -14,6 +14,12 @@ pub enum KugouError {
 
     #[error("Unsupported cipher version: {0}")]
     UnsupportedCipherVersion(u32),
+
+    #[error("Not KGM File (magic mismatch)")]
+    NotKGMFile,
+
+    #[error("Unsupported cipher (self-test failed)")]
+    SelfTestFailed,
 }
 
 pub trait Decipher {