um_cli/src/cmd/kgm.rs

@@ -4,7 +4,6 @@ use std::fs::File;
 use std::io::{Read, Seek, SeekFrom, Write};
 use std::path::PathBuf;
 use umc_kgm::header::Header;
-use umc_kgm::Decipher;
 
 /// Decrypt a KGM/VPR file (Kugou Music)
 #[derive(Args)]
@@ -24,7 +23,7 @@ impl ArgsKGM {
         let mut header = [0u8; 0x40];
         file_input.read_exact(&mut header)?;
         let kgm_header = Header::from_buffer(&mut header)?;
-        let decipher = Decipher::new(&kgm_header)?;
+        let decipher = kgm_header.make_decipher()?;
         file_input.seek(SeekFrom::Start(kgm_header.offset_to_data as u64))?;
 
         let mut offset = 0usize;

um_crypto/kgm/src/header.rs

@@ -1,4 +1,6 @@
-use crate::KugouError;
+use crate::v2::DecipherV2;
+use crate::v3::DecipherV3;
+use crate::{Decipher, KugouError};
 use byteorder::{ByteOrder, LE};
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -46,8 +48,25 @@ impl Header {
         })
     }
 
-    pub fn get_challenge_data(&self) -> [u8; 0x10] {
-        self.challenge_data
+    pub fn make_decipher(&self) -> Result<Box<dyn Decipher>, KugouError> {
+        let slot_key: &[u8] = match self.key_slot {
+            1 => b"l,/'",
+            slot => Err(KugouError::UnsupportedKeySlot(slot))?,
+        };
+
+        let decipher: Box<dyn Decipher> = match self.crypto_version {
+            2 => Box::from(DecipherV2::new(self, slot_key)?),
+            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)
     }
 }
 

um_crypto/kgm/src/lib.rs

@@ -1,10 +1,7 @@
 pub mod header;
 pub mod v2;
-pub mod v3;
+mod v3;
 
-use crate::header::Header;
-use crate::v2::DecipherV2;
-use crate::v3::DecipherV3;
 use thiserror::Error;
 
 #[derive(Debug, Error)]
@@ -25,37 +22,6 @@ pub enum KugouError {
     SelfTestFailed,
 }
 
-pub enum Decipher {
-    V2(DecipherV2),
-    V3(DecipherV3),
-}
-
-impl Decipher {
-    pub fn new(header: &Header) -> Result<Self, KugouError> {
-        let slot_key: &[u8] = match header.key_slot {
-            1 => b"l,/'",
-            slot => Err(KugouError::UnsupportedKeySlot(slot))?,
-        };
-
-        let decipher = match header.crypto_version {
-            2 => Decipher::V2(DecipherV2::new(header, slot_key)?),
-            3 => Decipher::V3(DecipherV3::new(header, slot_key)?),
-            version => Err(KugouError::UnsupportedCipherVersion(version))?,
-        };
-
-        let mut test_data = header.decrypt_test_data;
-        decipher.decrypt(&mut test_data, 0);
-        if test_data != header.get_challenge_data() {
-            Err(KugouError::SelfTestFailed)?;
-        }
-
-        Ok(decipher)
-    }
-
-    pub fn decrypt<T: AsMut<[u8]> + ?Sized>(&self, buffer: &mut T, offset: usize) {
-        match self {
-            Decipher::V2(decipher) => decipher.decrypt(buffer, offset),
-            Decipher::V3(decipher) => decipher.decrypt(buffer, offset),
-        }
-    }
+pub trait Decipher {
+    fn decrypt(&self, buffer: &mut [u8], offset: usize);
 }

um_crypto/kgm/src/v2.rs

@@ -1,5 +1,5 @@
 use crate::header::Header;
-use crate::KugouError;
+use crate::{Decipher, KugouError};
 
 pub struct DecipherV2 {
     key: [u8; 4],
@@ -11,9 +11,11 @@ impl DecipherV2 {
         key.copy_from_slice(slot_key);
         Ok(Self { key })
     }
+}
 
-    pub fn decrypt<T: AsMut<[u8]> + ?Sized>(&self, buffer: &mut T, offset: usize) {
-        for (datum, offset) in buffer.as_mut().iter_mut().zip(offset..) {
+impl Decipher for DecipherV2 {
+    fn decrypt(&self, buffer: &mut [u8], offset: usize) {
+        for (datum, offset) in buffer.iter_mut().zip(offset..) {
             *datum ^= self.key[offset % self.key.len()];
         }
     }

um_crypto/kgm/src/v3.rs

@@ -1,5 +1,5 @@
 use crate::header::Header;
-use crate::KugouError;
+use crate::{Decipher, KugouError};
 
 pub struct DecipherV3 {
     slot_key: [u8; 16],
@@ -30,9 +30,11 @@ impl DecipherV3 {
         let offset_key = (offset as u32).to_ne_bytes();
         offset_key[0] ^ offset_key[1] ^ offset_key[2] ^ offset_key[3]
     }
+}
 
-    pub fn decrypt<T: AsMut<[u8]> + ?Sized>(&self, buffer: &mut T, offset: usize) {
-        for (datum, offset) in buffer.as_mut().iter_mut().zip(offset..) {
+impl Decipher for DecipherV3 {
+    fn decrypt(&self, buffer: &mut [u8], offset: usize) {
+        for (datum, offset) in buffer.iter_mut().zip(offset..) {
             let offset_key = Self::offset_key(offset);
 
             let file_key = self.file_key[offset % self.file_key.len()];

um_crypto/kuwo/src/lib.rs

@@ -43,32 +43,19 @@ impl fmt::Display for HeaderMagicBytes {
 
 pub const DATA_START_OFFSET: usize = 0x400;
 
-pub enum Decipher {
+pub enum Cipher {
     V1(CipherV1),
     V2(CipherV2),
 }
 
-impl Decipher {
-    pub fn new<T: AsRef<[u8]>>(header: &Header, ekey: Option<T>) -> Result<Decipher> {
-        let cipher = match header.version {
-            1 => Decipher::V1(CipherV1::new(header.resource_id)),
-            2 => match ekey {
-                Some(ekey) => Decipher::V2(CipherV2::new_from_ekey(ekey)?),
-                None => Err(KuwoCryptoError::V2EKeyRequired)?,
-            },
-            version => Err(KuwoCryptoError::UnsupportedVersion(version as usize))?,
-        };
-
-        Ok(cipher)
-    }
-
+impl Cipher {
     pub fn decrypt<T>(&self, data: &mut T, offset: usize)
     where
         T: AsMut<[u8]> + ?Sized,
     {
         match self {
-            Decipher::V1(cipher) => cipher.decrypt(data, offset),
-            Decipher::V2(cipher) => cipher.decrypt(data, offset),
+            Cipher::V1(cipher) => cipher.decrypt(data, offset),
+            Cipher::V2(cipher) => cipher.decrypt(data, offset),
         }
     }
 }
@@ -118,6 +105,22 @@ impl Header {
         })
     }
 
+    pub fn get_decipher<T>(&self, ekey: Option<T>) -> Result<Cipher>
+    where
+        T: AsRef<[u8]>,
+    {
+        let cipher = match self.version {
+            1 => Cipher::V1(CipherV1::new(self.resource_id)),
+            2 => match ekey {
+                Some(ekey) => Cipher::V2(CipherV2::new_from_ekey(ekey)?),
+                None => Err(KuwoCryptoError::V2EKeyRequired)?,
+            },
+            version => Err(KuwoCryptoError::UnsupportedVersion(version as usize))?,
+        };
+
+        Ok(cipher)
+    }
+
     /// Get the quality id
     /// Used for matching Android MMKV id.
     pub fn get_quality_id(&self) -> u32 {

um_wasm/src/exports/kuwo.rs

@@ -1,7 +1,7 @@
 use crate::errors::map_js_error;
 use crate::exports::qmc::JsQMC2;
 use umc_kuwo::kwm_v1::CipherV1;
-use umc_kuwo::{Decipher, Header};
+use umc_kuwo::{Cipher, Header};
 use wasm_bindgen::prelude::wasm_bindgen;
 use wasm_bindgen::JsError;
 
@@ -27,7 +27,7 @@ impl JsKuwoHeader {
     /// Create an instance of cipher (decipher) for decryption
     #[wasm_bindgen(js_name=makeDecipher)]
     pub fn make_decipher(&self, ekey: Option<String>) -> Result<JsCipher, JsError> {
-        let cipher = Decipher::new(&self.0, ekey).map_err(map_js_error)?;
+        let cipher = self.0.get_decipher(ekey).map_err(map_js_error)?;
         Ok(JsCipher(cipher))
     }
 }
@@ -59,7 +59,7 @@ pub fn js_kuwo_v2_cipher_factory(ekey: &str) -> Result<JsQMC2, JsError> {
 
 /// Common V1/V2 wrapper interface, derived from `KuwoHeader.makeCipher`
 #[wasm_bindgen(js_name=KWMCipher)]
-pub struct JsCipher(Decipher);
+pub struct JsCipher(Cipher);
 
 #[wasm_bindgen(js_class=KWMCipher)]
 impl JsCipher {