feat: added support for ncm (#15)

src/decrypt-worker/crypto/CryptoFactory.ts

@@ -1,4 +1,5 @@
 import { CryptoFactory } from './CryptoBase';
+import { NCMCrypto } from './ncm/ncm_pc';
 
 import { QMC1Crypto } from './qmc/qmc_v1';
 import { QMC2Crypto } from './qmc/qmc_v2';
@@ -12,6 +13,9 @@ export const allCryptoFactories: CryptoFactory[] = [
   // QMCv2 (*.mflac)
   QMC2Crypto.make,
 
+  // NCM (*.ncm)
+  NCMCrypto.make,
+
   // Crypto that does not implement "checkBySignature" or need to decrypt the entire file and then check audio type,
   //   should be moved to the bottom of the list for performance reasons.
 

src/decrypt-worker/crypto/ncm/ncm_pc.key.ts

@@ -0,0 +1,2 @@
+export const NCM_KEY = 'hzHRAmso5kInbaxW';
+export const NCM_MAGIC_HEADER = new Uint8Array([0x43, 0x54, 0x45, 0x4e, 0x46, 0x44, 0x41, 0x4d]);

src/decrypt-worker/crypto/ncm/ncm_pc.ts

@@ -0,0 +1,21 @@
+import { transformBlob } from '~/decrypt-worker/util/transformBlob';
+import type { CryptoBase } from '../CryptoBase';
+import { NCM_KEY, NCM_MAGIC_HEADER } from './ncm_pc.key';
+
+export class NCMCrypto implements CryptoBase {
+  cryptoName = 'NCM/PC';
+  checkByDecryptHeader = false;
+
+  async checkBySignature(buffer: ArrayBuffer) {
+    const view = new DataView(buffer, 0, NCM_MAGIC_HEADER.byteLength);
+    return NCM_MAGIC_HEADER.every((value, i) => value === view.getUint8(i));
+  }
+
+  async decrypt(buffer: ArrayBuffer): Promise<Blob> {
+    return transformBlob(buffer, (p) => p.make.NeteaseNCM(NCM_KEY));
+  }
+
+  public static make() {
+    return new NCMCrypto();
+  }
+}