feat: Completed the NCM decryption tool class.

完成 NCM 解密工具类。

src/ZonyLrcTools.Cli/Infrastructure/MusicDecryption/DecryptionResult.cs

@@ -0,0 +1,16 @@
+using System.Collections.Generic;
+
+namespace ZonyLrcTools.Cli.Infrastructure.MusicDecryption
+{
+    public class DecryptionResult
+    {
+        public byte[] Data { get; protected set; }
+
+        public Dictionary<string, object> ExtensionObjects { get; set; }
+
+        public DecryptionResult(byte[] data)
+        {
+            Data = data;
+        }
+    }
+}

src/ZonyLrcTools.Cli/Infrastructure/MusicDecryption/IMusicDecryptor.cs

@@ -12,6 +12,6 @@ namespace ZonyLrcTools.Cli.Infrastructure.MusicDecryption
         /// </summary>
         /// <param name="sourceBytes">源加密的歌曲数据。</param>
         /// <returns>解密完成的歌曲数据。</returns>
-        Task<byte[]> Convert(byte[] sourceBytes);
+        Task<DecryptionResult> ConvertMusic(byte[] sourceBytes);
     }
 }

src/ZonyLrcTools.Cli/Infrastructure/MusicDecryption/NcmMusicDecryptor.cs

@@ -1,10 +1,11 @@
 using System;
+using System.Collections.Generic;
 using System.IO;
-using System.Linq;
 using System.Security.Cryptography;
+using System.Text;
 using System.Threading.Tasks;
+using Newtonsoft.Json.Linq;
 using ZonyLrcTools.Cli.Infrastructure.DependencyInject;
-using ZonyLrcTools.Cli.Infrastructure.Exceptions;
 
 namespace ZonyLrcTools.Cli.Infrastructure.MusicDecryption
 {
@@ -16,7 +17,7 @@ namespace ZonyLrcTools.Cli.Infrastructure.MusicDecryption
         protected readonly byte[] AesCoreKey = {0x68, 0x7A, 0x48, 0x52, 0x41, 0x6D, 0x73, 0x6F, 0x35, 0x6B, 0x49, 0x6E, 0x62, 0x61, 0x78, 0x57};
         protected readonly byte[] AesModifyKey = {0x23, 0x31, 0x34, 0x6C, 0x6A, 0x6B, 0x5F, 0x21, 0x5C, 0x5D, 0x26, 0x30, 0x55, 0x3C, 0x27, 0x28};
 
-        public Task<byte[]> Convert(byte[] sourceBytes)
+        public async Task<DecryptionResult> ConvertMusic(byte[] sourceBytes)
         {
             var stream = new MemoryStream(sourceBytes);
             var streamReader = new BinaryReader(stream);
@@ -46,7 +47,7 @@ namespace ZonyLrcTools.Cli.Infrastructure.MusicDecryption
                 keyBytes[i] ^= 0x64;
             }
 
-            var deKeyDataBytes = GetBytesByOffset(DecryptAes128Ecb(AesCoreKey, keyBytes), 17);
+            var coreKeyBytes = GetBytesByOffset(DecryptAes128Ecb(AesCoreKey, keyBytes), 17);
 
             var modifyDataBytes = new byte[streamReader.ReadInt32()];
             stream.Read(modifyDataBytes);
@@ -55,7 +56,25 @@ namespace ZonyLrcTools.Cli.Infrastructure.MusicDecryption
                 modifyDataBytes[i] ^= 0x63;
             }
 
-            throw new System.NotImplementedException();
+            var decryptBase64Bytes = Convert.FromBase64String(Encoding.UTF8.GetString(GetBytesByOffset(modifyDataBytes, 22)));
+            var decryptModifyData = DecryptAes128Ecb(AesModifyKey, decryptBase64Bytes);
+
+            var musicInfoJson = JObject.Parse(Encoding.UTF8.GetString(GetBytesByOffset(decryptModifyData, 6)));
+
+            // CRC 校验
+            stream.Seek(4, SeekOrigin.Current);
+            stream.Seek(5, SeekOrigin.Current);
+
+            GetAlbumImageBytes(stream, streamReader);
+
+            var sBox = BuildKeyBox(coreKeyBytes);
+            return new DecryptionResult(GetMusicBytes(sBox, stream).ToArray())
+            {
+                ExtensionObjects = new Dictionary<string, object>
+                {
+                    {"JSON", musicInfoJson}
+                }
+            };
         }
 
         private byte[] GetBytesByOffset(byte[] srcBytes, int offset = 0)
@@ -75,5 +94,91 @@ namespace ZonyLrcTools.Cli.Infrastructure.MusicDecryption
 
             return result;
         }
+
+        /// <summary>
+        /// RC4 加密，生成 KeyBox。
+        /// </summary>
+        /// <param name="key"></param>
+        /// <returns></returns>
+        private byte[] BuildKeyBox(byte[] key)
+        {
+            byte[] box = new byte[256];
+            for (int i = 0; i < 256; ++i)
+            {
+                box[i] = (byte) i;
+            }
+
+            byte keyLength = (byte) key.Length;
+            byte c;
+            byte lastByte = 0;
+            byte keyOffset = 0;
+            byte swap;
+
+            for (int i = 0; i < 256; ++i)
+            {
+                swap = box[i];
+                c = (byte) ((swap + lastByte + key[keyOffset++]) & 0xff);
+
+                if (keyOffset >= keyLength)
+                {
+                    keyOffset = 0;
+                }
+
+                box[i] = box[c];
+                box[c] = swap;
+                lastByte = c;
+            }
+
+            return box;
+        }
+
+        /// <summary>
+        /// 获得歌曲的专辑图像信息。
+        /// </summary>
+        /// <param name="stream">原始文件流。</param>
+        /// <param name="streamReader">二进制读取器。</param>
+        private byte[] GetAlbumImageBytes(Stream stream, BinaryReader streamReader)
+        {
+            var imgLength = streamReader.ReadInt32();
+
+            if (imgLength <= 0)
+            {
+                return null;
+            }
+
+            var imgBuffer = streamReader.ReadBytes(imgLength);
+
+            return imgBuffer;
+        }
+
+        /// <summary>
+        /// 获得歌曲的完整数据。
+        /// </summary>
+        /// <param name="sBox"></param>
+        /// <param name="stream">原始文件流。</param>
+        private MemoryStream GetMusicBytes(byte[] sBox, Stream stream)
+        {
+            var n = 0x8000;
+            var memoryStream = new MemoryStream();
+
+            while (true)
+            {
+                var tb = new byte[n];
+                var result = stream.Read(tb);
+                if (result <= 0) break;
+
+                for (int i = 0; i < n; i++)
+                {
+                    var j = (byte) ((i + 1) & 0xff);
+                    tb[i] ^= sBox[sBox[j] + sBox[(sBox[j] + j) & 0xff] & 0xff];
+                }
+
+                memoryStream.Write(tb);
+            }
+
+            memoryStream.Flush();
+
+            return memoryStream;
+        }
     }
 }

tests/ZonyLrcTools.Tests/Infrastructure/MusicDecryption/NcmMusicDecryptor_Tests.cs

@@ -0,0 +1,35 @@
+using System.IO;
+using System.Threading.Tasks;
+using Microsoft.Extensions.DependencyInjection;
+using Newtonsoft.Json.Linq;
+using Xunit;
+using ZonyLrcTools.Cli.Infrastructure.MusicDecryption;
+
+namespace ZonyLrcTools.Tests.Infrastructure.MusicDecryption
+{
+    public class NcmMusicDecryptorTests : TestBase
+    {
+        [Fact]
+        public async Task ConvertMusic_Test()
+        {
+            var decryptor = ServiceProvider.GetRequiredService<IMusicDecryptor>();
+
+            await using var fs = File.Open(Path.Combine(Directory.GetCurrentDirectory(), "MusicFiles", "Loren Gray - Queen.ncm"), FileMode.Open);
+            using var reader = new BinaryReader(fs);
+            var response = await decryptor.ConvertMusic(reader.ReadBytes((int) fs.Length));
+
+            var musicFilePath = Path.Combine(Directory.GetCurrentDirectory(),
+                "MusicFiles",
+                $"Loren Gray - Queen.{((JObject) response.ExtensionObjects["JSON"]).SelectToken("$.format").Value<string>()}");
+
+            if (File.Exists(musicFilePath))
+            {
+                File.Delete(musicFilePath);
+            }
+
+            await using var musicFileStream = File.Create(musicFilePath);
+            await musicFileStream.WriteAsync(response.Data);
+            await musicFileStream.FlushAsync();
+        }
+    }
+}

tests/ZonyLrcTools.Tests/ZonyLrcTools.Tests.csproj

@@ -29,6 +29,10 @@
       <Content Include="MusicFiles\曾经艺也 - 荀彧(纯音乐版).mp3">
         <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
       </Content>
+      <None Remove="MusicFiles\Loren Gray - Queen.ncm" />
+      <Content Include="MusicFiles\Loren Gray - Queen.ncm">
+        <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+      </Content>
     </ItemGroup>
 
 </Project>