NCM Toolkit

Solutions for analysing music acquired from NetEase Cloud Music.

Tip

NCM stands for NetEase Cloud Music.

Tools (Publicly Available)

NCM file (*.ncm) decryptor
163 key reader (Not implemented)
Lyrics downloader (Not implemented)

Usage

As of the submission of this commit, I haven't made a proper GUI yet, as all the planned features of this application are not yet implemented.

So you can run this program from the command line.

Usage:

./NCMTool.exe NCMFile [-n output_path] [-d]

Parameter:

-n: Name the output file with a specific name;
-d: Enable logging.

If nothing goes wrong, you may see the following text on your terminal:

> .\NCMTool.exe 'YOASOBI - Halzion.ncm' -d
Log Start...
[Log] RC4 Key:
[Log] Length = 128
[Log] Key= 273581793719377E7fT49x7dof9OKCgg9cdvhEuezy3iZCL1nFvBFd1T4uSktAJKmwZXsijPbijliionVUXXg9plTbXEclAE9Lb
[Log] Metadata Info:
[Log] Length= 598
[Log] Turned into GBK
[Log] Successfully Parsed into Metadata 
[Log] Album Cover:
[Log] Length= 606725
[Log] Successfully Loaded Music Cover.
[Log] Music:
[Log] Load block 0
[Log] Decrypted Music Data. 
[Info] Main Metadata
Name:
             Halzion
Author:
             YOASOBI            33927412

Album:
                      E-SIDE 2
Alias:
             ハルジオン
TransNames:
                   春紫菀
ID:             1994998091
Album ID:       154291740
[Log] Wrote Music to YOASOBI - Halzion.mp3
[Log] Wrote Cover to YOASOBI - Halzion.jpg

It will export the decrypted music files and album art to the current directory under the name "Author - Name".

There is currently no code implemented to add album art to music files. But as you can see, I've added id3v3lib to the project and the relevant code is being written ~~(why I don't use Python)~~. Before adding this feature, if you have ffmpeg installed on your computer, you can add the album art into the file with the following command.

ffmpeg -i [sourcefile].mp3 -i [coverfile] -map 0:a -map 1:v -map_metadata 0 -id3v2_version 3 -c:a copy -c:v copy [outputfile].mp3

Hopefully this project will save your Netease Cloud Music.

Installation

You can get an executeable file by using the following commands:

mkdir ./build && cd ./build
cmake ..
make

If all goes well, you'll see NCMTool.exe in the ./build directory.

About NCM File

NCM File = Netease Cloud Music Music File

I. File Structure

Data Type	Size	Description
Magic Header	10B	File Header
Key Length	4B	Length of AES128 encrypted RC4 Key (little-endian)
Key Data	Key Length	(See Below)
Metadata Length	4B	Length of Metadata (little-endian)
Metadata	Metadata Length	(See Below)
CRC	4B	Skip
Gap	4B	Skip
Cover Size	4B	Size of Cover Image
Cover	Cover Size	JFIF Picture
Music	-	(See Below)

II. Decryption

RC4 Key:
- Decrypt Method:
  1. XOR 0x64 by byte
  2. AES decrypt
  3. Remove filling area
  4. Remove front 17 bytes:neteasecloudmusic
- AES key: 0x68,0x7A,0x48,0x52,0x41,0x6D,0x73，0x6F,0x35,0x6B,0x49,0x6E,0x62,0x61,0x78,0x57
Metadata
- Data Type: JSON
- Decrypt Method:
  1. XOR 0x63 by byte
  2. Remove front 22 bytes
  3. Base64 decode
  4. AES decrypt
  5. Remove front 6 bytes
- AES key: 0x23,0x31,0x34,0x6C,0x6A,0x6B,0x5F,0x21,0x5C,0x5D,0x26,0x30,0x55,0x3C,0x27,0x28
Music
- Generate S-Box by RC4-KSA using RC4 Key
- Decrypt by S-Box

III. Metadata

Metadata is stored as compressed JSON text, typically has 15 key-value pairs.

Key	Value	Description
musicId	Integer	Music ID in Netease Cloud Music
musicName	String	Music Name
artist	List(List(String, Integer))	Name & ID of the authors
albumId	Integer	Album ID
album	String	Album Name
albumPicDocId	String	Album cover ID
albumPic	String	URL pointing to the album cover
bitrate	Integer	Bitrate
mp3DocId	String	~~I don't get it.~~
duration	Integer	Music length, calculated by bitrate
mvID	Integer	~~I don't get it.~~
alias	List(String)	Music alias, often used as a subtitle
transNames	List(String)	Music name in different languages
format	String	File extension of the decrypted music
flag	Integer	~~I don't get it.~~

Example:

{
"musicId":          1991012773,
"musicName":        "ギターと孤独と蒼い惑星",
"artist":           [["結束バンド", 54103171]],
"albumId":          153542094,
"album":            "ギターと孤独と蒼い惑星",
"albumPicDocId":    "109951167983448236",
"albumPic":         "https://p4.music.126.net/rfstzrVK05hCPjU-4mzSFA==/109951167983448236.jpg",
"bitrate":          320000,
"mp3DocId":         "f481d20151f01d5d681d2768d753ad64",
"duration":         229015,
"mvId":             0,
"alias":            ["TV动画《孤独摇滚！》插曲"],
"transNames":       [],
"format":           "mp3",
"flag":             4
}

kinney-08/NCMToolkit