feat: first version of kgg support

algo/kgm/kgm.go

@@ -14,10 +14,12 @@ type Decoder struct {
 	offset int
 
 	header header
+
+	KggDatabasePath string
 }
 
 func NewDecoder(p *common.DecoderParams) common.Decoder {
-	return &Decoder{rd: p.Reader}
+	return &Decoder{rd: p.Reader, KggDatabasePath: p.KggDatabasePath}
 }
 
 // Validate checks if the file is a valid Kugou (.kgm, .vpr, .kgma) file.
@@ -34,6 +36,11 @@ func (d *Decoder) Validate() (err error) {
 		if err != nil {
 			return fmt.Errorf("kgm init crypto v3: %w", err)
 		}
+	case 5:
+		d.cipher, err = newKgmCryptoV5(&d.header, d.KggDatabasePath)
+		if err != nil {
+			return fmt.Errorf("kgm init crypto v5: %w", err)
+		}
 	default:
 		return fmt.Errorf("kgm: unsupported crypto version %d", d.header.CryptoVersion)
 	}
@@ -57,6 +64,7 @@ func (d *Decoder) Read(buf []byte) (int, error) {
 
 func init() {
 	// Kugou
+	common.RegisterDecoder("kgg", false, NewDecoder)
 	common.RegisterDecoder("kgm", false, NewDecoder)
 	common.RegisterDecoder("kgma", false, NewDecoder)
 	// Viper

algo/kgm/kgm_header.go

@@ -29,6 +29,8 @@ type header struct {
 	CryptoSlot     uint32 // 0x18-0x1b: crypto key slot
 	CryptoTestData []byte // 0x1c-0x2b: crypto test data
 	CryptoKey      []byte // 0x2c-0x3b: crypto key
+
+	AudioHash string // v5: audio hash
 }
 
 func (h *header) FromFile(rd io.ReadSeeker) error {
@@ -36,29 +38,56 @@ func (h *header) FromFile(rd io.ReadSeeker) error {
 		return fmt.Errorf("kgm seek start: %w", err)
 	}
 
-	buf := make([]byte, 0x3c)
-	if _, err := io.ReadFull(rd, buf); err != nil {
-		return fmt.Errorf("kgm read header: %w", err)
-	}
-
-	return h.FromBytes(buf)
+	return h.FromBytes(rd)
 }
 
-func (h *header) FromBytes(buf []byte) error {
-	if len(buf) < 0x3c {
-		return errors.New("invalid kgm header length")
+func (h *header) FromBytes(r io.ReadSeeker) error {
+	h.MagicHeader = make([]byte, 16)
+	_, err := r.Read(h.MagicHeader)
+	if err != nil {
+		return err
 	}
-
-	h.MagicHeader = buf[:0x10]
 	if !bytes.Equal(kgmHeader, h.MagicHeader) && !bytes.Equal(vprHeader, h.MagicHeader) {
 		return ErrKgmMagicHeader
 	}
 
-	h.AudioOffset = binary.LittleEndian.Uint32(buf[0x10:0x14])
-	h.CryptoVersion = binary.LittleEndian.Uint32(buf[0x14:0x18])
-	h.CryptoSlot = binary.LittleEndian.Uint32(buf[0x18:0x1c])
-	h.CryptoTestData = buf[0x1c:0x2c]
-	h.CryptoKey = buf[0x2c:0x3c]
+	err = binary.Read(r, binary.LittleEndian, &h.AudioOffset)
+	if err != nil {
+		return err
+	}
+	err = binary.Read(r, binary.LittleEndian, &h.CryptoVersion)
+	if err != nil {
+		return err
+	}
+	err = binary.Read(r, binary.LittleEndian, &h.CryptoSlot)
+	if err != nil {
+		return err
+	}
+	h.CryptoTestData = make([]byte, 0x10)
+	_, err = r.Read(h.CryptoTestData)
+	if err != nil {
+		return err
+	}
+	h.CryptoKey = make([]byte, 0x10)
+	_, err = r.Read(h.CryptoKey)
+	if err != nil {
+		return err
+	}
+
+	if h.CryptoVersion == 5 {
+		r.Seek(0x08, io.SeekCurrent)
+		var audioHashLen uint32 = 0
+		err = binary.Read(r, binary.LittleEndian, &audioHashLen)
+		if err != nil {
+			return err
+		}
+		audioHashBuffer := make([]byte, audioHashLen)
+		_, err = r.Read(audioHashBuffer)
+		if err != nil {
+			return err
+		}
+		h.AudioHash = string(audioHashBuffer)
+	}
 
 	return nil
 }

algo/kgm/kgm_v5.go

@@ -0,0 +1,30 @@
+package kgm
+
+import (
+	"fmt"
+
+	"unlock-music.dev/cli/algo/common"
+	"unlock-music.dev/cli/algo/kgm/pc_kugou_db"
+	"unlock-music.dev/cli/algo/qmc"
+)
+
+func newKgmCryptoV5(header *header, kggDatabasePath string) (common.StreamDecoder, error) {
+	if header.AudioHash == "" {
+		return nil, fmt.Errorf("kgm v5: missing audio hash")
+	}
+
+	if kggDatabasePath == "" {
+		return nil, fmt.Errorf("kgm v5: missing kgg database path")
+	}
+
+	m, err := pc_kugou_db.CachedDumpEKey(kggDatabasePath)
+	if err != nil {
+		return nil, fmt.Errorf("kgm v5: decrypt kgg database: %w", err)
+	}
+	ekey, ok := m[header.AudioHash]
+	if !ok || ekey == "" {
+		return nil, fmt.Errorf("kgm v5: ekey missing from db (audio_hash=%s)", header.AudioHash)
+	}
+
+	return qmc.NewQmcCipherDecoderFromEKey([]byte(ekey))
+}

algo/kgm/pc_kugou_db/cipher.go

@@ -0,0 +1,238 @@
+package pc_kugou_db
+
+// ported from lib_um_crypto_rust:
+//   https://git.unlock-music.dev/um/lib_um_crypto_rust/src/tag/v0.1.10/um_crypto/kgm/src/pc_db_decrypt
+
+import (
+	"bytes"
+	"context"
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/md5"
+	"database/sql"
+	"encoding/binary"
+	"fmt"
+	"os"
+	"sync"
+
+	_ "modernc.org/sqlite"
+)
+
+const PAGE_SIZE = 0x400
+
+var SQLITE_HEADER = []byte("SQLite format 3\x00")
+var DEFAULT_MASTER_KEY = []byte{
+	// master key (0x10 bytes)
+	0x1D, 0x61, 0x31, 0x45, 0xB2, 0x47, 0xBF, 0x7F, 0x3D, 0x18, 0x96, 0x72, 0x14, 0x4F, 0xE4, 0xBF,
+	0x00, 0x00, 0x00, 0x00, // page number (le)
+	0x73, 0x41, 0x6C, 0x54, // fixed value
+}
+
+func next_page_iv(seed uint32) uint32 {
+	var left uint32 = seed * 0x9EF4
+	var right uint32 = seed / 0xce26 * 0x7FFFFF07
+	var value uint32 = left - right
+	if value&0x8000_0000 == 0 {
+		return value
+	}
+	return value + 0x7FFF_FF07
+}
+
+func derive_page_aes_key(seed uint32) []byte {
+	master_key := make([]byte, len(DEFAULT_MASTER_KEY))
+	copy(master_key, DEFAULT_MASTER_KEY)
+	binary.LittleEndian.PutUint32(master_key[0x10:0x14], seed)
+	digest := md5.Sum(master_key)
+	return digest[:]
+}
+
+func derive_page_aes_iv(seed uint32) []byte {
+	iv := make([]byte, 0x10)
+	seed = seed + 1
+	for i := 0; i < 0x10; i += 4 {
+		seed = next_page_iv(seed)
+		binary.LittleEndian.PutUint32(iv[i:i+4], seed)
+	}
+	digest := md5.Sum(iv)
+	return digest[:]
+}
+
+func aes128cbcDecryptNoPadding(buffer, key, iv []byte) error {
+	if len(key) != 16 {
+		return fmt.Errorf("invalid key size: %d (must be 16 bytes for AES-128)", len(key))
+	}
+	if len(iv) != aes.BlockSize {
+		return fmt.Errorf("invalid IV size: %d (must be %d bytes)", len(iv), aes.BlockSize)
+	}
+	if len(buffer)%aes.BlockSize != 0 {
+		return fmt.Errorf("ciphertext length must be a multiple of %d bytes", aes.BlockSize)
+	}
+
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return err
+	}
+
+	mode := cipher.NewCBCDecrypter(block, iv)
+	mode.CryptBlocks(buffer, buffer)
+	return nil
+}
+
+func decrypt_db_page(buffer []byte, page_number uint32) error {
+	key := derive_page_aes_key(page_number)
+	iv := derive_page_aes_iv(page_number)
+
+	return aes128cbcDecryptNoPadding(buffer, key, iv)
+}
+
+func decrypt_page_1(page []byte) error {
+	if err := validate_page_1_header(page); err != nil {
+		return err
+	}
+
+	// Backup expected hdr value
+
+	expected_hdr_value := make([]byte, 8)
+	copy(expected_hdr_value, page[0x10:0x18])
+
+	// Copy encrypted hdr over
+	hdr := page[:0x10]
+	copy(page[0x10:0x18], hdr[0x08:0x10])
+
+	if err := decrypt_db_page(page[0x10:], 1); err != nil {
+		return err
+	}
+
+	// Validate header
+	if !bytes.Equal(page[0x10:0x18], expected_hdr_value[:8]) {
+		return fmt.Errorf("decrypt page 1 failed")
+	}
+
+	// Apply SQLite header
+	copy(hdr, SQLITE_HEADER)
+
+	return nil
+}
+
+func validate_page_1_header(header []byte) error {
+	o10 := binary.LittleEndian.Uint32(header[0x10:0x14])
+	o14 := binary.LittleEndian.Uint32(header[0x14:0x18])
+
+	v6 := ((o10 & 0xff) << 8) | ((o10 & 0xff00) << 16)
+	ok := o14 == 0x20204000 && (v6-0x200) <= 0xFE00 && ((v6-1)&v6) == 0
+	if !ok {
+		return fmt.Errorf("invalid page 1 header")
+	}
+	return nil
+}
+
+func decryptPcDatabase(buffer []byte) error {
+	db_size := len(buffer)
+
+	// not encrypted
+	if bytes.Equal(buffer[:len(SQLITE_HEADER)], SQLITE_HEADER) {
+		return nil
+	}
+
+	if db_size%PAGE_SIZE != 0 || db_size == 0 {
+		return fmt.Errorf("invalid database size: %d", db_size)
+	}
+
+	last_page := db_size / PAGE_SIZE
+
+	// page 1 is the header
+	if err := decrypt_page_1(buffer[:PAGE_SIZE]); err != nil {
+		return err
+	}
+
+	offset := PAGE_SIZE
+	for page_no := 2; page_no <= last_page; page_no++ {
+		if err := decrypt_db_page(buffer[offset:offset+PAGE_SIZE], uint32(page_no)); err != nil {
+			return err
+		}
+		offset += PAGE_SIZE
+	}
+
+	return nil
+}
+
+func extractKeyMapping(buffer []byte) (map[string]string, error) {
+	// Create an in-memory SQLite database
+	db, err := sql.Open("sqlite", "file::memory:?mode=memory&cache=shared")
+	if err != nil {
+		return nil, err
+	}
+	defer db.Close()
+
+	conn, err := db.Conn(context.Background())
+	if err != nil {
+		return nil, err
+	}
+
+	err = func() error {
+		defer conn.Close()
+		return conn.Raw(func(driverConn any) error {
+			type serializer interface {
+				Serialize() ([]byte, error)
+				Deserialize([]byte) error
+			}
+			return driverConn.(serializer).Deserialize(buffer)
+		})
+	}()
+
+	if err != nil {
+		return nil, fmt.Errorf("failed to import db: %w", err)
+	}
+
+	conn, err = db.Conn(context.Background())
+	if err != nil {
+		return nil, err
+	}
+
+	rows, err := conn.QueryContext(context.Background(), `
+		select EncryptionKeyId, EncryptionKey from ShareFileItems
+		where EncryptionKey != '' and EncryptionKey is not null
+	`)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	m := make(map[string]string)
+	for rows.Next() {
+		var keyId, key string
+		if err := rows.Scan(&keyId, &key); err != nil {
+			continue
+		}
+		m[keyId] = key
+	}
+
+	return m, err
+}
+
+var kugouPcDatabaseDumpLock = &sync.Mutex{}
+var kugouPcDatabaseDump = make(map[string]map[string]string)
+
+func CachedDumpEKey(dbPath string) (map[string]string, error) {
+	dump, exist := kugouPcDatabaseDump[dbPath]
+	if !exist {
+		kugouPcDatabaseDumpLock.Lock()
+		defer kugouPcDatabaseDumpLock.Unlock()
+
+		if dump, exist = kugouPcDatabaseDump[dbPath]; !exist {
+			buffer, err := os.ReadFile(dbPath)
+			if err != nil {
+				return nil, err
+			}
+			if err = decryptPcDatabase(buffer); err != nil {
+				return nil, err
+			}
+			dump, err = extractKeyMapping(buffer)
+			if err != nil {
+				return nil, err
+			}
+			kugouPcDatabaseDump[dbPath] = dump
+		}
+	}
+
+	return dump, nil
+}

algo/kgm/pc_kugou_db/cipher_test.go

@@ -0,0 +1,22 @@
+package pc_kugou_db
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestDerivePageAESKey_Page0(t *testing.T) {
+	expectedKey := []byte{0x19, 0x62, 0xc0, 0x5f, 0xa2, 0xeb, 0xbe, 0x24, 0x28, 0xff, 0x52, 0x2b, 0x9e, 0x03, 0xea, 0xd4}
+	pageKey := derive_page_aes_key(0)
+	if !reflect.DeepEqual(expectedKey, pageKey) {
+		t.Errorf("Derived AES key for page 0 does not match expected value: got %v, want %v", pageKey, expectedKey)
+	}
+}
+
+func TestDerivePageAESIv_Page0(t *testing.T) {
+	expectedIv := []byte{0x05, 0x5a, 0x67, 0x35, 0x93, 0x89, 0x2d, 0xdf, 0x3a, 0xb3, 0xb3, 0xc6, 0x21, 0xc3, 0x48, 0x02}
+	pageKey := derive_page_aes_iv(0)
+	if !reflect.DeepEqual(expectedIv, pageKey) {
+		t.Errorf("Derived AES iv for page 0 does not match expected value: got %v, want %v", pageKey, expectedIv)
+	}
+}