feat: first version of kgg support

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)
+	}
+}