refactor: use kgm crypto from parakeet-rs

chore: update deps

algo/kgm/kgm_v3.go

@@ -0,0 +1,66 @@
+package kgm
+
+import (
+	"crypto/md5"
+	"fmt"
+	"io"
+)
+
+// kgmCryptoV3 is kgm file crypto v3
+type kgmCryptoV3 struct {
+	slotBox []byte
+	fileBox []byte
+
+	rd     io.Reader
+	offset int
+}
+
+var kgmV3Slot2Key = map[uint32][]byte{
+	1: {0x6C, 0x2C, 0x2F, 0x27},
+}
+
+func newKgmCryptoV3(header *Header, body io.Reader) (io.Reader, error) {
+	c := &kgmCryptoV3{rd: body}
+
+	slotKey, ok := kgmV3Slot2Key[header.CryptoSlot]
+	if !ok {
+		return nil, fmt.Errorf("kgm3: unknown crypto slot %d", header.CryptoSlot)
+	}
+	c.slotBox = kugouMD5(slotKey)
+
+	c.fileBox = append(kugouMD5(header.CryptoKey), 0x6b)
+
+	return c, nil
+}
+
+func (d *kgmCryptoV3) Read(buf []byte) (int, error) {
+	n, err := d.rd.Read(buf)
+	if n > 0 {
+		d.decrypt(buf[:n], d.offset)
+		d.offset += n
+	}
+	return n, err
+}
+
+func (d *kgmCryptoV3) decrypt(b []byte, offset int) {
+	for i := 0; i < len(b); i++ {
+		b[i] ^= d.fileBox[(offset+i)%len(d.fileBox)]
+		b[i] ^= b[i] << 4
+		b[i] ^= d.slotBox[(offset+i)%len(d.slotBox)]
+		b[i] ^= xorCollapseUint32(uint32(offset + i))
+	}
+}
+
+func xorCollapseUint32(i uint32) byte {
+	return byte(i) ^ byte(i>>8) ^ byte(i>>16) ^ byte(i>>24)
+}
+
+func kugouMD5(b []byte) []byte {
+	digest := md5.Sum(b)
+	ret := make([]byte, 16)
+	for i := 0; i < md5.Size; i += 2 {
+		ret[i] = digest[14-i]
+		ret[i+1] = digest[14-i+1]
+	}
+	return ret
+}