cli/algo/kgm/kgm_v3.go

56 lines
1.1 KiB
Go

package kgm
import (
"crypto/md5"
"fmt"
"github.com/unlock-music/cli/algo/common"
)
// kgmCryptoV3 is kgm file crypto v3
type kgmCryptoV3 struct {
slotBox []byte
fileBox []byte
}
var kgmV3Slot2Key = map[uint32][]byte{
1: {0x6C, 0x2C, 0x2F, 0x27},
}
func newKgmCryptoV3(header *header) (common.StreamDecoder, error) {
c := &kgmCryptoV3{}
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) 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
}