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 }