func NewSimpleXORBlockCrypt(key []byte) (BlockCrypt, error) {
	c := new(simpleXORBlockCrypt)
	c.xortbl = pbkdf2.Key(key, []byte(saltxor), 32, mtuLimit, sha1.New)
	return c, nil
}
NewSimpleXORBlockCrypt simple xor with key expanding
package kcp
import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/des"
	"crypto/sha1"
	"unsafe"
	xor "github.com/templexxx/xorsimd"
	"github.com/tjfoc/gmsm/sm4"
	"golang.org/x/crypto/blowfish"
	"golang.org/x/crypto/cast5"
	"golang.org/x/crypto/pbkdf2"
	"golang.org/x/crypto/salsa20"
	"golang.org/x/crypto/tea"
	"golang.org/x/crypto/twofish"
	"golang.org/x/crypto/xtea"
)
var (
	initialVector = []byte{167, 115, 79, 156, 18, 172, 27, 1, 164, 21, 242, 193, 252, 120, 230, 107}
	saltxor       = `sH3CIVoF#rWLtJo6`
)
type BlockCrypt interface {
	Encrypt(dst, src []byte)
	Decrypt(dst, src []byte)
}
type salsa20BlockCrypt struct {
	key [32]byte
}
func NewSalsa20BlockCrypt(key []byte) (BlockCrypt, error) {
	c := new(salsa20BlockCrypt)
	copy(c.key[:], key)
	return c, nil
}
func (c *salsa20BlockCrypt) Encrypt(dst, src []byte) {
	salsa20.XORKeyStream(dst[8:], src[8:], src[:8], &c.key)
	copy(dst[:8], src[:8])
}
func (c *salsa20BlockCrypt) Decrypt(dst, src []byte) {
	salsa20.XORKeyStream(dst[8:], src[8:], src[:8], &c.key)
	copy(dst[:8], src[:8])
}
type sm4BlockCrypt struct {
	encbuf [sm4.BlockSize]byte  
	decbuf [2 * sm4.BlockSize]byte
	block  cipher.Block
}
func NewSM4BlockCrypt(key []byte) (BlockCrypt, error) {
	c := new(sm4BlockCrypt)
	block, err := sm4.NewCipher(key)
	if err != nil {
		return nil, err
	}
	c.block = block
	return c, nil
}
func (c *sm4BlockCrypt) Encrypt(dst, src []byte) { encrypt(c.block, dst, src, c.encbuf[:]) }
func (c *sm4BlockCrypt) Decrypt(dst, src []byte) { decrypt(c.block, dst, src, c.decbuf[:]) }
type twofishBlockCrypt struct {
	encbuf [twofish.BlockSize]byte
	decbuf [2 * twofish.BlockSize]byte
	block  cipher.Block
}
func NewTwofishBlockCrypt(key []byte) (BlockCrypt, error) {
	c := new(twofishBlockCrypt)
	block, err := twofish.NewCipher(key)
	if err != nil {
		return nil, err
	}
	c.block = block
	return c, nil
}
func (c *twofishBlockCrypt) Encrypt(dst, src []byte) { encrypt(c.block, dst, src, c.encbuf[:]) }
func (c *twofishBlockCrypt) Decrypt(dst, src []byte) { decrypt(c.block, dst, src, c.decbuf[:]) }
type tripleDESBlockCrypt struct {
	encbuf [des.BlockSize]byte
	decbuf [2 * des.BlockSize]byte
	block  cipher.Block
}
func NewTripleDESBlockCrypt(key []byte) (BlockCrypt, error) {
	c := new(tripleDESBlockCrypt)
	block, err := des.NewTripleDESCipher(key)
	if err != nil {
		return nil, err
	}
	c.block = block
	return c, nil
}
func (c *tripleDESBlockCrypt) Encrypt(dst, src []byte) { encrypt(c.block, dst, src, c.encbuf[:]) }
func (c *tripleDESBlockCrypt) Decrypt(dst, src []byte) { decrypt(c.block, dst, src, c.decbuf[:]) }
type cast5BlockCrypt struct {
	encbuf [cast5.BlockSize]byte
	decbuf [2 * cast5.BlockSize]byte
	block  cipher.Block
}
func NewCast5BlockCrypt(key []byte) (BlockCrypt, error) {
	c := new(cast5BlockCrypt)
	block, err := cast5.NewCipher(key)
	if err != nil {
		return nil, err
	}
	c.block = block
	return c, nil
}
func (c *cast5BlockCrypt) Encrypt(dst, src []byte) { encrypt(c.block, dst, src, c.encbuf[:]) }
func (c *cast5BlockCrypt) Decrypt(dst, src []byte) { decrypt(c.block, dst, src, c.decbuf[:]) }
type blowfishBlockCrypt struct {
	encbuf [blowfish.BlockSize]byte
	decbuf [2 * blowfish.BlockSize]byte
	block  cipher.Block
}
func NewBlowfishBlockCrypt(key []byte) (BlockCrypt, error) {
	c := new(blowfishBlockCrypt)
	block, err := blowfish.NewCipher(key)
	if err != nil {
		return nil, err
	}
	c.block = block
	return c, nil
}
func (c *blowfishBlockCrypt) Encrypt(dst, src []byte) { encrypt(c.block, dst, src, c.encbuf[:]) }
func (c *blowfishBlockCrypt) Decrypt(dst, src []byte) { decrypt(c.block, dst, src, c.decbuf[:]) }
type aesBlockCrypt struct {
	encbuf [aes.BlockSize]byte
	decbuf [2 * aes.BlockSize]byte
	block  cipher.Block
}
func NewAESBlockCrypt(key []byte) (BlockCrypt, error) {
	c := new(aesBlockCrypt)
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	c.block = block
	return c, nil
}
func (c *aesBlockCrypt) Encrypt(dst, src []byte) { encrypt(c.block, dst, src, c.encbuf[:]) }
func (c *aesBlockCrypt) Decrypt(dst, src []byte) { decrypt(c.block, dst, src, c.decbuf[:]) }
type teaBlockCrypt struct {
	encbuf [tea.BlockSize]byte
	decbuf [2 * tea.BlockSize]byte
	block  cipher.Block
}
func NewTEABlockCrypt(key []byte) (BlockCrypt, error) {
	c := new(teaBlockCrypt)
	block, err := tea.NewCipherWithRounds(key, 16)
	if err != nil {
		return nil, err
	}
	c.block = block
	return c, nil
}
func (c *teaBlockCrypt) Encrypt(dst, src []byte) { encrypt(c.block, dst, src, c.encbuf[:]) }
func (c *teaBlockCrypt) Decrypt(dst, src []byte) { decrypt(c.block, dst, src, c.decbuf[:]) }
type xteaBlockCrypt struct {
	encbuf [xtea.BlockSize]byte
	decbuf [2 * xtea.BlockSize]byte
	block  cipher.Block
}
func NewXTEABlockCrypt(key []byte) (BlockCrypt, error) {
	c := new(xteaBlockCrypt)
	block, err := xtea.NewCipher(key)
	if err != nil {
		return nil, err
	}
	c.block = block
	return c, nil
}
func (c *xteaBlockCrypt) Encrypt(dst, src []byte) { encrypt(c.block, dst, src, c.encbuf[:]) }
func (c *xteaBlockCrypt) Decrypt(dst, src []byte) { decrypt(c.block, dst, src, c.decbuf[:]) }
type simpleXORBlockCrypt struct {
	xortbl []byte
}