package shadowstream import ( "crypto/rand" "errors" "io" "net" "github.com/Dreamacro/clash/common/pool" ) // ErrShortPacket means the packet is too short to be a valid encrypted packet. var ErrShortPacket = errors.New("short packet") // Pack encrypts plaintext using stream cipher s and a random IV. // Returns a slice of dst containing random IV and ciphertext. // Ensure len(dst) >= s.IVSize() + len(plaintext). func Pack(dst, plaintext []byte, s Cipher) ([]byte, error) { if len(dst) < s.IVSize()+len(plaintext) { return nil, io.ErrShortBuffer } iv := dst[:s.IVSize()] _, err := rand.Read(iv) if err != nil { return nil, err } s.Encrypter(iv).XORKeyStream(dst[len(iv):], plaintext) return dst[:len(iv)+len(plaintext)], nil } // Unpack decrypts pkt using stream cipher s. // Returns a slice of dst containing decrypted plaintext. func Unpack(dst, pkt []byte, s Cipher) ([]byte, error) { if len(pkt) < s.IVSize() { return nil, ErrShortPacket } if len(dst) < len(pkt)-s.IVSize() { return nil, io.ErrShortBuffer } iv := pkt[:s.IVSize()] s.Decrypter(iv).XORKeyStream(dst, pkt[len(iv):]) return dst[:len(pkt)-len(iv)], nil } type PacketConn struct { net.PacketConn Cipher } // NewPacketConn wraps a net.PacketConn with stream cipher encryption/decryption. func NewPacketConn(c net.PacketConn, ciph Cipher) *PacketConn { return &PacketConn{PacketConn: c, Cipher: ciph} } const maxPacketSize = 64 * 1024 func (c *PacketConn) WriteTo(b []byte, addr net.Addr) (int, error) { buf := pool.Get(maxPacketSize) defer pool.Put(buf) buf, err := Pack(buf, b, c.Cipher) if err != nil { return 0, err } _, err = c.PacketConn.WriteTo(buf, addr) return len(b), err } func (c *PacketConn) ReadFrom(b []byte) (int, net.Addr, error) { n, addr, err := c.PacketConn.ReadFrom(b) if err != nil { return n, addr, err } bb, err := Unpack(b[c.IVSize():], b[:n], c.Cipher) if err != nil { return n, addr, err } copy(b, bb) return len(bb), addr, err }