Chore: split component to transport

transport/snell/cipher.go

@@ -0,0 +1,54 @@
+package snell
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+
+	"github.com/Dreamacro/go-shadowsocks2/shadowaead"
+	"golang.org/x/crypto/argon2"
+	"golang.org/x/crypto/chacha20poly1305"
+)
+
+type snellCipher struct {
+	psk      []byte
+	keySize  int
+	makeAEAD func(key []byte) (cipher.AEAD, error)
+}
+
+func (sc *snellCipher) KeySize() int  { return sc.keySize }
+func (sc *snellCipher) SaltSize() int { return 16 }
+func (sc *snellCipher) Encrypter(salt []byte) (cipher.AEAD, error) {
+	return sc.makeAEAD(snellKDF(sc.psk, salt, sc.KeySize()))
+}
+func (sc *snellCipher) Decrypter(salt []byte) (cipher.AEAD, error) {
+	return sc.makeAEAD(snellKDF(sc.psk, salt, sc.KeySize()))
+}
+
+func snellKDF(psk, salt []byte, keySize int) []byte {
+	// snell use a special kdf function
+	return argon2.IDKey(psk, salt, 3, 8, 1, 32)[:keySize]
+}
+
+func aesGCM(key []byte) (cipher.AEAD, error) {
+	blk, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+	return cipher.NewGCM(blk)
+}
+
+func NewAES128GCM(psk []byte) shadowaead.Cipher {
+	return &snellCipher{
+		psk:      psk,
+		keySize:  16,
+		makeAEAD: aesGCM,
+	}
+}
+
+func NewChacha20Poly1305(psk []byte) shadowaead.Cipher {
+	return &snellCipher{
+		psk:      psk,
+		keySize:  32,
+		makeAEAD: chacha20poly1305.New,
+	}
+}