make handshake and crypto internal packages

internal/crypto/source_address_token.go

@@ -0,0 +1,76 @@
+package crypto
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"crypto/sha256"
+	"fmt"
+	"io"
+
+	"golang.org/x/crypto/hkdf"
+)
+
+// StkSource is used to create and verify source address tokens
+type StkSource interface {
+	// NewToken creates a new token
+	NewToken([]byte) ([]byte, error)
+	// DecodeToken decodes a token
+	DecodeToken([]byte) ([]byte, error)
+}
+
+type stkSource struct {
+	aead cipher.AEAD
+}
+
+const stkKeySize = 16
+
+// Chrome currently sets this to 12, but discusses changing it to 16. We start
+// at 16 :)
+const stkNonceSize = 16
+
+// NewStkSource creates a source for source address tokens
+func NewStkSource() (StkSource, error) {
+	secret := make([]byte, 32)
+	if _, err := rand.Read(secret); err != nil {
+		return nil, err
+	}
+	key, err := deriveKey(secret)
+	if err != nil {
+		return nil, err
+	}
+	c, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+	aead, err := cipher.NewGCMWithNonceSize(c, stkNonceSize)
+	if err != nil {
+		return nil, err
+	}
+	return &stkSource{aead: aead}, nil
+}
+
+func (s *stkSource) NewToken(data []byte) ([]byte, error) {
+	nonce := make([]byte, stkNonceSize)
+	if _, err := rand.Read(nonce); err != nil {
+		return nil, err
+	}
+	return s.aead.Seal(nonce, nonce, data, nil), nil
+}
+
+func (s *stkSource) DecodeToken(p []byte) ([]byte, error) {
+	if len(p) < stkNonceSize {
+		return nil, fmt.Errorf("STK too short: %d", len(p))
+	}
+	nonce := p[:stkNonceSize]
+	return s.aead.Open(nil, nonce, p[stkNonceSize:], nil)
+}
+
+func deriveKey(secret []byte) ([]byte, error) {
+	r := hkdf.New(sha256.New, secret, nil, []byte("QUIC source address token key"))
+	key := make([]byte, stkKeySize)
+	if _, err := io.ReadFull(r, key); err != nil {
+		return nil, err
+	}
+	return key, nil
+}