1 files changed, 252 insertions, 0 deletions
diff --git a/cookie.go b/cookie.go
new file mode 100644
index 0000000..a13ad49
--- /dev/null
+++ b/cookie.go
@@ -0,0 +1,252 @@
+package main
+
+import (
+	"crypto/hmac"
+	"crypto/rand"
+	"golang.org/x/crypto/blake2s"
+	"golang.org/x/crypto/chacha20poly1305"
+	"sync"
+	"time"
+)
+
+type CookieChecker struct {
+	mutex sync.RWMutex
+	mac1  struct {
+		key [blake2s.Size]byte
+	}
+	mac2 struct {
+		secret        [blake2s.Size]byte
+		secretSet     time.Time
+		encryptionKey [chacha20poly1305.KeySize]byte
+	}
+}
+
+type CookieGenerator struct {
+	mutex sync.RWMutex
+	mac1  struct {
+		key [blake2s.Size]byte
+	}
+	mac2 struct {
+		cookie        [blake2s.Size128]byte
+		cookieSet     time.Time
+		hasLastMAC1   bool
+		lastMAC1      [blake2s.Size128]byte
+		encryptionKey [chacha20poly1305.KeySize]byte
+	}
+}
+
+func (st *CookieChecker) Init(pk NoisePublicKey) {
+	st.mutex.Lock()
+	defer st.mutex.Unlock()
+
+	// mac1 state
+
+	func() {
+		hsh, _ := blake2s.New256(nil)
+		hsh.Write([]byte(WGLabelMAC1))
+		hsh.Write(pk[:])
+		hsh.Sum(st.mac1.key[:0])
+	}()
+
+	// mac2 state
+
+	func() {
+		hsh, _ := blake2s.New256(nil)
+		hsh.Write([]byte(WGLabelCookie))
+		hsh.Write(pk[:])
+		hsh.Sum(st.mac2.encryptionKey[:0])
+	}()
+
+	st.mac2.secretSet = time.Time{}
+}
+
+func (st *CookieChecker) CheckMAC1(msg []byte) bool {
+	size := len(msg)
+	smac2 := size - blake2s.Size128
+	smac1 := smac2 - blake2s.Size128
+
+	var mac1 [blake2s.Size128]byte
+
+	mac, _ := blake2s.New128(st.mac1.key[:])
+	mac.Write(msg[:smac1])
+	mac.Sum(mac1[:0])
+
+	return hmac.Equal(mac1[:], msg[smac1:smac2])
+}
+
+func (st *CookieChecker) CheckMAC2(msg []byte, src []byte) bool {
+	st.mutex.RLock()
+	defer st.mutex.RUnlock()
+
+	if time.Now().Sub(st.mac2.secretSet) > CookieRefreshTime {
+		return false
+	}
+
+	// derive cookie key
+
+	var cookie [blake2s.Size128]byte
+	func() {
+		mac, _ := blake2s.New128(st.mac2.secret[:])
+		mac.Write(src)
+		mac.Sum(cookie[:0])
+	}()
+
+	// calculate mac of packet (including mac1)
+
+	smac2 := len(msg) - blake2s.Size128
+
+	var mac2 [blake2s.Size128]byte
+	func() {
+		mac, _ := blake2s.New128(cookie[:])
+		mac.Write(msg[:smac2])
+		mac.Sum(mac2[:0])
+	}()
+
+	return hmac.Equal(mac2[:], msg[smac2:])
+}
+
+func (st *CookieChecker) CreateReply(
+	msg []byte,
+	recv uint32,
+	src []byte,
+) (*MessageCookieReply, error) {
+
+	st.mutex.RLock()
+
+	// refresh cookie secret
+
+	if time.Now().Sub(st.mac2.secretSet) > CookieRefreshTime {
+		st.mutex.RUnlock()
+		st.mutex.Lock()
+		_, err := rand.Read(st.mac2.secret[:])
+		if err != nil {
+			st.mutex.Unlock()
+			return nil, err
+		}
+		st.mac2.secretSet = time.Now()
+		st.mutex.Unlock()
+		st.mutex.RLock()
+	}
+
+	// derive cookie
+
+	var cookie [blake2s.Size128]byte
+	func() {
+		mac, _ := blake2s.New128(st.mac2.secret[:])
+		mac.Write(src)
+		mac.Sum(cookie[:0])
+	}()
+
+	// encrypt cookie
+
+	size := len(msg)
+
+	smac2 := size - blake2s.Size128
+	smac1 := smac2 - blake2s.Size128
+
+	reply := new(MessageCookieReply)
+	reply.Type = MessageCookieReplyType
+	reply.Receiver = recv
+
+	_, err := rand.Read(reply.Nonce[:])
+	if err != nil {
+		st.mutex.RUnlock()
+		return nil, err
+	}
+
+	XChaCha20Poly1305Encrypt(
+		reply.Cookie[:0],
+		&reply.Nonce,
+		cookie[:],
+		msg[smac1:smac2],
+		&st.mac2.encryptionKey,
+	)
+
+	st.mutex.RUnlock()
+
+	return reply, nil
+}
+
+func (st *CookieGenerator) Init(pk NoisePublicKey) {
+	st.mutex.Lock()
+	defer st.mutex.Unlock()
+
+	func() {
+		hsh, _ := blake2s.New256(nil)
+		hsh.Write([]byte(WGLabelMAC1))
+		hsh.Write(pk[:])
+		hsh.Sum(st.mac1.key[:0])
+	}()
+
+	func() {
+		hsh, _ := blake2s.New256(nil)
+		hsh.Write([]byte(WGLabelCookie))
+		hsh.Write(pk[:])
+		hsh.Sum(st.mac2.encryptionKey[:0])
+	}()
+
+	st.mac2.cookieSet = time.Time{}
+}
+
+func (st *CookieGenerator) ConsumeReply(msg *MessageCookieReply) bool {
+	st.mutex.Lock()
+	defer st.mutex.Unlock()
+
+	if !st.mac2.hasLastMAC1 {
+		return false
+	}
+
+	var cookie [blake2s.Size128]byte
+
+	_, err := XChaCha20Poly1305Decrypt(
+		cookie[:0],
+		&msg.Nonce,
+		msg.Cookie[:],
+		st.mac2.lastMAC1[:],
+		&st.mac2.encryptionKey,
+	)
+
+	if err != nil {
+		return false
+	}
+
+	st.mac2.cookieSet = time.Now()
+	st.mac2.cookie = cookie
+	return true
+}
+
+func (st *CookieGenerator) AddMacs(msg []byte) {
+
+	size := len(msg)
+
+	smac2 := size - blake2s.Size128
+	smac1 := smac2 - blake2s.Size128
+
+	mac1 := msg[smac1:smac2]
+	mac2 := msg[smac2:]
+
+	st.mutex.Lock()
+	defer st.mutex.Unlock()
+
+	// set mac1
+
+	func() {
+		mac, _ := blake2s.New128(st.mac1.key[:])
+		mac.Write(msg[:smac1])
+		mac.Sum(mac1[:0])
+	}()
+	copy(st.mac2.lastMAC1[:], mac1)
+	st.mac2.hasLastMAC1 = true
+
+	// set mac2
+
+	if time.Now().Sub(st.mac2.cookieSet) > CookieRefreshTime {
+		return
+	}
+
+	func() {
+		mac, _ := blake2s.New128(st.mac2.cookie[:])
+		mac.Write(msg[:smac2])
+		mac.Sum(mac2[:0])
+	}()
+}