1 files changed, 268 insertions, 0 deletions
diff --git a/src/macs.go b/src/macs.go
new file mode 100644
index 0000000..841ef31
--- /dev/null
+++ b/src/macs.go
@@ -0,0 +1,268 @@
+package main
+
+import (
+	"crypto/hmac"
+	"crypto/rand"
+	"errors"
+	"golang.org/x/crypto/blake2s"
+	"net"
+	"sync"
+	"time"
+)
+
+type MACStateDevice struct {
+	mutex     sync.RWMutex
+	refreshed time.Time
+	secret    [blake2s.Size]byte
+	keyMAC1   [blake2s.Size]byte
+	keyMAC2   [blake2s.Size]byte
+}
+
+type MACStatePeer struct {
+	mutex     sync.RWMutex
+	cookieSet time.Time
+	cookie    [blake2s.Size128]byte
+	lastMAC1  [blake2s.Size128]byte
+	keyMAC1   [blake2s.Size]byte
+	keyMAC2   [blake2s.Size]byte
+}
+
+/* Methods for verifing MAC fields
+ * and creating/consuming cookies replies
+ * (per device)
+ */
+
+func (state *MACStateDevice) Init(pk NoisePublicKey) {
+	state.mutex.Lock()
+	defer state.mutex.Unlock()
+
+	func() {
+		hsh, _ := blake2s.New256(nil)
+		hsh.Write([]byte(WGLabelMAC1))
+		hsh.Write(pk[:])
+		hsh.Sum(state.keyMAC1[:0])
+	}()
+
+	func() {
+		hsh, _ := blake2s.New256(nil)
+		hsh.Write([]byte(WGLabelCookie))
+		hsh.Write(pk[:])
+		hsh.Sum(state.keyMAC2[:0])
+	}()
+
+	state.refreshed = time.Time{}
+}
+
+func (state *MACStateDevice) CheckMAC1(msg []byte) bool {
+	size := len(msg)
+	startMac1 := size - (blake2s.Size128 * 2)
+	startMac2 := size - blake2s.Size128
+
+	var mac1 [blake2s.Size128]byte
+	func() {
+		mac, _ := blake2s.New128(state.keyMAC1[:])
+		mac.Write(msg[:startMac1])
+		mac.Sum(mac1[:0])
+	}()
+
+	return hmac.Equal(mac1[:], msg[startMac1:startMac2])
+}
+
+func (state *MACStateDevice) CheckMAC2(msg []byte, addr *net.UDPAddr) bool {
+	state.mutex.RLock()
+	defer state.mutex.RUnlock()
+
+	if time.Now().Sub(state.refreshed) > CookieRefreshTime {
+		return false
+	}
+
+	// derive cookie key
+
+	var cookie [blake2s.Size128]byte
+	func() {
+		port := [2]byte{byte(addr.Port >> 8), byte(addr.Port)}
+		mac, _ := blake2s.New128(state.secret[:])
+		mac.Write(addr.IP)
+		mac.Write(port[:])
+		mac.Sum(cookie[:0])
+	}()
+
+	// calculate mac of packet
+
+	start := len(msg) - blake2s.Size128
+
+	var mac2 [blake2s.Size128]byte
+	func() {
+		mac, _ := blake2s.New128(cookie[:])
+		mac.Write(msg[:start])
+		mac.Sum(mac2[:0])
+	}()
+
+	return hmac.Equal(mac2[:], msg[start:])
+}
+
+func (device *Device) CreateMessageCookieReply(
+	msg []byte, receiver uint32, addr *net.UDPAddr,
+) (*MessageCookieReply, error) {
+
+	state := &device.mac
+	state.mutex.RLock()
+
+	// refresh cookie secret
+
+	if time.Now().Sub(state.refreshed) > CookieRefreshTime {
+		state.mutex.RUnlock()
+		state.mutex.Lock()
+		_, err := rand.Read(state.secret[:])
+		if err != nil {
+			state.mutex.Unlock()
+			return nil, err
+		}
+		state.refreshed = time.Now()
+		state.mutex.Unlock()
+		state.mutex.RLock()
+	}
+
+	// derive cookie key
+
+	var cookie [blake2s.Size128]byte
+	func() {
+		port := [2]byte{byte(addr.Port >> 8), byte(addr.Port)}
+		mac, _ := blake2s.New128(state.secret[:])
+		mac.Write(addr.IP)
+		mac.Write(port[:])
+		mac.Sum(cookie[:0])
+	}()
+
+	// encrypt cookie
+
+	size := len(msg)
+
+	startMac1 := size - (blake2s.Size128 * 2)
+	startMac2 := size - blake2s.Size128
+
+	mac1 := msg[startMac1:startMac2]
+
+	reply := new(MessageCookieReply)
+	reply.Type = MessageCookieReplyType
+	reply.Receiver = receiver
+	_, err := rand.Read(reply.Nonce[:])
+	if err != nil {
+		state.mutex.RUnlock()
+		return nil, err
+	}
+
+	XChaCha20Poly1305Encrypt(
+		reply.Cookie[:0],
+		&reply.Nonce,
+		cookie[:],
+		mac1,
+		&state.keyMAC2,
+	)
+
+	state.mutex.RUnlock()
+	return reply, nil
+}
+
+func (device *Device) ConsumeMessageCookieReply(msg *MessageCookieReply) bool {
+
+	if msg.Type != MessageCookieReplyType {
+		return false
+	}
+
+	// lookup peer
+
+	lookup := device.indices.Lookup(msg.Receiver)
+	if lookup.handshake == nil {
+		return false
+	}
+
+	// decrypt and store cookie
+
+	var cookie [blake2s.Size128]byte
+	state := &lookup.peer.mac
+
+	state.mutex.Lock()
+	defer state.mutex.Unlock()
+
+	_, err := XChaCha20Poly1305Decrypt(
+		cookie[:0],
+		&msg.Nonce,
+		msg.Cookie[:],
+		state.lastMAC1[:],
+		&state.keyMAC2,
+	)
+
+	if err != nil {
+		return false
+	}
+	state.cookieSet = time.Now()
+	state.cookie = cookie
+	return true
+}
+
+/* Methods for generating the MAC fields
+ * (per peer)
+ */
+
+func (state *MACStatePeer) Init(pk NoisePublicKey) {
+	state.mutex.Lock()
+	defer state.mutex.Unlock()
+
+	func() {
+		hsh, _ := blake2s.New256(nil)
+		hsh.Write([]byte(WGLabelMAC1))
+		hsh.Write(pk[:])
+		hsh.Sum(state.keyMAC1[:0])
+	}()
+
+	func() {
+		hsh, _ := blake2s.New256(nil)
+		hsh.Write([]byte(WGLabelCookie))
+		hsh.Write(pk[:])
+		hsh.Sum(state.keyMAC2[:0])
+	}()
+
+	state.cookieSet = time.Time{} // never
+}
+
+func (state *MACStatePeer) AddMacs(msg []byte) {
+	size := len(msg)
+
+	if size < blake2s.Size128*2 {
+		panic(errors.New("bug: message too short"))
+	}
+
+	startMac1 := size - (blake2s.Size128 * 2)
+	startMac2 := size - blake2s.Size128
+
+	mac1 := msg[startMac1 : startMac1+blake2s.Size128]
+	mac2 := msg[startMac2 : startMac2+blake2s.Size128]
+
+	state.mutex.Lock()
+	defer state.mutex.Unlock()
+
+	// set mac1
+
+	func() {
+		mac, _ := blake2s.New128(state.keyMAC1[:])
+		mac.Write(msg[:startMac1])
+		mac.Sum(mac1[:0])
+	}()
+	copy(state.lastMAC1[:], mac1)
+
+	// set mac2
+
+	if state.cookieSet.IsZero() {
+		return
+	}
+	if time.Now().Sub(state.cookieSet) > CookieRefreshTime {
+		state.cookieSet = time.Time{}
+		return
+	}
+	func() {
+		mac, _ := blake2s.New128(state.cookie[:])
+		mac.Write(msg[:startMac2])
+		mac.Sum(mac2[:0])
+	}()
+}