1 files changed, 73 insertions, 0 deletions
diff --git a/src/macs_peer.go b/src/macs_peer.go
new file mode 100644
index 0000000..d70c8f3
--- /dev/null
+++ b/src/macs_peer.go
@@ -0,0 +1,73 @@
+package main
+
+import (
+	"crypto/cipher"
+	"errors"
+	"github.com/aead/chacha20poly1305" // Needed for XChaCha20Poly1305, TODO:
+	"golang.org/x/crypto/blake2s"
+	"sync"
+	"time"
+)
+
+type MacStatePeer struct {
+	mutex     sync.RWMutex
+	cookieSet time.Time
+	cookie    [blake2s.Size128]byte
+	lastMac1  [blake2s.Size128]byte
+	keyMac1   [blake2s.Size]byte
+	xaead     cipher.AEAD
+}
+
+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])
+	}()
+	state.xaead, _ = chacha20poly1305.NewXCipher(state.keyMac1[:])
+	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(state.lastMac1[:0])
+	}()
+	copy(mac1, state.lastMac1[:])
+
+	// 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])
+	}()
+}