diff --git a/internal/protocol/protocol.go b/internal/protocol/protocol.go
index 130cb1bf..9f19bef9 100644
--- a/internal/protocol/protocol.go
+++ b/internal/protocol/protocol.go
@@ -34,6 +34,27 @@ func (t PacketType) String() string {
 	}
 }
 
+// KeyPhase is the key phase
+type KeyPhase bool
+
+const (
+	// KeyPhaseZero is key phase 0
+	KeyPhaseZero KeyPhase = false
+	// KeyPhaseOne is key phase 1
+	KeyPhaseOne KeyPhase = true
+)
+
+func (p KeyPhase) String() string {
+	if p == KeyPhaseZero {
+		return "0"
+	}
+	return "1"
+}
+
+func (p KeyPhase) Next() KeyPhase {
+	return !p
+}
+
 // A ByteCount in QUIC
 type ByteCount uint64
 
diff --git a/internal/protocol/protocol_test.go b/internal/protocol/protocol_test.go
index a89f732f..057e87b7 100644
--- a/internal/protocol/protocol_test.go
+++ b/internal/protocol/protocol_test.go
@@ -15,4 +15,16 @@ var _ = Describe("Protocol", func() {
 			Expect(PacketType(10).String()).To(Equal("unknown packet type: 10"))
 		})
 	})
+
+	Context("Key Phases", func() {
+		It("has the correct string representation", func() {
+			Expect(KeyPhaseZero.String()).To(Equal("0"))
+			Expect(KeyPhaseOne.String()).To(Equal("1"))
+		})
+
+		It("returns the next key phase", func() {
+			Expect(KeyPhaseZero.Next()).To(Equal(KeyPhaseOne))
+			Expect(KeyPhaseOne.Next()).To(Equal(KeyPhaseZero))
+		})
+	})
 })
diff --git a/internal/wire/extended_header.go b/internal/wire/extended_header.go
index 19a0b064..4c50e050 100644
--- a/internal/wire/extended_header.go
+++ b/internal/wire/extended_header.go
@@ -19,7 +19,7 @@ type ExtendedHeader struct {
 	PacketNumberLen protocol.PacketNumberLen
 	PacketNumber    protocol.PacketNumber
 
-	KeyPhase int
+	KeyPhase protocol.KeyPhase
 }
 
 func (h *ExtendedHeader) parse(b *bytes.Reader, v protocol.VersionNumber) (*ExtendedHeader, error) {
@@ -53,7 +53,10 @@ func (h *ExtendedHeader) parseShortHeader(b *bytes.Reader, v protocol.VersionNum
 		return nil, errors.New("4th and 5th bit must be 0")
 	}
 
-	h.KeyPhase = int(h.typeByte&0x4) >> 2
+	h.KeyPhase = protocol.KeyPhaseZero
+	if h.typeByte&0x4 > 0 {
+		h.KeyPhase = protocol.KeyPhaseOne
+	}
 
 	if err := h.readPacketNumber(b); err != nil {
 		return nil, err
@@ -129,7 +132,9 @@ func (h *ExtendedHeader) writeLongHeader(b *bytes.Buffer, v protocol.VersionNumb
 // TODO: add support for the key phase
 func (h *ExtendedHeader) writeShortHeader(b *bytes.Buffer, v protocol.VersionNumber) error {
 	typeByte := 0x40 | uint8(h.PacketNumberLen-1)
-	typeByte |= byte(h.KeyPhase << 2)
+	if h.KeyPhase == protocol.KeyPhaseOne {
+		typeByte |= byte(1 << 2)
+	}
 
 	b.WriteByte(typeByte)
 	b.Write(h.DestConnectionID.Bytes())
@@ -176,7 +181,7 @@ func (h *ExtendedHeader) Log(logger utils.Logger) {
 		}
 		logger.Debugf("\tLong Header{Type: %s, DestConnectionID: %s, SrcConnectionID: %s, %sPacketNumber: %#x, PacketNumberLen: %d, Length: %d, Version: %s}", h.Type, h.DestConnectionID, h.SrcConnectionID, token, h.PacketNumber, h.PacketNumberLen, h.Length, h.Version)
 	} else {
-		logger.Debugf("\tShort Header{DestConnectionID: %s, PacketNumber: %#x, PacketNumberLen: %d, KeyPhase: %d}", h.DestConnectionID, h.PacketNumber, h.PacketNumberLen, h.KeyPhase)
+		logger.Debugf("\tShort Header{DestConnectionID: %s, PacketNumber: %#x, PacketNumberLen: %d, KeyPhase: %s}", h.DestConnectionID, h.PacketNumber, h.PacketNumberLen, h.KeyPhase)
 	}
 }
 
diff --git a/internal/wire/extended_header_test.go b/internal/wire/extended_header_test.go
index e669fd09..86f85d84 100644
--- a/internal/wire/extended_header_test.go
+++ b/internal/wire/extended_header_test.go
@@ -199,7 +199,7 @@ var _ = Describe("Header", func() {
 
 			It("writes the Key Phase Bit", func() {
 				Expect((&ExtendedHeader{
-					KeyPhase:        1,
+					KeyPhase:        protocol.KeyPhaseOne,
 					PacketNumberLen: protocol.PacketNumberLen1,
 					PacketNumber:    0x42,
 				}).Write(buf, versionIETFHeader)).To(Succeed())
@@ -407,7 +407,7 @@ var _ = Describe("Header", func() {
 				Header: Header{
 					DestConnectionID: protocol.ConnectionID{0xde, 0xad, 0xbe, 0xef, 0xca, 0xfe, 0x13, 0x37},
 				},
-				KeyPhase:        1,
+				KeyPhase:        protocol.KeyPhaseOne,
 				PacketNumber:    0x1337,
 				PacketNumberLen: 4,
 			}).Log(logger)
diff --git a/internal/wire/header_test.go b/internal/wire/header_test.go
index 67a3fb4f..e9ef160d 100644
--- a/internal/wire/header_test.go
+++ b/internal/wire/header_test.go
@@ -425,7 +425,7 @@ var _ = Describe("Header Parsing", func() {
 			b := bytes.NewReader(data)
 			extHdr, err := hdr.ParseExtended(b, versionIETFFrames)
 			Expect(err).ToNot(HaveOccurred())
-			Expect(extHdr.KeyPhase).To(Equal(0))
+			Expect(extHdr.KeyPhase).To(Equal(protocol.KeyPhaseZero))
 			Expect(extHdr.DestConnectionID).To(Equal(connID))
 			Expect(extHdr.SrcConnectionID).To(BeEmpty())
 			Expect(extHdr.PacketNumber).To(Equal(protocol.PacketNumber(0x42)))
@@ -462,7 +462,7 @@ var _ = Describe("Header Parsing", func() {
 			b := bytes.NewReader(data)
 			extHdr, err := hdr.ParseExtended(b, versionIETFFrames)
 			Expect(err).ToNot(HaveOccurred())
-			Expect(extHdr.KeyPhase).To(Equal(0))
+			Expect(extHdr.KeyPhase).To(Equal(protocol.KeyPhaseZero))
 			Expect(extHdr.DestConnectionID).To(Equal(connID))
 			Expect(extHdr.SrcConnectionID).To(BeEmpty())
 			Expect(rest).To(BeEmpty())
@@ -480,7 +480,7 @@ var _ = Describe("Header Parsing", func() {
 			b := bytes.NewReader(data)
 			extHdr, err := hdr.ParseExtended(b, versionIETFFrames)
 			Expect(err).ToNot(HaveOccurred())
-			Expect(extHdr.KeyPhase).To(Equal(1))
+			Expect(extHdr.KeyPhase).To(Equal(protocol.KeyPhaseOne))
 			Expect(b.Len()).To(BeZero())
 		})