diff --git a/internal/handshake/interface.go b/internal/handshake/interface.go
index 55bc035d..34cf7855 100644
--- a/internal/handshake/interface.go
+++ b/internal/handshake/interface.go
@@ -34,7 +34,7 @@ type LongHeaderOpener interface {
 // ShortHeaderOpener opens a short header packet
 type ShortHeaderOpener interface {
 	headerDecryptor
-	Open(dst, src []byte, pn protocol.PacketNumber, kp protocol.KeyPhase, associatedData []byte) ([]byte, error)
+	Open(dst, src []byte, pn protocol.PacketNumber, kp protocol.KeyPhaseBit, associatedData []byte) ([]byte, error)
 }
 
 // LongHeaderSealer seals a long header packet
@@ -47,7 +47,7 @@ type LongHeaderSealer interface {
 // ShortHeaderSealer seals a short header packet
 type ShortHeaderSealer interface {
 	LongHeaderSealer
-	KeyPhase() protocol.KeyPhase
+	KeyPhase() protocol.KeyPhaseBit
 }
 
 // A tlsExtensionHandler sends and received the QUIC TLS extension.
diff --git a/internal/handshake/updatable_aead.go b/internal/handshake/updatable_aead.go
index 4fe8767b..e086846c 100644
--- a/internal/handshake/updatable_aead.go
+++ b/internal/handshake/updatable_aead.go
@@ -43,7 +43,7 @@ func setKeyUpdateInterval() {
 type updatableAEAD struct {
 	suite cipherSuite
 
-	keyPhase          protocol.KeyPhase
+	keyPhase          protocol.KeyPhaseBit
 	largestAcked      protocol.PacketNumber
 	keyUpdateInterval uint64
 
@@ -134,7 +134,7 @@ func (a *updatableAEAD) SetWriteKey(suite cipherSuite, trafficSecret []byte) {
 	a.nextSendAEAD = createAEAD(suite, a.nextSendTrafficSecret)
 }
 
-func (a *updatableAEAD) Open(dst, src []byte, pn protocol.PacketNumber, kp protocol.KeyPhase, ad []byte) ([]byte, error) {
+func (a *updatableAEAD) Open(dst, src []byte, pn protocol.PacketNumber, kp protocol.KeyPhaseBit, ad []byte) ([]byte, error) {
 	binary.BigEndian.PutUint64(a.nonceBuf[len(a.nonceBuf)-8:], uint64(pn))
 	if kp != a.keyPhase {
 		if a.firstRcvdWithCurrentKey == protocol.InvalidPacketNumber || pn < a.firstRcvdWithCurrentKey {
@@ -215,7 +215,7 @@ func (a *updatableAEAD) shouldInitiateKeyUpdate() bool {
 	return false
 }
 
-func (a *updatableAEAD) KeyPhase() protocol.KeyPhase {
+func (a *updatableAEAD) KeyPhase() protocol.KeyPhaseBit {
 	if a.shouldInitiateKeyUpdate() {
 		a.rollKeys()
 	}
diff --git a/internal/mocks/short_header_opener.go b/internal/mocks/short_header_opener.go
index a51f9eb5..3d834b3b 100644
--- a/internal/mocks/short_header_opener.go
+++ b/internal/mocks/short_header_opener.go
@@ -47,7 +47,7 @@ func (mr *MockShortHeaderOpenerMockRecorder) DecryptHeader(arg0, arg1, arg2 inte
 }
 
 // Open mocks base method
-func (m *MockShortHeaderOpener) Open(arg0, arg1 []byte, arg2 protocol.PacketNumber, arg3 protocol.KeyPhase, arg4 []byte) ([]byte, error) {
+func (m *MockShortHeaderOpener) Open(arg0, arg1 []byte, arg2 protocol.PacketNumber, arg3 protocol.KeyPhaseBit, arg4 []byte) ([]byte, error) {
 	m.ctrl.T.Helper()
 	ret := m.ctrl.Call(m, "Open", arg0, arg1, arg2, arg3, arg4)
 	ret0, _ := ret[0].([]byte)
diff --git a/internal/mocks/short_header_sealer.go b/internal/mocks/short_header_sealer.go
index 1f269b51..81825543 100644
--- a/internal/mocks/short_header_sealer.go
+++ b/internal/mocks/short_header_sealer.go
@@ -47,10 +47,10 @@ func (mr *MockShortHeaderSealerMockRecorder) EncryptHeader(arg0, arg1, arg2 inte
 }
 
 // KeyPhase mocks base method
-func (m *MockShortHeaderSealer) KeyPhase() protocol.KeyPhase {
+func (m *MockShortHeaderSealer) KeyPhase() protocol.KeyPhaseBit {
 	m.ctrl.T.Helper()
 	ret := m.ctrl.Call(m, "KeyPhase")
-	ret0, _ := ret[0].(protocol.KeyPhase)
+	ret0, _ := ret[0].(protocol.KeyPhaseBit)
 	return ret0
 }
 
diff --git a/internal/protocol/key_phase.go b/internal/protocol/key_phase.go
new file mode 100644
index 00000000..693aeb15
--- /dev/null
+++ b/internal/protocol/key_phase.go
@@ -0,0 +1,22 @@
+package protocol
+
+// KeyPhaseBit is the key phase bit
+type KeyPhaseBit bool
+
+const (
+	// KeyPhaseZero is key phase 0
+	KeyPhaseZero KeyPhaseBit = false
+	// KeyPhaseOne is key phase 1
+	KeyPhaseOne KeyPhaseBit = true
+)
+
+func (p KeyPhaseBit) String() string {
+	if p == KeyPhaseZero {
+		return "0"
+	}
+	return "1"
+}
+
+func (p KeyPhaseBit) Next() KeyPhaseBit {
+	return !p
+}
diff --git a/internal/protocol/key_phase_test.go b/internal/protocol/key_phase_test.go
new file mode 100644
index 00000000..67e3aabf
--- /dev/null
+++ b/internal/protocol/key_phase_test.go
@@ -0,0 +1,18 @@
+package protocol
+
+import (
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("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/protocol/protocol.go b/internal/protocol/protocol.go
index 9f19bef9..130cb1bf 100644
--- a/internal/protocol/protocol.go
+++ b/internal/protocol/protocol.go
@@ -34,27 +34,6 @@ 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 057e87b7..a89f732f 100644
--- a/internal/protocol/protocol_test.go
+++ b/internal/protocol/protocol_test.go
@@ -15,16 +15,4 @@ 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 081ed01a..4ab3951d 100644
--- a/internal/wire/extended_header.go
+++ b/internal/wire/extended_header.go
@@ -25,7 +25,7 @@ type ExtendedHeader struct {
 	PacketNumberLen protocol.PacketNumberLen
 	PacketNumber    protocol.PacketNumber
 
-	KeyPhase protocol.KeyPhase
+	KeyPhase protocol.KeyPhaseBit
 }
 
 func (h *ExtendedHeader) parse(b *bytes.Reader, v protocol.VersionNumber) (*ExtendedHeader, error) {
diff --git a/packet_packer.go b/packet_packer.go
index 9c437445..419d90c1 100644
--- a/packet_packer.go
+++ b/packet_packer.go
@@ -432,7 +432,7 @@ func (p *packetPacker) composeNextPacket(maxFrameSize protocol.ByteCount) (paylo
 	return payload, nil
 }
 
-func (p *packetPacker) getShortHeader(kp protocol.KeyPhase) *wire.ExtendedHeader {
+func (p *packetPacker) getShortHeader(kp protocol.KeyPhaseBit) *wire.ExtendedHeader {
 	pn, pnLen := p.pnManager.PeekPacketNumber(protocol.Encryption1RTT)
 	hdr := &wire.ExtendedHeader{}
 	hdr.PacketNumber = pn