diff --git a/noise_test.go b/noise_test.go
index 9634cfa..2839d33 100644
--- a/noise_test.go
+++ b/noise_test.go
@@ -27,7 +27,7 @@ func (NoiseSuite) TestN(c *C) {
 	cs := NewCipherSuite(DH25519, CipherAESGCM, HashSHA256)
 	rng := new(RandomInc)
 	staticR := cs.GenerateKeypair(rng)
-	hs := NewHandshakeState(cs, rng, HandshakeN, true, nil, nil, nil, staticR.Public, nil)
+	hs := NewHandshakeState(cs, rng, HandshakeN, true, nil, nil, nil, nil, staticR.Public, nil)
 
 	hello, _, _ := hs.WriteMessage(nil, nil)
 	expected, _ := hex.DecodeString("358072d6365880d1aeea329adf9121383851ed21a28e3b75e965d0d2cd1662548331a3d1e93b490263abc7a4633867f4")
@@ -39,7 +39,7 @@ func (NoiseSuite) TestX(c *C) {
 	rng := new(RandomInc)
 	staticI := cs.GenerateKeypair(rng)
 	staticR := cs.GenerateKeypair(rng)
-	hs := NewHandshakeState(cs, rng, HandshakeX, true, nil, &staticI, nil, staticR.Public, nil)
+	hs := NewHandshakeState(cs, rng, HandshakeX, true, nil, nil, &staticI, nil, staticR.Public, nil)
 
 	hello, _, _ := hs.WriteMessage(nil, nil)
 	expected, _ := hex.DecodeString("79a631eede1bf9c98f12032cdeadd0e7a079398fc786b88cc846ec89af85a51ad203cd28d81cf65a2da637f557a05728b3ae4abdc3a42d1cda5f719d6cf41d7f2cf1b1c5af10e38a09a9bb7e3b1d589a99492cc50293eaa1f3f391b59bb6990d")
@@ -52,8 +52,8 @@ func (NoiseSuite) TestNN(c *C) {
 	rngR := new(RandomInc)
 	*rngR = 1
 
-	hsI := NewHandshakeState(cs, rngI, HandshakeNN, true, nil, nil, nil, nil, nil)
-	hsR := NewHandshakeState(cs, rngR, HandshakeNN, false, nil, nil, nil, nil, nil)
+	hsI := NewHandshakeState(cs, rngI, HandshakeNN, true, nil, nil, nil, nil, nil, nil)
+	hsR := NewHandshakeState(cs, rngR, HandshakeNN, false, nil, nil, nil, nil, nil, nil)
 
 	msg, _, _ := hsI.WriteMessage(nil, []byte("abc"))
 	c.Assert(msg, HasLen, 35)
@@ -80,8 +80,8 @@ func (NoiseSuite) TestXX(c *C) {
 	staticI := cs.GenerateKeypair(rngI)
 	staticR := cs.GenerateKeypair(rngR)
 
-	hsI := NewHandshakeState(cs, rngI, HandshakeXX, true, nil, &staticI, nil, nil, nil)
-	hsR := NewHandshakeState(cs, rngR, HandshakeXX, false, nil, &staticR, nil, nil, nil)
+	hsI := NewHandshakeState(cs, rngI, HandshakeXX, true, nil, nil, &staticI, nil, nil, nil)
+	hsR := NewHandshakeState(cs, rngR, HandshakeXX, false, nil, nil, &staticR, nil, nil, nil)
 
 	msg, _, _ := hsI.WriteMessage(nil, []byte("abc"))
 	c.Assert(msg, HasLen, 35)
@@ -114,8 +114,8 @@ func (NoiseSuite) TestIK(c *C) {
 	staticI := cs.GenerateKeypair(rngI)
 	staticR := cs.GenerateKeypair(rngR)
 
-	hsI := NewHandshakeState(cs, rngI, HandshakeIK, true, []byte("ABC"), &staticI, nil, staticR.Public, nil)
-	hsR := NewHandshakeState(cs, rngR, HandshakeIK, false, []byte("ABC"), &staticR, nil, nil, nil)
+	hsI := NewHandshakeState(cs, rngI, HandshakeIK, true, []byte("ABC"), nil, &staticI, nil, staticR.Public, nil)
+	hsR := NewHandshakeState(cs, rngR, HandshakeIK, false, []byte("ABC"), nil, &staticR, nil, nil, nil)
 
 	msg, _, _ := hsI.WriteMessage(nil, []byte("abc"))
 	c.Assert(msg, HasLen, 99)
@@ -143,8 +143,8 @@ func (NoiseSuite) TestXE(c *C) {
 	staticR := cs.GenerateKeypair(rngR)
 	ephR := cs.GenerateKeypair(rngR)
 
-	hsI := NewHandshakeState(cs, rngI, HandshakeXE, true, nil, &staticI, nil, staticR.Public, ephR.Public)
-	hsR := NewHandshakeState(cs, rngR, HandshakeXE, false, nil, &staticR, &ephR, nil, nil)
+	hsI := NewHandshakeState(cs, rngI, HandshakeXE, true, nil, nil, &staticI, nil, staticR.Public, ephR.Public)
+	hsR := NewHandshakeState(cs, rngR, HandshakeXE, false, nil, nil, &staticR, &ephR, nil, nil)
 
 	msg, _, _ := hsI.WriteMessage(nil, []byte("abc"))
 	c.Assert(msg, HasLen, 51)
@@ -177,8 +177,8 @@ func (NoiseSuite) TestXXRoundtrip(c *C) {
 	staticI := cs.GenerateKeypair(rngI)
 	staticR := cs.GenerateKeypair(rngR)
 
-	hsI := NewHandshakeState(cs, rngI, HandshakeXX, true, nil, &staticI, nil, nil, nil)
-	hsR := NewHandshakeState(cs, rngR, HandshakeXX, false, nil, &staticR, nil, nil, nil)
+	hsI := NewHandshakeState(cs, rngI, HandshakeXX, true, nil, nil, &staticI, nil, nil, nil)
+	hsR := NewHandshakeState(cs, rngR, HandshakeXX, false, nil, nil, &staticR, nil, nil, nil)
 
 	// -> e
 	msg, _, _ := hsI.WriteMessage(nil, []byte("abcdef"))
@@ -220,3 +220,39 @@ func (NoiseSuite) TestXXRoundtrip(c *C) {
 	c.Assert(err, IsNil)
 	c.Assert(string(res), Equals, "worri")
 }
+
+func (NoiseSuite) TestPSK_NN_Roundtrip(c *C) {
+	cs := NewCipherSuite(DH25519, CipherChaChaPoly, HashBLAKE2b)
+	rngI := new(RandomInc)
+	rngR := new(RandomInc)
+	*rngR = 1
+
+	hsI := NewHandshakeState(cs, rngI, HandshakeNN, true, nil, []byte("supersecret"), nil, nil, nil, nil)
+	hsR := NewHandshakeState(cs, rngI, HandshakeNN, false, nil, []byte("supersecret"), nil, nil, nil, nil)
+
+	// -> e
+	msg, _, _ := hsI.WriteMessage(nil, nil)
+	c.Assert(msg, HasLen, 48)
+	res, _, _, err := hsR.ReadMessage(nil, msg)
+	c.Assert(err, IsNil)
+	c.Assert(res, HasLen, 0)
+
+	// <- e, dhee
+	msg, csR0, csR1 := hsR.WriteMessage(nil, nil)
+	c.Assert(msg, HasLen, 48)
+	res, csI0, csI1, err := hsI.ReadMessage(nil, msg)
+	c.Assert(err, IsNil)
+	c.Assert(res, HasLen, 0)
+
+	// transport I -> R
+	msg = csI0.Encrypt(nil, nil, []byte("foo"))
+	res, err = csR0.Decrypt(nil, nil, msg)
+	c.Assert(err, IsNil)
+	c.Assert(string(res), Equals, "foo")
+
+	// transport R -> I
+	msg = csR1.Encrypt(nil, nil, []byte("bar"))
+	res, err = csI1.Decrypt(nil, nil, msg)
+	c.Assert(err, IsNil)
+	c.Assert(string(res), Equals, "bar")
+}
diff --git a/patterns.go b/patterns.go
index b9d8144..c17543d 100644
--- a/patterns.go
+++ b/patterns.go
@@ -84,7 +84,7 @@ var HandshakeXN = HandshakePattern{
 var HandshakeIN = HandshakePattern{
 	Name: "IN",
 	Messages: [][]MessagePattern{
-		{MessagePatternS, MessagePatternE},
+		{MessagePatternE, MessagePatternS},
 		{MessagePatternE, MessagePatternDHEE, MessagePatternDHES},
 	},
 }
@@ -139,7 +139,7 @@ var HandshakeXX = HandshakePattern{
 var HandshakeIX = HandshakePattern{
 	Name: "IX",
 	Messages: [][]MessagePattern{
-		{MessagePatternS, MessagePatternE},
+		{MessagePatternE, MessagePatternS},
 		{MessagePatternE, MessagePatternDHEE, MessagePatternDHES, MessagePatternS, MessagePatternDHSE},
 	},
 }
diff --git a/state.go b/state.go
index f5aeec6..ede2c54 100644
--- a/state.go
+++ b/state.go
@@ -119,16 +119,18 @@ type HandshakeState struct {
 	e               DHKey  // local ephemeral keypair
 	rs              []byte // remote party's static public key
 	re              []byte // remote party's ephemeral public key
+	psk             bool
 	messagePatterns [][]MessagePattern
 	shouldWrite     bool
 	msgIdx          int
 	rng             io.Reader
 }
 
-func NewHandshakeState(cs CipherSuite, rng io.Reader, newHandshakePattern HandshakePattern, initiator bool, prologue []byte, newS, newE *DHKey, newRS, newRE []byte) *HandshakeState {
+func NewHandshakeState(cs CipherSuite, rng io.Reader, newHandshakePattern HandshakePattern, initiator bool, prologue, presharedKey []byte, newS, newE *DHKey, newRS, newRE []byte) *HandshakeState {
 	hs := &HandshakeState{
 		rs:              newRS,
 		re:              newRE,
+		psk:             len(presharedKey) > 0,
 		messagePatterns: newHandshakePattern.Messages,
 		shouldWrite:     initiator,
 		rng:             rng,
@@ -140,8 +142,15 @@ func NewHandshakeState(cs CipherSuite, rng io.Reader, newHandshakePattern Handsh
 	if newS != nil {
 		hs.s = *newS
 	}
-	hs.InitializeSymmetric([]byte("Noise_" + newHandshakePattern.Name + "_" + string(cs.Name())))
+	namePrefix := "Noise_"
+	if hs.psk {
+		namePrefix = "NoisePSK_"
+	}
+	hs.InitializeSymmetric([]byte(namePrefix + newHandshakePattern.Name + "_" + string(cs.Name())))
 	hs.MixHash(prologue)
+	if hs.psk {
+		hs.MixHash(presharedKey)
+	}
 	for _, m := range newHandshakePattern.InitiatorPreMessages {
 		switch {
 		case initiator && m == MessagePatternS:
@@ -184,7 +193,11 @@ func (s *HandshakeState) WriteMessage(out, payload []byte) ([]byte, *CipherState
 		switch msg {
 		case MessagePatternE:
 			s.e = s.cs.GenerateKeypair(s.rng)
-			out = s.EncryptAndHash(out, s.e.Public)
+			out = append(out, s.e.Public...)
+			s.MixHash(s.e.Public)
+			if s.psk {
+				s.MixKey(s.e.Public)
+			}
 		case MessagePatternS:
 			if len(s.s.Public) == 0 {
 				panic("noise: invalid state, s.Public is nil")
@@ -227,7 +240,7 @@ func (s *HandshakeState) ReadMessage(out, message []byte) ([]byte, *CipherState,
 		switch msg {
 		case MessagePatternE, MessagePatternS:
 			expected := s.cs.DHLen()
-			if s.hasKey {
+			if msg == MessagePatternS && s.hasKey {
 				expected += 16
 			}
 			if len(message) < expected {
@@ -235,7 +248,15 @@ func (s *HandshakeState) ReadMessage(out, message []byte) ([]byte, *CipherState,
 			}
 			switch msg {
 			case MessagePatternE:
-				s.re, err = s.DecryptAndHash(s.re[:0], message[:expected])
+				if cap(s.re) < s.cs.DHLen() {
+					s.re = make([]byte, s.cs.DHLen())
+				}
+				s.re = s.re[:s.cs.DHLen()]
+				copy(s.re, message)
+				s.MixHash(s.re)
+				if s.psk {
+					s.MixKey(s.re)
+				}
 			case MessagePatternS:
 				if len(s.rs) > 0 {
 					panic("noise: invalid state, rs is not nil")