crypto/tls: add new X25519Kyber768Draft00 code point

* Point tls.X25519Kyber768Draft00 to the new 0x6399 identifier while the
  old 0xfe31 identifier is available as tls.X25519Kyber768Draft00Old.
* Make sure that the kem.PrivateKey can always be mapped to the CurveID
  that was linked to it. This is needed since we now have two ID
  aliasing to the same scheme, and clients need to be able to detect
  whether the key share presented by the server actually matches the key
  share that the client originally sent.
* Update tests, add the new identifier and remove unnecessary code.

Link: https://mailarchive.ietf.org/arch/msg/tls/HAWpNpgptl--UZNSYuvsjB-Pc2k/
Link: https://datatracker.ietf.org/doc/draft-tls-westerbaan-xyber768d00/02/

Author: Lekensteyn

src/crypto/tls/cfkem.go

@@ -6,13 +6,12 @@
 // To enable set CurvePreferences with the desired scheme as the first element:
 //
 //   import (
-//      "github.com/cloudflare/circl/kem/tls"
-//      "github.com/cloudflare/circl/kem/hybrid"
+//      "crypto/tls"
 //
 //          [...]
 //
 //   config.CurvePreferences = []tls.CurveID{
-//      hybrid.X25519Kyber512Draft00().(tls.TLSScheme).TLSCurveID(),
+//      tls.X25519Kyber768Draft00,
 //      tls.X25519,
 //      tls.P256,
 //   }
@@ -29,38 +28,27 @@ import (
 	"github.com/cloudflare/circl/kem/hybrid"
 )
 
-// Either ecdheParameters or kem.PrivateKey
+// Either *ecdh.PrivateKey or *kemPrivateKey
 type clientKeySharePrivate interface{}
 
+type kemPrivateKey struct {
+	secretKey kem.PrivateKey
+	curveID   CurveID
+}
+
 var (
-	X25519Kyber512Draft00 = CurveID(0xfe30)
-	X25519Kyber768Draft00 = CurveID(0xfe31)
-	P256Kyber768Draft00   = CurveID(0xfe32)
-	invalidCurveID        = CurveID(0)
+	X25519Kyber512Draft00    = CurveID(0xfe30)
+	X25519Kyber768Draft00    = CurveID(0x6399)
+	X25519Kyber768Draft00Old = CurveID(0xfe31)
+	P256Kyber768Draft00      = CurveID(0xfe32)
+	invalidCurveID           = CurveID(0)
 )
 
-func kemSchemeKeyToCurveID(s kem.Scheme) CurveID {
-	switch s.Name() {
-	case "Kyber512-X25519":
-		return X25519Kyber512Draft00
-	case "Kyber768-X25519":
-		return X25519Kyber768Draft00
-	case "P256Kyber768Draft00":
-		return P256Kyber768Draft00
-	default:
-		return invalidCurveID
-	}
-}
-
 // Extract CurveID from clientKeySharePrivate
 func clientKeySharePrivateCurveID(ks clientKeySharePrivate) CurveID {
 	switch v := ks.(type) {
-	case kem.PrivateKey:
-		ret := kemSchemeKeyToCurveID(v.Scheme())
-		if ret == invalidCurveID {
-			panic("cfkem: internal error: don't know CurveID for this KEM")
-		}
-		return ret
+	case *kemPrivateKey:
+		return v.curveID
 	case *ecdh.PrivateKey:
 		ret, ok := curveIDForCurve(v.Curve())
 		if !ok {
@@ -77,7 +65,7 @@ func curveIdToCirclScheme(id CurveID) kem.Scheme {
 	switch id {
 	case X25519Kyber512Draft00:
 		return hybrid.Kyber512X25519()
-	case X25519Kyber768Draft00:
+	case X25519Kyber768Draft00, X25519Kyber768Draft00Old:
 		return hybrid.Kyber768X25519()
 	case P256Kyber768Draft00:
 		return hybrid.P256Kyber768Draft00()
@@ -102,12 +90,12 @@ func encapsulateForKem(scheme kem.Scheme, rnd io.Reader, ppk []byte) (
 }
 
 // Generate a new keypair using randomness from rnd.
-func generateKemKeyPair(scheme kem.Scheme, rnd io.Reader) (
-	kem.PublicKey, kem.PrivateKey, error) {
+func generateKemKeyPair(scheme kem.Scheme, curveID CurveID, rnd io.Reader) (
+	kem.PublicKey, *kemPrivateKey, error) {
 	seed := make([]byte, scheme.SeedSize())
 	if _, err := io.ReadFull(rnd, seed); err != nil {
 		return nil, nil, err
 	}
 	pk, sk := scheme.DeriveKeyPair(seed)
-	return pk, sk, nil
+	return pk, &kemPrivateKey{sk, curveID}, nil
 }

src/crypto/tls/cfkem_test.go

@@ -7,28 +7,16 @@ import (
 	"context"
 	"fmt"
 	"testing"
-
-	"github.com/cloudflare/circl/kem"
-	"github.com/cloudflare/circl/kem/hybrid"
 )
 
-func testHybridKEX(t *testing.T, scheme kem.Scheme, clientPQ, serverPQ,
+func testHybridKEX(t *testing.T, curveID CurveID, clientPQ, serverPQ,
 	clientTLS12, serverTLS12 bool) {
 	var clientSelectedKEX *CurveID
 	var retry bool
 
-	rsaCert := Certificate{
-		Certificate: [][]byte{testRSACertificate},
-		PrivateKey:  testRSAPrivateKey,
-	}
-	serverCerts := []Certificate{rsaCert}
-
 	clientConfig := testConfig.Clone()
 	if clientPQ {
-		clientConfig.CurvePreferences = []CurveID{
-			kemSchemeKeyToCurveID(scheme),
-			X25519,
-		}
+		clientConfig.CurvePreferences = []CurveID{curveID, X25519}
 	}
 	clientCFEventHandler := func(ev CFEvent) {
 		switch e := ev.(type) {
@@ -44,15 +32,13 @@ func testHybridKEX(t *testing.T, scheme kem.Scheme, clientPQ, serverPQ,
 
 	serverConfig := testConfig.Clone()
 	if serverPQ {
-		serverConfig.CurvePreferences = []CurveID{
-			kemSchemeKeyToCurveID(scheme),
-			X25519,
-		}
+		serverConfig.CurvePreferences = []CurveID{curveID, X25519}
+	} else {
+		serverConfig.CurvePreferences = []CurveID{X25519}
 	}
 	if serverTLS12 {
 		serverConfig.MaxVersion = VersionTLS12
 	}
-	serverConfig.Certificates = serverCerts
 
 	c, s := localPipe(t)
 	done := make(chan error)
@@ -78,44 +64,43 @@ func testHybridKEX(t *testing.T, scheme kem.Scheme, clientPQ, serverPQ,
 	var expectedRetry bool
 
 	if clientPQ && serverPQ && !clientTLS12 && !serverTLS12 {
-		expectedKEX = kemSchemeKeyToCurveID(scheme)
+		expectedKEX = curveID
 	} else {
 		expectedKEX = X25519
 	}
 	if !clientTLS12 && clientPQ && !serverPQ {
 		expectedRetry = true
 	}
 
+	if expectedRetry != retry {
+		t.Errorf("Expected retry=%v, got retry=%v", expectedRetry, retry)
+	}
 	if clientSelectedKEX == nil {
 		t.Error("No KEX happened?")
-	}
-
-	if *clientSelectedKEX != expectedKEX {
+	} else if *clientSelectedKEX != expectedKEX {
 		t.Errorf("failed to negotiate: expected %d, got %d",
 			expectedKEX, *clientSelectedKEX)
 	}
-	if expectedRetry != retry {
-		t.Errorf("Expected retry=%v, got retry=%v", expectedRetry, retry)
-	}
 }
 
 func TestHybridKEX(t *testing.T) {
-	run := func(scheme kem.Scheme, clientPQ, serverPQ, clientTLS12, serverTLS12 bool) {
-		t.Run(fmt.Sprintf("%s serverPQ:%v clientPQ:%v serverTLS12:%v clientTLS12:%v", scheme.Name(),
+	run := func(curveID CurveID, clientPQ, serverPQ, clientTLS12, serverTLS12 bool) {
+		t.Run(fmt.Sprintf("%#04x serverPQ:%v clientPQ:%v serverTLS12:%v clientTLS12:%v", uint16(curveID),
 			serverPQ, clientPQ, serverTLS12, clientTLS12), func(t *testing.T) {
-			testHybridKEX(t, scheme, clientPQ, serverPQ, clientTLS12, serverTLS12)
+			testHybridKEX(t, curveID, clientPQ, serverPQ, clientTLS12, serverTLS12)
 		})
 	}
-	for _, scheme := range []kem.Scheme{
-		hybrid.Kyber512X25519(),
-		hybrid.Kyber768X25519(),
-		hybrid.P256Kyber768Draft00(),
+	for _, curveID := range []CurveID{
+		X25519Kyber512Draft00,
+		X25519Kyber768Draft00,
+		X25519Kyber768Draft00Old,
+		P256Kyber768Draft00,
 	} {
-		run(scheme, true, true, false, false)
-		run(scheme, true, false, false, false)
-		run(scheme, false, true, false, false)
-		run(scheme, true, true, true, false)
-		run(scheme, true, true, false, true)
-		run(scheme, true, true, true, true)
+		run(curveID, true, true, false, false)
+		run(curveID, true, false, false, false)
+		run(curveID, false, true, false, false)
+		run(curveID, true, true, true, false)
+		run(curveID, true, true, false, true)
+		run(curveID, true, true, true, true)
 	}
 }

src/crypto/tls/handshake_client.go

@@ -146,7 +146,7 @@ func (c *Conn) makeClientHello(minVersion uint16) (*clientHelloMsg, clientKeySha
 
 		curveID := config.curvePreferences()[0]
 		if scheme := curveIdToCirclScheme(curveID); scheme != nil {
-			pk, sk, err := generateKemKeyPair(scheme, config.rand())
+			pk, sk, err := generateKemKeyPair(scheme, curveID, config.rand())
 			if err != nil {
 				return nil, nil, fmt.Errorf("generateKemKeyPair %s: %w",
 					scheme.Name(), err)

src/crypto/tls/handshake_client_tls13.go

@@ -16,8 +16,6 @@ import (
 	"fmt"
 	"hash"
 	"time"
-
-	circlKem "github.com/cloudflare/circl/kem"
 )
 
 type clientHandshakeStateTLS13 struct {
@@ -386,7 +384,7 @@ func (hs *clientHandshakeStateTLS13) processHelloRetryRequest() error {
 			return errors.New("tls: server sent an unnecessary HelloRetryRequest key_share")
 		}
 		if scheme := curveIdToCirclScheme(curveID); scheme != nil {
-			pk, sk, err := generateKemKeyPair(scheme, c.config.rand())
+			pk, sk, err := generateKemKeyPair(scheme, curveID, c.config.rand())
 			if err != nil {
 				c.sendAlert(alertInternalError)
 				return fmt.Errorf("HRR generateKemKeyPair %s: %w",
@@ -620,7 +618,8 @@ func (hs *clientHandshakeStateTLS13) establishHandshakeKeys() error {
 		if err == nil {
 			sharedKey, _ = key.ECDH(peerKey)
 		}
-	} else if sk, ok := hs.keySharePrivate.(circlKem.PrivateKey); ok {
+	} else if key, ok := hs.keySharePrivate.(*kemPrivateKey); ok {
+		sk := key.secretKey
 		sharedKey, err = sk.Scheme().Decapsulate(sk, hs.serverHello.serverShare.data)
 		if err != nil {
 			c.sendAlert(alertIllegalParameter)