Import crypto/tls

tls/key_schedule.go

@@ -0,0 +1,158 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tls
+
+import (
+	"crypto/ecdh"
+	"crypto/hmac"
+	"errors"
+	"fmt"
+	"hash"
+	"io"
+
+	"golang.org/x/crypto/cryptobyte"
+	"golang.org/x/crypto/hkdf"
+)
+
+// This file contains the functions necessary to compute the TLS 1.3 key
+// schedule. See RFC 8446, Section 7.
+
+const (
+	resumptionBinderLabel         = "res binder"
+	clientHandshakeTrafficLabel   = "c hs traffic"
+	serverHandshakeTrafficLabel   = "s hs traffic"
+	clientApplicationTrafficLabel = "c ap traffic"
+	serverApplicationTrafficLabel = "s ap traffic"
+	exporterLabel                 = "exp master"
+	resumptionLabel               = "res master"
+	trafficUpdateLabel            = "traffic upd"
+)
+
+// expandLabel implements HKDF-Expand-Label from RFC 8446, Section 7.1.
+func (c *cipherSuiteTLS13) expandLabel(secret []byte, label string, context []byte, length int) []byte {
+	var hkdfLabel cryptobyte.Builder
+	hkdfLabel.AddUint16(uint16(length))
+	hkdfLabel.AddUint8LengthPrefixed(func(b *cryptobyte.Builder) {
+		b.AddBytes([]byte("tls13 "))
+		b.AddBytes([]byte(label))
+	})
+	hkdfLabel.AddUint8LengthPrefixed(func(b *cryptobyte.Builder) {
+		b.AddBytes(context)
+	})
+	hkdfLabelBytes, err := hkdfLabel.Bytes()
+	if err != nil {
+		// Rather than calling BytesOrPanic, we explicitly handle this error, in
+		// order to provide a reasonable error message. It should be basically
+		// impossible for this to panic, and routing errors back through the
+		// tree rooted in this function is quite painful. The labels are fixed
+		// size, and the context is either a fixed-length computed hash, or
+		// parsed from a field which has the same length limitation. As such, an
+		// error here is likely to only be caused during development.
+		//
+		// NOTE: another reasonable approach here might be to return a
+		// randomized slice if we encounter an error, which would break the
+		// connection, but avoid panicking. This would perhaps be safer but
+		// significantly more confusing to users.
+		panic(fmt.Errorf("failed to construct HKDF label: %s", err))
+	}
+	out := make([]byte, length)
+	n, err := hkdf.Expand(c.hash.New, secret, hkdfLabelBytes).Read(out)
+	if err != nil || n != length {
+		panic("tls: HKDF-Expand-Label invocation failed unexpectedly")
+	}
+	return out
+}
+
+// deriveSecret implements Derive-Secret from RFC 8446, Section 7.1.
+func (c *cipherSuiteTLS13) deriveSecret(secret []byte, label string, transcript hash.Hash) []byte {
+	if transcript == nil {
+		transcript = c.hash.New()
+	}
+	return c.expandLabel(secret, label, transcript.Sum(nil), c.hash.Size())
+}
+
+// extract implements HKDF-Extract with the cipher suite hash.
+func (c *cipherSuiteTLS13) extract(newSecret, currentSecret []byte) []byte {
+	if newSecret == nil {
+		newSecret = make([]byte, c.hash.Size())
+	}
+	return hkdf.Extract(c.hash.New, newSecret, currentSecret)
+}
+
+// nextTrafficSecret generates the next traffic secret, given the current one,
+// according to RFC 8446, Section 7.2.
+func (c *cipherSuiteTLS13) nextTrafficSecret(trafficSecret []byte) []byte {
+	return c.expandLabel(trafficSecret, trafficUpdateLabel, nil, c.hash.Size())
+}
+
+// trafficKey generates traffic keys according to RFC 8446, Section 7.3.
+func (c *cipherSuiteTLS13) trafficKey(trafficSecret []byte) (key, iv []byte) {
+	key = c.expandLabel(trafficSecret, "key", nil, c.keyLen)
+	iv = c.expandLabel(trafficSecret, "iv", nil, aeadNonceLength)
+	return
+}
+
+// finishedHash generates the Finished verify_data or PskBinderEntry according
+// to RFC 8446, Section 4.4.4. See sections 4.4 and 4.2.11.2 for the baseKey
+// selection.
+func (c *cipherSuiteTLS13) finishedHash(baseKey []byte, transcript hash.Hash) []byte {
+	finishedKey := c.expandLabel(baseKey, "finished", nil, c.hash.Size())
+	verifyData := hmac.New(c.hash.New, finishedKey)
+	verifyData.Write(transcript.Sum(nil))
+	return verifyData.Sum(nil)
+}
+
+// exportKeyingMaterial implements RFC5705 exporters for TLS 1.3 according to
+// RFC 8446, Section 7.5.
+func (c *cipherSuiteTLS13) exportKeyingMaterial(masterSecret []byte, transcript hash.Hash) func(string, []byte, int) ([]byte, error) {
+	expMasterSecret := c.deriveSecret(masterSecret, exporterLabel, transcript)
+	return func(label string, context []byte, length int) ([]byte, error) {
+		secret := c.deriveSecret(expMasterSecret, label, nil)
+		h := c.hash.New()
+		h.Write(context)
+		return c.expandLabel(secret, "exporter", h.Sum(nil), length), nil
+	}
+}
+
+// generateECDHEKey returns a PrivateKey that implements Diffie-Hellman
+// according to RFC 8446, Section 4.2.8.2.
+func generateECDHEKey(rand io.Reader, curveID CurveID) (*ecdh.PrivateKey, error) {
+	curve, ok := curveForCurveID(curveID)
+	if !ok {
+		return nil, errors.New("tls: internal error: unsupported curve")
+	}
+
+	return curve.GenerateKey(rand)
+}
+
+func curveForCurveID(id CurveID) (ecdh.Curve, bool) {
+	switch id {
+	case X25519:
+		return ecdh.X25519(), true
+	case CurveP256:
+		return ecdh.P256(), true
+	case CurveP384:
+		return ecdh.P384(), true
+	case CurveP521:
+		return ecdh.P521(), true
+	default:
+		return nil, false
+	}
+}
+
+func curveIDForCurve(curve ecdh.Curve) (CurveID, bool) {
+	switch curve {
+	case ecdh.X25519():
+		return X25519, true
+	case ecdh.P256():
+		return CurveP256, true
+	case ecdh.P384():
+		return CurveP384, true
+	case ecdh.P521():
+		return CurveP521, true
+	default:
+		return 0, false
+	}
+}