1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
|
// 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/elliptic"
"crypto/hmac"
"errors"
"hash"
"io"
"math/big"
"golang.org/x/crypto/cryptobyte"
"golang.org/x/crypto/curve25519"
"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)
})
out := make([]byte, length)
n, err := hkdf.Expand(c.hash.New, secret, hkdfLabel.BytesOrPanic()).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
}
}
// ecdheParameters implements Diffie-Hellman with either NIST curves or X25519,
// according to RFC 8446, Section 4.2.8.2.
type ecdheParameters interface {
CurveID() CurveID
PublicKey() []byte
SharedKey(peerPublicKey []byte) []byte
}
func generateECDHEParameters(rand io.Reader, curveID CurveID) (ecdheParameters, error) {
if curveID == X25519 {
privateKey := make([]byte, curve25519.ScalarSize)
if _, err := io.ReadFull(rand, privateKey); err != nil {
return nil, err
}
publicKey, err := curve25519.X25519(privateKey, curve25519.Basepoint)
if err != nil {
return nil, err
}
return &x25519Parameters{privateKey: privateKey, publicKey: publicKey}, nil
}
curve, ok := curveForCurveID(curveID)
if !ok {
return nil, errors.New("tls: internal error: unsupported curve")
}
p := &nistParameters{curveID: curveID}
var err error
p.privateKey, p.x, p.y, err = elliptic.GenerateKey(curve, rand)
if err != nil {
return nil, err
}
return p, nil
}
func curveForCurveID(id CurveID) (elliptic.Curve, bool) {
switch id {
case CurveP256:
return elliptic.P256(), true
case CurveP384:
return elliptic.P384(), true
case CurveP521:
return elliptic.P521(), true
default:
return nil, false
}
}
type nistParameters struct {
privateKey []byte
x, y *big.Int // public key
curveID CurveID
}
func (p *nistParameters) CurveID() CurveID {
return p.curveID
}
func (p *nistParameters) PublicKey() []byte {
curve, _ := curveForCurveID(p.curveID)
return elliptic.Marshal(curve, p.x, p.y)
}
func (p *nistParameters) SharedKey(peerPublicKey []byte) []byte {
curve, _ := curveForCurveID(p.curveID)
// Unmarshal also checks whether the given point is on the curve.
x, y := elliptic.Unmarshal(curve, peerPublicKey)
if x == nil {
return nil
}
xShared, _ := curve.ScalarMult(x, y, p.privateKey)
sharedKey := make([]byte, (curve.Params().BitSize+7)/8)
return xShared.FillBytes(sharedKey)
}
type x25519Parameters struct {
privateKey []byte
publicKey []byte
}
func (p *x25519Parameters) CurveID() CurveID {
return X25519
}
func (p *x25519Parameters) PublicKey() []byte {
return p.publicKey[:]
}
func (p *x25519Parameters) SharedKey(peerPublicKey []byte) []byte {
sharedKey, err := curve25519.X25519(p.privateKey, peerPublicKey)
if err != nil {
return nil
}
return sharedKey
}
|
