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
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
|
// Copyright 2010 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 (
"big"
"crypto"
"crypto/elliptic"
"crypto/md5"
"crypto/rsa"
"crypto/sha1"
"crypto/x509"
"io"
"os"
)
// rsaKeyAgreement implements the standard TLS key agreement where the client
// encrypts the pre-master secret to the server's public key.
type rsaKeyAgreement struct{}
func (ka rsaKeyAgreement) generateServerKeyExchange(config *Config, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, os.Error) {
return nil, nil
}
func (ka rsaKeyAgreement) processClientKeyExchange(config *Config, ckx *clientKeyExchangeMsg) ([]byte, os.Error) {
preMasterSecret := make([]byte, 48)
_, err := io.ReadFull(config.rand(), preMasterSecret[2:])
if err != nil {
return nil, err
}
if len(ckx.ciphertext) < 2 {
return nil, os.NewError("bad ClientKeyExchange")
}
ciphertextLen := int(ckx.ciphertext[0])<<8 | int(ckx.ciphertext[1])
if ciphertextLen != len(ckx.ciphertext)-2 {
return nil, os.NewError("bad ClientKeyExchange")
}
ciphertext := ckx.ciphertext[2:]
err = rsa.DecryptPKCS1v15SessionKey(config.rand(), config.Certificates[0].PrivateKey, ciphertext, preMasterSecret)
if err != nil {
return nil, err
}
// We don't check the version number in the premaster secret. For one,
// by checking it, we would leak information about the validity of the
// encrypted pre-master secret. Secondly, it provides only a small
// benefit against a downgrade attack and some implementations send the
// wrong version anyway. See the discussion at the end of section
// 7.4.7.1 of RFC 4346.
return preMasterSecret, nil
}
func (ka rsaKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) os.Error {
return os.NewError("unexpected ServerKeyExchange")
}
func (ka rsaKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, os.Error) {
preMasterSecret := make([]byte, 48)
preMasterSecret[0] = byte(clientHello.vers >> 8)
preMasterSecret[1] = byte(clientHello.vers)
_, err := io.ReadFull(config.rand(), preMasterSecret[2:])
if err != nil {
return nil, nil, err
}
encrypted, err := rsa.EncryptPKCS1v15(config.rand(), cert.PublicKey.(*rsa.PublicKey), preMasterSecret)
if err != nil {
return nil, nil, err
}
ckx := new(clientKeyExchangeMsg)
ckx.ciphertext = make([]byte, len(encrypted)+2)
ckx.ciphertext[0] = byte(len(encrypted) >> 8)
ckx.ciphertext[1] = byte(len(encrypted))
copy(ckx.ciphertext[2:], encrypted)
return preMasterSecret, ckx, nil
}
// md5SHA1Hash implements TLS 1.0's hybrid hash function which consists of the
// concatenation of an MD5 and SHA1 hash.
func md5SHA1Hash(slices ...[]byte) []byte {
md5sha1 := make([]byte, md5.Size+sha1.Size)
hmd5 := md5.New()
for _, slice := range slices {
hmd5.Write(slice)
}
copy(md5sha1, hmd5.Sum())
hsha1 := sha1.New()
for _, slice := range slices {
hsha1.Write(slice)
}
copy(md5sha1[md5.Size:], hsha1.Sum())
return md5sha1
}
// ecdheRSAKeyAgreement implements a TLS key agreement where the server
// generates a ephemeral EC public/private key pair and signs it. The
// pre-master secret is then calculated using ECDH.
type ecdheRSAKeyAgreement struct {
privateKey []byte
curve *elliptic.Curve
x, y *big.Int
}
func (ka *ecdheRSAKeyAgreement) generateServerKeyExchange(config *Config, clientHello *clientHelloMsg, hello *serverHelloMsg) (*serverKeyExchangeMsg, os.Error) {
var curveid uint16
Curve:
for _, c := range clientHello.supportedCurves {
switch c {
case curveP256:
ka.curve = elliptic.P256()
curveid = c
break Curve
case curveP384:
ka.curve = elliptic.P384()
curveid = c
break Curve
case curveP521:
ka.curve = elliptic.P521()
curveid = c
break Curve
}
}
var x, y *big.Int
var err os.Error
ka.privateKey, x, y, err = ka.curve.GenerateKey(config.rand())
if err != nil {
return nil, err
}
ecdhePublic := ka.curve.Marshal(x, y)
// http://tools.ietf.org/html/rfc4492#section-5.4
serverECDHParams := make([]byte, 1+2+1+len(ecdhePublic))
serverECDHParams[0] = 3 // named curve
serverECDHParams[1] = byte(curveid >> 8)
serverECDHParams[2] = byte(curveid)
serverECDHParams[3] = byte(len(ecdhePublic))
copy(serverECDHParams[4:], ecdhePublic)
md5sha1 := md5SHA1Hash(clientHello.random, hello.random, serverECDHParams)
sig, err := rsa.SignPKCS1v15(config.rand(), config.Certificates[0].PrivateKey, crypto.MD5SHA1, md5sha1)
if err != nil {
return nil, os.NewError("failed to sign ECDHE parameters: " + err.String())
}
skx := new(serverKeyExchangeMsg)
skx.key = make([]byte, len(serverECDHParams)+2+len(sig))
copy(skx.key, serverECDHParams)
k := skx.key[len(serverECDHParams):]
k[0] = byte(len(sig) >> 8)
k[1] = byte(len(sig))
copy(k[2:], sig)
return skx, nil
}
func (ka *ecdheRSAKeyAgreement) processClientKeyExchange(config *Config, ckx *clientKeyExchangeMsg) ([]byte, os.Error) {
if len(ckx.ciphertext) == 0 || int(ckx.ciphertext[0]) != len(ckx.ciphertext)-1 {
return nil, os.NewError("bad ClientKeyExchange")
}
x, y := ka.curve.Unmarshal(ckx.ciphertext[1:])
if x == nil {
return nil, os.NewError("bad ClientKeyExchange")
}
x, _ = ka.curve.ScalarMult(x, y, ka.privateKey)
preMasterSecret := make([]byte, (ka.curve.BitSize+7)>>3)
xBytes := x.Bytes()
copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
return preMasterSecret, nil
}
var errServerKeyExchange = os.NewError("invalid ServerKeyExchange")
func (ka *ecdheRSAKeyAgreement) processServerKeyExchange(config *Config, clientHello *clientHelloMsg, serverHello *serverHelloMsg, cert *x509.Certificate, skx *serverKeyExchangeMsg) os.Error {
if len(skx.key) < 4 {
return errServerKeyExchange
}
if skx.key[0] != 3 { // named curve
return os.NewError("server selected unsupported curve")
}
curveid := uint16(skx.key[1])<<8 | uint16(skx.key[2])
switch curveid {
case curveP256:
ka.curve = elliptic.P256()
case curveP384:
ka.curve = elliptic.P384()
case curveP521:
ka.curve = elliptic.P521()
default:
return os.NewError("server selected unsupported curve")
}
publicLen := int(skx.key[3])
if publicLen+4 > len(skx.key) {
return errServerKeyExchange
}
ka.x, ka.y = ka.curve.Unmarshal(skx.key[4 : 4+publicLen])
if ka.x == nil {
return errServerKeyExchange
}
serverECDHParams := skx.key[:4+publicLen]
sig := skx.key[4+publicLen:]
if len(sig) < 2 {
return errServerKeyExchange
}
sigLen := int(sig[0])<<8 | int(sig[1])
if sigLen+2 != len(sig) {
return errServerKeyExchange
}
sig = sig[2:]
md5sha1 := md5SHA1Hash(clientHello.random, serverHello.random, serverECDHParams)
return rsa.VerifyPKCS1v15(cert.PublicKey.(*rsa.PublicKey), crypto.MD5SHA1, md5sha1, sig)
}
func (ka *ecdheRSAKeyAgreement) generateClientKeyExchange(config *Config, clientHello *clientHelloMsg, cert *x509.Certificate) ([]byte, *clientKeyExchangeMsg, os.Error) {
if ka.curve == nil {
return nil, nil, os.NewError("missing ServerKeyExchange message")
}
priv, mx, my, err := ka.curve.GenerateKey(config.rand())
if err != nil {
return nil, nil, err
}
x, _ := ka.curve.ScalarMult(ka.x, ka.y, priv)
preMasterSecret := make([]byte, (ka.curve.BitSize+7)>>3)
xBytes := x.Bytes()
copy(preMasterSecret[len(preMasterSecret)-len(xBytes):], xBytes)
serialized := ka.curve.Marshal(mx, my)
ckx := new(clientKeyExchangeMsg)
ckx.ciphertext = make([]byte, 1+len(serialized))
ckx.ciphertext[0] = byte(len(serialized))
copy(ckx.ciphertext[1:], serialized)
return preMasterSecret, ckx, nil
}
|
