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
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
|
// Copyright 2018 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package scwallet
import (
"bytes"
"crypto/aes"
"crypto/cipher"
"crypto/rand"
"crypto/sha256"
"crypto/sha512"
"fmt"
"github.com/ebfe/scard"
"github.com/ethereum/go-ethereum/crypto"
"github.com/wsddn/go-ecdh"
)
const (
maxPayloadSize = 223
pairP1FirstStep = 0
pairP1LastStep = 1
scSecretLength = 32
scBlockSize = 16
insOpenSecureChannel = 0x10
insMutuallyAuthenticate = 0x11
insPair = 0x12
insUnpair = 0x13
)
// SecureChannelSession enables secure communication with a hardware wallet.
type SecureChannelSession struct {
card *scard.Card // A handle to the smartcard for communication
secret []byte // A shared secret generated from our ECDSA keys
publicKey []byte // Our own ephemeral public key
PairingKey []byte // A permanent shared secret for a pairing, if present
sessionEncKey []byte // The current session encryption key
sessionMacKey []byte // The current session MAC key
iv []byte // The current IV
PairingIndex uint8 // The pairing index
}
// NewSecureChannelSession creates a new secure channel for the given card and public key.
func NewSecureChannelSession(card *scard.Card, keyData []byte) (*SecureChannelSession, error) {
// Generate an ECDSA keypair for ourselves
gen := ecdh.NewEllipticECDH(crypto.S256())
private, public, err := gen.GenerateKey(rand.Reader)
if err != nil {
return nil, err
}
cardPublic, ok := gen.Unmarshal(keyData)
if !ok {
return nil, fmt.Errorf("Could not unmarshal public key from card")
}
secret, err := gen.GenerateSharedSecret(private, cardPublic)
if err != nil {
return nil, err
}
return &SecureChannelSession{
card: card,
secret: secret,
publicKey: gen.Marshal(public),
}, nil
}
// Pair establishes a new pairing with the smartcard.
func (s *SecureChannelSession) Pair(sharedSecret []byte) error {
secretHash := sha256.Sum256(sharedSecret)
challenge := make([]byte, 32)
if _, err := rand.Read(challenge); err != nil {
return err
}
response, err := s.pair(pairP1FirstStep, challenge)
if err != nil {
return err
}
md := sha256.New()
md.Write(secretHash[:])
md.Write(challenge)
expectedCryptogram := md.Sum(nil)
cardCryptogram := response.Data[:32]
cardChallenge := response.Data[32:]
if !bytes.Equal(expectedCryptogram, cardCryptogram) {
return fmt.Errorf("Invalid card cryptogram")
}
md.Reset()
md.Write(secretHash[:])
md.Write(cardChallenge)
response, err = s.pair(pairP1LastStep, md.Sum(nil))
if err != nil {
return err
}
md.Reset()
md.Write(secretHash[:])
md.Write(response.Data[1:])
s.PairingKey = md.Sum(nil)
s.PairingIndex = response.Data[0]
return nil
}
// Unpair disestablishes an existing pairing.
func (s *SecureChannelSession) Unpair() error {
if s.PairingKey == nil {
return fmt.Errorf("Cannot unpair: not paired")
}
_, err := s.TransmitEncrypted(claSCWallet, insUnpair, s.PairingIndex, 0, []byte{})
if err != nil {
return err
}
s.PairingKey = nil
// Close channel
s.iv = nil
return nil
}
// Open initializes the secure channel.
func (s *SecureChannelSession) Open() error {
if s.iv != nil {
return fmt.Errorf("Session already opened")
}
response, err := s.open()
if err != nil {
return err
}
// Generate the encryption/mac key by hashing our shared secret,
// pairing key, and the first bytes returned from the Open APDU.
md := sha512.New()
md.Write(s.secret)
md.Write(s.PairingKey)
md.Write(response.Data[:scSecretLength])
keyData := md.Sum(nil)
s.sessionEncKey = keyData[:scSecretLength]
s.sessionMacKey = keyData[scSecretLength : scSecretLength*2]
// The IV is the last bytes returned from the Open APDU.
s.iv = response.Data[scSecretLength:]
return s.mutuallyAuthenticate()
}
// mutuallyAuthenticate is an internal method to authenticate both ends of the
// connection.
func (s *SecureChannelSession) mutuallyAuthenticate() error {
data := make([]byte, scSecretLength)
if _, err := rand.Read(data); err != nil {
return err
}
response, err := s.TransmitEncrypted(claSCWallet, insMutuallyAuthenticate, 0, 0, data)
if err != nil {
return err
}
if response.Sw1 != 0x90 || response.Sw2 != 0x00 {
return fmt.Errorf("Got unexpected response from MUTUALLY_AUTHENTICATE: 0x%x%x", response.Sw1, response.Sw2)
}
if len(response.Data) != scSecretLength {
return fmt.Errorf("Response from MUTUALLY_AUTHENTICATE was %d bytes, expected %d", len(response.Data), scSecretLength)
}
return nil
}
// open is an internal method that sends an open APDU.
func (s *SecureChannelSession) open() (*responseAPDU, error) {
return transmit(s.card, &commandAPDU{
Cla: claSCWallet,
Ins: insOpenSecureChannel,
P1: s.PairingIndex,
P2: 0,
Data: s.publicKey,
Le: 0,
})
}
// pair is an internal method that sends a pair APDU.
func (s *SecureChannelSession) pair(p1 uint8, data []byte) (*responseAPDU, error) {
return transmit(s.card, &commandAPDU{
Cla: claSCWallet,
Ins: insPair,
P1: p1,
P2: 0,
Data: data,
Le: 0,
})
}
// TransmitEncrypted sends an encrypted message, and decrypts and returns the response.
func (s *SecureChannelSession) TransmitEncrypted(cla, ins, p1, p2 byte, data []byte) (*responseAPDU, error) {
if s.iv == nil {
return nil, fmt.Errorf("Channel not open")
}
data, err := s.encryptAPDU(data)
if err != nil {
return nil, err
}
meta := []byte{cla, ins, p1, p2, byte(len(data) + scBlockSize), 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
if err = s.updateIV(meta, data); err != nil {
return nil, err
}
fulldata := make([]byte, len(s.iv)+len(data))
copy(fulldata, s.iv)
copy(fulldata[len(s.iv):], data)
response, err := transmit(s.card, &commandAPDU{
Cla: cla,
Ins: ins,
P1: p1,
P2: p2,
Data: fulldata,
})
if err != nil {
return nil, err
}
rmeta := []byte{byte(len(response.Data)), 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
rmac := response.Data[:len(s.iv)]
rdata := response.Data[len(s.iv):]
plainData, err := s.decryptAPDU(rdata)
if err != nil {
return nil, err
}
if err = s.updateIV(rmeta, rdata); err != nil {
return nil, err
}
if !bytes.Equal(s.iv, rmac) {
return nil, fmt.Errorf("Invalid MAC in response")
}
rapdu := &responseAPDU{}
rapdu.deserialize(plainData)
if rapdu.Sw1 != sw1Ok {
return nil, fmt.Errorf("Unexpected response status Cla=0x%x, Ins=0x%x, Sw=0x%x%x", cla, ins, rapdu.Sw1, rapdu.Sw2)
}
return rapdu, nil
}
// encryptAPDU is an internal method that serializes and encrypts an APDU.
func (s *SecureChannelSession) encryptAPDU(data []byte) ([]byte, error) {
if len(data) > maxPayloadSize {
return nil, fmt.Errorf("Payload of %d bytes exceeds maximum of %d", len(data), maxPayloadSize)
}
data = pad(data, 0x80)
ret := make([]byte, len(data))
a, err := aes.NewCipher(s.sessionEncKey)
if err != nil {
return nil, err
}
crypter := cipher.NewCBCEncrypter(a, s.iv)
crypter.CryptBlocks(ret, data)
return ret, nil
}
// pad applies message padding to a 16 byte boundary.
func pad(data []byte, terminator byte) []byte {
padded := make([]byte, (len(data)/16+1)*16)
copy(padded, data)
padded[len(data)] = terminator
return padded
}
// decryptAPDU is an internal method that decrypts and deserializes an APDU.
func (s *SecureChannelSession) decryptAPDU(data []byte) ([]byte, error) {
a, err := aes.NewCipher(s.sessionEncKey)
if err != nil {
return nil, err
}
ret := make([]byte, len(data))
crypter := cipher.NewCBCDecrypter(a, s.iv)
crypter.CryptBlocks(ret, data)
return unpad(ret, 0x80)
}
// unpad strips padding from a message.
func unpad(data []byte, terminator byte) ([]byte, error) {
for i := 1; i <= 16; i++ {
switch data[len(data)-i] {
case 0:
continue
case terminator:
return data[:len(data)-i], nil
default:
return nil, fmt.Errorf("Expected end of padding, got %d", data[len(data)-i])
}
}
return nil, fmt.Errorf("Expected end of padding, got 0")
}
// updateIV is an internal method that updates the initialization vector after
// each message exchanged.
func (s *SecureChannelSession) updateIV(meta, data []byte) error {
data = pad(data, 0)
a, err := aes.NewCipher(s.sessionMacKey)
if err != nil {
return err
}
crypter := cipher.NewCBCEncrypter(a, make([]byte, 16))
crypter.CryptBlocks(meta, meta)
crypter.CryptBlocks(data, data)
// The first 16 bytes of the last block is the MAC
s.iv = data[len(data)-32 : len(data)-16]
return nil
}
|