-
Notifications
You must be signed in to change notification settings - Fork 244
/
ecies.go
366 lines (321 loc) · 9.53 KB
/
ecies.go
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
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
// Copyright (c) 2013 Kyle Isom <kyle@tyrfingr.is>
// Copyright (c) 2012 The Go Authors. All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
package ecies
import (
"crypto/cipher"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/hmac"
"crypto/subtle"
"fmt"
"hash"
"io"
"math/big"
)
var (
ErrImport = fmt.Errorf("ecies: failed to import key")
ErrInvalidCurve = fmt.Errorf("ecies: invalid elliptic curve")
ErrInvalidParams = fmt.Errorf("ecies: invalid ECIES parameters")
ErrInvalidPublicKey = fmt.Errorf("ecies: invalid public key")
ErrSharedKeyIsPointAtInfinity = fmt.Errorf("ecies: shared key is point at infinity")
ErrSharedKeyTooBig = fmt.Errorf("ecies: shared key params are too big")
)
// PublicKey is a representation of an elliptic curve public key.
type PublicKey struct {
X *big.Int
Y *big.Int
elliptic.Curve
Params *ECIESParams
}
// Export an ECIES public key as an ECDSA public key.
func (pub *PublicKey) ExportECDSA() *ecdsa.PublicKey {
return &ecdsa.PublicKey{Curve: pub.Curve, X: pub.X, Y: pub.Y}
}
// Import an ECDSA public key as an ECIES public key.
func ImportECDSAPublic(pub *ecdsa.PublicKey) *PublicKey {
return &PublicKey{
X: pub.X,
Y: pub.Y,
Curve: pub.Curve,
Params: ParamsFromCurve(pub.Curve),
}
}
// PrivateKey is a representation of an elliptic curve private key.
type PrivateKey struct {
PublicKey
D *big.Int
}
// Export an ECIES private key as an ECDSA private key.
func (prv *PrivateKey) ExportECDSA() *ecdsa.PrivateKey {
pub := &prv.PublicKey
pubECDSA := pub.ExportECDSA()
return &ecdsa.PrivateKey{PublicKey: *pubECDSA, D: prv.D}
}
// Import an ECDSA private key as an ECIES private key.
func ImportECDSA(prv *ecdsa.PrivateKey) *PrivateKey {
pub := ImportECDSAPublic(&prv.PublicKey)
return &PrivateKey{*pub, prv.D}
}
// Generate an elliptic curve public / private keypair. If params is nil,
// the recommended default parameters for the key will be chosen.
func GenerateKey(rand io.Reader, curve elliptic.Curve, params *ECIESParams) (prv *PrivateKey, err error) {
pb, x, y, err := elliptic.GenerateKey(curve, rand)
if err != nil {
return
}
prv = new(PrivateKey)
prv.PublicKey.X = x
prv.PublicKey.Y = y
prv.PublicKey.Curve = curve
prv.D = new(big.Int).SetBytes(pb)
if params == nil {
params = ParamsFromCurve(curve)
}
prv.PublicKey.Params = params
return
}
// MaxSharedKeyLength returns the maximum length of the shared key the
// public key can produce.
func MaxSharedKeyLength(pub *PublicKey) int {
return (pub.Curve.Params().BitSize + 7) / 8
}
// ECDH key agreement method used to establish secret keys for encryption.
func (prv *PrivateKey) GenerateShared(pub *PublicKey, skLen, macLen int) (sk []byte, err error) {
if prv.PublicKey.Curve != pub.Curve {
return nil, ErrInvalidCurve
}
if skLen+macLen > MaxSharedKeyLength(pub) {
return nil, ErrSharedKeyTooBig
}
x, _ := pub.Curve.ScalarMult(pub.X, pub.Y, prv.D.Bytes())
if x == nil {
return nil, ErrSharedKeyIsPointAtInfinity
}
sk = make([]byte, skLen+macLen)
skBytes := x.Bytes()
copy(sk[len(sk)-len(skBytes):], skBytes)
return sk, nil
}
var (
ErrKeyDataTooLong = fmt.Errorf("ecies: can't supply requested key data")
ErrSharedTooLong = fmt.Errorf("ecies: shared secret is too long")
ErrInvalidMessage = fmt.Errorf("ecies: invalid message")
)
var (
big2To32 = new(big.Int).Exp(big.NewInt(2), big.NewInt(32), nil)
big2To32M1 = new(big.Int).Sub(big2To32, big.NewInt(1))
)
func incCounter(ctr []byte) {
if ctr[3]++; ctr[3] != 0 {
return
}
if ctr[2]++; ctr[2] != 0 {
return
}
if ctr[1]++; ctr[1] != 0 {
return
}
if ctr[0]++; ctr[0] != 0 {
return
}
}
// NIST SP 800-56 Concatenation Key Derivation Function (see section 5.8.1).
func concatKDF(hash hash.Hash, z, s1 []byte, kdLen int) (k []byte, err error) {
if s1 == nil {
s1 = make([]byte, 0)
}
reps := ((kdLen + 7) * 8) / (hash.BlockSize() * 8)
if big.NewInt(int64(reps)).Cmp(big2To32M1) > 0 {
fmt.Println(big2To32M1)
return nil, ErrKeyDataTooLong
}
counter := []byte{0, 0, 0, 1}
k = make([]byte, 0)
for i := 0; i <= reps; i++ {
hash.Write(counter)
hash.Write(z)
hash.Write(s1)
k = append(k, hash.Sum(nil)...)
hash.Reset()
incCounter(counter)
}
k = k[:kdLen]
return
}
// messageTag computes the MAC of a message (called the tag) as per
// SEC 1, 3.5.
func messageTag(hash func() hash.Hash, km, msg, shared []byte) []byte {
mac := hmac.New(hash, km)
mac.Write(msg)
mac.Write(shared)
tag := mac.Sum(nil)
return tag
}
// Generate an initialisation vector for CTR mode.
func generateIV(params *ECIESParams, rand io.Reader) (iv []byte, err error) {
iv = make([]byte, params.BlockSize)
_, err = io.ReadFull(rand, iv)
return
}
// symEncrypt carries out CTR encryption using the block cipher specified in the
// parameters.
func symEncrypt(rand io.Reader, params *ECIESParams, key, m []byte) (ct []byte, err error) {
c, err := params.Cipher(key)
if err != nil {
return
}
iv, err := generateIV(params, rand)
if err != nil {
return
}
ctr := cipher.NewCTR(c, iv)
ct = make([]byte, len(m)+params.BlockSize)
copy(ct, iv)
ctr.XORKeyStream(ct[params.BlockSize:], m)
return
}
// symDecrypt carries out CTR decryption using the block cipher specified in
// the parameters
func symDecrypt(params *ECIESParams, key, ct []byte) (m []byte, err error) {
c, err := params.Cipher(key)
if err != nil {
return
}
ctr := cipher.NewCTR(c, ct[:params.BlockSize])
m = make([]byte, len(ct)-params.BlockSize)
ctr.XORKeyStream(m, ct[params.BlockSize:])
return
}
// Encrypt encrypts a message using ECIES as specified in SEC 1, 5.1.
//
// s1 and s2 contain shared information that is not part of the resulting
// ciphertext. s1 is fed into key derivation, s2 is fed into the MAC. If the
// shared information parameters aren't being used, they should be nil.
func Encrypt(rand io.Reader, pub *PublicKey, m, s1, s2 []byte) (ct []byte, err error) {
params := pub.Params
if params == nil {
if params = ParamsFromCurve(pub.Curve); params == nil {
err = ErrUnsupportedECIESParameters
return
}
}
R, err := GenerateKey(rand, pub.Curve, params)
if err != nil {
return
}
hash := params.Hash()
z, err := R.GenerateShared(pub, params.KeyLen, params.KeyLen)
if err != nil {
return
}
K, err := concatKDF(hash, z, s1, params.KeyLen+params.KeyLen)
if err != nil {
return
}
Ke := K[:params.KeyLen]
Km := K[params.KeyLen:]
hash.Write(Km)
Km = hash.Sum(nil)
hash.Reset()
em, err := symEncrypt(rand, params, Ke, m)
if err != nil || len(em) <= params.BlockSize {
return
}
d := messageTag(params.Hash, Km, em, s2)
Rb := elliptic.Marshal(pub.Curve, R.PublicKey.X, R.PublicKey.Y)
ct = make([]byte, len(Rb)+len(em)+len(d))
copy(ct, Rb)
copy(ct[len(Rb):], em)
copy(ct[len(Rb)+len(em):], d)
return
}
// Decrypt decrypts an ECIES ciphertext.
func (prv *PrivateKey) Decrypt(c, s1, s2 []byte) (m []byte, err error) {
if len(c) == 0 {
return nil, ErrInvalidMessage
}
params := prv.PublicKey.Params
if params == nil {
if params = ParamsFromCurve(prv.PublicKey.Curve); params == nil {
err = ErrUnsupportedECIESParameters
return
}
}
hash := params.Hash()
var (
rLen int
hLen int = hash.Size()
mStart int
mEnd int
)
switch c[0] {
case 2, 3, 4:
rLen = (prv.PublicKey.Curve.Params().BitSize + 7) / 4
if len(c) < (rLen + hLen + 1) {
err = ErrInvalidMessage
return
}
default:
err = ErrInvalidPublicKey
return
}
mStart = rLen
mEnd = len(c) - hLen
R := new(PublicKey)
R.Curve = prv.PublicKey.Curve
R.X, R.Y = elliptic.Unmarshal(R.Curve, c[:rLen])
if R.X == nil {
err = ErrInvalidPublicKey
return
}
if !R.Curve.IsOnCurve(R.X, R.Y) {
err = ErrInvalidCurve
return
}
z, err := prv.GenerateShared(R, params.KeyLen, params.KeyLen)
if err != nil {
return
}
K, err := concatKDF(hash, z, s1, params.KeyLen+params.KeyLen)
if err != nil {
return
}
Ke := K[:params.KeyLen]
Km := K[params.KeyLen:]
hash.Write(Km)
Km = hash.Sum(nil)
hash.Reset()
d := messageTag(params.Hash, Km, c[mStart:mEnd], s2)
if subtle.ConstantTimeCompare(c[mEnd:], d) != 1 {
err = ErrInvalidMessage
return
}
m, err = symDecrypt(params, Ke, c[mStart:mEnd])
return
}