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
|
// Copyright 2015 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.
//go:build amd64 || arm64
package aes
import (
"crypto/cipher"
subtleoverlap "crypto/internal/subtle"
"crypto/subtle"
"errors"
)
// The following functions are defined in gcm_*.s.
//go:noescape
func gcmAesInit(productTable *[256]byte, ks []uint32)
//go:noescape
func gcmAesData(productTable *[256]byte, data []byte, T *[16]byte)
//go:noescape
func gcmAesEnc(productTable *[256]byte, dst, src []byte, ctr, T *[16]byte, ks []uint32)
//go:noescape
func gcmAesDec(productTable *[256]byte, dst, src []byte, ctr, T *[16]byte, ks []uint32)
//go:noescape
func gcmAesFinish(productTable *[256]byte, tagMask, T *[16]byte, pLen, dLen uint64)
const (
gcmBlockSize = 16
gcmTagSize = 16
gcmMinimumTagSize = 12 // NIST SP 800-38D recommends tags with 12 or more bytes.
gcmStandardNonceSize = 12
)
var errOpen = errors.New("cipher: message authentication failed")
// aesCipherGCM implements crypto/cipher.gcmAble so that crypto/cipher.NewGCM
// will use the optimised implementation in this file when possible. Instances
// of this type only exist when hasGCMAsm returns true.
type aesCipherGCM struct {
aesCipherAsm
}
// Assert that aesCipherGCM implements the gcmAble interface.
var _ gcmAble = (*aesCipherGCM)(nil)
// NewGCM returns the AES cipher wrapped in Galois Counter Mode. This is only
// called by crypto/cipher.NewGCM via the gcmAble interface.
func (c *aesCipherGCM) NewGCM(nonceSize, tagSize int) (cipher.AEAD, error) {
g := &gcmAsm{ks: c.enc, nonceSize: nonceSize, tagSize: tagSize}
gcmAesInit(&g.productTable, g.ks)
return g, nil
}
type gcmAsm struct {
// ks is the key schedule, the length of which depends on the size of
// the AES key.
ks []uint32
// productTable contains pre-computed multiples of the binary-field
// element used in GHASH.
productTable [256]byte
// nonceSize contains the expected size of the nonce, in bytes.
nonceSize int
// tagSize contains the size of the tag, in bytes.
tagSize int
}
func (g *gcmAsm) NonceSize() int {
return g.nonceSize
}
func (g *gcmAsm) Overhead() int {
return g.tagSize
}
// sliceForAppend takes a slice and a requested number of bytes. It returns a
// slice with the contents of the given slice followed by that many bytes and a
// second slice that aliases into it and contains only the extra bytes. If the
// original slice has sufficient capacity then no allocation is performed.
func sliceForAppend(in []byte, n int) (head, tail []byte) {
if total := len(in) + n; cap(in) >= total {
head = in[:total]
} else {
head = make([]byte, total)
copy(head, in)
}
tail = head[len(in):]
return
}
// Seal encrypts and authenticates plaintext. See the cipher.AEAD interface for
// details.
func (g *gcmAsm) Seal(dst, nonce, plaintext, data []byte) []byte {
if len(nonce) != g.nonceSize {
panic("crypto/cipher: incorrect nonce length given to GCM")
}
if uint64(len(plaintext)) > ((1<<32)-2)*BlockSize {
panic("crypto/cipher: message too large for GCM")
}
var counter, tagMask [gcmBlockSize]byte
if len(nonce) == gcmStandardNonceSize {
// Init counter to nonce||1
copy(counter[:], nonce)
counter[gcmBlockSize-1] = 1
} else {
// Otherwise counter = GHASH(nonce)
gcmAesData(&g.productTable, nonce, &counter)
gcmAesFinish(&g.productTable, &tagMask, &counter, uint64(len(nonce)), uint64(0))
}
encryptBlockAsm(len(g.ks)/4-1, &g.ks[0], &tagMask[0], &counter[0])
var tagOut [gcmTagSize]byte
gcmAesData(&g.productTable, data, &tagOut)
ret, out := sliceForAppend(dst, len(plaintext)+g.tagSize)
if subtleoverlap.InexactOverlap(out[:len(plaintext)], plaintext) {
panic("crypto/cipher: invalid buffer overlap")
}
if len(plaintext) > 0 {
gcmAesEnc(&g.productTable, out, plaintext, &counter, &tagOut, g.ks)
}
gcmAesFinish(&g.productTable, &tagMask, &tagOut, uint64(len(plaintext)), uint64(len(data)))
copy(out[len(plaintext):], tagOut[:])
return ret
}
// Open authenticates and decrypts ciphertext. See the cipher.AEAD interface
// for details.
func (g *gcmAsm) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
if len(nonce) != g.nonceSize {
panic("crypto/cipher: incorrect nonce length given to GCM")
}
// Sanity check to prevent the authentication from always succeeding if an implementation
// leaves tagSize uninitialized, for example.
if g.tagSize < gcmMinimumTagSize {
panic("crypto/cipher: incorrect GCM tag size")
}
if len(ciphertext) < g.tagSize {
return nil, errOpen
}
if uint64(len(ciphertext)) > ((1<<32)-2)*uint64(BlockSize)+uint64(g.tagSize) {
return nil, errOpen
}
tag := ciphertext[len(ciphertext)-g.tagSize:]
ciphertext = ciphertext[:len(ciphertext)-g.tagSize]
// See GCM spec, section 7.1.
var counter, tagMask [gcmBlockSize]byte
if len(nonce) == gcmStandardNonceSize {
// Init counter to nonce||1
copy(counter[:], nonce)
counter[gcmBlockSize-1] = 1
} else {
// Otherwise counter = GHASH(nonce)
gcmAesData(&g.productTable, nonce, &counter)
gcmAesFinish(&g.productTable, &tagMask, &counter, uint64(len(nonce)), uint64(0))
}
encryptBlockAsm(len(g.ks)/4-1, &g.ks[0], &tagMask[0], &counter[0])
var expectedTag [gcmTagSize]byte
gcmAesData(&g.productTable, data, &expectedTag)
ret, out := sliceForAppend(dst, len(ciphertext))
if subtleoverlap.InexactOverlap(out, ciphertext) {
panic("crypto/cipher: invalid buffer overlap")
}
if len(ciphertext) > 0 {
gcmAesDec(&g.productTable, out, ciphertext, &counter, &expectedTag, g.ks)
}
gcmAesFinish(&g.productTable, &tagMask, &expectedTag, uint64(len(ciphertext)), uint64(len(data)))
if subtle.ConstantTimeCompare(expectedTag[:g.tagSize], tag) != 1 {
for i := range out {
out[i] = 0
}
return nil, errOpen
}
return ret, nil
}
|
