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
|
<?php
namespace Aws\Crypto\Polyfill;
use Aws\Exception\CryptoPolyfillException;
use InvalidArgumentException;
use RangeException;
/**
* Class AesGcm
*
* This provides a polyfill for AES-GCM encryption/decryption, with caveats:
*
* 1. Only 96-bit nonces are supported.
* 2. Only 128-bit authentication tags are supported. (i.e. non-truncated)
*
* Supports AES key sizes of 128-bit, 192-bit, and 256-bit.
*
* @package Aws\Crypto\Polyfill
*/
class AesGcm
{
use NeedsTrait;
/** @var Key $aesKey */
private $aesKey;
/** @var int $keySize */
private $keySize;
/** @var int $blockSize */
protected $blockSize = 8192;
/**
* AesGcm constructor.
*
* @param Key $aesKey
* @param int $keySize
* @param int $blockSize
*
* @throws CryptoPolyfillException
* @throws InvalidArgumentException
* @throws RangeException
*/
public function __construct(Key $aesKey, $keySize = 256, $blockSize = 8192)
{
/* Preconditions: */
self::needs(
\in_array($keySize, [128, 192, 256], true),
"Key size must be 128, 192, or 256 bits; {$keySize} given",
InvalidArgumentException::class
);
self::needs(
\is_int($blockSize) && $blockSize > 0 && $blockSize <= PHP_INT_MAX,
'Block size must be a positive integer.',
RangeException::class
);
self::needs(
$aesKey->length() << 3 === $keySize,
'Incorrect key size; expected ' . $keySize . ' bits, got ' . ($aesKey->length() << 3) . ' bits.'
);
$this->aesKey = $aesKey;
$this->keySize = $keySize;
}
/**
* Encryption interface for AES-GCM
*
* @param string $plaintext Message to be encrypted
* @param string $nonce Number to be used ONCE
* @param Key $key AES Key
* @param string $aad Additional authenticated data
* @param string &$tag Reference to variable to hold tag
* @param int $keySize Key size (bits)
* @param int $blockSize Block size (bytes) -- How much memory to buffer
* @return string
* @throws InvalidArgumentException
*/
public static function encrypt(
$plaintext,
$nonce,
Key $key,
$aad,
&$tag,
$keySize = 256,
$blockSize = 8192
) {
self::needs(
self::strlen($nonce) === 12,
'Nonce must be exactly 12 bytes',
InvalidArgumentException::class
);
$encryptor = new AesGcm($key, $keySize, $blockSize);
list($aadLength, $gmac) = $encryptor->gmacInit($nonce, $aad);
$ciphertext = \openssl_encrypt(
$plaintext,
"aes-{$encryptor->keySize}-ctr",
$key->get(),
OPENSSL_NO_PADDING | OPENSSL_RAW_DATA,
$nonce . "\x00\x00\x00\x02"
);
/* Calculate auth tag in a streaming fashion to minimize memory usage: */
$ciphertextLength = self::strlen($ciphertext);
for ($i = 0; $i < $ciphertextLength; $i += $encryptor->blockSize) {
$cBlock = new ByteArray(self::substr($ciphertext, $i, $encryptor->blockSize));
$gmac->update($cBlock);
}
$tag = $gmac->finish($aadLength, $ciphertextLength)->toString();
return $ciphertext;
}
/**
* Decryption interface for AES-GCM
*
* @param string $ciphertext Ciphertext to decrypt
* @param string $nonce Number to be used ONCE
* @param Key $key AES key
* @param string $aad Additional authenticated data
* @param string $tag Authentication tag
* @param int $keySize Key size (bits)
* @param int $blockSize Block size (bytes) -- How much memory to buffer
* @return string Plaintext
*
* @throws CryptoPolyfillException
* @throws InvalidArgumentException
*/
public static function decrypt(
$ciphertext,
$nonce,
Key $key,
$aad,
&$tag,
$keySize = 256,
$blockSize = 8192
) {
/* Precondition: */
self::needs(
self::strlen($nonce) === 12,
'Nonce must be exactly 12 bytes',
InvalidArgumentException::class
);
$encryptor = new AesGcm($key, $keySize, $blockSize);
list($aadLength, $gmac) = $encryptor->gmacInit($nonce, $aad);
/* Calculate auth tag in a streaming fashion to minimize memory usage: */
$ciphertextLength = self::strlen($ciphertext);
for ($i = 0; $i < $ciphertextLength; $i += $encryptor->blockSize) {
$cBlock = new ByteArray(self::substr($ciphertext, $i, $encryptor->blockSize));
$gmac->update($cBlock);
}
/* Validate auth tag in constant-time: */
$calc = $gmac->finish($aadLength, $ciphertextLength);
$expected = new ByteArray($tag);
self::needs($calc->equals($expected), 'Invalid authentication tag');
/* Return plaintext if auth tag check succeeded: */
return \openssl_decrypt(
$ciphertext,
"aes-{$encryptor->keySize}-ctr",
$key->get(),
OPENSSL_NO_PADDING | OPENSSL_RAW_DATA,
$nonce . "\x00\x00\x00\x02"
);
}
/**
* Initialize a Gmac object with the nonce and this object's key.
*
* @param string $nonce Must be exactly 12 bytes long.
* @param string|null $aad
* @return array
*/
protected function gmacInit($nonce, $aad = null)
{
$gmac = new Gmac(
$this->aesKey,
$nonce . "\x00\x00\x00\x01",
$this->keySize
);
$aadBlock = new ByteArray($aad);
$aadLength = $aadBlock->count();
$gmac->update($aadBlock);
$gmac->flush();
return [$aadLength, $gmac];
}
/**
* Calculate the length of a string.
*
* Uses the appropriate PHP function without being brittle to
* mbstring.func_overload.
*
* @param string $string
* @return int
*/
protected static function strlen($string)
{
if (\is_callable('\\mb_strlen')) {
return (int) \mb_strlen($string, '8bit');
}
return (int) \strlen($string);
}
/**
* Return a substring of the provided string.
*
* Uses the appropriate PHP function without being brittle to
* mbstring.func_overload.
*
* @param string $string
* @param int $offset
* @param int|null $length
* @return string
*/
protected static function substr($string, $offset = 0, $length = null)
{
if (\is_callable('\\mb_substr')) {
return \mb_substr($string, $offset, $length, '8bit');
} elseif (!\is_null($length)) {
return \substr($string, $offset, $length);
}
return \substr($string, $offset);
}
}
|
