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
|
/******************************************************************************
*
* Copyright 2008-2012 Broadcom Corporation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
******************************************************************************/
/******************************************************************************
*
* This file contains the implementation of the AES128 and AES CMAC algorithm.
*
******************************************************************************/
#include <algorithm>
#include "crypto_toolbox/aes.h"
#include "crypto_toolbox/crypto_toolbox.h"
namespace bluetooth {
namespace crypto_toolbox {
namespace {
typedef struct {
uint8_t* text;
uint16_t len;
uint16_t round;
} tCMAC_CB;
thread_local tCMAC_CB cmac_cb;
/* Rb for AES-128 as block cipher, LSB as [0] */
Octet16 const_Rb{0x87, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
/** utility function to do an biteise exclusive-OR of two bit strings of the
* length of OCTET16_LEN. Result is stored in first argument.
*/
static void xor_128(Octet16* a, const Octet16& b) {
// CHECK(a);
uint8_t i, *aa = a->data();
const uint8_t* bb = b.data();
for (i = 0; i < OCTET16_LEN; i++) {
aa[i] = aa[i] ^ bb[i];
}
}
} // namespace
/* This function computes AES_128(key, message) */
Octet16 aes_128(const Octet16& key, const Octet16& message) {
Octet16 key_reversed;
Octet16 message_reversed;
Octet16 output;
std::reverse_copy(key.begin(), key.end(), key_reversed.begin());
std::reverse_copy(message.begin(), message.end(), message_reversed.begin());
aes_context ctx;
aes_set_key(key_reversed.data(), key_reversed.size(), &ctx);
aes_encrypt(message_reversed.data(), output.data(), &ctx);
std::reverse(output.begin(), output.end());
return output;
}
/** utility function to padding the given text to be a 128 bits data. The
* parameter dest is input and output parameter, it must point to a
* OCTET16_LEN memory space; where include length bytes valid data. */
static void padding(Octet16* dest, uint8_t length) {
uint8_t i, *p = dest->data();
/* original last block */
for (i = length; i < OCTET16_LEN; i++) p[OCTET16_LEN - i - 1] = (i == length) ? 0x80 : 0;
}
/** utility function to left shift one bit for a 128 bits value. */
static void leftshift_onebit(uint8_t* input, uint8_t* output) {
uint8_t i, overflow = 0, next_overflow = 0;
/* input[0] is LSB */
for (i = 0; i < OCTET16_LEN; i++) {
next_overflow = (input[i] & 0x80) ? 1 : 0;
output[i] = (input[i] << 1) | overflow;
overflow = next_overflow;
}
return;
}
/** This function is the calculation of block cipher using AES-128. */
static Octet16 cmac_aes_k_calculate(const Octet16& key) {
Octet16 output;
Octet16 x{0}; // zero initialized
uint8_t i = 1;
while (i <= cmac_cb.round) {
/* Mi' := Mi (+) X */
xor_128((Octet16*)&cmac_cb.text[(cmac_cb.round - i) * OCTET16_LEN], x);
output = aes_128(key, &cmac_cb.text[(cmac_cb.round - i) * OCTET16_LEN], OCTET16_LEN);
x = output;
i++;
}
return output;
}
/** This function proceeed to prepare the last block of message Mn depending on
* the size of the message.
*/
static void cmac_prepare_last_block(const Octet16& k1, const Octet16& k2) {
// uint8_t x[16] = {0};
bool flag;
/* last block is a complete block set flag to 1 */
flag = ((cmac_cb.len % OCTET16_LEN) == 0 && cmac_cb.len != 0) ? true : false;
if (flag) { /* last block is complete block */
xor_128((Octet16*)&cmac_cb.text[0], k1);
} else /* padding then xor with k2 */
{
padding((Octet16*)&cmac_cb.text[0], (uint8_t)(cmac_cb.len % 16));
xor_128((Octet16*)&cmac_cb.text[0], k2);
}
}
/** This is the function to generate the two subkeys.
* |key| is CMAC key, expect SRK when used by SMP.
*/
static void cmac_generate_subkey(const Octet16& key) {
Octet16 zero{};
Octet16 p = aes_128(key, zero.data(), OCTET16_LEN);
Octet16 k1, k2;
uint8_t* pp = p.data();
/* If MSB(L) = 0, then K1 = L << 1 */
if ((pp[OCTET16_LEN - 1] & 0x80) != 0) {
/* Else K1 = ( L << 1 ) (+) Rb */
leftshift_onebit(pp, k1.data());
xor_128(&k1, const_Rb);
} else {
leftshift_onebit(pp, k1.data());
}
if ((k1[OCTET16_LEN - 1] & 0x80) != 0) {
/* K2 = (K1 << 1) (+) Rb */
leftshift_onebit(k1.data(), k2.data());
xor_128(&k2, const_Rb);
} else {
/* If MSB(K1) = 0, then K2 = K1 << 1 */
leftshift_onebit(k1.data(), k2.data());
}
cmac_prepare_last_block(k1, k2);
}
/** key - CMAC key in little endian order
* input - text to be signed in little endian byte order.
* length - length of the input in byte.
*/
Octet16 aes_cmac(const Octet16& key, const uint8_t* input, uint16_t length) {
uint32_t len;
uint16_t diff;
/* n is number of rounds */
uint16_t n = (length + OCTET16_LEN - 1) / OCTET16_LEN;
if (n == 0) n = 1;
len = n * OCTET16_LEN;
/* allocate a memory space of multiple of 16 bytes to hold text */
cmac_cb.text = (uint8_t*)alloca(len);
cmac_cb.round = n;
diff = len - length;
if (input != NULL && length > 0) {
memcpy(&cmac_cb.text[diff], input, (int)length);
cmac_cb.len = length;
} else {
cmac_cb.len = 0;
}
/* prepare calculation for subkey s and last block of data */
cmac_generate_subkey(key);
/* start calculation */
Octet16 signature = cmac_aes_k_calculate(key);
/* clean up */
memset(&cmac_cb, 0, sizeof(tCMAC_CB));
// cmac_cb.text is auto-freed by alloca
return signature;
}
} // namespace crypto_toolbox
} // namespace bluetooth
|
