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1 | /***************************************************************************** | |
2 | * WARNING | |
3 | * | |
4 | * THIS CODE IS CREATED FOR EXPERIMENTATION AND EDUCATIONAL USE ONLY. | |
5 | * | |
6 | * USAGE OF THIS CODE IN OTHER WAYS MAY INFRINGE UPON THE INTELLECTUAL | |
7 | * PROPERTY OF OTHER PARTIES, SUCH AS INSIDE SECURE AND HID GLOBAL, | |
8 | * AND MAY EXPOSE YOU TO AN INFRINGEMENT ACTION FROM THOSE PARTIES. | |
9 | * | |
10 | * THIS CODE SHOULD NEVER BE USED TO INFRINGE PATENTS OR INTELLECTUAL PROPERTY RIGHTS. | |
11 | * | |
12 | ***************************************************************************** | |
13 | * | |
14 | * This file is part of loclass. It is a reconstructon of the cipher engine | |
15 | * used in iClass, and RFID techology. | |
16 | * | |
17 | * The implementation is based on the work performed by | |
18 | * Flavio D. Garcia, Gerhard de Koning Gans, Roel Verdult and | |
19 | * Milosch Meriac in the paper "Dismantling IClass". | |
20 | * | |
21 | * Copyright (C) 2014 Martin Holst Swende | |
22 | * | |
23 | * This is free software: you can redistribute it and/or modify | |
24 | * it under the terms of the GNU General Public License version 2 as published | |
25 | * by the Free Software Foundation, or, at your option, any later version. | |
26 | * | |
27 | * This file is distributed in the hope that it will be useful, | |
28 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
29 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
30 | * GNU General Public License for more details. | |
31 | * | |
32 | * You should have received a copy of the GNU General Public License | |
33 | * along with loclass. If not, see <http://www.gnu.org/licenses/>. | |
34 | * | |
35 | * | |
36 | * | |
37 | ****************************************************************************/ | |
38 | ||
39 | /** | |
40 | ||
41 | This file contains an optimized version of the MAC-calculation algorithm. Some measurements on | |
42 | a std laptop showed it runs in about 1/3 of the time: | |
43 | ||
44 | Std: 0.428962 | |
45 | Opt: 0.151609 | |
46 | ||
47 | Additionally, it is self-reliant, not requiring e.g. bitstreams from the cipherutils, thus can | |
48 | be easily dropped into a code base. | |
49 | ||
50 | The optimizations have been performed in the following steps: | |
51 | * Parameters passed by reference instead of by value. | |
52 | * Iteration instead of recursion, un-nesting recursive loops into for-loops. | |
53 | * Handling of bytes instead of individual bits, for less shuffling and masking | |
54 | * Less creation of "objects", structs, and instead reuse of alloc:ed memory | |
55 | * Inlining some functions via #define:s | |
56 | ||
57 | As a consequence, this implementation is less generic. Also, I haven't bothered documenting this. | |
58 | For a thorough documentation, check out the MAC-calculation within cipher.c instead. | |
59 | ||
60 | -- MHS 2015 | |
61 | **/ | |
62 | ||
63 | #include "optimized_cipher.h" | |
64 | #include <stddef.h> | |
65 | #include <stdbool.h> | |
66 | #include <stdint.h> | |
67 | ||
68 | ||
69 | #define opt_T(s) (0x1 & ((s->t >> 15) ^ (s->t >> 14)^ (s->t >> 10)^ (s->t >> 8)^ (s->t >> 5)^ (s->t >> 4)^ (s->t >> 1)^ s->t)) | |
70 | ||
71 | #define opt_B(s) (((s->b >> 6) ^ (s->b >> 5) ^ (s->b >> 4) ^ (s->b)) & 0x1) | |
72 | ||
73 | #define opt__select(x,y,r) (4 & (((r & (r << 2)) >> 5) ^ ((r & ~(r << 2)) >> 4) ^ ( (r | r << 2) >> 3)))\ | |
74 | |(2 & (((r | r << 2) >> 6) ^ ( (r | r << 2) >> 1) ^ (r >> 5) ^ r ^ ((x^y) << 1)))\ | |
75 | |(1 & (((r & ~(r << 2)) >> 4) ^ ((r & (r << 2)) >> 3) ^ r ^ x)) | |
76 | ||
77 | /* | |
78 | * Some background on the expression above can be found here... | |
79 | uint8_t xopt__select(bool x, bool y, uint8_t r) | |
80 | { | |
81 | uint8_t r_ls2 = r << 2; | |
82 | uint8_t r_and_ls2 = r & r_ls2; | |
83 | uint8_t r_or_ls2 = r | r_ls2; | |
84 | ||
85 | //r: r0 r1 r2 r3 r4 r5 r6 r7 | |
86 | //r_ls2: r2 r3 r4 r5 r6 r7 0 0 | |
87 | // z0 | |
88 | // z1 | |
89 | ||
90 | // uint8_t z0 = (r0 & r2) ^ (r1 & ~r3) ^ (r2 | r4); // <-- original | |
91 | uint8_t z0 = (r_and_ls2 >> 5) ^ ((r & ~r_ls2) >> 4) ^ ( r_or_ls2 >> 3); | |
92 | ||
93 | // uint8_t z1 = (r0 | r2) ^ ( r5 | r7) ^ r1 ^ r6 ^ x ^ y; // <-- original | |
94 | uint8_t z1 = (r_or_ls2 >> 6) ^ ( r_or_ls2 >> 1) ^ (r >> 5) ^ r ^ ((x^y) << 1); | |
95 | ||
96 | // uint8_t z2 = (r3 & ~r5) ^ (r4 & r6 ) ^ r7 ^ x; // <-- original | |
97 | uint8_t z2 = ((r & ~r_ls2) >> 4) ^ (r_and_ls2 >> 3) ^ r ^ x; | |
98 | ||
99 | return (z0 & 4) | (z1 & 2) | (z2 & 1); | |
100 | } | |
101 | */ | |
102 | ||
103 | void opt_successor(const uint8_t *k, State *s, bool y, State *successor) { | |
104 | uint8_t Tt = 1 & opt_T(s); | |
105 | ||
106 | successor->t = (s->t >> 1); | |
107 | successor->t |= (Tt ^ (s->r >> 7 & 0x1) ^ (s->r >> 3 & 0x1)) << 15; | |
108 | ||
109 | successor->b = s->b >> 1; | |
110 | successor->b |= (opt_B(s) ^ (s->r & 0x1)) << 7; | |
111 | ||
112 | successor->r = (k[opt__select(Tt, y, s->r)] ^ successor->b) + s->l ; | |
113 | successor->l = successor->r + s->r; | |
114 | } | |
115 | ||
116 | void opt_suc(const uint8_t *k, State *s, uint8_t *in, uint8_t length, bool add32Zeroes) { | |
117 | State x2; | |
118 | for (int i = 0; i < length; i++) { | |
119 | uint8_t head; | |
120 | head = 1 & (in[i] >> 7); | |
121 | opt_successor(k, s, head, &x2); | |
122 | ||
123 | head = 1 & (in[i] >> 6); | |
124 | opt_successor(k, &x2, head, s); | |
125 | ||
126 | head = 1 & (in[i] >> 5); | |
127 | opt_successor(k, s, head, &x2); | |
128 | ||
129 | head = 1 & (in[i] >> 4); | |
130 | opt_successor(k, &x2, head, s); | |
131 | ||
132 | head = 1 & (in[i] >> 3); | |
133 | opt_successor(k, s, head, &x2); | |
134 | ||
135 | head = 1 & (in[i] >> 2); | |
136 | opt_successor(k, &x2, head, s); | |
137 | ||
138 | head = 1 & (in[i] >> 1); | |
139 | opt_successor(k, s, head, &x2); | |
140 | ||
141 | head = 1 & in[i]; | |
142 | opt_successor(k, &x2, head, s); | |
143 | } | |
144 | //For tag MAC, an additional 32 zeroes | |
145 | if (add32Zeroes) { | |
146 | for(int i = 0; i < 16; i++) { | |
147 | opt_successor(k, s, 0, &x2); | |
148 | opt_successor(k, &x2, 0, s); | |
149 | } | |
150 | } | |
151 | } | |
152 | ||
153 | void opt_output(const uint8_t *k, State *s, uint8_t *buffer) { | |
154 | State temp = {0, 0, 0, 0}; | |
155 | for (uint8_t times = 0; times < 4; times++) { | |
156 | uint8_t bout = 0; | |
157 | bout |= (s->r & 0x4) << 5; | |
158 | opt_successor(k, s, 0, &temp); | |
159 | bout |= (temp.r & 0x4) << 4; | |
160 | opt_successor(k, &temp, 0, s); | |
161 | bout |= (s->r & 0x4) << 3; | |
162 | opt_successor(k, s, 0, &temp); | |
163 | bout |= (temp.r & 0x4) << 2; | |
164 | opt_successor(k, &temp, 0, s); | |
165 | bout |= (s->r & 0x4) << 1; | |
166 | opt_successor(k, s, 0, &temp); | |
167 | bout |= (temp.r & 0x4) ; | |
168 | opt_successor(k, &temp, 0, s); | |
169 | bout |= (s->r & 0x4) >> 1; | |
170 | opt_successor(k, s, 0, &temp); | |
171 | bout |= (temp.r & 0x4) >> 2; | |
172 | opt_successor(k, &temp, 0, s); | |
173 | buffer[times] = bout; | |
174 | } | |
175 | } | |
176 | ||
177 | void opt_MAC(uint8_t *k, uint8_t *input, uint8_t *out) { | |
178 | State _init = { | |
179 | ((k[0] ^ 0x4c) + 0xEC) & 0xFF,// l | |
180 | ((k[0] ^ 0x4c) + 0x21) & 0xFF,// r | |
181 | 0x4c, // b | |
182 | 0xE012 // t | |
183 | }; | |
184 | ||
185 | opt_suc(k, &_init, input, 12, false); | |
186 | //printf("\noutp "); | |
187 | opt_output(k, &_init, out); | |
188 | } | |
189 | ||
190 | uint8_t rev_byte(uint8_t b) { | |
191 | b = (b & 0xF0) >> 4 | (b & 0x0F) << 4; | |
192 | b = (b & 0xCC) >> 2 | (b & 0x33) << 2; | |
193 | b = (b & 0xAA) >> 1 | (b & 0x55) << 1; | |
194 | return b; | |
195 | } | |
196 | ||
197 | void opt_reverse_arraybytecpy(uint8_t *dest, uint8_t *src, size_t len) { | |
198 | for (size_t i = 0; i < len; i++) { | |
199 | dest[i] = rev_byte(src[i]); | |
200 | } | |
201 | } | |
202 | ||
203 | void opt_doReaderMAC(uint8_t *cc_nr_p, uint8_t *div_key_p, uint8_t mac[4]) { | |
204 | static uint8_t cc_nr[12]; | |
205 | opt_reverse_arraybytecpy(cc_nr, cc_nr_p, 12); | |
206 | uint8_t dest[] = {0, 0, 0, 0, 0, 0, 0, 0}; | |
207 | opt_MAC(div_key_p, cc_nr, dest); | |
208 | //The output MAC must also be reversed | |
209 | opt_reverse_arraybytecpy(mac, dest, 4); | |
210 | return; | |
211 | } | |
212 | ||
213 | void opt_doTagMAC(uint8_t *cc_p, const uint8_t *div_key_p, uint8_t mac[4]) { | |
214 | static uint8_t cc_nr[8+4+4]; | |
215 | opt_reverse_arraybytecpy(cc_nr, cc_p, 12); | |
216 | State _init = { | |
217 | ((div_key_p[0] ^ 0x4c) + 0xEC) & 0xFF,// l | |
218 | ((div_key_p[0] ^ 0x4c) + 0x21) & 0xFF,// r | |
219 | 0x4c, // b | |
220 | 0xE012 // t | |
221 | }; | |
222 | opt_suc(div_key_p, &_init,cc_nr, 12, true); | |
223 | uint8_t dest[] = {0, 0, 0, 0}; | |
224 | opt_output(div_key_p, &_init, dest); | |
225 | //The output MAC must also be reversed | |
226 | opt_reverse_arraybytecpy(mac, dest, 4); | |
227 | return; | |
228 | } | |
229 | ||
230 | /** | |
231 | * The tag MAC can be divided (both can, but no point in dividing the reader mac) into | |
232 | * two functions, since the first 8 bytes are known, we can pre-calculate the state | |
233 | * reached after feeding CC to the cipher. | |
234 | * @param cc_p | |
235 | * @param div_key_p | |
236 | * @return the cipher state | |
237 | */ | |
238 | State opt_doTagMAC_1(uint8_t *cc_p, const uint8_t *div_key_p) { | |
239 | static uint8_t cc_nr[8]; | |
240 | opt_reverse_arraybytecpy(cc_nr, cc_p, 8); | |
241 | State _init = { | |
242 | ((div_key_p[0] ^ 0x4c) + 0xEC) & 0xFF,// l | |
243 | ((div_key_p[0] ^ 0x4c) + 0x21) & 0xFF,// r | |
244 | 0x4c, // b | |
245 | 0xE012 // t | |
246 | }; | |
247 | opt_suc(div_key_p, &_init, cc_nr, 8, false); | |
248 | return _init; | |
249 | } | |
250 | ||
251 | /** | |
252 | * The second part of the tag MAC calculation, since the CC is already calculated into the state, | |
253 | * this function is fed only the NR, and internally feeds the remaining 32 0-bits to generate the tag | |
254 | * MAC response. | |
255 | * @param _init - precalculated cipher state | |
256 | * @param nr - the reader challenge | |
257 | * @param mac - where to store the MAC | |
258 | * @param div_key_p - the key to use | |
259 | */ | |
260 | void opt_doTagMAC_2(State _init, uint8_t *nr, uint8_t mac[4], const uint8_t *div_key_p) { | |
261 | static uint8_t _nr[4]; | |
262 | opt_reverse_arraybytecpy(_nr, nr, 4); | |
263 | opt_suc(div_key_p, &_init, _nr, 4, true); | |
264 | //opt_suc(div_key_p, &_init,nr, 4, false); | |
265 | uint8_t dest[] = {0, 0, 0, 0}; | |
266 | opt_output(div_key_p, &_init, dest); | |
267 | //The output MAC must also be reversed | |
268 | opt_reverse_arraybytecpy(mac, dest, 4); | |
269 | return; | |
270 | } |