1 /*
2 * Copyright 2014-2018 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the OpenSSL license (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
8 */
9
10 #ifndef HEADER_CONSTANT_TIME_LOCL_H
11 # define HEADER_CONSTANT_TIME_LOCL_H
12
13 # include <stdlib.h>
14 # include <string.h>
15 # include <openssl/e_os2.h> /* For 'ossl_inline' */
16
17 /*-
18 * The boolean methods return a bitmask of all ones (0xff...f) for true
19 * and 0 for false. This is useful for choosing a value based on the result
20 * of a conditional in constant time. For example,
21 * if (a < b) {
22 * c = a;
23 * } else {
24 * c = b;
25 * }
26 * can be written as
27 * unsigned int lt = constant_time_lt(a, b);
28 * c = constant_time_select(lt, a, b);
29 */
30
31 /* Returns the given value with the MSB copied to all the other bits. */
32 static ossl_inline unsigned int constant_time_msb(unsigned int a);
33 /* Convenience method for uint32_t. */
34 static ossl_inline uint32_t constant_time_msb_32(uint32_t a);
35 /* Convenience method for uint64_t. */
36 static ossl_inline uint64_t constant_time_msb_64(uint64_t a);
37
38 /* Returns 0xff..f if a < b and 0 otherwise. */
39 static ossl_inline unsigned int constant_time_lt(unsigned int a,
40 unsigned int b);
41 /* Convenience method for getting an 8-bit mask. */
42 static ossl_inline unsigned char constant_time_lt_8(unsigned int a,
43 unsigned int b);
44 /* Convenience method for uint64_t. */
45 static ossl_inline uint64_t constant_time_lt_64(uint64_t a, uint64_t b);
46
47 /* Returns 0xff..f if a >= b and 0 otherwise. */
48 static ossl_inline unsigned int constant_time_ge(unsigned int a,
49 unsigned int b);
50 /* Convenience method for getting an 8-bit mask. */
51 static ossl_inline unsigned char constant_time_ge_8(unsigned int a,
52 unsigned int b);
53
54 /* Returns 0xff..f if a == 0 and 0 otherwise. */
55 static ossl_inline unsigned int constant_time_is_zero(unsigned int a);
56 /* Convenience method for getting an 8-bit mask. */
57 static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a);
58 /* Convenience method for getting a 32-bit mask. */
59 static ossl_inline uint32_t constant_time_is_zero_32(uint32_t a);
60
61 /* Returns 0xff..f if a == b and 0 otherwise. */
62 static ossl_inline unsigned int constant_time_eq(unsigned int a,
63 unsigned int b);
64 /* Convenience method for getting an 8-bit mask. */
65 static ossl_inline unsigned char constant_time_eq_8(unsigned int a,
66 unsigned int b);
67 /* Signed integers. */
68 static ossl_inline unsigned int constant_time_eq_int(int a, int b);
69 /* Convenience method for getting an 8-bit mask. */
70 static ossl_inline unsigned char constant_time_eq_int_8(int a, int b);
71
72 /*-
73 * Returns (mask & a) | (~mask & b).
74 *
75 * When |mask| is all 1s or all 0s (as returned by the methods above),
76 * the select methods return either |a| (if |mask| is nonzero) or |b|
77 * (if |mask| is zero).
78 */
79 static ossl_inline unsigned int constant_time_select(unsigned int mask,
80 unsigned int a,
81 unsigned int b);
82 /* Convenience method for unsigned chars. */
83 static ossl_inline unsigned char constant_time_select_8(unsigned char mask,
84 unsigned char a,
85 unsigned char b);
86
87 /* Convenience method for uint32_t. */
88 static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a,
89 uint32_t b);
90
91 /* Convenience method for uint64_t. */
92 static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a,
93 uint64_t b);
94 /* Convenience method for signed integers. */
95 static ossl_inline int constant_time_select_int(unsigned int mask, int a,
96 int b);
97
98
constant_time_msb(unsigned int a)99 static ossl_inline unsigned int constant_time_msb(unsigned int a)
100 {
101 return 0 - (a >> (sizeof(a) * 8 - 1));
102 }
103
104
constant_time_msb_32(uint32_t a)105 static ossl_inline uint32_t constant_time_msb_32(uint32_t a)
106 {
107 return 0 - (a >> 31);
108 }
109
constant_time_msb_64(uint64_t a)110 static ossl_inline uint64_t constant_time_msb_64(uint64_t a)
111 {
112 return 0 - (a >> 63);
113 }
114
constant_time_msb_s(size_t a)115 static ossl_inline size_t constant_time_msb_s(size_t a)
116 {
117 return 0 - (a >> (sizeof(a) * 8 - 1));
118 }
119
constant_time_lt(unsigned int a,unsigned int b)120 static ossl_inline unsigned int constant_time_lt(unsigned int a,
121 unsigned int b)
122 {
123 return constant_time_msb(a ^ ((a ^ b) | ((a - b) ^ b)));
124 }
125
constant_time_lt_s(size_t a,size_t b)126 static ossl_inline size_t constant_time_lt_s(size_t a, size_t b)
127 {
128 return constant_time_msb_s(a ^ ((a ^ b) | ((a - b) ^ b)));
129 }
130
constant_time_lt_8(unsigned int a,unsigned int b)131 static ossl_inline unsigned char constant_time_lt_8(unsigned int a,
132 unsigned int b)
133 {
134 return (unsigned char)constant_time_lt(a, b);
135 }
136
constant_time_lt_64(uint64_t a,uint64_t b)137 static ossl_inline uint64_t constant_time_lt_64(uint64_t a, uint64_t b)
138 {
139 return constant_time_msb_64(a ^ ((a ^ b) | ((a - b) ^ b)));
140 }
141
constant_time_ge(unsigned int a,unsigned int b)142 static ossl_inline unsigned int constant_time_ge(unsigned int a,
143 unsigned int b)
144 {
145 return ~constant_time_lt(a, b);
146 }
147
constant_time_ge_s(size_t a,size_t b)148 static ossl_inline size_t constant_time_ge_s(size_t a, size_t b)
149 {
150 return ~constant_time_lt_s(a, b);
151 }
152
constant_time_ge_8(unsigned int a,unsigned int b)153 static ossl_inline unsigned char constant_time_ge_8(unsigned int a,
154 unsigned int b)
155 {
156 return (unsigned char)constant_time_ge(a, b);
157 }
158
constant_time_ge_8_s(size_t a,size_t b)159 static ossl_inline unsigned char constant_time_ge_8_s(size_t a, size_t b)
160 {
161 return (unsigned char)constant_time_ge_s(a, b);
162 }
163
constant_time_is_zero(unsigned int a)164 static ossl_inline unsigned int constant_time_is_zero(unsigned int a)
165 {
166 return constant_time_msb(~a & (a - 1));
167 }
168
constant_time_is_zero_s(size_t a)169 static ossl_inline size_t constant_time_is_zero_s(size_t a)
170 {
171 return constant_time_msb_s(~a & (a - 1));
172 }
173
constant_time_is_zero_8(unsigned int a)174 static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a)
175 {
176 return (unsigned char)constant_time_is_zero(a);
177 }
178
constant_time_is_zero_32(uint32_t a)179 static ossl_inline uint32_t constant_time_is_zero_32(uint32_t a)
180 {
181 return constant_time_msb_32(~a & (a - 1));
182 }
183
constant_time_eq(unsigned int a,unsigned int b)184 static ossl_inline unsigned int constant_time_eq(unsigned int a,
185 unsigned int b)
186 {
187 return constant_time_is_zero(a ^ b);
188 }
189
constant_time_eq_s(size_t a,size_t b)190 static ossl_inline size_t constant_time_eq_s(size_t a, size_t b)
191 {
192 return constant_time_is_zero_s(a ^ b);
193 }
194
constant_time_eq_8(unsigned int a,unsigned int b)195 static ossl_inline unsigned char constant_time_eq_8(unsigned int a,
196 unsigned int b)
197 {
198 return (unsigned char)constant_time_eq(a, b);
199 }
200
constant_time_eq_8_s(size_t a,size_t b)201 static ossl_inline unsigned char constant_time_eq_8_s(size_t a, size_t b)
202 {
203 return (unsigned char)constant_time_eq_s(a, b);
204 }
205
constant_time_eq_int(int a,int b)206 static ossl_inline unsigned int constant_time_eq_int(int a, int b)
207 {
208 return constant_time_eq((unsigned)(a), (unsigned)(b));
209 }
210
constant_time_eq_int_8(int a,int b)211 static ossl_inline unsigned char constant_time_eq_int_8(int a, int b)
212 {
213 return constant_time_eq_8((unsigned)(a), (unsigned)(b));
214 }
215
constant_time_select(unsigned int mask,unsigned int a,unsigned int b)216 static ossl_inline unsigned int constant_time_select(unsigned int mask,
217 unsigned int a,
218 unsigned int b)
219 {
220 return (mask & a) | (~mask & b);
221 }
222
constant_time_select_s(size_t mask,size_t a,size_t b)223 static ossl_inline size_t constant_time_select_s(size_t mask,
224 size_t a,
225 size_t b)
226 {
227 return (mask & a) | (~mask & b);
228 }
229
constant_time_select_8(unsigned char mask,unsigned char a,unsigned char b)230 static ossl_inline unsigned char constant_time_select_8(unsigned char mask,
231 unsigned char a,
232 unsigned char b)
233 {
234 return (unsigned char)constant_time_select(mask, a, b);
235 }
236
constant_time_select_int(unsigned int mask,int a,int b)237 static ossl_inline int constant_time_select_int(unsigned int mask, int a,
238 int b)
239 {
240 return (int)constant_time_select(mask, (unsigned)(a), (unsigned)(b));
241 }
242
constant_time_select_int_s(size_t mask,int a,int b)243 static ossl_inline int constant_time_select_int_s(size_t mask, int a, int b)
244 {
245 return (int)constant_time_select((unsigned)mask, (unsigned)(a),
246 (unsigned)(b));
247 }
248
constant_time_select_32(uint32_t mask,uint32_t a,uint32_t b)249 static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a,
250 uint32_t b)
251 {
252 return (mask & a) | (~mask & b);
253 }
254
constant_time_select_64(uint64_t mask,uint64_t a,uint64_t b)255 static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a,
256 uint64_t b)
257 {
258 return (mask & a) | (~mask & b);
259 }
260
261 /*
262 * mask must be 0xFFFFFFFF or 0x00000000.
263 *
264 * if (mask) {
265 * uint32_t tmp = *a;
266 *
267 * *a = *b;
268 * *b = tmp;
269 * }
270 */
constant_time_cond_swap_32(uint32_t mask,uint32_t * a,uint32_t * b)271 static ossl_inline void constant_time_cond_swap_32(uint32_t mask, uint32_t *a,
272 uint32_t *b)
273 {
274 uint32_t xor = *a ^ *b;
275
276 xor &= mask;
277 *a ^= xor;
278 *b ^= xor;
279 }
280
281 /*
282 * mask must be 0xFFFFFFFF or 0x00000000.
283 *
284 * if (mask) {
285 * uint64_t tmp = *a;
286 *
287 * *a = *b;
288 * *b = tmp;
289 * }
290 */
constant_time_cond_swap_64(uint64_t mask,uint64_t * a,uint64_t * b)291 static ossl_inline void constant_time_cond_swap_64(uint64_t mask, uint64_t *a,
292 uint64_t *b)
293 {
294 uint64_t xor = *a ^ *b;
295
296 xor &= mask;
297 *a ^= xor;
298 *b ^= xor;
299 }
300
301 /*
302 * table is a two dimensional array of bytes. Each row has rowsize elements.
303 * Copies row number idx into out. rowsize and numrows are not considered
304 * private.
305 */
constant_time_lookup(void * out,const void * table,size_t rowsize,size_t numrows,size_t idx)306 static ossl_inline void constant_time_lookup(void *out,
307 const void *table,
308 size_t rowsize,
309 size_t numrows,
310 size_t idx)
311 {
312 size_t i, j;
313 const unsigned char *tablec = (const unsigned char *)table;
314 unsigned char *outc = (unsigned char *)out;
315 unsigned char mask;
316
317 memset(out, 0, rowsize);
318
319 /* Note idx may underflow - but that is well defined */
320 for (i = 0; i < numrows; i++, idx--) {
321 mask = (unsigned char)constant_time_is_zero_s(idx);
322 for (j = 0; j < rowsize; j++)
323 *(outc + j) |= constant_time_select_8(mask, *(tablec++), 0);
324 }
325 }
326
327 /*
328 * Expected usage pattern is to unconditionally set error and then
329 * wipe it if there was no actual error. |clear| is 1 or 0.
330 */
331 void err_clear_last_constant_time(int clear);
332
333 #endif /* HEADER_CONSTANT_TIME_LOCL_H */
334