]>
Commit | Line | Data |
---|---|---|
5a3d21c0 EK |
1 | /* crypto/constant_time_locl.h */ |
2 | /* | |
3 | * Utilities for constant-time cryptography. | |
4 | * | |
5 | * Author: Emilia Kasper (emilia@openssl.org) | |
6 | * Based on previous work by Bodo Moeller, Emilia Kasper, Adam Langley | |
7 | * (Google). | |
8 | * ==================================================================== | |
9 | * Copyright (c) 2014 The OpenSSL Project. All rights reserved. | |
10 | * | |
11 | * Redistribution and use in source and binary forms, with or without | |
12 | * modification, are permitted provided that the following conditions | |
13 | * are met: | |
14 | * 1. Redistributions of source code must retain the copyright | |
15 | * notice, this list of conditions and the following disclaimer. | |
16 | * 2. Redistributions in binary form must reproduce the above copyright | |
17 | * notice, this list of conditions and the following disclaimer in the | |
18 | * documentation and/or other materials provided with the distribution. | |
19 | * 3. All advertising materials mentioning features or use of this software | |
20 | * must display the following acknowledgement: | |
21 | * "This product includes cryptographic software written by | |
22 | * Eric Young (eay@cryptsoft.com)" | |
23 | * The word 'cryptographic' can be left out if the rouines from the library | |
24 | * being used are not cryptographic related :-). | |
25 | * 4. If you include any Windows specific code (or a derivative thereof) from | |
26 | * the apps directory (application code) you must include an acknowledgement: | |
27 | * "This product includes software written by Tim Hudson (tjh@cryptsoft.com)" | |
28 | * | |
29 | * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND | |
30 | * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |
31 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |
32 | * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE | |
33 | * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |
34 | * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | |
35 | * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |
36 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |
37 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | |
38 | * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |
39 | * SUCH DAMAGE. | |
40 | * | |
41 | * The licence and distribution terms for any publically available version or | |
42 | * derivative of this code cannot be changed. i.e. this code cannot simply be | |
43 | * copied and put under another distribution licence | |
44 | * [including the GNU Public Licence.] | |
45 | */ | |
46 | ||
47 | #ifndef HEADER_CONSTANT_TIME_LOCL_H | |
48 | #define HEADER_CONSTANT_TIME_LOCL_H | |
49 | ||
50 | #include "e_os.h" /* For 'inline' */ | |
51 | ||
52 | #ifdef __cplusplus | |
53 | extern "C" { | |
54 | #endif | |
55 | ||
56 | /* | |
57 | * The following methods return a bitmask of all ones (0xff...f) for true | |
58 | * and 0 for false. This is useful for choosing a value based on the result | |
59 | * of a conditional in constant time. For example, | |
60 | * | |
61 | * if (a < b) { | |
62 | * c = a; | |
63 | * } else { | |
64 | * c = b; | |
65 | * } | |
66 | * | |
67 | * can be written as | |
68 | * | |
69 | * unsigned int lt = constant_time_lt(a, b); | |
70 | * c = a & lt | b & ~lt; | |
71 | */ | |
72 | ||
73 | /* | |
74 | * Returns the given value with the MSB copied to all the other | |
75 | * bits. Uses the fact that arithmetic shift shifts-in the sign bit. | |
76 | * However, this is not ensured by the C standard so you may need to | |
77 | * replace this with something else on odd CPUs. | |
78 | */ | |
79 | static inline unsigned int constant_time_msb(unsigned int a); | |
80 | ||
81 | /* | |
82 | * Returns 0xff..f if a < b and 0 otherwise. | |
83 | */ | |
86f50b36 | 84 | static inline unsigned int constant_time_lt(unsigned int a, unsigned int b); |
5a3d21c0 | 85 | /* Convenience method for getting an 8-bit mask. */ |
86f50b36 | 86 | static inline unsigned char constant_time_lt_8(unsigned int a, unsigned int b); |
5a3d21c0 EK |
87 | |
88 | /* | |
89 | * Returns 0xff..f if a >= b and 0 otherwise. | |
90 | */ | |
86f50b36 | 91 | static inline unsigned int constant_time_ge(unsigned int a, unsigned int b); |
5a3d21c0 | 92 | /* Convenience method for getting an 8-bit mask. */ |
86f50b36 | 93 | static inline unsigned char constant_time_ge_8(unsigned int a, unsigned int b); |
5a3d21c0 EK |
94 | |
95 | /* | |
96 | * Returns 0xff..f if a == 0 and 0 otherwise. | |
97 | */ | |
86f50b36 | 98 | static inline unsigned int constant_time_is_zero(unsigned int a); |
5a3d21c0 | 99 | /* Convenience method for getting an 8-bit mask. */ |
86f50b36 | 100 | static inline unsigned char constant_time_is_zero_8(unsigned int a); |
5a3d21c0 EK |
101 | |
102 | ||
103 | /* | |
104 | * Returns 0xff..f if a == b and 0 otherwise. | |
105 | */ | |
86f50b36 | 106 | static inline unsigned int constant_time_eq(unsigned int a, unsigned int b); |
5a3d21c0 | 107 | /* Convenience method for getting an 8-bit mask. */ |
86f50b36 | 108 | static inline unsigned char constant_time_eq_8(unsigned int a, unsigned int b); |
5a3d21c0 EK |
109 | |
110 | static inline unsigned int constant_time_msb(unsigned int a) | |
111 | { | |
112 | return (unsigned int)((int)(a) >> (sizeof(int) * 8 - 1)); | |
113 | } | |
114 | ||
86f50b36 | 115 | static inline unsigned int constant_time_lt(unsigned int a, unsigned int b) |
5a3d21c0 EK |
116 | { |
117 | unsigned int lt; | |
118 | /* Case 1: msb(a) == msb(b). a < b iff the MSB of a - b is set.*/ | |
119 | lt = ~(a ^ b) & (a - b); | |
120 | /* Case 2: msb(a) != msb(b). a < b iff the MSB of b is set. */ | |
121 | lt |= ~a & b; | |
122 | return constant_time_msb(lt); | |
123 | } | |
124 | ||
86f50b36 | 125 | static inline unsigned char constant_time_lt_8(unsigned int a, unsigned int b) |
5a3d21c0 EK |
126 | { |
127 | return (unsigned char)(constant_time_lt(a, b)); | |
128 | } | |
129 | ||
86f50b36 | 130 | static inline unsigned int constant_time_ge(unsigned int a, unsigned int b) |
5a3d21c0 EK |
131 | { |
132 | unsigned int ge; | |
133 | /* Case 1: msb(a) == msb(b). a >= b iff the MSB of a - b is not set.*/ | |
134 | ge = ~((a ^ b) | (a - b)); | |
135 | /* Case 2: msb(a) != msb(b). a >= b iff the MSB of a is set. */ | |
136 | ge |= a & ~b; | |
137 | return constant_time_msb(ge); | |
138 | } | |
139 | ||
86f50b36 | 140 | static inline unsigned char constant_time_ge_8(unsigned int a, unsigned int b) |
5a3d21c0 EK |
141 | { |
142 | return (unsigned char)(constant_time_ge(a, b)); | |
143 | } | |
144 | ||
86f50b36 | 145 | static inline unsigned int constant_time_is_zero(unsigned int a) |
5a3d21c0 EK |
146 | { |
147 | return constant_time_msb(~a & (a - 1)); | |
148 | } | |
149 | ||
86f50b36 | 150 | static inline unsigned char constant_time_is_zero_8(unsigned int a) |
5a3d21c0 EK |
151 | { |
152 | return (unsigned char)(constant_time_is_zero(a)); | |
153 | } | |
154 | ||
86f50b36 | 155 | static inline unsigned int constant_time_eq(unsigned int a, unsigned int b) |
5a3d21c0 EK |
156 | { |
157 | return constant_time_is_zero(a ^ b); | |
158 | } | |
159 | ||
86f50b36 | 160 | static inline unsigned char constant_time_eq_8(unsigned int a, unsigned int b) |
5a3d21c0 EK |
161 | { |
162 | return (unsigned char)(constant_time_eq(a, b)); | |
163 | } | |
164 | ||
165 | #ifdef __cplusplus | |
166 | } | |
167 | #endif | |
168 | ||
169 | #endif /* HEADER_CONSTANT_TIME_LOCL_H */ |