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 #ifdef __cplusplus 51 extern "C" { 52 #endif 53 54 /*- 55 * The boolean methods return a bitmask of all ones (0xff...f) for true 56 * and 0 for false. This is useful for choosing a value based on the result 57 * of a conditional in constant time. For example, 58 * 59 * if (a < b) { 60 * c = a; 61 * } else { 62 * c = b; 63 * } 64 * 65 * can be written as 66 * 67 * unsigned int lt = constant_time_lt(a, b); 68 * c = constant_time_select(lt, a, b); 69 */ 70 71 /* 72 * Returns the given value with the MSB copied to all the other 73 * bits. Uses the fact that arithmetic shift shifts-in the sign bit. 74 * However, this is not ensured by the C standard so you may need to 75 * replace this with something else on odd CPUs. 76 */ 77 static inline unsigned int constant_time_msb(unsigned int a); 78 79 /* 80 * Returns 0xff..f if a < b and 0 otherwise. 81 */ 82 static inline unsigned int constant_time_lt(unsigned int a, unsigned int b); 83 /* Convenience method for getting an 8-bit mask. */ 84 static inline unsigned char constant_time_lt_8(unsigned int a, 85 unsigned int b); 86 87 /* 88 * Returns 0xff..f if a >= b and 0 otherwise. 89 */ 90 static inline unsigned int constant_time_ge(unsigned int a, unsigned int b); 91 /* Convenience method for getting an 8-bit mask. */ 92 static inline unsigned char constant_time_ge_8(unsigned int a, 93 unsigned int b); 94 95 /* 96 * Returns 0xff..f if a == 0 and 0 otherwise. 97 */ 98 static inline unsigned int constant_time_is_zero(unsigned int a); 99 /* Convenience method for getting an 8-bit mask. */ 100 static inline unsigned char constant_time_is_zero_8(unsigned int a); 101 102 /* 103 * Returns 0xff..f if a == b and 0 otherwise. 104 */ 105 static inline unsigned int constant_time_eq(unsigned int a, unsigned int b); 106 /* Convenience method for getting an 8-bit mask. */ 107 static inline unsigned char constant_time_eq_8(unsigned int a, 108 unsigned int b); 109 /* Signed integers. */ 110 static inline unsigned int constant_time_eq_int(int a, int b); 111 /* Convenience method for getting an 8-bit mask. */ 112 static inline unsigned char constant_time_eq_int_8(int a, int b); 113 114 /*- 115 * Returns (mask & a) | (~mask & b). 116 * 117 * When |mask| is all 1s or all 0s (as returned by the methods above), 118 * the select methods return either |a| (if |mask| is nonzero) or |b| 119 * (if |mask| is zero). 120 */ 121 static inline unsigned int constant_time_select(unsigned int mask, 122 unsigned int a, 123 unsigned int b); 124 /* Convenience method for unsigned chars. */ 125 static inline unsigned char constant_time_select_8(unsigned char mask, 126 unsigned char a, 127 unsigned char b); 128 /* Convenience method for signed integers. */ 129 static inline int constant_time_select_int(unsigned int mask, int a, int b); 130 131 static inline unsigned int constant_time_msb(unsigned int a) 132 { 133 return 0 - (a >> (sizeof(a) * 8 - 1)); 134 } 135 136 static inline unsigned int constant_time_lt(unsigned int a, unsigned int b) 137 { 138 return constant_time_msb(a ^ ((a ^ b) | ((a - b) ^ b))); 139 } 140 141 static inline unsigned char constant_time_lt_8(unsigned int a, unsigned int b) 142 { 143 return (unsigned char)(constant_time_lt(a, b)); 144 } 145 146 static inline unsigned int constant_time_ge(unsigned int a, unsigned int b) 147 { 148 return ~constant_time_lt(a, b); 149 } 150 151 static inline unsigned char constant_time_ge_8(unsigned int a, unsigned int b) 152 { 153 return (unsigned char)(constant_time_ge(a, b)); 154 } 155 156 static inline unsigned int constant_time_is_zero(unsigned int a) 157 { 158 return constant_time_msb(~a & (a - 1)); 159 } 160 161 static inline unsigned char constant_time_is_zero_8(unsigned int a) 162 { 163 return (unsigned char)(constant_time_is_zero(a)); 164 } 165 166 static inline unsigned int constant_time_eq(unsigned int a, unsigned int b) 167 { 168 return constant_time_is_zero(a ^ b); 169 } 170 171 static inline unsigned char constant_time_eq_8(unsigned int a, unsigned int b) 172 { 173 return (unsigned char)(constant_time_eq(a, b)); 174 } 175 176 static inline unsigned int constant_time_eq_int(int a, int b) 177 { 178 return constant_time_eq((unsigned)(a), (unsigned)(b)); 179 } 180 181 static inline unsigned char constant_time_eq_int_8(int a, int b) 182 { 183 return constant_time_eq_8((unsigned)(a), (unsigned)(b)); 184 } 185 186 static inline unsigned int constant_time_select(unsigned int mask, 187 unsigned int a, 188 unsigned int b) 189 { 190 return (mask & a) | (~mask & b); 191 } 192 193 static inline unsigned char constant_time_select_8(unsigned char mask, 194 unsigned char a, 195 unsigned char b) 196 { 197 return (unsigned char)(constant_time_select(mask, a, b)); 198 } 199 200 static inline int constant_time_select_int(unsigned int mask, int a, int b) 201 { 202 return (int)(constant_time_select(mask, (unsigned)(a), (unsigned)(b))); 203 } 204 205 #ifdef __cplusplus 206 } 207 #endif 208 209 #endif /* HEADER_CONSTANT_TIME_LOCL_H */ 210