constant_time_locl.h revision 296341
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 53extern "C" { 54#endif 55 56/*- 57 * The boolean 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 = constant_time_select(lt, a, b); 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 */ 79static inline unsigned int constant_time_msb(unsigned int a); 80 81/* 82 * Returns 0xff..f if a < b and 0 otherwise. 83 */ 84static inline unsigned int constant_time_lt(unsigned int a, unsigned int b); 85/* Convenience method for getting an 8-bit mask. */ 86static inline unsigned char constant_time_lt_8(unsigned int a, 87 unsigned int b); 88 89/* 90 * Returns 0xff..f if a >= b and 0 otherwise. 91 */ 92static inline unsigned int constant_time_ge(unsigned int a, unsigned int b); 93/* Convenience method for getting an 8-bit mask. */ 94static inline unsigned char constant_time_ge_8(unsigned int a, 95 unsigned int b); 96 97/* 98 * Returns 0xff..f if a == 0 and 0 otherwise. 99 */ 100static inline unsigned int constant_time_is_zero(unsigned int a); 101/* Convenience method for getting an 8-bit mask. */ 102static inline unsigned char constant_time_is_zero_8(unsigned int a); 103 104/* 105 * Returns 0xff..f if a == b and 0 otherwise. 106 */ 107static inline unsigned int constant_time_eq(unsigned int a, unsigned int b); 108/* Convenience method for getting an 8-bit mask. */ 109static inline unsigned char constant_time_eq_8(unsigned int a, 110 unsigned int b); 111/* Signed integers. */ 112static inline unsigned int constant_time_eq_int(int a, int b); 113/* Convenience method for getting an 8-bit mask. */ 114static inline unsigned char constant_time_eq_int_8(int a, int b); 115 116/*- 117 * Returns (mask & a) | (~mask & b). 118 * 119 * When |mask| is all 1s or all 0s (as returned by the methods above), 120 * the select methods return either |a| (if |mask| is nonzero) or |b| 121 * (if |mask| is zero). 122 */ 123static inline unsigned int constant_time_select(unsigned int mask, 124 unsigned int a, 125 unsigned int b); 126/* Convenience method for unsigned chars. */ 127static inline unsigned char constant_time_select_8(unsigned char mask, 128 unsigned char a, 129 unsigned char b); 130/* Convenience method for signed integers. */ 131static inline int constant_time_select_int(unsigned int mask, int a, int b); 132 133static inline unsigned int constant_time_msb(unsigned int a) 134{ 135 return 0 - (a >> (sizeof(a) * 8 - 1)); 136} 137 138static inline unsigned int constant_time_lt(unsigned int a, unsigned int b) 139{ 140 return constant_time_msb(a ^ ((a ^ b) | ((a - b) ^ b))); 141} 142 143static inline unsigned char constant_time_lt_8(unsigned int a, unsigned int b) 144{ 145 return (unsigned char)(constant_time_lt(a, b)); 146} 147 148static inline unsigned int constant_time_ge(unsigned int a, unsigned int b) 149{ 150 return ~constant_time_lt(a, b); 151} 152 153static inline unsigned char constant_time_ge_8(unsigned int a, unsigned int b) 154{ 155 return (unsigned char)(constant_time_ge(a, b)); 156} 157 158static inline unsigned int constant_time_is_zero(unsigned int a) 159{ 160 return constant_time_msb(~a & (a - 1)); 161} 162 163static inline unsigned char constant_time_is_zero_8(unsigned int a) 164{ 165 return (unsigned char)(constant_time_is_zero(a)); 166} 167 168static inline unsigned int constant_time_eq(unsigned int a, unsigned int b) 169{ 170 return constant_time_is_zero(a ^ b); 171} 172 173static inline unsigned char constant_time_eq_8(unsigned int a, unsigned int b) 174{ 175 return (unsigned char)(constant_time_eq(a, b)); 176} 177 178static inline unsigned int constant_time_eq_int(int a, int b) 179{ 180 return constant_time_eq((unsigned)(a), (unsigned)(b)); 181} 182 183static inline unsigned char constant_time_eq_int_8(int a, int b) 184{ 185 return constant_time_eq_8((unsigned)(a), (unsigned)(b)); 186} 187 188static inline unsigned int constant_time_select(unsigned int mask, 189 unsigned int a, 190 unsigned int b) 191{ 192 return (mask & a) | (~mask & b); 193} 194 195static inline unsigned char constant_time_select_8(unsigned char mask, 196 unsigned char a, 197 unsigned char b) 198{ 199 return (unsigned char)(constant_time_select(mask, a, b)); 200} 201 202static inline int constant_time_select_int(unsigned int mask, int a, int b) 203{ 204 return (int)(constant_time_select(mask, (unsigned)(a), (unsigned)(b))); 205} 206 207#ifdef __cplusplus 208} 209#endif 210 211#endif /* HEADER_CONSTANT_TIME_LOCL_H */ 212