1279265Sdelphij/* crypto/constant_time_locl.h */ 2296465Sdelphij/*- 3279265Sdelphij * Utilities for constant-time cryptography. 4279265Sdelphij * 5279265Sdelphij * Author: Emilia Kasper (emilia@openssl.org) 6279265Sdelphij * Based on previous work by Bodo Moeller, Emilia Kasper, Adam Langley 7279265Sdelphij * (Google). 8279265Sdelphij * ==================================================================== 9279265Sdelphij * Copyright (c) 2014 The OpenSSL Project. All rights reserved. 10279265Sdelphij * 11279265Sdelphij * Redistribution and use in source and binary forms, with or without 12279265Sdelphij * modification, are permitted provided that the following conditions 13279265Sdelphij * are met: 14279265Sdelphij * 1. Redistributions of source code must retain the copyright 15279265Sdelphij * notice, this list of conditions and the following disclaimer. 16279265Sdelphij * 2. Redistributions in binary form must reproduce the above copyright 17279265Sdelphij * notice, this list of conditions and the following disclaimer in the 18279265Sdelphij * documentation and/or other materials provided with the distribution. 19279265Sdelphij * 3. All advertising materials mentioning features or use of this software 20279265Sdelphij * must display the following acknowledgement: 21279265Sdelphij * "This product includes cryptographic software written by 22279265Sdelphij * Eric Young (eay@cryptsoft.com)" 23279265Sdelphij * The word 'cryptographic' can be left out if the rouines from the library 24279265Sdelphij * being used are not cryptographic related :-). 25279265Sdelphij * 4. If you include any Windows specific code (or a derivative thereof) from 26279265Sdelphij * the apps directory (application code) you must include an acknowledgement: 27279265Sdelphij * "This product includes software written by Tim Hudson (tjh@cryptsoft.com)" 28279265Sdelphij * 29279265Sdelphij * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND 30279265Sdelphij * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 31279265Sdelphij * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 32279265Sdelphij * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 33279265Sdelphij * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 34279265Sdelphij * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 35279265Sdelphij * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 36279265Sdelphij * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 37279265Sdelphij * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 38279265Sdelphij * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 39279265Sdelphij * SUCH DAMAGE. 40279265Sdelphij * 41279265Sdelphij * The licence and distribution terms for any publically available version or 42279265Sdelphij * derivative of this code cannot be changed. i.e. this code cannot simply be 43279265Sdelphij * copied and put under another distribution licence 44279265Sdelphij * [including the GNU Public Licence.] 45279265Sdelphij */ 46279265Sdelphij 47279265Sdelphij#ifndef HEADER_CONSTANT_TIME_LOCL_H 48296465Sdelphij# define HEADER_CONSTANT_TIME_LOCL_H 49279265Sdelphij 50296465Sdelphij# include "e_os.h" /* For 'inline' */ 51279265Sdelphij 52279265Sdelphij#ifdef __cplusplus 53279265Sdelphijextern "C" { 54279265Sdelphij#endif 55279265Sdelphij 56296465Sdelphij/*- 57279265Sdelphij * The boolean methods return a bitmask of all ones (0xff...f) for true 58279265Sdelphij * and 0 for false. This is useful for choosing a value based on the result 59279265Sdelphij * of a conditional in constant time. For example, 60279265Sdelphij * 61279265Sdelphij * if (a < b) { 62279265Sdelphij * c = a; 63279265Sdelphij * } else { 64279265Sdelphij * c = b; 65279265Sdelphij * } 66279265Sdelphij * 67279265Sdelphij * can be written as 68279265Sdelphij * 69279265Sdelphij * unsigned int lt = constant_time_lt(a, b); 70279265Sdelphij * c = constant_time_select(lt, a, b); 71279265Sdelphij */ 72279265Sdelphij 73279265Sdelphij/* 74279265Sdelphij * Returns the given value with the MSB copied to all the other 75279265Sdelphij * bits. Uses the fact that arithmetic shift shifts-in the sign bit. 76279265Sdelphij * However, this is not ensured by the C standard so you may need to 77279265Sdelphij * replace this with something else on odd CPUs. 78279265Sdelphij */ 79279265Sdelphijstatic inline unsigned int constant_time_msb(unsigned int a); 80279265Sdelphij 81279265Sdelphij/* 82279265Sdelphij * Returns 0xff..f if a < b and 0 otherwise. 83279265Sdelphij */ 84279265Sdelphijstatic inline unsigned int constant_time_lt(unsigned int a, unsigned int b); 85279265Sdelphij/* Convenience method for getting an 8-bit mask. */ 86296465Sdelphijstatic inline unsigned char constant_time_lt_8(unsigned int a, 87296465Sdelphij unsigned int b); 88279265Sdelphij 89279265Sdelphij/* 90279265Sdelphij * Returns 0xff..f if a >= b and 0 otherwise. 91279265Sdelphij */ 92279265Sdelphijstatic inline unsigned int constant_time_ge(unsigned int a, unsigned int b); 93279265Sdelphij/* Convenience method for getting an 8-bit mask. */ 94296465Sdelphijstatic inline unsigned char constant_time_ge_8(unsigned int a, 95296465Sdelphij unsigned int b); 96279265Sdelphij 97279265Sdelphij/* 98279265Sdelphij * Returns 0xff..f if a == 0 and 0 otherwise. 99279265Sdelphij */ 100279265Sdelphijstatic inline unsigned int constant_time_is_zero(unsigned int a); 101279265Sdelphij/* Convenience method for getting an 8-bit mask. */ 102279265Sdelphijstatic inline unsigned char constant_time_is_zero_8(unsigned int a); 103279265Sdelphij 104279265Sdelphij/* 105279265Sdelphij * Returns 0xff..f if a == b and 0 otherwise. 106279265Sdelphij */ 107279265Sdelphijstatic inline unsigned int constant_time_eq(unsigned int a, unsigned int b); 108279265Sdelphij/* Convenience method for getting an 8-bit mask. */ 109296465Sdelphijstatic inline unsigned char constant_time_eq_8(unsigned int a, 110296465Sdelphij unsigned int b); 111279265Sdelphij/* Signed integers. */ 112279265Sdelphijstatic inline unsigned int constant_time_eq_int(int a, int b); 113279265Sdelphij/* Convenience method for getting an 8-bit mask. */ 114279265Sdelphijstatic inline unsigned char constant_time_eq_int_8(int a, int b); 115279265Sdelphij 116296465Sdelphij/*- 117279265Sdelphij * Returns (mask & a) | (~mask & b). 118279265Sdelphij * 119279265Sdelphij * When |mask| is all 1s or all 0s (as returned by the methods above), 120279265Sdelphij * the select methods return either |a| (if |mask| is nonzero) or |b| 121279265Sdelphij * (if |mask| is zero). 122279265Sdelphij */ 123279265Sdelphijstatic inline unsigned int constant_time_select(unsigned int mask, 124296465Sdelphij unsigned int a, 125296465Sdelphij unsigned int b); 126279265Sdelphij/* Convenience method for unsigned chars. */ 127279265Sdelphijstatic inline unsigned char constant_time_select_8(unsigned char mask, 128296465Sdelphij unsigned char a, 129296465Sdelphij unsigned char b); 130279265Sdelphij/* Convenience method for signed integers. */ 131279265Sdelphijstatic inline int constant_time_select_int(unsigned int mask, int a, int b); 132279265Sdelphij 133279265Sdelphijstatic inline unsigned int constant_time_msb(unsigned int a) 134296465Sdelphij{ 135296465Sdelphij return 0 - (a >> (sizeof(a) * 8 - 1)); 136296465Sdelphij} 137279265Sdelphij 138279265Sdelphijstatic inline unsigned int constant_time_lt(unsigned int a, unsigned int b) 139296465Sdelphij{ 140296465Sdelphij return constant_time_msb(a ^ ((a ^ b) | ((a - b) ^ b))); 141296465Sdelphij} 142279265Sdelphij 143279265Sdelphijstatic inline unsigned char constant_time_lt_8(unsigned int a, unsigned int b) 144296465Sdelphij{ 145296465Sdelphij return (unsigned char)(constant_time_lt(a, b)); 146296465Sdelphij} 147279265Sdelphij 148279265Sdelphijstatic inline unsigned int constant_time_ge(unsigned int a, unsigned int b) 149296465Sdelphij{ 150296465Sdelphij return ~constant_time_lt(a, b); 151296465Sdelphij} 152279265Sdelphij 153279265Sdelphijstatic inline unsigned char constant_time_ge_8(unsigned int a, unsigned int b) 154296465Sdelphij{ 155296465Sdelphij return (unsigned char)(constant_time_ge(a, b)); 156296465Sdelphij} 157279265Sdelphij 158279265Sdelphijstatic inline unsigned int constant_time_is_zero(unsigned int a) 159296465Sdelphij{ 160296465Sdelphij return constant_time_msb(~a & (a - 1)); 161296465Sdelphij} 162279265Sdelphij 163279265Sdelphijstatic inline unsigned char constant_time_is_zero_8(unsigned int a) 164296465Sdelphij{ 165296465Sdelphij return (unsigned char)(constant_time_is_zero(a)); 166296465Sdelphij} 167279265Sdelphij 168279265Sdelphijstatic inline unsigned int constant_time_eq(unsigned int a, unsigned int b) 169296465Sdelphij{ 170296465Sdelphij return constant_time_is_zero(a ^ b); 171296465Sdelphij} 172279265Sdelphij 173279265Sdelphijstatic inline unsigned char constant_time_eq_8(unsigned int a, unsigned int b) 174296465Sdelphij{ 175296465Sdelphij return (unsigned char)(constant_time_eq(a, b)); 176296465Sdelphij} 177279265Sdelphij 178279265Sdelphijstatic inline unsigned int constant_time_eq_int(int a, int b) 179296465Sdelphij{ 180296465Sdelphij return constant_time_eq((unsigned)(a), (unsigned)(b)); 181296465Sdelphij} 182279265Sdelphij 183279265Sdelphijstatic inline unsigned char constant_time_eq_int_8(int a, int b) 184296465Sdelphij{ 185296465Sdelphij return constant_time_eq_8((unsigned)(a), (unsigned)(b)); 186296465Sdelphij} 187279265Sdelphij 188279265Sdelphijstatic inline unsigned int constant_time_select(unsigned int mask, 189296465Sdelphij unsigned int a, 190296465Sdelphij unsigned int b) 191296465Sdelphij{ 192296465Sdelphij return (mask & a) | (~mask & b); 193296465Sdelphij} 194279265Sdelphij 195279265Sdelphijstatic inline unsigned char constant_time_select_8(unsigned char mask, 196296465Sdelphij unsigned char a, 197296465Sdelphij unsigned char b) 198296465Sdelphij{ 199296465Sdelphij return (unsigned char)(constant_time_select(mask, a, b)); 200296465Sdelphij} 201279265Sdelphij 202279265Sdelphijstatic inline int constant_time_select_int(unsigned int mask, int a, int b) 203296465Sdelphij{ 204296465Sdelphij return (int)(constant_time_select(mask, (unsigned)(a), (unsigned)(b))); 205296465Sdelphij} 206279265Sdelphij 207279265Sdelphij#ifdef __cplusplus 208279265Sdelphij} 209279265Sdelphij#endif 210279265Sdelphij 211296465Sdelphij#endif /* HEADER_CONSTANT_TIME_LOCL_H */ 212