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IABSD.fr/src/lib/libcrypto/constant_time.h
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- lib/libcrypto/constant_time.h
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/* $OpenBSD: constant_time.h,v 1.3 2023/04/06 18:43:47 tb Exp $ */ /*- * Utilities for constant-time cryptography. * * Author: Emilia Kasper (emilia@openssl.org) * Based on previous work by Bodo Moeller, Emilia Kasper, Adam Langley * (Google). * ==================================================================== * Copyright (c) 2014 The OpenSSL Project. All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. All advertising materials mentioning features or use of this software * must display the following acknowledgement: * "This product includes cryptographic software written by * Eric Young (eay@cryptsoft.com)" * The word 'cryptographic' can be left out if the rouines from the library * being used are not cryptographic related :-). * 4. If you include any Windows specific code (or a derivative thereof) from * the apps directory (application code) you must include an acknowledgement: * "This product includes software written by Tim Hudson (tjh@cryptsoft.com)" * * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * The licence and distribution terms for any publically available version or * derivative of this code cannot be changed. i.e. this code cannot simply be * copied and put under another distribution licence * [including the GNU Public Licence.] */ #ifndef HEADER_CONSTANT_TIME_H #define HEADER_CONSTANT_TIME_H __BEGIN_HIDDEN_DECLS /*- * The boolean methods return a bitmask of all ones (0xff...f) for true * and 0 for false. This is useful for choosing a value based on the result * of a conditional in constant time. For example, * * if (a < b) { * c = a; * } else { * c = b; * } * * can be written as * * unsigned int lt = constant_time_lt(a, b); * c = constant_time_select(lt, a, b); */ /* * Returns the given value with the MSB copied to all the other * bits. Uses the fact that arithmetic shift shifts-in the sign bit. * However, this is not ensured by the C standard so you may need to * replace this with something else on odd CPUs. */ static inline unsigned int constant_time_msb(unsigned int a); /* * Returns 0xff..f if a < b and 0 otherwise. */ static inline unsigned int constant_time_lt(unsigned int a, unsigned int b); /* Convenience method for getting an 8-bit mask. */ static inline unsigned char constant_time_lt_8(unsigned int a, unsigned int b); /* * Returns 0xff..f if a >= b and 0 otherwise. */ static inline unsigned int constant_time_ge(unsigned int a, unsigned int b); /* Convenience method for getting an 8-bit mask. */ static inline unsigned char constant_time_ge_8(unsigned int a, unsigned int b); /* * Returns 0xff..f if a == 0 and 0 otherwise. */ static inline unsigned int constant_time_is_zero(unsigned int a); /* Convenience method for getting an 8-bit mask. */ static inline unsigned char constant_time_is_zero_8(unsigned int a); /* * Returns 0xff..f if a == b and 0 otherwise. */ static inline unsigned int constant_time_eq(unsigned int a, unsigned int b); /* Convenience method for getting an 8-bit mask. */ static inline unsigned char constant_time_eq_8(unsigned int a, unsigned int b); /* Signed integers. */ static inline unsigned int constant_time_eq_int(int a, int b); /* Convenience method for getting an 8-bit mask. */ static inline unsigned char constant_time_eq_int_8(int a, int b); /*- * Returns (mask & a) | (~mask & b). * * When |mask| is all 1s or all 0s (as returned by the methods above), * the select methods return either |a| (if |mask| is nonzero) or |b| * (if |mask| is zero). */ static inline unsigned int constant_time_select(unsigned int mask, unsigned int a, unsigned int b); /* Convenience method for unsigned chars. */ static inline unsigned char constant_time_select_8(unsigned char mask, unsigned char a, unsigned char b); /* Convenience method for signed integers. */ static inline int constant_time_select_int(unsigned int mask, int a, int b); static inline unsigned int constant_time_msb(unsigned int a) { return 0 - (a >> (sizeof(a) * 8 - 1)); } static inline unsigned int constant_time_lt(unsigned int a, unsigned int b) { return constant_time_msb(a ^ ((a ^ b) | ((a - b) ^ b))); } static inline unsigned char constant_time_lt_8(unsigned int a, unsigned int b) { return (unsigned char)(constant_time_lt(a, b)); } static inline unsigned int constant_time_ge(unsigned int a, unsigned int b) { return ~constant_time_lt(a, b); } static inline unsigned char constant_time_ge_8(unsigned int a, unsigned int b) { return (unsigned char)(constant_time_ge(a, b)); } static inline unsigned int constant_time_is_zero(unsigned int a) { return constant_time_msb(~a & (a - 1)); } static inline unsigned char constant_time_is_zero_8(unsigned int a) { return (unsigned char)(constant_time_is_zero(a)); } static inline unsigned int constant_time_eq(unsigned int a, unsigned int b) { return constant_time_is_zero(a ^ b); } static inline unsigned char constant_time_eq_8(unsigned int a, unsigned int b) { return (unsigned char)(constant_time_eq(a, b)); } static inline unsigned int constant_time_eq_int(int a, int b) { return constant_time_eq((unsigned)(a), (unsigned)(b)); } static inline unsigned char constant_time_eq_int_8(int a, int b) { return constant_time_eq_8((unsigned)(a), (unsigned)(b)); } static inline unsigned int constant_time_select(unsigned int mask, unsigned int a, unsigned int b) { return (mask & a) | (~mask & b); } static inline unsigned char constant_time_select_8(unsigned char mask, unsigned char a, unsigned char b) { return (unsigned char)(constant_time_select(mask, a, b)); } static inline int constant_time_select_int(unsigned int mask, int a, int b) { return (int)(constant_time_select(mask, (unsigned)(a), (unsigned)(b))); } void err_clear_last_constant_time(int clear); __END_HIDDEN_DECLS #endif /* !HEADER_CONSTANT_TIME_H */