| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * Constant-time operations |
| 4 | * |
| 5 | * (c) 2013 Straylight/Edgeware |
| 6 | */ |
| 7 | |
| 8 | /*----- Licensing notice --------------------------------------------------* |
| 9 | * |
| 10 | * This file is part of Catacomb. |
| 11 | * |
| 12 | * Catacomb is free software; you can redistribute it and/or modify |
| 13 | * it under the terms of the GNU Library General Public License as |
| 14 | * published by the Free Software Foundation; either version 2 of the |
| 15 | * License, or (at your option) any later version. |
| 16 | * |
| 17 | * Catacomb is distributed in the hope that it will be useful, |
| 18 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 19 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 20 | * GNU Library General Public License for more details. |
| 21 | * |
| 22 | * You should have received a copy of the GNU Library General Public |
| 23 | * License along with Catacomb; if not, write to the Free |
| 24 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
| 25 | * MA 02111-1307, USA. |
| 26 | */ |
| 27 | |
| 28 | #ifndef CATACOMB_CT_H |
| 29 | #define CATACOMB_CT_H |
| 30 | |
| 31 | #ifdef __cplusplus |
| 32 | extern "C" { |
| 33 | #endif |
| 34 | |
| 35 | /*----- Header files ------------------------------------------------------*/ |
| 36 | |
| 37 | #include <mLib/bits.h> |
| 38 | |
| 39 | /*----- Miscellaneous constant-time utilities -----------------------------*/ |
| 40 | |
| 41 | /* --- @ct_inteq@ --- * |
| 42 | * |
| 43 | * Arguments: @uint32 x, y@ = two 32-bit unsigned integers |
| 44 | * |
| 45 | * Returns: One if @x@ and @y@ are equal, zero if they differ. |
| 46 | * |
| 47 | * Use: Answers whether two integers are equal, in constant time. |
| 48 | */ |
| 49 | |
| 50 | extern int ct_inteq(uint32 /*x*/, uint32 /*y*/); |
| 51 | |
| 52 | /* --- @ct_intle@ --- * |
| 53 | * |
| 54 | * Arguments: @uint32 x, y@ = two 32-bit unsigned integers |
| 55 | * |
| 56 | * Returns: One if %$x \le y$%, zero if @x@ is greater. |
| 57 | * |
| 58 | * Use: Answers whether two integers are ordered, in constant time. |
| 59 | */ |
| 60 | |
| 61 | extern int ct_intle(uint32 /*x*/, uint32 /*y*/); |
| 62 | |
| 63 | /* --- @ct_pick@ --- * |
| 64 | * |
| 65 | * Arguments: @uint32 a@ = a switch, either zero or one |
| 66 | * @uint32 x0, x1@ = two 32-bit unsigned integers |
| 67 | * |
| 68 | * Returns: @x0@ if @a@ is zero; @x1@ if @a@ is one. Other values of @a@ |
| 69 | * will give you unhelpful results. |
| 70 | * |
| 71 | * Use: Picks one of two results according to a switch variable, in |
| 72 | * constant time. |
| 73 | */ |
| 74 | |
| 75 | extern int ct_pick(uint32 /*a*/, uint32 /*x0*/, uint32 /*x1*/); |
| 76 | |
| 77 | /* --- @ct_condcopy@ --- * |
| 78 | * |
| 79 | * Arguments: @uint32 a@ = a switch, either zero or one |
| 80 | * @void *d@ = destination pointer |
| 81 | * @const void *s@ = source pointer |
| 82 | * @size_t n@ amount to copy |
| 83 | * |
| 84 | * Returns: --- |
| 85 | * |
| 86 | * Use: If @a@ is one then copy the @n@ bytes starting at @s@ to |
| 87 | * @d@; if @a@ is zero then leave @d@ unchanged (but it will |
| 88 | * still be written). All of this is done in constant time. |
| 89 | */ |
| 90 | |
| 91 | extern void ct_condcopy(uint32 /*a*/, |
| 92 | void */*d*/, const void */*s*/, size_t /*n*/); |
| 93 | |
| 94 | /* --- @ct_memeq@ --- |
| 95 | * |
| 96 | * Arguments: @const void *p, *q@ = two pointers to buffers |
| 97 | * @size_t n@ = the (common) size of the buffers |
| 98 | * |
| 99 | * Returns: One if the two buffers are equal, zero if they aren't. |
| 100 | * |
| 101 | * Use: Compares two chunks of memory, in constant time. |
| 102 | */ |
| 103 | |
| 104 | extern int ct_memeq(const void */*p*/, const void */*q*/, size_t /*n*/); |
| 105 | |
| 106 | /*----- Utilities for testing ---------------------------------------------*/ |
| 107 | |
| 108 | /* --- @ct_poison@ --- * |
| 109 | * |
| 110 | * Arguments: @const void *p@ = pointer to a secret |
| 111 | * @size_t sz@ = size of the secret |
| 112 | * |
| 113 | * Returns: --- |
| 114 | * |
| 115 | * Use: Ordinarily, does nothing. If the process is running under |
| 116 | * the control of Valgrind's `memcheck' utility, then mark the |
| 117 | * secret as `uninitialized', so that Valgrind warns about |
| 118 | * conditional execution or memory addressing based on the value |
| 119 | * of the secret. |
| 120 | * |
| 121 | * Credit for this idea goes to Adam Langley, who described it |
| 122 | * in https://www.imperialviolet.org/2010/04/01/ctgrind.html, |
| 123 | * though this implementation doesn't require patching Valgrind. |
| 124 | */ |
| 125 | |
| 126 | extern void ct_poison(const void */*p*/, size_t /*sz*/); |
| 127 | |
| 128 | /* --- @ct_remedy@ --- * |
| 129 | * |
| 130 | * Arguments: @const void *p@ = pointer to a secret |
| 131 | * @size_t sz@ = size of the secret |
| 132 | * |
| 133 | * Returns: --- |
| 134 | * |
| 135 | * Use: Ordinarily, does nothing. If the process is running under |
| 136 | * the control of Valgrind's `memcheck' utility, then mark the |
| 137 | * secret as `initialized'. This is intended to reverse the |
| 138 | * effect of @ct_poison@ so that a test program can verify |
| 139 | * function outputs wihtout Valgrind warning. |
| 140 | */ |
| 141 | |
| 142 | extern void ct_remedy(const void */*p*/, size_t /*sz*/); |
| 143 | |
| 144 | /*----- That's all, folks -------------------------------------------------*/ |
| 145 | |
| 146 | #ifdef __cplusplus |
| 147 | } |
| 148 | #endif |
| 149 | |
| 150 | #endif |