1 /* crypto/constant_time_locl.h */
3 * Utilities for constant-time cryptography.
5 * Author: Emilia Kasper (emilia@openssl.org)
6 * Based on previous work by Bodo Moeller, Emilia Kasper, Adam Langley
8 * ====================================================================
9 * Copyright (c) 2014 The OpenSSL Project. All rights reserved.
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
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)"
29 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
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31 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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34 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
35 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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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
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.]
47 #ifndef HEADER_CONSTANT_TIME_LOCL_H
48 # define HEADER_CONSTANT_TIME_LOCL_H
50 # include "e_os.h" /* For 'inline' */
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,
69 * unsigned int lt = constant_time_lt(a, b);
70 * c = constant_time_select(lt, a, b);
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.
79 static inline unsigned int constant_time_msb(unsigned int a);
82 * Returns 0xff..f if a < b and 0 otherwise.
84 static inline unsigned int constant_time_lt(unsigned int a, unsigned int b);
85 /* Convenience method for getting an 8-bit mask. */
86 static inline unsigned char constant_time_lt_8(unsigned int a,
90 * Returns 0xff..f if a >= b and 0 otherwise.
92 static inline unsigned int constant_time_ge(unsigned int a, unsigned int b);
93 /* Convenience method for getting an 8-bit mask. */
94 static inline unsigned char constant_time_ge_8(unsigned int a,
98 * Returns 0xff..f if a == 0 and 0 otherwise.
100 static inline unsigned int constant_time_is_zero(unsigned int a);
101 /* Convenience method for getting an 8-bit mask. */
102 static inline unsigned char constant_time_is_zero_8(unsigned int a);
105 * Returns 0xff..f if a == b and 0 otherwise.
107 static inline unsigned int constant_time_eq(unsigned int a, unsigned int b);
108 /* Convenience method for getting an 8-bit mask. */
109 static inline unsigned char constant_time_eq_8(unsigned int a,
111 /* Signed integers. */
112 static inline unsigned int constant_time_eq_int(int a, int b);
113 /* Convenience method for getting an 8-bit mask. */
114 static inline unsigned char constant_time_eq_int_8(int a, int b);
117 * Returns (mask & a) | (~mask & b).
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).
123 static inline unsigned int constant_time_select(unsigned int mask,
126 /* Convenience method for unsigned chars. */
127 static inline unsigned char constant_time_select_8(unsigned char mask,
130 /* Convenience method for signed integers. */
131 static inline int constant_time_select_int(unsigned int mask, int a, int b);
133 static inline unsigned int constant_time_msb(unsigned int a)
135 return 0 - (a >> (sizeof(a) * 8 - 1));
138 static inline unsigned int constant_time_lt(unsigned int a, unsigned int b)
140 return constant_time_msb(a ^ ((a ^ b) | ((a - b) ^ b)));
143 static inline unsigned char constant_time_lt_8(unsigned int a, unsigned int b)
145 return (unsigned char)(constant_time_lt(a, b));
148 static inline unsigned int constant_time_ge(unsigned int a, unsigned int b)
150 return ~constant_time_lt(a, b);
153 static inline unsigned char constant_time_ge_8(unsigned int a, unsigned int b)
155 return (unsigned char)(constant_time_ge(a, b));
158 static inline unsigned int constant_time_is_zero(unsigned int a)
160 return constant_time_msb(~a & (a - 1));
163 static inline unsigned char constant_time_is_zero_8(unsigned int a)
165 return (unsigned char)(constant_time_is_zero(a));
168 static inline unsigned int constant_time_eq(unsigned int a, unsigned int b)
170 return constant_time_is_zero(a ^ b);
173 static inline unsigned char constant_time_eq_8(unsigned int a, unsigned int b)
175 return (unsigned char)(constant_time_eq(a, b));
178 static inline unsigned int constant_time_eq_int(int a, int b)
180 return constant_time_eq((unsigned)(a), (unsigned)(b));
183 static inline unsigned char constant_time_eq_int_8(int a, int b)
185 return constant_time_eq_8((unsigned)(a), (unsigned)(b));
188 static inline unsigned int constant_time_select(unsigned int mask,
192 return (mask & a) | (~mask & b);
195 static inline unsigned char constant_time_select_8(unsigned char mask,
199 return (unsigned char)(constant_time_select(mask, a, b));
202 static inline int constant_time_select_int(unsigned int mask, int a, int b)
204 return (int)(constant_time_select(mask, (unsigned)(a), (unsigned)(b)));
211 #endif /* HEADER_CONSTANT_TIME_LOCL_H */