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/*
* Copyright 2014-2016 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the OpenSSL license (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#ifndef HEADER_CONSTANT_TIME_LOCL_H
# define HEADER_CONSTANT_TIME_LOCL_H
# include <openssl/e_os2.h> /* For 'ossl_inline' */
#ifdef __cplusplus
extern "C" {
#endif
/*-
* 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 ossl_inline unsigned int constant_time_msb(unsigned int a);
/*
* Returns 0xff..f if a < b and 0 otherwise.
*/
static ossl_inline unsigned int constant_time_lt(unsigned int a,
unsigned int b);
/* Convenience method for getting an 8-bit mask. */
static ossl_inline unsigned char constant_time_lt_8(unsigned int a,
unsigned int b);
/*
* Returns 0xff..f if a >= b and 0 otherwise.
*/
static ossl_inline unsigned int constant_time_ge(unsigned int a,
unsigned int b);
/* Convenience method for getting an 8-bit mask. */
static ossl_inline unsigned char constant_time_ge_8(unsigned int a,
unsigned int b);
/*
* Returns 0xff..f if a == 0 and 0 otherwise.
*/
static ossl_inline unsigned int constant_time_is_zero(unsigned int a);
/* Convenience method for getting an 8-bit mask. */
static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a);
/*
* Returns 0xff..f if a == b and 0 otherwise.
*/
static ossl_inline unsigned int constant_time_eq(unsigned int a,
unsigned int b);
/* Convenience method for getting an 8-bit mask. */
static ossl_inline unsigned char constant_time_eq_8(unsigned int a,
unsigned int b);
/* Signed integers. */
static ossl_inline unsigned int constant_time_eq_int(int a, int b);
/* Convenience method for getting an 8-bit mask. */
static ossl_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 ossl_inline unsigned int constant_time_select(unsigned int mask,
unsigned int a,
unsigned int b);
/* Convenience method for unsigned chars. */
static ossl_inline unsigned char constant_time_select_8(unsigned char mask,
unsigned char a,
unsigned char b);
/* Convenience method for signed integers. */
static ossl_inline int constant_time_select_int(unsigned int mask, int a,
int b);
static ossl_inline unsigned int constant_time_msb(unsigned int a)
{
return 0 - (a >> (sizeof(a) * 8 - 1));
}
static ossl_inline unsigned int constant_time_lt(unsigned int a,
unsigned int b)
{
return constant_time_msb(a ^ ((a ^ b) | ((a - b) ^ b)));
}
static ossl_inline unsigned char constant_time_lt_8(unsigned int a,
unsigned int b)
{
return (unsigned char)(constant_time_lt(a, b));
}
static ossl_inline unsigned int constant_time_ge(unsigned int a,
unsigned int b)
{
return ~constant_time_lt(a, b);
}
static ossl_inline unsigned char constant_time_ge_8(unsigned int a,
unsigned int b)
{
return (unsigned char)(constant_time_ge(a, b));
}
static ossl_inline unsigned int constant_time_is_zero(unsigned int a)
{
return constant_time_msb(~a & (a - 1));
}
static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a)
{
return (unsigned char)(constant_time_is_zero(a));
}
static ossl_inline unsigned int constant_time_eq(unsigned int a,
unsigned int b)
{
return constant_time_is_zero(a ^ b);
}
static ossl_inline unsigned char constant_time_eq_8(unsigned int a,
unsigned int b)
{
return (unsigned char)(constant_time_eq(a, b));
}
static ossl_inline unsigned int constant_time_eq_int(int a, int b)
{
return constant_time_eq((unsigned)(a), (unsigned)(b));
}
static ossl_inline unsigned char constant_time_eq_int_8(int a, int b)
{
return constant_time_eq_8((unsigned)(a), (unsigned)(b));
}
static ossl_inline unsigned int constant_time_select(unsigned int mask,
unsigned int a,
unsigned int b)
{
return (mask & a) | (~mask & b);
}
static ossl_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 ossl_inline int constant_time_select_int(unsigned int mask, int a,
int b)
{
return (int)(constant_time_select(mask, (unsigned)(a), (unsigned)(b)));
}
#ifdef __cplusplus
}
#endif
#endif /* HEADER_CONSTANT_TIME_LOCL_H */
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