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openssl/include/internal/constant_time.h

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/*
* Copyright 2014-2018 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the Apache License 2.0 (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 OSSL_INTERNAL_CONSTANT_TIME_H
# define OSSL_INTERNAL_CONSTANT_TIME_H
# include <stdlib.h>
# include <string.h>
# include <openssl/e_os2.h> /* For 'ossl_inline' */
/*-
* 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. */
static ossl_inline unsigned int constant_time_msb(unsigned int a);
/* Convenience method for uint32_t. */
static ossl_inline uint32_t constant_time_msb_32(uint32_t a);
/* Convenience method for uint64_t. */
static ossl_inline uint64_t constant_time_msb_64(uint64_t 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);
/* Convenience method for uint64_t. */
static ossl_inline uint64_t constant_time_lt_64(uint64_t a, uint64_t 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);
/* Convenience method for getting a 32-bit mask. */
static ossl_inline uint32_t constant_time_is_zero_32(uint32_t 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 uint32_t. */
static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a,
uint32_t b);
/* Convenience method for uint64_t. */
static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a,
uint64_t 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 uint32_t constant_time_msb_32(uint32_t a)
{
return 0 - (a >> 31);
}
static ossl_inline uint64_t constant_time_msb_64(uint64_t a)
{
return 0 - (a >> 63);
}
static ossl_inline size_t constant_time_msb_s(size_t 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 size_t constant_time_lt_s(size_t a, size_t b)
{
return constant_time_msb_s(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 uint64_t constant_time_lt_64(uint64_t a, uint64_t b)
{
return constant_time_msb_64(a ^ ((a ^ b) | ((a - b) ^ b)));
}
static ossl_inline unsigned int constant_time_ge(unsigned int a,
unsigned int b)
{
return ~constant_time_lt(a, b);
}
static ossl_inline size_t constant_time_ge_s(size_t a, size_t b)
{
return ~constant_time_lt_s(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 char constant_time_ge_8_s(size_t a, size_t b)
{
return (unsigned char)constant_time_ge_s(a, b);
}
static ossl_inline unsigned int constant_time_is_zero(unsigned int a)
{
return constant_time_msb(~a & (a - 1));
}
static ossl_inline size_t constant_time_is_zero_s(size_t a)
{
return constant_time_msb_s(~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 uint32_t constant_time_is_zero_32(uint32_t a)
{
return constant_time_msb_32(~a & (a - 1));
}
static ossl_inline unsigned int constant_time_eq(unsigned int a,
unsigned int b)
{
return constant_time_is_zero(a ^ b);
}
static ossl_inline size_t constant_time_eq_s(size_t a, size_t b)
{
return constant_time_is_zero_s(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 char constant_time_eq_8_s(size_t a, size_t b)
{
return (unsigned char)constant_time_eq_s(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));
}
/*
* Returns the value unmodified, but avoids optimizations.
* The barriers prevent the compiler from narrowing down the
* possible value range of the mask and ~mask in the select
* statements, which avoids the recognition of the select
* and turning it into a conditional load or branch.
*/
static ossl_inline unsigned int value_barrier(unsigned int a)
{
#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
unsigned int r;
__asm__("" : "=r"(r) : "0"(a));
#else
volatile unsigned int r = a;
#endif
return r;
}
/* Convenience method for uint32_t. */
static ossl_inline uint32_t value_barrier_32(uint32_t a)
{
#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
uint32_t r;
__asm__("" : "=r"(r) : "0"(a));
#else
volatile uint32_t r = a;
#endif
return r;
}
/* Convenience method for uint64_t. */
static ossl_inline uint64_t value_barrier_64(uint64_t a)
{
#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
uint64_t r;
__asm__("" : "=r"(r) : "0"(a));
#else
volatile uint64_t r = a;
#endif
return r;
}
/* Convenience method for size_t. */
static ossl_inline size_t value_barrier_s(size_t a)
{
#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
size_t r;
__asm__("" : "=r"(r) : "0"(a));
#else
volatile size_t r = a;
#endif
return r;
}
static ossl_inline unsigned int constant_time_select(unsigned int mask,
unsigned int a,
unsigned int b)
{
return (value_barrier(mask) & a) | (value_barrier(~mask) & b);
}
static ossl_inline size_t constant_time_select_s(size_t mask,
size_t a,
size_t b)
{
return (value_barrier_s(mask) & a) | (value_barrier_s(~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));
}
static ossl_inline int constant_time_select_int_s(size_t mask, int a, int b)
{
return (int)constant_time_select((unsigned)mask, (unsigned)(a),
(unsigned)(b));
}
static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a,
uint32_t b)
{
return (value_barrier_32(mask) & a) | (value_barrier_32(~mask) & b);
}
static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a,
uint64_t b)
{
return (value_barrier_64(mask) & a) | (value_barrier_64(~mask) & b);
}
/*
* mask must be 0xFFFFFFFF or 0x00000000.
*
* if (mask) {
* uint32_t tmp = *a;
*
* *a = *b;
* *b = tmp;
* }
*/
static ossl_inline void constant_time_cond_swap_32(uint32_t mask, uint32_t *a,
uint32_t *b)
{
uint32_t xor = *a ^ *b;
xor &= mask;
*a ^= xor;
*b ^= xor;
}
/*
* mask must be 0xFFFFFFFF or 0x00000000.
*
* if (mask) {
* uint64_t tmp = *a;
*
* *a = *b;
* *b = tmp;
* }
*/
static ossl_inline void constant_time_cond_swap_64(uint64_t mask, uint64_t *a,
uint64_t *b)
{
uint64_t xor = *a ^ *b;
xor &= mask;
*a ^= xor;
*b ^= xor;
}
/*
* table is a two dimensional array of bytes. Each row has rowsize elements.
* Copies row number idx into out. rowsize and numrows are not considered
* private.
*/
static ossl_inline void constant_time_lookup(void *out,
const void *table,
size_t rowsize,
size_t numrows,
size_t idx)
{
size_t i, j;
const unsigned char *tablec = (const unsigned char *)table;
unsigned char *outc = (unsigned char *)out;
unsigned char mask;
memset(out, 0, rowsize);
/* Note idx may underflow - but that is well defined */
for (i = 0; i < numrows; i++, idx--) {
mask = (unsigned char)constant_time_is_zero_s(idx);
for (j = 0; j < rowsize; j++)
*(outc + j) |= constant_time_select_8(mask, *(tablec++), 0);
}
}
/*
* Expected usage pattern is to unconditionally set error and then
* wipe it if there was no actual error. |clear| is 1 or 0.
*/
void err_clear_last_constant_time(int clear);
#endif /* OSSL_INTERNAL_CONSTANT_TIME_H */
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