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boringssl/crypto/fipsmodule/bn/internal.h
David Benjamin 6f564afbdd Make BN_mod_*_quick constant-time. 
As the EC code will ultimately want to use these in "words" form by way
of EC_FELEM, and because it's much easier, I've implement these as
low-level words-based functions that require all inputs have the same
width. The BIGNUM versions which RSA and, for now, EC calls are
implemented on top of that.

Unfortunately, doing such things in constant-time and accounting for
undersized inputs requires some scratch space, and these functions don't
take BN_CTX. So I've added internal bn_mod_*_quick_ctx functions that
take a BN_CTX and the old functions now allocate a bit unnecessarily.
RSA only needs lshift (for BN_MONT_CTX) and sub (for CRT), but the
generic EC code wants add as well.

The generic EC code isn't even remotely constant-time, and I hope to
ultimately use stack-allocated EC_FELEMs, so I've made the actual
implementations here implemented in "words", which is much simpler
anyway due to not having to take care of widths.

I've also gone ahead and switched the EC code to these functions,
largely as a test of their performance (an earlier iteration made the EC
code noticeably slower). These operations are otherwise not
performance-critical in RSA.

The conversion from BIGNUM to BIGNUM+BN_CTX should be dropped by the
static linker already, and the unused BIGNUM+BN_CTX functions will fall
off when EC_FELEM happens.

Update-Note: BN_mod_*_quick bounce on malloc a bit now, but they're not
    really used externally. The one caller I found was wpa_supplicant
    which bounces on malloc already. They appear to be implementing
    compressed coordinates by hand? We may be able to convince them to
    call EC_POINT_set_compressed_coordinates_GFp.

Bug: 233, 236
Change-Id: I2bf361e9c089e0211b97d95523dbc06f1168e12b
Reviewed-on: https://boringssl-review.googlesource.com/25261
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>
2018-02-06 01:16:04 +00:00

492 lines
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/* Copyright (C) 1995-1997 Eric Young (eay@cryptsoft.com)
* All rights reserved.
*
* This package is an SSL implementation written
* by Eric Young (eay@cryptsoft.com).
* The implementation was written so as to conform with Netscapes SSL.
*
* This library is free for commercial and non-commercial use as long as
* the following conditions are aheared to. The following conditions
* apply to all code found in this distribution, be it the RC4, RSA,
* lhash, DES, etc., code; not just the SSL code. The SSL documentation
* included with this distribution is covered by the same copyright terms
* except that the holder is Tim Hudson (tjh@cryptsoft.com).
*
* Copyright remains Eric Young's, and as such any Copyright notices in
* the code are not to be removed.
* If this package is used in a product, Eric Young should be given attribution
* as the author of the parts of the library used.
* This can be in the form of a textual message at program startup or
* in documentation (online or textual) provided with the package.
*
* 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.]
*/
/* ====================================================================
* Copyright (c) 1998-2006 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 above 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 acknowledgment:
* "This product includes software developed by the OpenSSL Project
* for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
*
* 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
* endorse or promote products derived from this software without
* prior written permission. For written permission, please contact
* openssl-core@openssl.org.
*
* 5. Products derived from this software may not be called "OpenSSL"
* nor may "OpenSSL" appear in their names without prior written
* permission of the OpenSSL Project.
*
* 6. Redistributions of any form whatsoever must retain the following
* acknowledgment:
* "This product includes software developed by the OpenSSL Project
* for use in the OpenSSL Toolkit (http://www.openssl.org/)"
*
* THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
* EXPRESSED 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 OpenSSL PROJECT OR
* ITS 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.
* ====================================================================
*
* This product includes cryptographic software written by Eric Young
* (eay@cryptsoft.com). This product includes software written by Tim
* Hudson (tjh@cryptsoft.com).
*
*/
/* ====================================================================
* Copyright 2002 Sun Microsystems, Inc. ALL RIGHTS RESERVED.
*
* Portions of the attached software ("Contribution") are developed by
* SUN MICROSYSTEMS, INC., and are contributed to the OpenSSL project.
*
* The Contribution is licensed pursuant to the Eric Young open source
* license provided above.
*
* The binary polynomial arithmetic software is originally written by
* Sheueling Chang Shantz and Douglas Stebila of Sun Microsystems
* Laboratories. */
#ifndef OPENSSL_HEADER_BN_INTERNAL_H
#define OPENSSL_HEADER_BN_INTERNAL_H
#include <openssl/base.h>
#if defined(OPENSSL_X86_64) && defined(_MSC_VER)
OPENSSL_MSVC_PRAGMA(warning(push, 3))
#include <intrin.h>
OPENSSL_MSVC_PRAGMA(warning(pop))
#pragma intrinsic(__umulh, _umul128)
#endif
#include "../../internal.h"
#if defined(__cplusplus)
extern "C" {
#endif
#if defined(OPENSSL_64_BIT)
#if defined(BORINGSSL_HAS_UINT128)
// MSVC doesn't support two-word integers on 64-bit.
#define BN_ULLONG uint128_t
#if defined(BORINGSSL_CAN_DIVIDE_UINT128)
#define BN_CAN_DIVIDE_ULLONG
#endif
#endif
#define BN_BITS2 64
#define BN_BYTES 8
#define BN_BITS4 32
#define BN_MASK2 (0xffffffffffffffffUL)
#define BN_MASK2l (0xffffffffUL)
#define BN_MASK2h (0xffffffff00000000UL)
#define BN_MASK2h1 (0xffffffff80000000UL)
#define BN_MONT_CTX_N0_LIMBS 1
#define BN_DEC_CONV (10000000000000000000UL)
#define BN_DEC_NUM 19
#define TOBN(hi, lo) ((BN_ULONG)(hi) << 32 | (lo))
#elif defined(OPENSSL_32_BIT)
#define BN_ULLONG uint64_t
#define BN_CAN_DIVIDE_ULLONG
#define BN_BITS2 32
#define BN_BYTES 4
#define BN_BITS4 16
#define BN_MASK2 (0xffffffffUL)
#define BN_MASK2l (0xffffUL)
#define BN_MASK2h1 (0xffff8000UL)
#define BN_MASK2h (0xffff0000UL)
// On some 32-bit platforms, Montgomery multiplication is done using 64-bit
// arithmetic with SIMD instructions. On such platforms, |BN_MONT_CTX::n0|
// needs to be two words long. Only certain 32-bit platforms actually make use
// of n0[1] and shorter R value would suffice for the others. However,
// currently only the assembly files know which is which.
#define BN_MONT_CTX_N0_LIMBS 2
#define BN_DEC_CONV (1000000000UL)
#define BN_DEC_NUM 9
#define TOBN(hi, lo) (lo), (hi)
#else
#error "Must define either OPENSSL_32_BIT or OPENSSL_64_BIT"
#endif
#define STATIC_BIGNUM(x) \
{ \
(BN_ULONG *)(x), sizeof(x) / sizeof(BN_ULONG), \
sizeof(x) / sizeof(BN_ULONG), 0, BN_FLG_STATIC_DATA \
}
#if defined(BN_ULLONG)
#define Lw(t) ((BN_ULONG)(t))
#define Hw(t) ((BN_ULONG)((t) >> BN_BITS2))
#endif
// bn_minimal_width returns the minimal value of |bn->top| which fits the
// value of |bn|.
int bn_minimal_width(const BIGNUM *bn);
// bn_set_minimal_width sets |bn->width| to |bn_minimal_width(bn)|. If |bn| is
// zero, |bn->neg| is set to zero.
void bn_set_minimal_width(BIGNUM *bn);
// bn_wexpand ensures that |bn| has at least |words| works of space without
// altering its value. It returns one on success or zero on allocation
// failure.
int bn_wexpand(BIGNUM *bn, size_t words);
// bn_expand acts the same as |bn_wexpand|, but takes a number of bits rather
// than a number of words.
int bn_expand(BIGNUM *bn, size_t bits);
// bn_resize_words adjusts |bn->top| to be |words|. It returns one on success
// and zero on allocation error or if |bn|'s value is too large.
OPENSSL_EXPORT int bn_resize_words(BIGNUM *bn, size_t words);
// bn_set_words sets |bn| to the value encoded in the |num| words in |words|,
// least significant word first.
int bn_set_words(BIGNUM *bn, const BN_ULONG *words, size_t num);
// bn_fits_in_words returns one if |bn| may be represented in |num| words, plus
// a sign bit, and zero otherwise.
int bn_fits_in_words(const BIGNUM *bn, size_t num);
// bn_copy_words copies the value of |bn| to |out| and returns one if the value
// is representable in |num| words. Otherwise, it returns zero.
int bn_copy_words(BN_ULONG *out, size_t num, const BIGNUM *bn);
// bn_mul_add_words multiples |ap| by |w|, adds the result to |rp|, and places
// the result in |rp|. |ap| and |rp| must both be |num| words long. It returns
// the carry word of the operation. |ap| and |rp| may be equal but otherwise may
// not alias.
BN_ULONG bn_mul_add_words(BN_ULONG *rp, const BN_ULONG *ap, size_t num,
BN_ULONG w);
// bn_mul_words multiples |ap| by |w| and places the result in |rp|. |ap| and
// |rp| must both be |num| words long. It returns the carry word of the
// operation. |ap| and |rp| may be equal but otherwise may not alias.
BN_ULONG bn_mul_words(BN_ULONG *rp, const BN_ULONG *ap, size_t num, BN_ULONG w);
// bn_sqr_words sets |rp[2*i]| and |rp[2*i+1]| to |ap[i]|'s square, for all |i|
// up to |num|. |ap| is an array of |num| words and |rp| an array of |2*num|
// words. |ap| and |rp| may not alias.
//
// This gives the contribution of the |ap[i]*ap[i]| terms when squaring |ap|.
void bn_sqr_words(BN_ULONG *rp, const BN_ULONG *ap, size_t num);
// bn_add_words adds |ap| to |bp| and places the result in |rp|, each of which
// are |num| words long. It returns the carry bit, which is one if the operation
// overflowed and zero otherwise. Any pair of |ap|, |bp|, and |rp| may be equal
// to each other but otherwise may not alias.
BN_ULONG bn_add_words(BN_ULONG *rp, const BN_ULONG *ap, const BN_ULONG *bp,
size_t num);
// bn_sub_words subtracts |bp| from |ap| and places the result in |rp|. It
// returns the borrow bit, which is one if the computation underflowed and zero
// otherwise. Any pair of |ap|, |bp|, and |rp| may be equal to each other but
// otherwise may not alias.
BN_ULONG bn_sub_words(BN_ULONG *rp, const BN_ULONG *ap, const BN_ULONG *bp,
size_t num);
// bn_mul_comba4 sets |r| to the product of |a| and |b|.
void bn_mul_comba4(BN_ULONG r[8], const BN_ULONG a[4], const BN_ULONG b[4]);
// bn_mul_comba8 sets |r| to the product of |a| and |b|.
void bn_mul_comba8(BN_ULONG r[16], const BN_ULONG a[8], const BN_ULONG b[8]);
// bn_sqr_comba8 sets |r| to |a|^2.
void bn_sqr_comba8(BN_ULONG r[16], const BN_ULONG a[4]);
// bn_sqr_comba4 sets |r| to |a|^2.
void bn_sqr_comba4(BN_ULONG r[8], const BN_ULONG a[4]);
// bn_cmp_words returns a value less than, equal to or greater than zero if
// the, length |n|, array |a| is less than, equal to or greater than |b|.
int bn_cmp_words(const BN_ULONG *a, const BN_ULONG *b, int n);
// bn_cmp_words returns a value less than, equal to or greater than zero if the
// array |a| is less than, equal to or greater than |b|. The arrays can be of
// different lengths: |cl| gives the minimum of the two lengths and |dl| gives
// the length of |a| minus the length of |b|.
int bn_cmp_part_words(const BN_ULONG *a, const BN_ULONG *b, int cl, int dl);
// bn_less_than_words returns one if |a| < |b| and zero otherwise, where |a|
// and |b| both are |len| words long. It runs in constant time.
int bn_less_than_words(const BN_ULONG *a, const BN_ULONG *b, size_t len);
// bn_in_range_words returns one if |min_inclusive| <= |a| < |max_exclusive|,
// where |a| and |max_exclusive| both are |len| words long. This function leaks
// which of [0, min_inclusive), [min_inclusive, max_exclusive), and
// [max_exclusive, 2^(BN_BITS2*len)) contains |a|, but otherwise the value of
// |a| is secret.
int bn_in_range_words(const BN_ULONG *a, BN_ULONG min_inclusive,
const BN_ULONG *max_exclusive, size_t len);
// bn_rand_range_words sets |out| to a uniformly distributed random number from
// |min_inclusive| to |max_exclusive|. Both |out| and |max_exclusive| are |len|
// words long.
//
// This function runs in time independent of the result, but |min_inclusive| and
// |max_exclusive| are public data. (Information about the range is unavoidably
// leaked by how many iterations it took to select a number.)
int bn_rand_range_words(BN_ULONG *out, BN_ULONG min_inclusive,
const BN_ULONG *max_exclusive, size_t len,
const uint8_t additional_data[32]);
int bn_mul_mont(BN_ULONG *rp, const BN_ULONG *ap, const BN_ULONG *bp,
const BN_ULONG *np, const BN_ULONG *n0, int num);
uint64_t bn_mont_n0(const BIGNUM *n);
int bn_mod_exp_base_2_vartime(BIGNUM *r, unsigned p, const BIGNUM *n);
#if defined(OPENSSL_X86_64) && defined(_MSC_VER)
#define BN_UMULT_LOHI(low, high, a, b) ((low) = _umul128((a), (b), &(high)))
#endif
#if !defined(BN_ULLONG) && !defined(BN_UMULT_LOHI)
#error "Either BN_ULLONG or BN_UMULT_LOHI must be defined on every platform."
#endif
// bn_mod_inverse_prime sets |out| to the modular inverse of |a| modulo |p|,
// computed with Fermat's Little Theorem. It returns one on success and zero on
// error. If |mont_p| is NULL, one will be computed temporarily.
int bn_mod_inverse_prime(BIGNUM *out, const BIGNUM *a, const BIGNUM *p,
BN_CTX *ctx, const BN_MONT_CTX *mont_p);
// bn_mod_inverse_secret_prime behaves like |bn_mod_inverse_prime| but uses
// |BN_mod_exp_mont_consttime| instead of |BN_mod_exp_mont| in hopes of
// protecting the exponent.
int bn_mod_inverse_secret_prime(BIGNUM *out, const BIGNUM *a, const BIGNUM *p,
BN_CTX *ctx, const BN_MONT_CTX *mont_p);
// bn_jacobi returns the Jacobi symbol of |a| and |b| (which is -1, 0 or 1), or
// -2 on error.
int bn_jacobi(const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx);
// bn_is_bit_set_words returns one if bit |bit| is set in |a| and zero
// otherwise.
int bn_is_bit_set_words(const BN_ULONG *a, size_t num, unsigned bit);
// bn_one_to_montgomery sets |r| to one in Montgomery form. It returns one on
// success and zero on error. This function treats the bit width of the modulus
// as public.
int bn_one_to_montgomery(BIGNUM *r, const BN_MONT_CTX *mont, BN_CTX *ctx);
// bn_less_than_montgomery_R returns one if |bn| is less than the Montgomery R
// value for |mont| and zero otherwise.
int bn_less_than_montgomery_R(const BIGNUM *bn, const BN_MONT_CTX *mont);
// Fixed-width arithmetic.
//
// The following functions implement non-modular arithmetic in constant-time
// and pessimally set |r->width| to the largest possible word size.
//
// Note this means that, e.g., repeatedly multiplying by one will cause widths
// to increase without bound. The corresponding public API functions minimize
// their outputs to avoid regressing calculator consumers.
// bn_mul_fixed behaves like |BN_mul|, but it rejects negative inputs and
// pessimally sets |r->width| to |a->width| + |b->width|, to avoid leaking
// information about |a| and |b|.
int bn_mul_fixed(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx);
// bn_sqrt_fixed behaves like |BN_sqrt|, but it pessimally sets |r->width| to
// 2*|a->width|, to avoid leaking information about |a| and |b|.
int bn_sqr_fixed(BIGNUM *r, const BIGNUM *a, BN_CTX *ctx);
// Constant-time modular arithmetic.
//
// The following functions implement basic constant-time modular arithemtic on
// word arrays.
// bn_mod_add_quick_ctx acts like |BN_mod_add_quick| but takes a |BN_CTX|.
int bn_mod_add_quick_ctx(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
const BIGNUM *m, BN_CTX *ctx);
// bn_mod_sub_quick_ctx acts like |BN_mod_sub_quick| but takes a |BN_CTX|.
int bn_mod_sub_quick_ctx(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
const BIGNUM *m, BN_CTX *ctx);
// bn_mod_lshift1_quick_ctx acts like |BN_mod_lshift1_quick| but takes a
// |BN_CTX|.
int bn_mod_lshift1_quick_ctx(BIGNUM *r, const BIGNUM *a, const BIGNUM *m,
BN_CTX *ctx);
// bn_mod_lshift_quick_ctx acts like |BN_mod_lshift_quick| but takes a |BN_CTX|.
int bn_mod_lshift_quick_ctx(BIGNUM *r, const BIGNUM *a, int n, const BIGNUM *m,
BN_CTX *ctx);
// Low-level operations for small numbers.
//
// The following functions implement algorithms suitable for use with scalars
// and field elements in elliptic curves. They rely on the number being small
// both to stack-allocate various temporaries and because they do not implement
// optimizations useful for the larger values used in RSA.
// BN_SMALL_MAX_WORDS is the largest size input these functions handle. This
// limit allows temporaries to be more easily stack-allocated. This limit is set
// to accommodate P-521.
#if defined(OPENSSL_32_BIT)
#define BN_SMALL_MAX_WORDS 17
#else
#define BN_SMALL_MAX_WORDS 9
#endif
// bn_mul_small sets |r| to |a|*|b|. |num_r| must be |num_a| + |num_b|. |r| may
// not alias with |a| or |b|. This function returns one on success and zero if
// lengths are inconsistent.
int bn_mul_small(BN_ULONG *r, size_t num_r, const BN_ULONG *a, size_t num_a,
const BN_ULONG *b, size_t num_b);
// bn_sqr_small sets |r| to |a|^2. |num_a| must be at most |BN_SMALL_MAX_WORDS|.
// |num_r| must be |num_a|*2. |r| and |a| may not alias. This function returns
// one on success and zero on programmer error.
int bn_sqr_small(BN_ULONG *r, size_t num_r, const BN_ULONG *a, size_t num_a);
// In the following functions, the modulus must be at most |BN_SMALL_MAX_WORDS|
// words long.
// bn_to_montgomery_small sets |r| to |a| translated to the Montgomery domain.
// |num_a| and |num_r| must be the length of the modulus, which is
// |mont->N.top|. |a| must be fully reduced. This function returns one on
// success and zero if lengths are inconsistent. |r| and |a| may alias.
int bn_to_montgomery_small(BN_ULONG *r, size_t num_r, const BN_ULONG *a,
size_t num_a, const BN_MONT_CTX *mont);
// bn_from_montgomery_small sets |r| to |a| translated out of the Montgomery
// domain. |num_r| must be the length of the modulus, which is |mont->N.top|.
// |a| must be at most |mont->N.top| * R and |num_a| must be at most 2 *
// |mont->N.top|. This function returns one on success and zero if lengths are
// inconsistent. |r| and |a| may alias.
int bn_from_montgomery_small(BN_ULONG *r, size_t num_r, const BN_ULONG *a,
size_t num_a, const BN_MONT_CTX *mont);
// bn_one_to_montgomery_small sets |r| to one in Montgomery form. It returns one
// on success and zero on error. |num_r| must be the length of the modulus,
// which is |mont->N.top|. This function treats the bit width of the modulus as
// public.
int bn_one_to_montgomery_small(BN_ULONG *r, size_t num_r,
const BN_MONT_CTX *mont);
// bn_mod_mul_montgomery_small sets |r| to |a| * |b| mod |mont->N|. Both inputs
// and outputs are in the Montgomery domain. |num_r| must be the length of the
// modulus, which is |mont->N.top|. This function returns one on success and
// zero on internal error or inconsistent lengths. Any two of |r|, |a|, and |b|
// may alias.
//
// This function requires |a| * |b| < N * R, where N is the modulus and R is the
// Montgomery divisor, 2^(N.top * BN_BITS2). This should generally be satisfied
// by ensuring |a| and |b| are fully reduced, however ECDSA has one computation
// which requires the more general bound.
int bn_mod_mul_montgomery_small(BN_ULONG *r, size_t num_r, const BN_ULONG *a,
size_t num_a, const BN_ULONG *b, size_t num_b,
const BN_MONT_CTX *mont);
// bn_mod_exp_mont_small sets |r| to |a|^|p| mod |mont->N|. It returns one on
// success and zero on programmer or internal error. Both inputs and outputs are
// in the Montgomery domain. |num_r| and |num_a| must be |mont->N.top|, which
// must be at most |BN_SMALL_MAX_WORDS|. |a| must be fully-reduced. This
// function runs in time independent of |a|, but |p| and |mont->N| are public
// values.
//
// Note this function differs from |BN_mod_exp_mont| which uses Montgomery
// reduction but takes input and output outside the Montgomery domain. Combine
// this function with |bn_from_montgomery_small| and |bn_to_montgomery_small|
// if necessary.
int bn_mod_exp_mont_small(BN_ULONG *r, size_t num_r, const BN_ULONG *a,
size_t num_a, const BN_ULONG *p, size_t num_p,
const BN_MONT_CTX *mont);
// bn_mod_inverse_prime_mont_small sets |r| to |a|^-1 mod |mont->N|. |mont->N|
// must be a prime. |num_r| and |num_a| must be |mont->N.top|, which must be at
// most |BN_SMALL_MAX_WORDS|. |a| must be fully-reduced. This function runs in
// time independent of |a|, but |mont->N| is a public value.
int bn_mod_inverse_prime_mont_small(BN_ULONG *r, size_t num_r,
const BN_ULONG *a, size_t num_a,
const BN_MONT_CTX *mont);
#if defined(__cplusplus)
} // extern C
#endif
#endif // OPENSSL_HEADER_BN_INTERNAL_H
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