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boringssl/crypto/fipsmodule/bn/gcd.c
David Benjamin a44dae7fd3 Add a constant-time generic modular inverse function. 
This uses the full binary GCD algorithm, where all four of A, B, C, and
D must be retained. (BN_mod_inverse_odd implements the odd number
version which only needs A and C.) It is patterned after the version
in the Handbook of Applied Cryptography, but tweaked so the coefficients
are non-negative and bounded.

Median of 29 RSA keygens: 0m0.225s -> 0m0.220s
(Accuracy beyond 0.1s is questionable.)

Bug: 238
Change-Id: I6dc13524ea7c8ac1072592857880ddf141d87526
Reviewed-on: https://boringssl-review.googlesource.com/26370
Reviewed-by: Adam Langley <alangley@gmail.com>
2018-03-30 19:53:44 +00:00

684 lines
22 KiB
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/* Copyright (C) 1995-1998 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) 1998-2001 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). */
#include <openssl/bn.h>
#include <assert.h>
#include <openssl/err.h>
#include "internal.h"
static BN_ULONG word_is_odd_mask(BN_ULONG a) { return (BN_ULONG)0 - (a & 1); }
static void maybe_rshift1_words(BN_ULONG *a, BN_ULONG mask, BN_ULONG *tmp,
size_t num) {
bn_rshift1_words(tmp, a, num);
bn_select_words(a, mask, tmp, a, num);
}
static void maybe_rshift1_words_carry(BN_ULONG *a, BN_ULONG carry,
BN_ULONG mask, BN_ULONG *tmp,
size_t num) {
maybe_rshift1_words(a, mask, tmp, num);
if (num != 0) {
carry &= mask;
a[num - 1] |= carry << (BN_BITS2-1);
}
}
static BN_ULONG maybe_add_words(BN_ULONG *a, BN_ULONG mask, const BN_ULONG *b,
BN_ULONG *tmp, size_t num) {
BN_ULONG carry = bn_add_words(tmp, a, b, num);
bn_select_words(a, mask, tmp, a, num);
return carry & mask;
}
static int bn_gcd_consttime(BIGNUM *r, unsigned *out_shift, const BIGNUM *x,
const BIGNUM *y, BN_CTX *ctx) {
size_t width = x->width > y->width ? x->width : y->width;
if (width == 0) {
*out_shift = 0;
BN_zero(r);
return 1;
}
// This is a constant-time implementation of Stein's algorithm (binary GCD).
int ret = 0;
BN_CTX_start(ctx);
BIGNUM *u = BN_CTX_get(ctx);
BIGNUM *v = BN_CTX_get(ctx);
BIGNUM *tmp = BN_CTX_get(ctx);
if (u == NULL || v == NULL || tmp == NULL ||
!BN_copy(u, x) ||
!BN_copy(v, y) ||
!bn_resize_words(u, width) ||
!bn_resize_words(v, width) ||
!bn_resize_words(tmp, width)) {
goto err;
}
// Each loop iteration halves at least one of |u| and |v|. Thus we need at
// most the combined bit width of inputs for at least one value to be zero.
unsigned x_bits = x->width * BN_BITS2, y_bits = y->width * BN_BITS2;
unsigned num_iters = x_bits + y_bits;
if (num_iters < x_bits) {
OPENSSL_PUT_ERROR(BN, BN_R_BIGNUM_TOO_LONG);
goto err;
}
unsigned shift = 0;
for (unsigned i = 0; i < num_iters; i++) {
BN_ULONG both_odd = word_is_odd_mask(u->d[0]) & word_is_odd_mask(v->d[0]);
// If both |u| and |v| are odd, subtract the smaller from the larger.
BN_ULONG u_less_than_v =
(BN_ULONG)0 - bn_sub_words(tmp->d, u->d, v->d, width);
bn_select_words(u->d, both_odd & ~u_less_than_v, tmp->d, u->d, width);
bn_sub_words(tmp->d, v->d, u->d, width);
bn_select_words(v->d, both_odd & u_less_than_v, tmp->d, v->d, width);
// At least one of |u| and |v| is now even.
BN_ULONG u_is_odd = word_is_odd_mask(u->d[0]);
BN_ULONG v_is_odd = word_is_odd_mask(v->d[0]);
assert(!(u_is_odd & v_is_odd));
// If both are even, the final GCD gains a factor of two.
shift += 1 & (~u_is_odd & ~v_is_odd);
// Halve any which are even.
maybe_rshift1_words(u->d, ~u_is_odd, tmp->d, width);
maybe_rshift1_words(v->d, ~v_is_odd, tmp->d, width);
}
// One of |u| or |v| is zero at this point. The algorithm usually makes |u|
// zero, unless |y| was already zero on input. Fix this by combining the
// values.
assert(BN_is_zero(u) || BN_is_zero(v));
for (size_t i = 0; i < width; i++) {
v->d[i] |= u->d[i];
}
*out_shift = shift;
ret = bn_set_words(r, v->d, width);
err:
BN_CTX_end(ctx);
return ret;
}
int BN_gcd(BIGNUM *r, const BIGNUM *x, const BIGNUM *y, BN_CTX *ctx) {
unsigned shift;
return bn_gcd_consttime(r, &shift, x, y, ctx) &&
BN_lshift(r, r, shift);
}
int bn_is_relatively_prime(int *out_relatively_prime, const BIGNUM *x,
const BIGNUM *y, BN_CTX *ctx) {
int ret = 0;
BN_CTX_start(ctx);
unsigned shift;
BIGNUM *gcd = BN_CTX_get(ctx);
if (gcd == NULL ||
!bn_gcd_consttime(gcd, &shift, x, y, ctx)) {
goto err;
}
// Check that 2^|shift| * |gcd| is one.
if (gcd->width == 0) {
*out_relatively_prime = 0;
} else {
BN_ULONG mask = shift | (gcd->d[0] ^ 1);
for (int i = 1; i < gcd->width; i++) {
mask |= gcd->d[i];
}
*out_relatively_prime = mask == 0;
}
ret = 1;
err:
BN_CTX_end(ctx);
return ret;
}
int bn_lcm_consttime(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx) {
BN_CTX_start(ctx);
unsigned shift;
BIGNUM *gcd = BN_CTX_get(ctx);
int ret = gcd != NULL &&
bn_mul_consttime(r, a, b, ctx) &&
bn_gcd_consttime(gcd, &shift, a, b, ctx) &&
bn_div_consttime(r, NULL, r, gcd, ctx) &&
bn_rshift_secret_shift(r, r, shift, ctx);
BN_CTX_end(ctx);
return ret;
}
int bn_mod_inverse_consttime(BIGNUM *r, int *out_no_inverse, const BIGNUM *a,
const BIGNUM *n, BN_CTX *ctx) {
*out_no_inverse = 0;
if (BN_is_negative(a) || BN_ucmp(a, n) >= 0) {
OPENSSL_PUT_ERROR(BN, BN_R_INPUT_NOT_REDUCED);
return 0;
}
if (BN_is_zero(a)) {
if (BN_is_one(n)) {
BN_zero(r);
return 1;
}
*out_no_inverse = 1;
OPENSSL_PUT_ERROR(BN, BN_R_NO_INVERSE);
return 0;
}
// This is a constant-time implementation of the extended binary GCD
// algorithm. It is adapted from the Handbook of Applied Cryptography, section
// 14.4.3, algorithm 14.51, and modified to bound coefficients and avoid
// negative numbers.
//
// For more details and proof of correctness, see
// https://github.com/mit-plv/fiat-crypto/pull/333. In particular, see |step|
// and |mod_inverse_consttime| for the algorithm in Gallina and see
// |mod_inverse_consttime_spec| for the correctness result.
if (!BN_is_odd(a) && !BN_is_odd(n)) {
*out_no_inverse = 1;
OPENSSL_PUT_ERROR(BN, BN_R_NO_INVERSE);
return 0;
}
// This function exists to compute the RSA private exponent, where |a| is one
// word. We'll thus use |a_width| when available.
size_t n_width = n->width, a_width = a->width;
if (a_width > n_width) {
a_width = n_width;
}
int ret = 0;
BN_CTX_start(ctx);
BIGNUM *u = BN_CTX_get(ctx);
BIGNUM *v = BN_CTX_get(ctx);
BIGNUM *A = BN_CTX_get(ctx);
BIGNUM *B = BN_CTX_get(ctx);
BIGNUM *C = BN_CTX_get(ctx);
BIGNUM *D = BN_CTX_get(ctx);
BIGNUM *tmp = BN_CTX_get(ctx);
BIGNUM *tmp2 = BN_CTX_get(ctx);
if (u == NULL || v == NULL || A == NULL || B == NULL || C == NULL ||
D == NULL || tmp == NULL || tmp2 == NULL ||
!BN_copy(u, a) ||
!BN_copy(v, n) ||
!BN_one(A) ||
!BN_one(D) ||
// For convenience, size |u| and |v| equivalently.
!bn_resize_words(u, n_width) ||
!bn_resize_words(v, n_width) ||
// |A| and |C| are bounded by |m|.
!bn_resize_words(A, n_width) ||
!bn_resize_words(C, n_width) ||
// |B| and |D| are bounded by |a|.
!bn_resize_words(B, a_width) ||
!bn_resize_words(D, a_width) ||
// |tmp| and |tmp2| may be used at either size.
!bn_resize_words(tmp, n_width) ||
!bn_resize_words(tmp2, n_width)) {
goto err;
}
// Each loop iteration halves at least one of |u| and |v|. Thus we need at
// most the combined bit width of inputs for at least one value to be zero.
unsigned a_bits = a_width * BN_BITS2, n_bits = n_width * BN_BITS2;
unsigned num_iters = a_bits + n_bits;
if (num_iters < a_bits) {
OPENSSL_PUT_ERROR(BN, BN_R_BIGNUM_TOO_LONG);
goto err;
}
// Before and after each loop iteration, the following hold:
//
// u = A*a - B*n
// v = D*n - C*a
// 0 < u <= a
// 0 <= v <= n
// 0 <= A < n
// 0 <= B <= a
// 0 <= C < n
// 0 <= D <= a
//
// After each loop iteration, u and v only get smaller, and at least one of
// them shrinks by at least a factor of two.
for (unsigned i = 0; i < num_iters; i++) {
BN_ULONG both_odd = word_is_odd_mask(u->d[0]) & word_is_odd_mask(v->d[0]);
// If both |u| and |v| are odd, subtract the smaller from the larger.
BN_ULONG v_less_than_u =
(BN_ULONG)0 - bn_sub_words(tmp->d, v->d, u->d, n_width);
bn_select_words(v->d, both_odd & ~v_less_than_u, tmp->d, v->d, n_width);
bn_sub_words(tmp->d, u->d, v->d, n_width);
bn_select_words(u->d, both_odd & v_less_than_u, tmp->d, u->d, n_width);
// If we updated one of the values, update the corresponding coefficient.
BN_ULONG carry = bn_add_words(tmp->d, A->d, C->d, n_width);
carry -= bn_sub_words(tmp2->d, tmp->d, n->d, n_width);
bn_select_words(tmp->d, carry, tmp->d, tmp2->d, n_width);
bn_select_words(A->d, both_odd & v_less_than_u, tmp->d, A->d, n_width);
bn_select_words(C->d, both_odd & ~v_less_than_u, tmp->d, C->d, n_width);
bn_add_words(tmp->d, B->d, D->d, a_width);
bn_sub_words(tmp2->d, tmp->d, a->d, a_width);
bn_select_words(tmp->d, carry, tmp->d, tmp2->d, a_width);
bn_select_words(B->d, both_odd & v_less_than_u, tmp->d, B->d, a_width);
bn_select_words(D->d, both_odd & ~v_less_than_u, tmp->d, D->d, a_width);
// Our loop invariants hold at this point. Additionally, exactly one of |u|
// and |v| is now even.
BN_ULONG u_is_even = ~word_is_odd_mask(u->d[0]);
BN_ULONG v_is_even = ~word_is_odd_mask(v->d[0]);
assert(u_is_even != v_is_even);
// Halve the even one and adjust the corresponding coefficient.
maybe_rshift1_words(u->d, u_is_even, tmp->d, n_width);
BN_ULONG A_or_B_is_odd =
word_is_odd_mask(A->d[0]) | word_is_odd_mask(B->d[0]);
BN_ULONG A_carry =
maybe_add_words(A->d, A_or_B_is_odd & u_is_even, n->d, tmp->d, n_width);
BN_ULONG B_carry =
maybe_add_words(B->d, A_or_B_is_odd & u_is_even, a->d, tmp->d, a_width);
maybe_rshift1_words_carry(A->d, A_carry, u_is_even, tmp->d, n_width);
maybe_rshift1_words_carry(B->d, B_carry, u_is_even, tmp->d, a_width);
maybe_rshift1_words(v->d, v_is_even, tmp->d, n_width);
BN_ULONG C_or_D_is_odd =
word_is_odd_mask(C->d[0]) | word_is_odd_mask(D->d[0]);
BN_ULONG C_carry =
maybe_add_words(C->d, C_or_D_is_odd & v_is_even, n->d, tmp->d, n_width);
BN_ULONG D_carry =
maybe_add_words(D->d, C_or_D_is_odd & v_is_even, a->d, tmp->d, a_width);
maybe_rshift1_words_carry(C->d, C_carry, v_is_even, tmp->d, n_width);
maybe_rshift1_words_carry(D->d, D_carry, v_is_even, tmp->d, a_width);
}
assert(BN_is_zero(v));
if (!BN_is_one(u)) {
*out_no_inverse = 1;
OPENSSL_PUT_ERROR(BN, BN_R_NO_INVERSE);
goto err;
}
ret = BN_copy(r, A) != NULL;
err:
BN_CTX_end(ctx);
return ret;
}
int BN_mod_inverse_odd(BIGNUM *out, int *out_no_inverse, const BIGNUM *a,
const BIGNUM *n, BN_CTX *ctx) {
*out_no_inverse = 0;
if (!BN_is_odd(n)) {
OPENSSL_PUT_ERROR(BN, BN_R_CALLED_WITH_EVEN_MODULUS);
return 0;
}
if (BN_is_negative(a) || BN_cmp(a, n) >= 0) {
OPENSSL_PUT_ERROR(BN, BN_R_INPUT_NOT_REDUCED);
return 0;
}
BIGNUM *A, *B, *X, *Y;
int ret = 0;
int sign;
BN_CTX_start(ctx);
A = BN_CTX_get(ctx);
B = BN_CTX_get(ctx);
X = BN_CTX_get(ctx);
Y = BN_CTX_get(ctx);
if (Y == NULL) {
goto err;
}
BIGNUM *R = out;
BN_zero(Y);
if (!BN_one(X) || BN_copy(B, a) == NULL || BN_copy(A, n) == NULL) {
goto err;
}
A->neg = 0;
sign = -1;
// From B = a mod |n|, A = |n| it follows that
//
// 0 <= B < A,
// -sign*X*a == B (mod |n|),
// sign*Y*a == A (mod |n|).
// Binary inversion algorithm; requires odd modulus. This is faster than the
// general algorithm if the modulus is sufficiently small (about 400 .. 500
// bits on 32-bit systems, but much more on 64-bit systems)
int shift;
while (!BN_is_zero(B)) {
// 0 < B < |n|,
// 0 < A <= |n|,
// (1) -sign*X*a == B (mod |n|),
// (2) sign*Y*a == A (mod |n|)
// Now divide B by the maximum possible power of two in the integers,
// and divide X by the same value mod |n|.
// When we're done, (1) still holds.
shift = 0;
while (!BN_is_bit_set(B, shift)) {
// note that 0 < B
shift++;
if (BN_is_odd(X)) {
if (!BN_uadd(X, X, n)) {
goto err;
}
}
// now X is even, so we can easily divide it by two
if (!BN_rshift1(X, X)) {
goto err;
}
}
if (shift > 0) {
if (!BN_rshift(B, B, shift)) {
goto err;
}
}
// Same for A and Y. Afterwards, (2) still holds.
shift = 0;
while (!BN_is_bit_set(A, shift)) {
// note that 0 < A
shift++;
if (BN_is_odd(Y)) {
if (!BN_uadd(Y, Y, n)) {
goto err;
}
}
// now Y is even
if (!BN_rshift1(Y, Y)) {
goto err;
}
}
if (shift > 0) {
if (!BN_rshift(A, A, shift)) {
goto err;
}
}
// We still have (1) and (2).
// Both A and B are odd.
// The following computations ensure that
//
// 0 <= B < |n|,
// 0 < A < |n|,
// (1) -sign*X*a == B (mod |n|),
// (2) sign*Y*a == A (mod |n|),
//
// and that either A or B is even in the next iteration.
if (BN_ucmp(B, A) >= 0) {
// -sign*(X + Y)*a == B - A (mod |n|)
if (!BN_uadd(X, X, Y)) {
goto err;
}
// NB: we could use BN_mod_add_quick(X, X, Y, n), but that
// actually makes the algorithm slower
if (!BN_usub(B, B, A)) {
goto err;
}
} else {
// sign*(X + Y)*a == A - B (mod |n|)
if (!BN_uadd(Y, Y, X)) {
goto err;
}
// as above, BN_mod_add_quick(Y, Y, X, n) would slow things down
if (!BN_usub(A, A, B)) {
goto err;
}
}
}
if (!BN_is_one(A)) {
*out_no_inverse = 1;
OPENSSL_PUT_ERROR(BN, BN_R_NO_INVERSE);
goto err;
}
// The while loop (Euclid's algorithm) ends when
// A == gcd(a,n);
// we have
// sign*Y*a == A (mod |n|),
// where Y is non-negative.
if (sign < 0) {
if (!BN_sub(Y, n, Y)) {
goto err;
}
}
// Now Y*a == A (mod |n|).
// Y*a == 1 (mod |n|)
if (!Y->neg && BN_ucmp(Y, n) < 0) {
if (!BN_copy(R, Y)) {
goto err;
}
} else {
if (!BN_nnmod(R, Y, n, ctx)) {
goto err;
}
}
ret = 1;
err:
BN_CTX_end(ctx);
return ret;
}
BIGNUM *BN_mod_inverse(BIGNUM *out, const BIGNUM *a, const BIGNUM *n,
BN_CTX *ctx) {
BIGNUM *new_out = NULL;
if (out == NULL) {
new_out = BN_new();
if (new_out == NULL) {
OPENSSL_PUT_ERROR(BN, ERR_R_MALLOC_FAILURE);
return NULL;
}
out = new_out;
}
int ok = 0;
BIGNUM *a_reduced = NULL;
if (a->neg || BN_ucmp(a, n) >= 0) {
a_reduced = BN_dup(a);
if (a_reduced == NULL) {
goto err;
}
if (!BN_nnmod(a_reduced, a_reduced, n, ctx)) {
goto err;
}
a = a_reduced;
}
int no_inverse;
if (!BN_is_odd(n)) {
if (!bn_mod_inverse_consttime(out, &no_inverse, a, n, ctx)) {
goto err;
}
} else if (!BN_mod_inverse_odd(out, &no_inverse, a, n, ctx)) {
goto err;
}
ok = 1;
err:
if (!ok) {
BN_free(new_out);
out = NULL;
}
BN_free(a_reduced);
return out;
}
int BN_mod_inverse_blinded(BIGNUM *out, int *out_no_inverse, const BIGNUM *a,
const BN_MONT_CTX *mont, BN_CTX *ctx) {
*out_no_inverse = 0;
if (BN_is_negative(a) || BN_cmp(a, &mont->N) >= 0) {
OPENSSL_PUT_ERROR(BN, BN_R_INPUT_NOT_REDUCED);
return 0;
}
int ret = 0;
BIGNUM blinding_factor;
BN_init(&blinding_factor);
if (!BN_rand_range_ex(&blinding_factor, 1, &mont->N) ||
!BN_mod_mul_montgomery(out, &blinding_factor, a, mont, ctx) ||
!BN_mod_inverse_odd(out, out_no_inverse, out, &mont->N, ctx) ||
!BN_mod_mul_montgomery(out, &blinding_factor, out, mont, ctx)) {
OPENSSL_PUT_ERROR(BN, ERR_R_BN_LIB);
goto err;
}
ret = 1;
err:
BN_free(&blinding_factor);
return ret;
}
int bn_mod_inverse_prime(BIGNUM *out, const BIGNUM *a, const BIGNUM *p,
BN_CTX *ctx, const BN_MONT_CTX *mont_p) {
BN_CTX_start(ctx);
BIGNUM *p_minus_2 = BN_CTX_get(ctx);
int ok = p_minus_2 != NULL &&
BN_copy(p_minus_2, p) &&
BN_sub_word(p_minus_2, 2) &&
BN_mod_exp_mont(out, a, p_minus_2, p, ctx, mont_p);
BN_CTX_end(ctx);
return ok;
}
int bn_mod_inverse_secret_prime(BIGNUM *out, const BIGNUM *a, const BIGNUM *p,
BN_CTX *ctx, const BN_MONT_CTX *mont_p) {
BN_CTX_start(ctx);
BIGNUM *p_minus_2 = BN_CTX_get(ctx);
int ok = p_minus_2 != NULL &&
BN_copy(p_minus_2, p) &&
BN_sub_word(p_minus_2, 2) &&
BN_mod_exp_mont_consttime(out, a, p_minus_2, p, ctx, mont_p);
BN_CTX_end(ctx);
return ok;
}
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