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/*
* Copyright 1995-2022 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
*/
#include <stdio.h>
#include "internal/cryptlib.h"
#include "bn_local.h"
#define TABLE_SIZE 32
int BN_mod_exp2_mont(BIGNUM *rr, const BIGNUM *a1, const BIGNUM *p1,
const BIGNUM *a2, const BIGNUM *p2, const BIGNUM *m,
BN_CTX *ctx, BN_MONT_CTX *in_mont)
{
int i, j, bits, b, bits1, bits2, ret =
0, wpos1, wpos2, window1, window2, wvalue1, wvalue2;
int r_is_one = 1;
BIGNUM *d, *r;
const BIGNUM *a_mod_m;
/* Tables of variables obtained from 'ctx' */
BIGNUM *val1[TABLE_SIZE], *val2[TABLE_SIZE];
BN_MONT_CTX *mont = NULL;
bn_check_top(a1);
bn_check_top(p1);
bn_check_top(a2);
bn_check_top(p2);
bn_check_top(m);
if (!BN_is_odd(m)) {
BNerr(BN_F_BN_MOD_EXP2_MONT, BN_R_CALLED_WITH_EVEN_MODULUS);
return 0;
}
bits1 = BN_num_bits(p1);
bits2 = BN_num_bits(p2);
if ((bits1 == 0) && (bits2 == 0)) {
ret = BN_one(rr);
return ret;
}
bits = (bits1 > bits2) ? bits1 : bits2;
BN_CTX_start(ctx);
d = BN_CTX_get(ctx);
r = BN_CTX_get(ctx);
val1[0] = BN_CTX_get(ctx);
val2[0] = BN_CTX_get(ctx);
if (val2[0] == NULL)
goto err;
if (in_mont != NULL)
mont = in_mont;
else {
if ((mont = BN_MONT_CTX_new()) == NULL)
goto err;
if (!BN_MONT_CTX_set(mont, m, ctx))
goto err;
}
window1 = BN_window_bits_for_exponent_size(bits1);
window2 = BN_window_bits_for_exponent_size(bits2);
/*
* Build table for a1: val1[i] := a1^(2*i + 1) mod m for i = 0 .. 2^(window1-1)
*/
if (a1->neg || BN_ucmp(a1, m) >= 0) {
if (!BN_mod(val1[0], a1, m, ctx))
goto err;
a_mod_m = val1[0];
} else
a_mod_m = a1;
if (BN_is_zero(a_mod_m)) {
BN_zero(rr);
ret = 1;
goto err;
}
if (!BN_to_montgomery(val1[0], a_mod_m, mont, ctx))
goto err;
if (window1 > 1) {
if (!BN_mod_mul_montgomery(d, val1[0], val1[0], mont, ctx))
goto err;
j = 1 << (window1 - 1);
for (i = 1; i < j; i++) {
if (((val1[i] = BN_CTX_get(ctx)) == NULL) ||
!BN_mod_mul_montgomery(val1[i], val1[i - 1], d, mont, ctx))
goto err;
}
}
/*
* Build table for a2: val2[i] := a2^(2*i + 1) mod m for i = 0 .. 2^(window2-1)
*/
if (a2->neg || BN_ucmp(a2, m) >= 0) {
if (!BN_mod(val2[0], a2, m, ctx))
goto err;
a_mod_m = val2[0];
} else
a_mod_m = a2;
if (BN_is_zero(a_mod_m)) {
BN_zero(rr);
ret = 1;
goto err;
}
if (!BN_to_montgomery(val2[0], a_mod_m, mont, ctx))
goto err;
if (window2 > 1) {
if (!BN_mod_mul_montgomery(d, val2[0], val2[0], mont, ctx))
goto err;
j = 1 << (window2 - 1);
for (i = 1; i < j; i++) {
if (((val2[i] = BN_CTX_get(ctx)) == NULL) ||
!BN_mod_mul_montgomery(val2[i], val2[i - 1], d, mont, ctx))
goto err;
}
}
/* Now compute the power product, using independent windows. */
r_is_one = 1;
wvalue1 = 0; /* The 'value' of the first window */
wvalue2 = 0; /* The 'value' of the second window */
wpos1 = 0; /* If wvalue1 > 0, the bottom bit of the
* first window */
wpos2 = 0; /* If wvalue2 > 0, the bottom bit of the
* second window */
if (!BN_to_montgomery(r, BN_value_one(), mont, ctx))
goto err;
for (b = bits - 1; b >= 0; b--) {
if (!r_is_one) {
if (!BN_mod_mul_montgomery(r, r, r, mont, ctx))
goto err;
}
if (!wvalue1)
if (BN_is_bit_set(p1, b)) {
/*
* consider bits b-window1+1 .. b for this window
*/
i = b - window1 + 1;
while (!BN_is_bit_set(p1, i)) /* works for i<0 */
i++;
wpos1 = i;
wvalue1 = 1;
for (i = b - 1; i >= wpos1; i--) {
wvalue1 <<= 1;
if (BN_is_bit_set(p1, i))
wvalue1++;
}
}
if (!wvalue2)
if (BN_is_bit_set(p2, b)) {
/*
* consider bits b-window2+1 .. b for this window
*/
i = b - window2 + 1;
while (!BN_is_bit_set(p2, i))
i++;
wpos2 = i;
wvalue2 = 1;
for (i = b - 1; i >= wpos2; i--) {
wvalue2 <<= 1;
if (BN_is_bit_set(p2, i))
wvalue2++;
}
}
if (wvalue1 && b == wpos1) {
/* wvalue1 is odd and < 2^window1 */
if (!BN_mod_mul_montgomery(r, r, val1[wvalue1 >> 1], mont, ctx))
goto err;
wvalue1 = 0;
r_is_one = 0;
}
if (wvalue2 && b == wpos2) {
/* wvalue2 is odd and < 2^window2 */
if (!BN_mod_mul_montgomery(r, r, val2[wvalue2 >> 1], mont, ctx))
goto err;
wvalue2 = 0;
r_is_one = 0;
}
}
if (!BN_from_montgomery(rr, r, mont, ctx))
goto err;
ret = 1;
err:
if (in_mont == NULL)
BN_MONT_CTX_free(mont);
BN_CTX_end(ctx);
bn_check_top(rr);
return ret;
}
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