[331] | 1 | /*
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| 2 | * Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
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| 3 | *
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| 4 | * Licensed under the OpenSSL license (the "License"). You may not use
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| 5 | * this file except in compliance with the License. You can obtain a copy
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| 6 | * in the file LICENSE in the source distribution or at
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| 7 | * https://www.openssl.org/source/license.html
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| 8 | */
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| 9 |
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| 10 | #include <stdio.h>
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| 11 | #include "internal/cryptlib.h"
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| 12 | #include "bn_lcl.h"
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| 13 |
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| 14 | #define TABLE_SIZE 32
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| 15 |
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| 16 | int BN_mod_exp2_mont(BIGNUM *rr, const BIGNUM *a1, const BIGNUM *p1,
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| 17 | const BIGNUM *a2, const BIGNUM *p2, const BIGNUM *m,
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| 18 | BN_CTX *ctx, BN_MONT_CTX *in_mont)
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| 19 | {
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| 20 | int i, j, bits, b, bits1, bits2, ret =
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| 21 | 0, wpos1, wpos2, window1, window2, wvalue1, wvalue2;
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| 22 | int r_is_one = 1;
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| 23 | BIGNUM *d, *r;
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| 24 | const BIGNUM *a_mod_m;
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| 25 | /* Tables of variables obtained from 'ctx' */
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| 26 | BIGNUM *val1[TABLE_SIZE], *val2[TABLE_SIZE];
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| 27 | BN_MONT_CTX *mont = NULL;
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| 28 |
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| 29 | bn_check_top(a1);
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| 30 | bn_check_top(p1);
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| 31 | bn_check_top(a2);
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| 32 | bn_check_top(p2);
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| 33 | bn_check_top(m);
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| 34 |
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| 35 | if (!(m->d[0] & 1)) {
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| 36 | BNerr(BN_F_BN_MOD_EXP2_MONT, BN_R_CALLED_WITH_EVEN_MODULUS);
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| 37 | return (0);
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| 38 | }
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| 39 | bits1 = BN_num_bits(p1);
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| 40 | bits2 = BN_num_bits(p2);
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| 41 | if ((bits1 == 0) && (bits2 == 0)) {
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| 42 | ret = BN_one(rr);
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| 43 | return ret;
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| 44 | }
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| 45 |
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| 46 | bits = (bits1 > bits2) ? bits1 : bits2;
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| 47 |
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| 48 | BN_CTX_start(ctx);
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| 49 | d = BN_CTX_get(ctx);
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| 50 | r = BN_CTX_get(ctx);
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| 51 | val1[0] = BN_CTX_get(ctx);
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| 52 | val2[0] = BN_CTX_get(ctx);
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| 53 | if (!d || !r || !val1[0] || !val2[0])
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| 54 | goto err;
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| 55 |
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| 56 | if (in_mont != NULL)
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| 57 | mont = in_mont;
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| 58 | else {
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| 59 | if ((mont = BN_MONT_CTX_new()) == NULL)
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| 60 | goto err;
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| 61 | if (!BN_MONT_CTX_set(mont, m, ctx))
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| 62 | goto err;
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| 63 | }
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| 64 |
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| 65 | window1 = BN_window_bits_for_exponent_size(bits1);
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| 66 | window2 = BN_window_bits_for_exponent_size(bits2);
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| 67 |
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| 68 | /*
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| 69 | * Build table for a1: val1[i] := a1^(2*i + 1) mod m for i = 0 .. 2^(window1-1)
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| 70 | */
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| 71 | if (a1->neg || BN_ucmp(a1, m) >= 0) {
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| 72 | if (!BN_mod(val1[0], a1, m, ctx))
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| 73 | goto err;
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| 74 | a_mod_m = val1[0];
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| 75 | } else
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| 76 | a_mod_m = a1;
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| 77 | if (BN_is_zero(a_mod_m)) {
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| 78 | BN_zero(rr);
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| 79 | ret = 1;
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| 80 | goto err;
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| 81 | }
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| 82 |
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| 83 | if (!BN_to_montgomery(val1[0], a_mod_m, mont, ctx))
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| 84 | goto err;
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| 85 | if (window1 > 1) {
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| 86 | if (!BN_mod_mul_montgomery(d, val1[0], val1[0], mont, ctx))
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| 87 | goto err;
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| 88 |
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| 89 | j = 1 << (window1 - 1);
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| 90 | for (i = 1; i < j; i++) {
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| 91 | if (((val1[i] = BN_CTX_get(ctx)) == NULL) ||
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| 92 | !BN_mod_mul_montgomery(val1[i], val1[i - 1], d, mont, ctx))
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| 93 | goto err;
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| 94 | }
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| 95 | }
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| 96 |
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| 97 | /*
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| 98 | * Build table for a2: val2[i] := a2^(2*i + 1) mod m for i = 0 .. 2^(window2-1)
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| 99 | */
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| 100 | if (a2->neg || BN_ucmp(a2, m) >= 0) {
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| 101 | if (!BN_mod(val2[0], a2, m, ctx))
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| 102 | goto err;
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| 103 | a_mod_m = val2[0];
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| 104 | } else
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| 105 | a_mod_m = a2;
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| 106 | if (BN_is_zero(a_mod_m)) {
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| 107 | BN_zero(rr);
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| 108 | ret = 1;
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| 109 | goto err;
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| 110 | }
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| 111 | if (!BN_to_montgomery(val2[0], a_mod_m, mont, ctx))
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| 112 | goto err;
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| 113 | if (window2 > 1) {
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| 114 | if (!BN_mod_mul_montgomery(d, val2[0], val2[0], mont, ctx))
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| 115 | goto err;
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| 116 |
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| 117 | j = 1 << (window2 - 1);
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| 118 | for (i = 1; i < j; i++) {
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| 119 | if (((val2[i] = BN_CTX_get(ctx)) == NULL) ||
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| 120 | !BN_mod_mul_montgomery(val2[i], val2[i - 1], d, mont, ctx))
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| 121 | goto err;
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| 122 | }
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| 123 | }
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| 124 |
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| 125 | /* Now compute the power product, using independent windows. */
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| 126 | r_is_one = 1;
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| 127 | wvalue1 = 0; /* The 'value' of the first window */
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| 128 | wvalue2 = 0; /* The 'value' of the second window */
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| 129 | wpos1 = 0; /* If wvalue1 > 0, the bottom bit of the
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| 130 | * first window */
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| 131 | wpos2 = 0; /* If wvalue2 > 0, the bottom bit of the
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| 132 | * second window */
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| 133 |
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| 134 | if (!BN_to_montgomery(r, BN_value_one(), mont, ctx))
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| 135 | goto err;
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| 136 | for (b = bits - 1; b >= 0; b--) {
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| 137 | if (!r_is_one) {
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| 138 | if (!BN_mod_mul_montgomery(r, r, r, mont, ctx))
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| 139 | goto err;
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| 140 | }
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| 141 |
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| 142 | if (!wvalue1)
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| 143 | if (BN_is_bit_set(p1, b)) {
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| 144 | /*
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| 145 | * consider bits b-window1+1 .. b for this window
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| 146 | */
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| 147 | i = b - window1 + 1;
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| 148 | while (!BN_is_bit_set(p1, i)) /* works for i<0 */
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| 149 | i++;
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| 150 | wpos1 = i;
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| 151 | wvalue1 = 1;
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| 152 | for (i = b - 1; i >= wpos1; i--) {
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| 153 | wvalue1 <<= 1;
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| 154 | if (BN_is_bit_set(p1, i))
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| 155 | wvalue1++;
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| 156 | }
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| 157 | }
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| 158 |
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| 159 | if (!wvalue2)
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| 160 | if (BN_is_bit_set(p2, b)) {
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| 161 | /*
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| 162 | * consider bits b-window2+1 .. b for this window
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| 163 | */
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| 164 | i = b - window2 + 1;
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| 165 | while (!BN_is_bit_set(p2, i))
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| 166 | i++;
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| 167 | wpos2 = i;
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| 168 | wvalue2 = 1;
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| 169 | for (i = b - 1; i >= wpos2; i--) {
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| 170 | wvalue2 <<= 1;
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| 171 | if (BN_is_bit_set(p2, i))
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| 172 | wvalue2++;
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| 173 | }
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| 174 | }
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| 175 |
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| 176 | if (wvalue1 && b == wpos1) {
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| 177 | /* wvalue1 is odd and < 2^window1 */
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| 178 | if (!BN_mod_mul_montgomery(r, r, val1[wvalue1 >> 1], mont, ctx))
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| 179 | goto err;
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| 180 | wvalue1 = 0;
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| 181 | r_is_one = 0;
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| 182 | }
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| 183 |
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| 184 | if (wvalue2 && b == wpos2) {
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| 185 | /* wvalue2 is odd and < 2^window2 */
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| 186 | if (!BN_mod_mul_montgomery(r, r, val2[wvalue2 >> 1], mont, ctx))
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| 187 | goto err;
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| 188 | wvalue2 = 0;
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| 189 | r_is_one = 0;
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| 190 | }
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| 191 | }
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| 192 | if (!BN_from_montgomery(rr, r, mont, ctx))
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| 193 | goto err;
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| 194 | ret = 1;
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| 195 | err:
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| 196 | if (in_mont == NULL)
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| 197 | BN_MONT_CTX_free(mont);
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| 198 | BN_CTX_end(ctx);
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| 199 | bn_check_top(rr);
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| 200 | return (ret);
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| 201 | }
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