202 lines
5.8 KiB
C
202 lines
5.8 KiB
C
/*
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* Copyright 1995-2022 The OpenSSL Project Authors. All Rights Reserved.
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*
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* Licensed under the Apache License 2.0 (the "License"). You may not use
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* this file except in compliance with the License. You can obtain a copy
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* in the file LICENSE in the source distribution or at
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* https://www.openssl.org/source/license.html
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*/
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#include <stdio.h>
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#include "internal/cryptlib.h"
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#include "bn_local.h"
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#define TABLE_SIZE 32
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int BN_mod_exp2_mont(BIGNUM *rr, const BIGNUM *a1, const BIGNUM *p1,
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const BIGNUM *a2, const BIGNUM *p2, const BIGNUM *m,
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BN_CTX *ctx, BN_MONT_CTX *in_mont)
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{
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int i, j, bits, b, bits1, bits2, ret =
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0, wpos1, wpos2, window1, window2, wvalue1, wvalue2;
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int r_is_one = 1;
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BIGNUM *d, *r;
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const BIGNUM *a_mod_m;
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/* Tables of variables obtained from 'ctx' */
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BIGNUM *val1[TABLE_SIZE], *val2[TABLE_SIZE];
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BN_MONT_CTX *mont = NULL;
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bn_check_top(a1);
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bn_check_top(p1);
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bn_check_top(a2);
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bn_check_top(p2);
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bn_check_top(m);
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if (!BN_is_odd(m)) {
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ERR_raise(ERR_LIB_BN, BN_R_CALLED_WITH_EVEN_MODULUS);
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return 0;
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}
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bits1 = BN_num_bits(p1);
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bits2 = BN_num_bits(p2);
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if ((bits1 == 0) && (bits2 == 0)) {
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ret = BN_one(rr);
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return ret;
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}
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bits = (bits1 > bits2) ? bits1 : bits2;
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BN_CTX_start(ctx);
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d = BN_CTX_get(ctx);
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r = BN_CTX_get(ctx);
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val1[0] = BN_CTX_get(ctx);
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val2[0] = BN_CTX_get(ctx);
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if (val2[0] == NULL)
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goto err;
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if (in_mont != NULL)
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mont = in_mont;
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else {
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if ((mont = BN_MONT_CTX_new()) == NULL)
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goto err;
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if (!BN_MONT_CTX_set(mont, m, ctx))
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goto err;
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}
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window1 = BN_window_bits_for_exponent_size(bits1);
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window2 = BN_window_bits_for_exponent_size(bits2);
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/*
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* Build table for a1: val1[i] := a1^(2*i + 1) mod m for i = 0 .. 2^(window1-1)
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*/
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if (a1->neg || BN_ucmp(a1, m) >= 0) {
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if (!BN_mod(val1[0], a1, m, ctx))
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goto err;
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a_mod_m = val1[0];
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} else
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a_mod_m = a1;
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if (BN_is_zero(a_mod_m)) {
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BN_zero(rr);
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ret = 1;
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goto err;
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}
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if (!BN_to_montgomery(val1[0], a_mod_m, mont, ctx))
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goto err;
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if (window1 > 1) {
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if (!BN_mod_mul_montgomery(d, val1[0], val1[0], mont, ctx))
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goto err;
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j = 1 << (window1 - 1);
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for (i = 1; i < j; i++) {
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if (((val1[i] = BN_CTX_get(ctx)) == NULL) ||
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!BN_mod_mul_montgomery(val1[i], val1[i - 1], d, mont, ctx))
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goto err;
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}
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}
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/*
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* Build table for a2: val2[i] := a2^(2*i + 1) mod m for i = 0 .. 2^(window2-1)
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*/
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if (a2->neg || BN_ucmp(a2, m) >= 0) {
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if (!BN_mod(val2[0], a2, m, ctx))
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goto err;
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a_mod_m = val2[0];
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} else
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a_mod_m = a2;
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if (BN_is_zero(a_mod_m)) {
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BN_zero(rr);
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ret = 1;
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goto err;
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}
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if (!BN_to_montgomery(val2[0], a_mod_m, mont, ctx))
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goto err;
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if (window2 > 1) {
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if (!BN_mod_mul_montgomery(d, val2[0], val2[0], mont, ctx))
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goto err;
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j = 1 << (window2 - 1);
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for (i = 1; i < j; i++) {
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if (((val2[i] = BN_CTX_get(ctx)) == NULL) ||
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!BN_mod_mul_montgomery(val2[i], val2[i - 1], d, mont, ctx))
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goto err;
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}
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}
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/* Now compute the power product, using independent windows. */
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r_is_one = 1;
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wvalue1 = 0; /* The 'value' of the first window */
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wvalue2 = 0; /* The 'value' of the second window */
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wpos1 = 0; /* If wvalue1 > 0, the bottom bit of the
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* first window */
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wpos2 = 0; /* If wvalue2 > 0, the bottom bit of the
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* second window */
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if (!BN_to_montgomery(r, BN_value_one(), mont, ctx))
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goto err;
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for (b = bits - 1; b >= 0; b--) {
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if (!r_is_one) {
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if (!BN_mod_mul_montgomery(r, r, r, mont, ctx))
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goto err;
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}
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if (!wvalue1)
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if (BN_is_bit_set(p1, b)) {
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/*
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* consider bits b-window1+1 .. b for this window
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*/
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i = b - window1 + 1;
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while (!BN_is_bit_set(p1, i)) /* works for i<0 */
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i++;
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wpos1 = i;
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wvalue1 = 1;
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for (i = b - 1; i >= wpos1; i--) {
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wvalue1 <<= 1;
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if (BN_is_bit_set(p1, i))
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wvalue1++;
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}
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}
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if (!wvalue2)
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if (BN_is_bit_set(p2, b)) {
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/*
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* consider bits b-window2+1 .. b for this window
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*/
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i = b - window2 + 1;
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while (!BN_is_bit_set(p2, i))
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i++;
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wpos2 = i;
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wvalue2 = 1;
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for (i = b - 1; i >= wpos2; i--) {
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wvalue2 <<= 1;
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if (BN_is_bit_set(p2, i))
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wvalue2++;
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}
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}
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if (wvalue1 && b == wpos1) {
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/* wvalue1 is odd and < 2^window1 */
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if (!BN_mod_mul_montgomery(r, r, val1[wvalue1 >> 1], mont, ctx))
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goto err;
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wvalue1 = 0;
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r_is_one = 0;
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}
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if (wvalue2 && b == wpos2) {
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/* wvalue2 is odd and < 2^window2 */
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if (!BN_mod_mul_montgomery(r, r, val2[wvalue2 >> 1], mont, ctx))
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goto err;
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wvalue2 = 0;
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r_is_one = 0;
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}
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}
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if (!BN_from_montgomery(rr, r, mont, ctx))
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goto err;
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ret = 1;
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err:
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if (in_mont == NULL)
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BN_MONT_CTX_free(mont);
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BN_CTX_end(ctx);
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bn_check_top(rr);
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return ret;
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}
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