1/* 2 * Copyright 1995-2022 The OpenSSL Project Authors. All Rights Reserved. 3 * 4 * Licensed under the Apache License 2.0 (the "License"). You may not use 5 * this file except in compliance with the License. You can obtain a copy 6 * in the file LICENSE in the source distribution or at 7 * https://www.openssl.org/source/license.html 8 */ 9 10#include <stdio.h> 11#include "internal/cryptlib.h" 12#include "bn_local.h" 13 14#define TABLE_SIZE 32 15 16int BN_mod_exp2_mont(BIGNUM *rr, const BIGNUM *a1, const BIGNUM *p1, 17 const BIGNUM *a2, const BIGNUM *p2, const BIGNUM *m, 18 BN_CTX *ctx, BN_MONT_CTX *in_mont) 19{ 20 int i, j, bits, b, bits1, bits2, ret = 21 0, wpos1, wpos2, window1, window2, wvalue1, wvalue2; 22 int r_is_one = 1; 23 BIGNUM *d, *r; 24 const BIGNUM *a_mod_m; 25 /* Tables of variables obtained from 'ctx' */ 26 BIGNUM *val1[TABLE_SIZE], *val2[TABLE_SIZE]; 27 BN_MONT_CTX *mont = NULL; 28 29 bn_check_top(a1); 30 bn_check_top(p1); 31 bn_check_top(a2); 32 bn_check_top(p2); 33 bn_check_top(m); 34 35 if (!BN_is_odd(m)) { 36 ERR_raise(ERR_LIB_BN, BN_R_CALLED_WITH_EVEN_MODULUS); 37 return 0; 38 } 39 bits1 = BN_num_bits(p1); 40 bits2 = BN_num_bits(p2); 41 if ((bits1 == 0) && (bits2 == 0)) { 42 ret = BN_one(rr); 43 return ret; 44 } 45 46 bits = (bits1 > bits2) ? bits1 : bits2; 47 48 BN_CTX_start(ctx); 49 d = BN_CTX_get(ctx); 50 r = BN_CTX_get(ctx); 51 val1[0] = BN_CTX_get(ctx); 52 val2[0] = BN_CTX_get(ctx); 53 if (val2[0] == NULL) 54 goto err; 55 56 if (in_mont != NULL) 57 mont = in_mont; 58 else { 59 if ((mont = BN_MONT_CTX_new()) == NULL) 60 goto err; 61 if (!BN_MONT_CTX_set(mont, m, ctx)) 62 goto err; 63 } 64 65 window1 = BN_window_bits_for_exponent_size(bits1); 66 window2 = BN_window_bits_for_exponent_size(bits2); 67 68 /* 69 * Build table for a1: val1[i] := a1^(2*i + 1) mod m for i = 0 .. 2^(window1-1) 70 */ 71 if (a1->neg || BN_ucmp(a1, m) >= 0) { 72 if (!BN_mod(val1[0], a1, m, ctx)) 73 goto err; 74 a_mod_m = val1[0]; 75 } else 76 a_mod_m = a1; 77 if (BN_is_zero(a_mod_m)) { 78 BN_zero(rr); 79 ret = 1; 80 goto err; 81 } 82 83 if (!BN_to_montgomery(val1[0], a_mod_m, mont, ctx)) 84 goto err; 85 if (window1 > 1) { 86 if (!BN_mod_mul_montgomery(d, val1[0], val1[0], mont, ctx)) 87 goto err; 88 89 j = 1 << (window1 - 1); 90 for (i = 1; i < j; i++) { 91 if (((val1[i] = BN_CTX_get(ctx)) == NULL) || 92 !BN_mod_mul_montgomery(val1[i], val1[i - 1], d, mont, ctx)) 93 goto err; 94 } 95 } 96 97 /* 98 * Build table for a2: val2[i] := a2^(2*i + 1) mod m for i = 0 .. 2^(window2-1) 99 */ 100 if (a2->neg || BN_ucmp(a2, m) >= 0) { 101 if (!BN_mod(val2[0], a2, m, ctx)) 102 goto err; 103 a_mod_m = val2[0]; 104 } else 105 a_mod_m = a2; 106 if (BN_is_zero(a_mod_m)) { 107 BN_zero(rr); 108 ret = 1; 109 goto err; 110 } 111 if (!BN_to_montgomery(val2[0], a_mod_m, mont, ctx)) 112 goto err; 113 if (window2 > 1) { 114 if (!BN_mod_mul_montgomery(d, val2[0], val2[0], mont, ctx)) 115 goto err; 116 117 j = 1 << (window2 - 1); 118 for (i = 1; i < j; i++) { 119 if (((val2[i] = BN_CTX_get(ctx)) == NULL) || 120 !BN_mod_mul_montgomery(val2[i], val2[i - 1], d, mont, ctx)) 121 goto err; 122 } 123 } 124 125 /* Now compute the power product, using independent windows. */ 126 r_is_one = 1; 127 wvalue1 = 0; /* The 'value' of the first window */ 128 wvalue2 = 0; /* The 'value' of the second window */ 129 wpos1 = 0; /* If wvalue1 > 0, the bottom bit of the 130 * first window */ 131 wpos2 = 0; /* If wvalue2 > 0, the bottom bit of the 132 * second window */ 133 134 if (!BN_to_montgomery(r, BN_value_one(), mont, ctx)) 135 goto err; 136 for (b = bits - 1; b >= 0; b--) { 137 if (!r_is_one) { 138 if (!BN_mod_mul_montgomery(r, r, r, mont, ctx)) 139 goto err; 140 } 141 142 if (!wvalue1) 143 if (BN_is_bit_set(p1, b)) { 144 /* 145 * consider bits b-window1+1 .. b for this window 146 */ 147 i = b - window1 + 1; 148 while (!BN_is_bit_set(p1, i)) /* works for i<0 */ 149 i++; 150 wpos1 = i; 151 wvalue1 = 1; 152 for (i = b - 1; i >= wpos1; i--) { 153 wvalue1 <<= 1; 154 if (BN_is_bit_set(p1, i)) 155 wvalue1++; 156 } 157 } 158 159 if (!wvalue2) 160 if (BN_is_bit_set(p2, b)) { 161 /* 162 * consider bits b-window2+1 .. b for this window 163 */ 164 i = b - window2 + 1; 165 while (!BN_is_bit_set(p2, i)) 166 i++; 167 wpos2 = i; 168 wvalue2 = 1; 169 for (i = b - 1; i >= wpos2; i--) { 170 wvalue2 <<= 1; 171 if (BN_is_bit_set(p2, i)) 172 wvalue2++; 173 } 174 } 175 176 if (wvalue1 && b == wpos1) { 177 /* wvalue1 is odd and < 2^window1 */ 178 if (!BN_mod_mul_montgomery(r, r, val1[wvalue1 >> 1], mont, ctx)) 179 goto err; 180 wvalue1 = 0; 181 r_is_one = 0; 182 } 183 184 if (wvalue2 && b == wpos2) { 185 /* wvalue2 is odd and < 2^window2 */ 186 if (!BN_mod_mul_montgomery(r, r, val2[wvalue2 >> 1], mont, ctx)) 187 goto err; 188 wvalue2 = 0; 189 r_is_one = 0; 190 } 191 } 192 if (!BN_from_montgomery(rr, r, mont, ctx)) 193 goto err; 194 ret = 1; 195 err: 196 if (in_mont == NULL) 197 BN_MONT_CTX_free(mont); 198 BN_CTX_end(ctx); 199 bn_check_top(rr); 200 return ret; 201} 202