1 | /*
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2 | * Copyright 1998-2016 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 "internal/cryptlib.h"
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11 | #include "bn_lcl.h"
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12 |
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13 | int BN_nnmod(BIGNUM *r, const BIGNUM *m, const BIGNUM *d, BN_CTX *ctx)
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14 | {
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15 | /*
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16 | * like BN_mod, but returns non-negative remainder (i.e., 0 <= r < |d|
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17 | * always holds)
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18 | */
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19 |
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20 | if (!(BN_mod(r, m, d, ctx)))
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21 | return 0;
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22 | if (!r->neg)
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23 | return 1;
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24 | /* now -|d| < r < 0, so we have to set r := r + |d| */
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25 | return (d->neg ? BN_sub : BN_add) (r, r, d);
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26 | }
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27 |
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28 | int BN_mod_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m,
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29 | BN_CTX *ctx)
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30 | {
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31 | if (!BN_add(r, a, b))
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32 | return 0;
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33 | return BN_nnmod(r, r, m, ctx);
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34 | }
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35 |
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36 | /*
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37 | * BN_mod_add variant that may be used if both a and b are non-negative and
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38 | * less than m
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39 | */
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40 | int BN_mod_add_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
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41 | const BIGNUM *m)
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42 | {
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43 | if (!BN_uadd(r, a, b))
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44 | return 0;
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45 | if (BN_ucmp(r, m) >= 0)
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46 | return BN_usub(r, r, m);
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47 | return 1;
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48 | }
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49 |
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50 | int BN_mod_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m,
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51 | BN_CTX *ctx)
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52 | {
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53 | if (!BN_sub(r, a, b))
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54 | return 0;
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55 | return BN_nnmod(r, r, m, ctx);
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56 | }
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57 |
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58 | /*
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59 | * BN_mod_sub variant that may be used if both a and b are non-negative and
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60 | * less than m
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61 | */
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62 | int BN_mod_sub_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
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63 | const BIGNUM *m)
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64 | {
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65 | if (!BN_sub(r, a, b))
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66 | return 0;
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67 | if (r->neg)
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68 | return BN_add(r, r, m);
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69 | return 1;
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70 | }
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71 |
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72 | /* slow but works */
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73 | int BN_mod_mul(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, const BIGNUM *m,
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74 | BN_CTX *ctx)
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75 | {
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76 | BIGNUM *t;
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77 | int ret = 0;
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78 |
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79 | bn_check_top(a);
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80 | bn_check_top(b);
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81 | bn_check_top(m);
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82 |
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83 | BN_CTX_start(ctx);
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84 | if ((t = BN_CTX_get(ctx)) == NULL)
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85 | goto err;
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86 | if (a == b) {
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87 | if (!BN_sqr(t, a, ctx))
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88 | goto err;
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89 | } else {
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90 | if (!BN_mul(t, a, b, ctx))
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91 | goto err;
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92 | }
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93 | if (!BN_nnmod(r, t, m, ctx))
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94 | goto err;
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95 | bn_check_top(r);
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96 | ret = 1;
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97 | err:
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98 | BN_CTX_end(ctx);
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99 | return (ret);
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100 | }
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101 |
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102 | int BN_mod_sqr(BIGNUM *r, const BIGNUM *a, const BIGNUM *m, BN_CTX *ctx)
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103 | {
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104 | if (!BN_sqr(r, a, ctx))
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105 | return 0;
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106 | /* r->neg == 0, thus we don't need BN_nnmod */
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107 | return BN_mod(r, r, m, ctx);
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108 | }
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109 |
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110 | int BN_mod_lshift1(BIGNUM *r, const BIGNUM *a, const BIGNUM *m, BN_CTX *ctx)
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111 | {
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112 | if (!BN_lshift1(r, a))
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113 | return 0;
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114 | bn_check_top(r);
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115 | return BN_nnmod(r, r, m, ctx);
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116 | }
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117 |
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118 | /*
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119 | * BN_mod_lshift1 variant that may be used if a is non-negative and less than
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120 | * m
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121 | */
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122 | int BN_mod_lshift1_quick(BIGNUM *r, const BIGNUM *a, const BIGNUM *m)
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123 | {
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124 | if (!BN_lshift1(r, a))
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125 | return 0;
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126 | bn_check_top(r);
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127 | if (BN_cmp(r, m) >= 0)
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128 | return BN_sub(r, r, m);
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129 | return 1;
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130 | }
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131 |
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132 | int BN_mod_lshift(BIGNUM *r, const BIGNUM *a, int n, const BIGNUM *m,
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133 | BN_CTX *ctx)
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134 | {
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135 | BIGNUM *abs_m = NULL;
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136 | int ret;
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137 |
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138 | if (!BN_nnmod(r, a, m, ctx))
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139 | return 0;
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140 |
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141 | if (m->neg) {
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142 | abs_m = BN_dup(m);
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143 | if (abs_m == NULL)
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144 | return 0;
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145 | abs_m->neg = 0;
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146 | }
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147 |
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148 | ret = BN_mod_lshift_quick(r, r, n, (abs_m ? abs_m : m));
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149 | bn_check_top(r);
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150 |
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151 | BN_free(abs_m);
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152 | return ret;
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153 | }
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154 |
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155 | /*
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156 | * BN_mod_lshift variant that may be used if a is non-negative and less than
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157 | * m
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158 | */
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159 | int BN_mod_lshift_quick(BIGNUM *r, const BIGNUM *a, int n, const BIGNUM *m)
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160 | {
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161 | if (r != a) {
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162 | if (BN_copy(r, a) == NULL)
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163 | return 0;
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164 | }
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165 |
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166 | while (n > 0) {
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167 | int max_shift;
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168 |
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169 | /* 0 < r < m */
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170 | max_shift = BN_num_bits(m) - BN_num_bits(r);
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171 | /* max_shift >= 0 */
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172 |
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173 | if (max_shift < 0) {
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174 | BNerr(BN_F_BN_MOD_LSHIFT_QUICK, BN_R_INPUT_NOT_REDUCED);
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175 | return 0;
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176 | }
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177 |
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178 | if (max_shift > n)
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179 | max_shift = n;
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180 |
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181 | if (max_shift) {
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182 | if (!BN_lshift(r, r, max_shift))
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183 | return 0;
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184 | n -= max_shift;
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185 | } else {
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186 | if (!BN_lshift1(r, r))
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187 | return 0;
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188 | --n;
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189 | }
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190 |
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191 | /* BN_num_bits(r) <= BN_num_bits(m) */
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192 |
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193 | if (BN_cmp(r, m) >= 0) {
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194 | if (!BN_sub(r, r, m))
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195 | return 0;
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196 | }
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197 | }
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198 | bn_check_top(r);
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199 |
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200 | return 1;
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201 | }
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