Mercurial > dropbear
annotate libtommath/bn_fast_mp_montgomery_reduce.c @ 1653:76189c9ffea2
External Public-Key Authentication API (#72)
* Implemented dynamic loading of an external plug-in shared library to delegate public key authentication
* Moved conditional compilation of the plugin infrastructure into the configure.ac script to be able to add -ldl to dropbear build only when the flag is enabled
* Added tags file to the ignore list
* Updated API to have the constructor to return function pointers in the pliugin instance. Added support for passing user name to the checkpubkey function. Added options to the session returned by the plugin and have dropbear to parse and process them
* Added -rdynamic to the linker flags when EPKA is enabled
* Changed the API to pass a previously created session to the checkPubKey function (created during preauth)
* Added documentation to the API
* Added parameter addrstring to plugin creation function
* Modified the API to retrieve the auth options. Instead of having them as field of the EPKASession struct, they are stored internally (plugin-dependent) in the plugin/session and retrieved through a pointer to a function (in the session)
* Changed option string to be a simple char * instead of unsigned char *
author | fabriziobertocci <fabriziobertocci@gmail.com> |
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date | Wed, 15 May 2019 09:43:57 -0400 |
parents | 8bba51a55704 |
children | f52919ffd3b1 |
rev | line source |
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1436 | 1 #include <tommath_private.h> |
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2 #ifdef BN_FAST_MP_MONTGOMERY_REDUCE_C |
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis |
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4 * |
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5 * LibTomMath is a library that provides multiple-precision |
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6 * integer arithmetic as well as number theoretic functionality. |
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7 * |
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8 * The library was designed directly after the MPI library by |
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9 * Michael Fromberger but has been written from scratch with |
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10 * additional optimizations in place. |
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11 * |
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12 * The library is free for all purposes without any express |
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13 * guarantee it works. |
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14 * |
1436 | 15 * Tom St Denis, [email protected], http://libtom.org |
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16 */ |
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17 |
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18 /* computes xR**-1 == x (mod N) via Montgomery Reduction |
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19 * |
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20 * This is an optimized implementation of montgomery_reduce |
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21 * which uses the comba method to quickly calculate the columns of the |
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22 * reduction. |
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23 * |
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24 * Based on Algorithm 14.32 on pp.601 of HAC. |
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25 */ |
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26 int fast_mp_montgomery_reduce (mp_int * x, mp_int * n, mp_digit rho) |
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27 { |
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28 int ix, res, olduse; |
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29 mp_word W[MP_WARRAY]; |
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30 |
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31 /* get old used count */ |
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32 olduse = x->used; |
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33 |
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34 /* grow a as required */ |
1436 | 35 if (x->alloc < (n->used + 1)) { |
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36 if ((res = mp_grow (x, n->used + 1)) != MP_OKAY) { |
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37 return res; |
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38 } |
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39 } |
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40 |
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41 /* first we have to get the digits of the input into |
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42 * an array of double precision words W[...] |
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43 */ |
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44 { |
1436 | 45 mp_word *_W; |
46 mp_digit *tmpx; | |
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47 |
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48 /* alias for the W[] array */ |
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49 _W = W; |
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50 |
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51 /* alias for the digits of x*/ |
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52 tmpx = x->dp; |
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53 |
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54 /* copy the digits of a into W[0..a->used-1] */ |
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55 for (ix = 0; ix < x->used; ix++) { |
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56 *_W++ = *tmpx++; |
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57 } |
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58 |
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59 /* zero the high words of W[a->used..m->used*2] */ |
1436 | 60 for (; ix < ((n->used * 2) + 1); ix++) { |
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61 *_W++ = 0; |
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62 } |
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63 } |
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64 |
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65 /* now we proceed to zero successive digits |
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66 * from the least significant upwards |
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67 */ |
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68 for (ix = 0; ix < n->used; ix++) { |
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69 /* mu = ai * m' mod b |
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70 * |
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71 * We avoid a double precision multiplication (which isn't required) |
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72 * by casting the value down to a mp_digit. Note this requires |
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73 * that W[ix-1] have the carry cleared (see after the inner loop) |
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74 */ |
1436 | 75 mp_digit mu; |
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76 mu = (mp_digit) (((W[ix] & MP_MASK) * rho) & MP_MASK); |
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77 |
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78 /* a = a + mu * m * b**i |
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79 * |
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80 * This is computed in place and on the fly. The multiplication |
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81 * by b**i is handled by offseting which columns the results |
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82 * are added to. |
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83 * |
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84 * Note the comba method normally doesn't handle carries in the |
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85 * inner loop In this case we fix the carry from the previous |
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86 * column since the Montgomery reduction requires digits of the |
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87 * result (so far) [see above] to work. This is |
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88 * handled by fixing up one carry after the inner loop. The |
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89 * carry fixups are done in order so after these loops the |
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90 * first m->used words of W[] have the carries fixed |
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91 */ |
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92 { |
1436 | 93 int iy; |
94 mp_digit *tmpn; | |
95 mp_word *_W; | |
284
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96 |
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97 /* alias for the digits of the modulus */ |
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98 tmpn = n->dp; |
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99 |
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100 /* Alias for the columns set by an offset of ix */ |
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101 _W = W + ix; |
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102 |
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103 /* inner loop */ |
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104 for (iy = 0; iy < n->used; iy++) { |
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105 *_W++ += ((mp_word)mu) * ((mp_word)*tmpn++); |
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106 } |
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107 } |
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108 |
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109 /* now fix carry for next digit, W[ix+1] */ |
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110 W[ix + 1] += W[ix] >> ((mp_word) DIGIT_BIT); |
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111 } |
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112 |
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113 /* now we have to propagate the carries and |
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114 * shift the words downward [all those least |
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115 * significant digits we zeroed]. |
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116 */ |
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117 { |
1436 | 118 mp_digit *tmpx; |
119 mp_word *_W, *_W1; | |
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120 |
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121 /* nox fix rest of carries */ |
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122 |
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123 /* alias for current word */ |
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124 _W1 = W + ix; |
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125 |
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126 /* alias for next word, where the carry goes */ |
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127 _W = W + ++ix; |
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128 |
1436 | 129 for (; ix <= ((n->used * 2) + 1); ix++) { |
284
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130 *_W++ += *_W1++ >> ((mp_word) DIGIT_BIT); |
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131 } |
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132 |
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133 /* copy out, A = A/b**n |
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134 * |
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135 * The result is A/b**n but instead of converting from an |
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136 * array of mp_word to mp_digit than calling mp_rshd |
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137 * we just copy them in the right order |
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138 */ |
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139 |
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140 /* alias for destination word */ |
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141 tmpx = x->dp; |
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142 |
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143 /* alias for shifted double precision result */ |
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144 _W = W + n->used; |
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145 |
1436 | 146 for (ix = 0; ix < (n->used + 1); ix++) { |
284
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147 *tmpx++ = (mp_digit)(*_W++ & ((mp_word) MP_MASK)); |
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148 } |
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149 |
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150 /* zero oldused digits, if the input a was larger than |
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151 * m->used+1 we'll have to clear the digits |
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152 */ |
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153 for (; ix < olduse; ix++) { |
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154 *tmpx++ = 0; |
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155 } |
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156 } |
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157 |
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158 /* set the max used and clamp */ |
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159 x->used = n->used + 1; |
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160 mp_clamp (x); |
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161 |
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162 /* if A >= m then A = A - m */ |
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163 if (mp_cmp_mag (x, n) != MP_LT) { |
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164 return s_mp_sub (x, n, x); |
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165 } |
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166 return MP_OKAY; |
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167 } |
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168 #endif |
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169 |
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170 /* ref: $Format:%D$ */ |
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171 /* git commit: $Format:%H$ */ |
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172 /* commit time: $Format:%ai$ */ |