LCOV - code coverage report
Current view: top level - mpi - mpi-inv.c (source / functions) Hit Total Coverage
Test: coverage.info Lines: 74 79 93.7 %
Date: 2016-09-12 12:56:58 Functions: 1 1 100.0 %

          Line data    Source code
       1             : /* mpi-inv.c  -  MPI functions
       2             :  *      Copyright (C) 1998, 2001, 2002, 2003 Free Software Foundation, Inc.
       3             :  *
       4             :  * This file is part of Libgcrypt.
       5             :  *
       6             :  * Libgcrypt is free software; you can redistribute it and/or modify
       7             :  * it under the terms of the GNU Lesser General Public License as
       8             :  * published by the Free Software Foundation; either version 2.1 of
       9             :  * the License, or (at your option) any later version.
      10             :  *
      11             :  * Libgcrypt is distributed in the hope that it will be useful,
      12             :  * but WITHOUT ANY WARRANTY; without even the implied warranty of
      13             :  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      14             :  * GNU Lesser General Public License for more details.
      15             :  *
      16             :  * You should have received a copy of the GNU Lesser General Public
      17             :  * License along with this program; if not, see <http://www.gnu.org/licenses/>.
      18             :  */
      19             : 
      20             : #include <config.h>
      21             : #include <stdio.h>
      22             : #include <stdlib.h>
      23             : #include "mpi-internal.h"
      24             : #include "g10lib.h"
      25             : 
      26             : /****************
      27             :  * Calculate the multiplicative inverse X of A mod N
      28             :  * That is: Find the solution x for
      29             :  *              1 = (a*x) mod n
      30             :  */
      31             : int
      32        7619 : _gcry_mpi_invm (gcry_mpi_t x, gcry_mpi_t a, gcry_mpi_t n)
      33             : {
      34             : #if 0
      35             :     gcry_mpi_t u, v, u1, u2, u3, v1, v2, v3, q, t1, t2, t3;
      36             :     gcry_mpi_t ta, tb, tc;
      37             : 
      38             :     u = mpi_copy(a);
      39             :     v = mpi_copy(n);
      40             :     u1 = mpi_alloc_set_ui(1);
      41             :     u2 = mpi_alloc_set_ui(0);
      42             :     u3 = mpi_copy(u);
      43             :     v1 = mpi_alloc_set_ui(0);
      44             :     v2 = mpi_alloc_set_ui(1);
      45             :     v3 = mpi_copy(v);
      46             :     q  = mpi_alloc( mpi_get_nlimbs(u)+1 );
      47             :     t1 = mpi_alloc( mpi_get_nlimbs(u)+1 );
      48             :     t2 = mpi_alloc( mpi_get_nlimbs(u)+1 );
      49             :     t3 = mpi_alloc( mpi_get_nlimbs(u)+1 );
      50             :     while( mpi_cmp_ui( v3, 0 ) ) {
      51             :         mpi_fdiv_q( q, u3, v3 );
      52             :         mpi_mul(t1, v1, q); mpi_mul(t2, v2, q); mpi_mul(t3, v3, q);
      53             :         mpi_sub(t1, u1, t1); mpi_sub(t2, u2, t2); mpi_sub(t3, u3, t3);
      54             :         mpi_set(u1, v1); mpi_set(u2, v2); mpi_set(u3, v3);
      55             :         mpi_set(v1, t1); mpi_set(v2, t2); mpi_set(v3, t3);
      56             :     }
      57             :     /*  log_debug("result:\n");
      58             :         log_mpidump("q =", q );
      59             :         log_mpidump("u1=", u1);
      60             :         log_mpidump("u2=", u2);
      61             :         log_mpidump("u3=", u3);
      62             :         log_mpidump("v1=", v1);
      63             :         log_mpidump("v2=", v2); */
      64             :     mpi_set(x, u1);
      65             : 
      66             :     mpi_free(u1);
      67             :     mpi_free(u2);
      68             :     mpi_free(u3);
      69             :     mpi_free(v1);
      70             :     mpi_free(v2);
      71             :     mpi_free(v3);
      72             :     mpi_free(q);
      73             :     mpi_free(t1);
      74             :     mpi_free(t2);
      75             :     mpi_free(t3);
      76             :     mpi_free(u);
      77             :     mpi_free(v);
      78             : #elif 0
      79             :     /* Extended Euclid's algorithm (See TAOCP Vol II, 4.5.2, Alg X)
      80             :      * modified according to Michael Penk's solution for Exercise 35 */
      81             : 
      82             :     /* FIXME: we can simplify this in most cases (see Knuth) */
      83             :     gcry_mpi_t u, v, u1, u2, u3, v1, v2, v3, t1, t2, t3;
      84             :     unsigned k;
      85             :     int sign;
      86             : 
      87             :     u = mpi_copy(a);
      88             :     v = mpi_copy(n);
      89             :     for(k=0; !mpi_test_bit(u,0) && !mpi_test_bit(v,0); k++ ) {
      90             :         mpi_rshift(u, u, 1);
      91             :         mpi_rshift(v, v, 1);
      92             :     }
      93             : 
      94             : 
      95             :     u1 = mpi_alloc_set_ui(1);
      96             :     u2 = mpi_alloc_set_ui(0);
      97             :     u3 = mpi_copy(u);
      98             :     v1 = mpi_copy(v);                              /* !-- used as const 1 */
      99             :     v2 = mpi_alloc( mpi_get_nlimbs(u) ); mpi_sub( v2, u1, u );
     100             :     v3 = mpi_copy(v);
     101             :     if( mpi_test_bit(u, 0) ) { /* u is odd */
     102             :         t1 = mpi_alloc_set_ui(0);
     103             :         t2 = mpi_alloc_set_ui(1); t2->sign = 1;
     104             :         t3 = mpi_copy(v); t3->sign = !t3->sign;
     105             :         goto Y4;
     106             :     }
     107             :     else {
     108             :         t1 = mpi_alloc_set_ui(1);
     109             :         t2 = mpi_alloc_set_ui(0);
     110             :         t3 = mpi_copy(u);
     111             :     }
     112             :     do {
     113             :         do {
     114             :             if( mpi_test_bit(t1, 0) || mpi_test_bit(t2, 0) ) { /* one is odd */
     115             :                 mpi_add(t1, t1, v);
     116             :                 mpi_sub(t2, t2, u);
     117             :             }
     118             :             mpi_rshift(t1, t1, 1);
     119             :             mpi_rshift(t2, t2, 1);
     120             :             mpi_rshift(t3, t3, 1);
     121             :           Y4:
     122             :             ;
     123             :         } while( !mpi_test_bit( t3, 0 ) ); /* while t3 is even */
     124             : 
     125             :         if( !t3->sign ) {
     126             :             mpi_set(u1, t1);
     127             :             mpi_set(u2, t2);
     128             :             mpi_set(u3, t3);
     129             :         }
     130             :         else {
     131             :             mpi_sub(v1, v, t1);
     132             :             sign = u->sign; u->sign = !u->sign;
     133             :             mpi_sub(v2, u, t2);
     134             :             u->sign = sign;
     135             :             sign = t3->sign; t3->sign = !t3->sign;
     136             :             mpi_set(v3, t3);
     137             :             t3->sign = sign;
     138             :         }
     139             :         mpi_sub(t1, u1, v1);
     140             :         mpi_sub(t2, u2, v2);
     141             :         mpi_sub(t3, u3, v3);
     142             :         if( t1->sign ) {
     143             :             mpi_add(t1, t1, v);
     144             :             mpi_sub(t2, t2, u);
     145             :         }
     146             :     } while( mpi_cmp_ui( t3, 0 ) ); /* while t3 != 0 */
     147             :     /* mpi_lshift( u3, k ); */
     148             :     mpi_set(x, u1);
     149             : 
     150             :     mpi_free(u1);
     151             :     mpi_free(u2);
     152             :     mpi_free(u3);
     153             :     mpi_free(v1);
     154             :     mpi_free(v2);
     155             :     mpi_free(v3);
     156             :     mpi_free(t1);
     157             :     mpi_free(t2);
     158             :     mpi_free(t3);
     159             : #else
     160             :     /* Extended Euclid's algorithm (See TAOCP Vol II, 4.5.2, Alg X)
     161             :      * modified according to Michael Penk's solution for Exercise 35
     162             :      * with further enhancement */
     163        7619 :     gcry_mpi_t u, v, u1, u2=NULL, u3, v1, v2=NULL, v3, t1, t2=NULL, t3;
     164             :     unsigned k;
     165             :     int sign;
     166             :     int odd ;
     167             : 
     168        7619 :     if (!mpi_cmp_ui (a, 0))
     169           0 :         return 0; /* Inverse does not exists.  */
     170        7619 :     if (!mpi_cmp_ui (n, 1))
     171           0 :         return 0; /* Inverse does not exists.  */
     172             : 
     173        7619 :     u = mpi_copy(a);
     174        7619 :     v = mpi_copy(n);
     175             : 
     176        7619 :     for(k=0; !mpi_test_bit(u,0) && !mpi_test_bit(v,0); k++ ) {
     177           0 :         mpi_rshift(u, u, 1);
     178           0 :         mpi_rshift(v, v, 1);
     179             :     }
     180        7619 :     odd = mpi_test_bit(v,0);
     181             : 
     182        7619 :     u1 = mpi_alloc_set_ui(1);
     183        7619 :     if( !odd )
     184          36 :         u2 = mpi_alloc_set_ui(0);
     185        7619 :     u3 = mpi_copy(u);
     186        7619 :     v1 = mpi_copy(v);
     187        7619 :     if( !odd ) {
     188          36 :         v2 = mpi_alloc( mpi_get_nlimbs(u) );
     189          36 :         mpi_sub( v2, u1, u ); /* U is used as const 1 */
     190             :     }
     191        7619 :     v3 = mpi_copy(v);
     192        7619 :     if( mpi_test_bit(u, 0) ) { /* u is odd */
     193        4324 :         t1 = mpi_alloc_set_ui(0);
     194        4324 :         if( !odd ) {
     195          36 :             t2 = mpi_alloc_set_ui(1); t2->sign = 1;
     196             :         }
     197        4324 :         t3 = mpi_copy(v); t3->sign = !t3->sign;
     198        4324 :         goto Y4;
     199             :     }
     200             :     else {
     201        3295 :         t1 = mpi_alloc_set_ui(1);
     202        3295 :         if( !odd )
     203           0 :             t2 = mpi_alloc_set_ui(0);
     204        3295 :         t3 = mpi_copy(u);
     205             :     }
     206             :     do {
     207             :         do {
     208     4109596 :             if( !odd ) {
     209       51098 :                 if( mpi_test_bit(t1, 0) || mpi_test_bit(t2, 0) ) { /* one is odd */
     210       25574 :                     mpi_add(t1, t1, v);
     211       25574 :                     mpi_sub(t2, t2, u);
     212             :                 }
     213       51098 :                 mpi_rshift(t1, t1, 1);
     214       51098 :                 mpi_rshift(t2, t2, 1);
     215       51098 :                 mpi_rshift(t3, t3, 1);
     216             :             }
     217             :             else {
     218     4058498 :                 if( mpi_test_bit(t1, 0) )
     219     2107866 :                     mpi_add(t1, t1, v);
     220     4058498 :                 mpi_rshift(t1, t1, 1);
     221     4058498 :                 mpi_rshift(t3, t3, 1);
     222             :             }
     223             :           Y4:
     224             :             ;
     225     4113920 :         } while( !mpi_test_bit( t3, 0 ) ); /* while t3 is even */
     226             : 
     227     2222218 :         if( !t3->sign ) {
     228      918295 :             mpi_set(u1, t1);
     229      918295 :             if( !odd )
     230        2663 :                 mpi_set(u2, t2);
     231      918295 :             mpi_set(u3, t3);
     232             :         }
     233             :         else {
     234     1303923 :             mpi_sub(v1, v, t1);
     235     1303923 :             sign = u->sign; u->sign = !u->sign;
     236     1303923 :             if( !odd )
     237       22870 :                 mpi_sub(v2, u, t2);
     238     1303923 :             u->sign = sign;
     239     1303923 :             sign = t3->sign; t3->sign = !t3->sign;
     240     1303923 :             mpi_set(v3, t3);
     241     1303923 :             t3->sign = sign;
     242             :         }
     243     2222218 :         mpi_sub(t1, u1, v1);
     244     2222218 :         if( !odd )
     245       25533 :             mpi_sub(t2, u2, v2);
     246     2222218 :         mpi_sub(t3, u3, v3);
     247     2222218 :         if( t1->sign ) {
     248     1323766 :             mpi_add(t1, t1, v);
     249     1323766 :             if( !odd )
     250       22939 :                 mpi_sub(t2, t2, u);
     251             :         }
     252     2222218 :     } while( mpi_cmp_ui( t3, 0 ) ); /* while t3 != 0 */
     253             :     /* mpi_lshift( u3, k ); */
     254        7619 :     mpi_set(x, u1);
     255             : 
     256        7619 :     mpi_free(u1);
     257        7619 :     mpi_free(v1);
     258        7619 :     mpi_free(t1);
     259        7619 :     if( !odd ) {
     260          36 :         mpi_free(u2);
     261          36 :         mpi_free(v2);
     262          36 :         mpi_free(t2);
     263             :     }
     264        7619 :     mpi_free(u3);
     265        7619 :     mpi_free(v3);
     266        7619 :     mpi_free(t3);
     267             : 
     268        7619 :     mpi_free(u);
     269        7619 :     mpi_free(v);
     270             : #endif
     271        7619 :     return 1;
     272             : }

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