git.distorted.org.uk Git - u/mdw/catacomb/blob - math/mpcrt.h

   1 /* -*-c-*-
   2  *
   3  * Chinese Remainder Theorem computations (Gauss's algorithm)
   4  *
   5  * (c) 1999 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of Catacomb.
  11  *
  12  * Catacomb is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU Library General Public License as
  14  * published by the Free Software Foundation; either version 2 of the
  15  * License, or (at your option) any later version.
  16  *
  17  * Catacomb is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU Library General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU Library General Public
  23  * License along with Catacomb; if not, write to the Free
  24  * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  25  * MA 02111-1307, USA.
  26  */
  27
  28 #ifndef CATACOMB_MPCRT_H
  29 #define CATACOMB_MPCRT_H
  30
  31 #ifdef __cplusplus
  32   extern "C" {
  33 #endif
  34
  35 /*----- Header files ------------------------------------------------------*/
  36
  37 #include <stddef.h>
  38
  39 #ifndef CATACOMB_MP_H
  40 #  include "mp.h"
  41 #endif
  42
  43 #ifndef CATACOMB_MPBARRETT_H
  44 #  include "mpbarrett.h"
  45 #endif
  46
  47 /*----- Data structures ---------------------------------------------------*/
  48
  49 typedef struct mpcrt_mod {
  50   mp *m;                                /* %$n_i$% -- the modulus */
  51   mp *n;                                /* %$N_i = n / n_i$% */
  52   mp *ni;                               /* %$M_i = N_i^{-1} \bmod n_i$% */
  53   mp *nni;                              /* %$N_i M_i \bmod m$% */
  54 } mpcrt_mod;
  55
  56 typedef struct mpcrt {
  57   size_t k;                             /* Number of distinct moduli */
  58   mpbarrett mb;                         /* Barrett context for product */
  59   mpcrt_mod *v;                         /* Vector of information for each */
  60 } mpcrt;
  61
  62 /*----- Functions provided ------------------------------------------------*/
  63
  64 /* --- @mpcrt_create@ --- *
  65  *
  66  * Arguments:   @mpcrt *c@ = pointer to CRT context
  67  *              @mpcrt_mod *v@ = pointer to vector of moduli
  68  *              @size_t k@ = number of moduli
  69  *              @mp *n@ = product of all moduli (@MP_NEW@ if unknown)
  70  *
  71  * Returns:     ---
  72  *
  73  * Use:         Initializes a context for solving Chinese Remainder Theorem
  74  *              problems.  The vector of moduli can be incomplete.  Omitted
  75  *              items must be left as null pointers.  Not all combinations of
  76  *              missing things can be coped with, even if there is
  77  *              technically enough information to cope.  For example, if @n@
  78  *              is unspecified, all the @m@ values must be present, even if
  79  *              there is one modulus with both @m@ and @n@ (from which the
  80  *              product of all moduli could clearly be calculated).
  81  */
  82
  83 extern void mpcrt_create(mpcrt */*c*/, mpcrt_mod */*v*/,
  84                          size_t /*k*/, mp */*n*/);
  85
  86 /* --- @mpcrt_destroy@ --- *
  87  *
  88  * Arguments:   @mpcrt *c@ - pointer to CRT context
  89  *
  90  * Returns:     ---
  91  *
  92  * Use:         Destroys a CRT context, releasing all the resources it holds.
  93  */
  94
  95 extern void mpcrt_destroy(mpcrt */*c*/);
  96
  97 /* --- @mpcrt_solve@ --- *
  98  *
  99  * Arguments:   @mpcrt *c@ = pointer to CRT context
 100  *              @mp *d@ = fake destination
 101  *              @mp **v@ = array of residues
 102  *
 103  * Returns:     The unique solution modulo the product of the individual
 104  *              moduli, which leaves the given residues.
 105  *
 106  * Use:         Constructs a result given its residue modulo an array of
 107  *              coprime integers.  This can be used to improve performance of
 108  *              RSA encryption or Blum-Blum-Shub generation if the factors
 109  *              of the modulus are known, since results can be computed mod
 110  *              each of the individual factors and then combined at the end.
 111  *              This is rather faster than doing the full-scale modular
 112  *              exponentiation.
 113  */
 114
 115 extern mp *mpcrt_solve(mpcrt */*c*/, mp */*d*/, mp **/*v*/);
 116
 117 /*----- That's all, folks -------------------------------------------------*/
 118
 119 #ifdef __cplusplus
 120   }
 121 #endif
 122
 123 #endif