Add support for solving Chinese Remainder Theorem problems.

[u/mdw/catacomb] / mpcrt.h

diff --git a/mpcrt.h b/mpcrt.h
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+/* -*-c-*-
+ *
+ * $Id: mpcrt.h,v 1.1 1999/11/22 20:50:57 mdw Exp $
+ *
+ * Chinese Remainder Theorem computations (Gauss's algorithm)
+ *
+ * (c) 1999 Straylight/Edgeware
+ */
+
+/*----- Licensing notice --------------------------------------------------* 
+ *
+ * This file is part of Catacomb.
+ *
+ * Catacomb is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Library General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ * 
+ * Catacomb is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Library General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Library General Public
+ * License along with Catacomb; if not, write to the Free
+ * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+ * MA 02111-1307, USA.
+ */
+
+/*----- Revision history --------------------------------------------------* 
+ *
+ * $Log: mpcrt.h,v $
+ * Revision 1.1  1999/11/22 20:50:57  mdw
+ * Add support for solving Chinese Remainder Theorem problems.
+ *
+ */
+
+#ifndef MPCRT_H
+#define MPCRT_H
+
+#ifdef __cplusplus
+  extern "C" {
+#endif
+
+/*----- Header files ------------------------------------------------------*/
+
+#include <stddef.h>
+
+#ifndef MP_H
+#  include "mp.h"
+#endif
+
+#ifndef MPMONT_H
+#  include "mpmont.h"
+#endif
+
+/*----- Data structures ---------------------------------------------------*/
+
+typedef struct mpcrt_mod {
+  mp *m;                               /* %$n_i$% -- the modulus */
+  mp *n;                               /* %$N_i = n / n_i$% */
+  mp *ni;                              /* %$M_i = N_i^{-1} \bmod n_i$% */
+  mp *nnir;                            /* %$N_i M_i R \bmod m$% */
+} mpcrt_mod;
+
+typedef struct mpcrt {
+  size_t k;                            /* Number of distinct moduli */
+  mpmont mm;                           /* Montgomery context for product */
+  mpcrt_mod *v;                                /* Vector of information for each */
+} mpcrt;
+
+/*----- Functions provided ------------------------------------------------*/
+
+/* --- @mpcrt_create@ --- *
+ *
+ * Arguments:  @mpcrt *c@ = pointer to CRT context
+ *             @mpcrt_mod *v@ = pointer to vector of moduli
+ *             @size_t k@ = number of moduli
+ *             @mp *n@ = product of all moduli (@MP_NEW@ if unknown)
+ *
+ * Returns:    ---
+ *
+ * Use:                Initializes a context for solving Chinese Remainder Theorem
+ *             problems.  The vector of moduli can be incomplete.  Omitted
+ *             items must be left as null pointers.  Not all combinations of
+ *             missing things can be coped with, even if there is
+ *             technically enough information to cope.  For example, if @n@
+ *             is unspecified, all the @m@ values must be present, even if
+ *             there is one modulus with both @m@ and @n@ (from which the
+ *             product of all moduli could clearly be calculated).
+ */
+
+extern void mpcrt_create(mpcrt */*c*/, mpcrt_mod */*v*/,
+                        size_t /*k*/, mp */*n*/);
+
+/* --- @mpcrt_destroy@ --- *
+ *
+ * Arguments:  @mpcrt *c@ - pointer to CRT context
+ *
+ * Returns:    ---
+ *
+ * Use:                Destroys a CRT context, releasing all the resources it holds.
+ */
+
+extern void mpcrt_destroy(mpcrt */*c*/);
+
+/* --- @mpcrt_solve@ --- *
+ *
+ * Arguments:  @mpcrt *c@ = pointer to CRT context
+ *             @mp **v@ = array of residues
+ *
+ * Returns:    The unique solution modulo the product of the individual
+ *             moduli, which leaves the given residues.
+ *
+ * Use:                Constructs a result given its residue modulo an array of
+ *             coprime integers.  This can be used to improve performance of
+ *             RSA encryption or Blum-Blum-Shub generation if the factors
+ *             of the modulus are known, since results can be computed mod
+ *             each of the individual factors and then combined at the end.
+ *             This is rather faster than doing the full-scale modular
+ *             exponentiation.
+ */
+
+extern mp *mpcrt_solve(mpcrt */*c*/, mp **/*v*/);
+
+/*----- That's all, folks -------------------------------------------------*/
+
+#ifdef __cplusplus
+  }
+#endif
+
+#endif