X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/1ba83484ee5bb486da9aa958576de4bc29ef0c1d..34e4f738bcba58e6d8c4cabbb0b3232a65b42a9d:/g-prime.c

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+/* -*-c-*-
+ *
+ * $Id: g-prime.c,v 1.1 2004/04/01 12:50:09 mdw Exp $
+ *
+ * Abstraction for prime groups
+ *
+ * (c) 2004 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: g-prime.c,v $
+ * Revision 1.1  2004/04/01 12:50:09  mdw
+ * Add cyclic group abstraction, with test code.  Separate off exponentation
+ * functions for better static linking.  Fix a buttload of bugs on the way.
+ * Generally ensure that negative exponents do inversion correctly.  Add
+ * table of standard prime-field subgroups.  (Binary field subgroups are
+ * currently unimplemented but easy to add if anyone ever finds a good one.)
+ *
+ */
+
+/*----- Header files ------------------------------------------------------*/
+
+#include <mLib/sub.h>
+
+#include "mpmont.h"
+#include "pgen.h"
+
+#define ge mp *
+#include "group.h"
+
+/*----- Data structures ---------------------------------------------------*/
+
+typedef struct gctx {
+  group g;
+  mp *gen;
+  mpmont mm;
+} gctx;
+
+/*----- Main code ---------------------------------------------------------*/
+
+/* --- Group operations --- */
+
+static void gdestroygroup(group *gg) {
+  gctx *g = (gctx *)gg;
+  mp_drop(g->gen); mp_drop(g->g.r); mp_drop(g->g.h);
+  mpmont_destroy(&g->mm);
+  DESTROY(g);
+}
+
+static mp **gcreate(group *gg)
+  { mp **x = CREATE(mp *); *x = MP_COPY(*gg->i); return (x); }
+
+static void gcopy(group *gg, mp **d, mp **x)
+  { mp *t = MP_COPY(*x); MP_DROP(*d); *d = t; }
+
+static void gburn(group *gg, mp **x) { (*x)->f |= MP_BURN; }
+
+static void gdestroy(group *gg, mp **x) { MP_DROP(*x); DESTROY(x); }
+
+static int gsamep(group *gg, group *hh)
+  { gctx *g = (gctx *)gg, *h = (gctx *)hh; return (g->mm.m == h->mm.m); }
+
+static int geq(group *gg, mp **x, mp **y) { return (MP_EQ(*x, *y)); }
+
+static const char *gcheck(group *gg, grand *gr) {
+  gctx *g = (gctx *)gg; int rc; mp *t;
+  if (!pgen_primep(g->mm.m, gr)) return ("p is not prime");
+  t = mp_mul(MP_NEW, g->g.r, g->g.h); t = mp_add(t, t, MP_ONE);
+  rc = MP_EQ(t, g->mm.m); MP_DROP(t); if (!rc) return ("not a subgroup");
+  return (group_stdcheck(gg, gr));
+}
+
+static void gmul(group *gg, mp **d, mp **x, mp **y)
+  { gctx *g = (gctx *)gg; *d = mpmont_mul(&g->mm, *d, *x, *y); }
+
+static void gsqr(group *gg, mp **d, mp **x) {
+  gctx *g = (gctx *)gg; mp *r = mp_sqr(*d, *x);
+  *d = mpmont_reduce(&g->mm, r, r);
+}
+
+static void ginv(group *gg, mp **d, mp **x) {
+  gctx *g = (gctx *)gg; mp *r = mpmont_reduce(&g->mm, *d, *x);
+  mp_gcd(0, 0, &r, g->mm.m, r); *d = mpmont_mul(&g->mm, r, r, g->mm.r2);
+}
+
+static void gexp(group *gg, mp **d, mp **x, mp *n)
+  { gctx *g = (gctx *)gg; *d = mpmont_expr(&g->mm, *d, *x, n); }
+
+static void gmexp(group *gg, mp **d, const group_expfactor *f, size_t n) {
+  gctx *g = (gctx *)gg; size_t i;
+  mp_expfactor *ff = xmalloc(n * sizeof(mp_expfactor));
+  for (i = 0; i < n; i++) { ff[i].base = *f[i].base; ff[i].exp = f[i].exp; }
+  *d = mpmont_mexpr(&g->mm, *d, ff, n); xfree(ff);
+}
+
+static int gread(group *gg, mp **d, const mptext_ops *ops, void *p) {
+  gctx *g = (gctx *)gg; mp *t;
+  if ((t = mp_read(MP_NEW, 0, ops, p)) == 0) return (-1);
+  mp_drop(*d); *d = mpmont_mul(&g->mm, t, t, g->mm.r2); return (0);
+}
+
+static int gwrite(group *gg, mp **x, const mptext_ops *ops, void *p) {
+  gctx *g = (gctx *)gg; mp *t = mpmont_reduce(&g->mm, MP_NEW, *x);
+  int rc = mp_write(t, 10, ops, p); MP_DROP(t); return (rc);
+}
+
+static mp *gtoint(group *gg, mp *d, mp **x)
+  { gctx *g = (gctx *)gg; return (mpmont_reduce(&g->mm, d, *x)); }
+
+static int gfromint(group *gg, mp **d, mp *x) {
+  gctx *g = (gctx *)gg; mp_div(0, &x, x, g->mm.m); mp_drop(*d);
+  *d = mpmont_mul(&g->mm, x, x, g->mm.r2); return (0);
+}
+
+static int gtobuf(group *gg, buf *b, mp **x) {
+  gctx *g = (gctx *)gg; mp *t = mpmont_reduce(&g->mm, MP_NEW, *x);
+  int rc = buf_putmp(b, t); MP_DROP(t); return (rc);
+}
+
+static int gfrombuf(group *gg, buf *b, mp **d) {
+  gctx * g = (gctx *)gg; mp *x; if ((x = buf_getmp(b)) == 0) return (-1);
+  mp_div(0, &x, x, g->mm.r2); mp_drop(*d);
+  *d = mpmont_mul(&g->mm, x, x, g->mm.r2); return(0);
+}
+
+/* --- @group_prime@ --- *
+ *
+ * Arguments:	@const gprime_param *gp@ = group parameters
+ *
+ * Returns:	A pointer to the group.
+ *
+ * Use:		Constructs an abstract group interface for a subgroup of a
+ *		prime field.  Group elements are @mp *@ pointers.
+ */
+
+static const group_ops gops = {
+  GTY_PRIME,
+  gdestroygroup, gcreate, gcopy, gburn, gdestroy,
+  gsamep, geq, group_stdidentp,
+  gcheck,
+  gmul, gsqr, ginv, group_stddiv, gexp, gmexp,
+  gread, gwrite,
+  gtoint, gfromint, group_stdtoec, group_stdfromec, gtobuf, gfrombuf
+};
+
+group *group_prime(const gprime_param *gp)
+{
+  gctx *g = CREATE(gctx);
+
+  g->g.ops = &gops;
+  g->g.nbits = mp_bits(gp->p);
+  g->g.noctets = (g->g.nbits + 7) >> 3;
+  mpmont_create(&g->mm, gp->p);
+  g->g.i = &g->mm.r;
+  g->gen = mpmont_mul(&g->mm, MP_NEW, gp->g, g->mm.r2);
+  g->g.g = &g->gen;
+  g->g.r = MP_COPY(gp->q);
+  g->g.h = MP_NEW; mp_div(&g->g.h, 0, gp->p, gp->q);
+  return (&g->g);
+}
+
+/*----- That's all, folks -------------------------------------------------*/