X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/ba6e6b64033b1f9de49feccb5c9cd438354481f7..0f00dc4c8eb47e67bc0f148c2dd109f73a451e0a:/math/group-stdops.c

diff --git a/math/group-stdops.c b/math/group-stdops.c
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+/* -*-c-*-
+ *
+ * Standard group operations
+ *
+ * (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.
+ */
+
+/*----- Header files ------------------------------------------------------*/
+
+#include "group.h"
+#include "pgen.h"
+
+/*----- Handy functions ---------------------------------------------------*/
+
+/* --- @group_check@ --- *
+ *
+ * Arguments:	@group *g@ = an abstract group
+ *		@ge *x@ = a group element
+ *
+ * Returns:	Zero on success, nonzero for failure.
+ *
+ * Use:		Checks that @x@ is a valid group element.  This may take a
+ *		while, since it checks that %$x \ne 1$% and %$x^r = 1$%.
+ */
+
+int group_check(group *g, ge *x)
+{
+  ge *d = G_CREATE(g);
+  int rc;
+
+  G_EXP(g, d, x, g->r);
+  rc = (G_IDENTP(g, d) && !G_IDENTP(g, x));
+  G_DESTROY(g, d);
+  if (!rc) return (-1);
+  return (0);
+}
+
+/* --- @group_samep@ --- *
+ *
+ * Arguments:	@group *g, *h@ = two abstract groups
+ *
+ * Returns:	Nonzero if the groups are in fact identical (not just
+ *		isomorphic).
+ *
+ * Use:		Checks to see whether two groups are actually the same.  This
+ *		function does the full check: the group operatrion @samep@
+ *		just does the group-specific details.
+ */
+
+int group_samep(group *g, group *h)
+{
+  return (g == h || (g->ops == h->ops &&
+		     MP_EQ(g->r, h->r) && MP_EQ(g->h, h->h) &&
+		     G_EQ(g, g->i, h->i) && G_EQ(g, g->g, h->g) &&
+		     G_SAMEP(g, h)));
+}
+
+/*----- Standard implementations ------------------------------------------*/
+
+/* --- @group_stdidentp@ --- *
+ *
+ * Arguments:	@group *g@ = abstract group
+ *		@ge *x@ = group element
+ *
+ * Returns:	Nonzero if %$x$% is the group identity.
+ */
+
+int group_stdidentp(group *g, ge *x) { return (G_EQ(g, x, g->i)); }
+
+/* --- @group_stdsqr@ --- *
+ *
+ * Arguments:	@group *g@ = abstract group
+ *		@ge *d@ = destination pointer
+ *		@ge *x@ = group element
+ *
+ * Returns:	---
+ *
+ * Use:		Computes %$d = x^2$% as %$d = x x$%.
+ */
+
+void group_stdsqr(group *g, ge *d, ge *x) { G_MUL(g, d, x, x); }
+
+/* --- @group_stddiv@ --- *
+ *
+ * Arguments:	@group *g@ = abstract group
+ *		@ge *d@ = destination pointer
+ *		@ge *x@ = dividend
+ *		@ge *y@ = divisor
+ *
+ * Returns:	---
+ *
+ * Use:		Computes %$d = x/y$% as %$d = x y^{-1}$%.
+ */
+
+void group_stddiv(group *g, ge *d, ge *x, ge *y)
+  { G_INV(g, d, y); G_MUL(g, d, x, d); }
+
+/* --- @group_stdtoec@ --- *
+ *
+ * Arguments:	@group *g@ = abstract group
+ *		@ec *d@ = destination point
+ *		@ge *x@ = group element
+ *
+ * Returns:	@-1@, indicating failure.
+ *
+ * Use:		Fails to convert a group element to an elliptic curve point.
+ */
+
+int group_stdtoec(group *g, ec *d, ge *x) { return (-1); }
+
+/* --- @group_stdfromec@ --- *
+ *
+ * Arguments:	@group *g@ = abstract group
+ *		@ge *d@ = destination pointer
+ *		@const ec *p@ = elliptic curve point
+ *
+ * Returns:	Zero for success, @-1@ on failure.
+ *
+ * Use:		Converts %$p$% to a group element by converting its %$x$%-
+ *		coordinate.
+ */
+
+int group_stdfromec(group *g, ge *d, const ec *p)
+  { if (EC_ATINF(p)) return (-1); return (G_FROMINT(g, d, p->x)); }
+
+/* --- @group_stdcheck@ --- *
+ *
+ * Arguments:	@group *g@ = abstract group
+ *		@grand *gr@ = random number source.
+ *
+ * Returns:	Null on success, or a pointer to an error message.
+ */
+
+const char *group_stdcheck(group *g, grand *gr)
+{
+  ge *t;
+  int rc;
+
+  if (!pgen_primep(g->r, gr)) return ("group order not prime");
+  t = G_CREATE(g); G_EXP(g, t, g->g, g->r);
+  rc = G_IDENTP(g, t); G_DESTROY(g, t);
+  if (!rc) return ("generator not in the group");
+  return (0);
+}
+
+/*----- That's all, folks -------------------------------------------------*/