--- /dev/null
+/* -*-c-*-
+ *
+ * $Id: ec.c,v 1.1 2001/04/29 18:12:33 mdw Exp $
+ *
+ * Elliptic curve definitions
+ *
+ * (c) 2001 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: ec.c,v $
+ * Revision 1.1 2001/04/29 18:12:33 mdw
+ * Prototype version.
+ *
+ */
+
+/*----- Header files ------------------------------------------------------*/
+
+#include "ec.h"
+
+/*----- Trivial wrappers --------------------------------------------------*/
+
+/* --- @ec_create@ --- *
+ *
+ * Arguments: @ec *p@ = pointer to an elliptic-curve point
+ *
+ * Returns: ---
+ *
+ * Use: Initializes a new point. The initial value is the additive
+ * identity (which is universal for all curves).
+ */
+
+void ec_create(ec *p) { EC_CREATE(p); }
+
+/* --- @ec_destroy@ --- *
+ *
+ * Arguments: @ec *p@ = pointer to an elliptic-curve point
+ *
+ * Returns: ---
+ *
+ * Use: Destroys a point, making it invalid.
+ */
+
+void ec_destroy(ec *p) { EC_DESTROY(p); }
+
+/* --- @ec_atinf@ --- *
+ *
+ * Arguments: @const ec *p@ = pointer to a point
+ *
+ * Returns: Nonzero if %$p = O$% is the point at infinity, zero
+ * otherwise.
+ */
+
+int ec_atinf(const ec *p) { return (EC_ATINF(p)); }
+
+/* --- @ec_setinf@ --- *
+ *
+ * Arguments: @ec *p@ = pointer to a point
+ *
+ * Returns: ---
+ *
+ * Use: Sets the given point to be the point %$O$% at infinity.
+ */
+
+void ec_setinf(ec *p) { EC_SETINF(p); }
+
+/* --- @ec_copy@ --- *
+ *
+ * Arguments: @ec *d@ = pointer to destination point
+ * @const ec *p@ = pointer to source point
+ *
+ * Returns: ---
+ *
+ * Use: Creates a copy of an elliptic curve point.
+ */
+
+void ec_copy(ec *d, const ec *p) { EC_COPY(d, p); }
+
+/*----- Real arithmetic ---------------------------------------------------*/
+
+/* --- @ec_denorm@ --- *
+ *
+ * Arguments: @ec_curve *c@ = pointer to an elliptic curve
+ * @ec *d@ = pointer to the destination point
+ * @const ec *p@ = pointer to the source point
+ *
+ * Returns: ---
+ *
+ * Use: Denormalizes the given point, converting to internal
+ * representations and setting the denominator to 1.
+ */
+
+void ec_denorm(ec_curve *c, ec *d, const ec *p)
+{
+ if (EC_ATINF(p))
+ EC_SETINF(d);
+ else {
+ field *f = c->f;
+ d->x = F_IN(f, d->x, p->x);
+ d->y = F_IN(f, d->y, p->y);
+ mp_drop(d->z);
+ d->z = MP_COPY(f->one);
+ }
+}
+
+/* --- @ec_norm@ --- *
+ *
+ * Arguments: @ec_curve *c@ = pointer to an elliptic curve
+ * @ec *d@ = pointer to the destination point
+ * @const ec *p@ = pointer to the source point
+ *
+ * Returns: ---
+ *
+ * Use: Normalizes the given point, by dividing through by the
+ * denominator and returning to external representation.
+ */
+
+void ec_norm(ec_curve *c, ec *d, const ec *p)
+{
+ if (EC_ATINF(p))
+ EC_SETINF(d);
+ else {
+ mp *x, *y, *z;
+ field *f = c->f;
+ z = F_INV(f, MP_NEW, p->z);
+ x = F_MUL(f, d->x, p->x, z);
+ y = F_MUL(f, d->y, p->y, z);
+ mp_drop(z);
+ mp_drop(d->z);
+ d->x = F_OUT(f, x, x);
+ d->y = F_OUT(f, y, y);
+ d->z = 0;
+ }
+}
+
+/* --- @ec_find@ --- *
+ *
+ * Arguments: @ec_curve *c@ = pointer to an elliptic curve
+ * @ec *d@ = pointer to the destination point
+ * @mp *x@ = a possible x-coordinate
+ *
+ * Returns: Zero if OK, nonzero if there isn't a point there.
+ *
+ * Use: Finds a point on an elliptic curve with a given x-coordinate.
+ */
+
+void ec_find(ec_curve *c, ec *d, mp *x)
+{
+ int rc;
+ x = F_IN(c->f, MP_NEW, x);
+ if ((rc = EC_FIND(c, d, x)) == 0)
+ ec_norm(c, d, d);
+ mp_drop(x);
+ return (rc);
+}
+
+/* --- @ec_add@ --- *
+ *
+ * Arguments: @ec_curve *c@ = pointer to an elliptic curve
+ * @ec *d@ = pointer to the destination point
+ * @const ec *p, *q@ = pointers to the operand points
+ *
+ * Returns: ---
+ *
+ * Use: Adds two points on an elliptic curve.
+ */
+
+void ec_add(ec_curve *c, ec *d, const ec *p, const ec *q)
+{
+ ec pp = EC_INIT, qq = EC_INIT;
+ ec_denorm(c, &pp, p);
+ ec_denorm(c, &qq, q);
+ EC_ADD(c, d, &pp, &qq);
+ ec_norm(c, d, d);
+ EC_DESTROY(&pp);
+ EC_DESTROY(&qq);
+}
+
+/* --- @ec_dbl@ --- *
+ *
+ * Arguments: @ec_curve *c@ = pointer to an elliptic curve
+ * @ec *d@ = pointer to the destination point
+ * @const ec *p@ = pointer to the operand point
+ *
+ * Returns: ---
+ *
+ * Use: Doubles a point on an elliptic curve.
+ */
+
+void ec_dbl(ec_curve *c, ec *d, const ec *p)
+{
+ ec_denorm(c, d, p);
+ EC_DBL(c, d, d);
+ ec_norm(c, d, d);
+}
+
+/* --- @ec_mul@ --- *
+ *
+ * Arguments: @ec_curve *c@ = pointer to an elliptic curve
+ * @ec *d@ = pointer to the destination point
+ * @const ec *p@ = pointer to the generator point
+ * @mp *n@ = integer multiplier
+ *
+ * Returns: ---
+ *
+ * Use: Multiplies a point by a scalar, returning %$n p$%.
+ */
+
+void ec_mul(ec_curve *c, ec *d, const ec *p, mp *n)
+{
+ mpscan sc;
+ ec g = EC_INIT;
+ unsigned sq = 0;
+
+ EC_SETINF(d);
+ if (EC_ATINF(p))
+ return;
+
+ mp_rscan(&sc, n);
+ if (!MP_RSTEP(&sc))
+ goto exit;
+ while (!MP_RBIT(&sc))
+ MP_RSTEP(&sc);
+
+ ec_denorm(c, &g, p);
+ if ((n->f & MP_BURN) && !(g.x->f & MP_BURN))
+ MP_DEST(g.x, 0, MP_BURN);
+ if ((n->f & MP_BURN) && !(g.y->f & MP_BURN))
+ MP_DEST(g.y, 0, MP_BURN);
+
+ for (;;) {
+ EC_ADD(c, d, d, &g);
+ sq = 0;
+ for (;;) {
+ if (!MP_RSTEP(&sc))
+ goto done;
+ if (MP_RBIT(&sc))
+ break;
+ sq++;
+ }
+ sq++;
+ while (sq) {
+ EC_DBL(c, d, d);
+ sq--;
+ }
+ }
+
+done:
+ while (sq) {
+ EC_DBL(c, d, d);
+ sq--;
+ }
+
+ EC_DESTROY(&g);
+exit:
+ ec_norm(c, d, d);
+}
+
+/*----- That's all, folks -------------------------------------------------*/
projects / u / mdw / catacomb / blobdiff