X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/b0ab12e6a6cb035df2b6312df7ad1736af0a6128..41cb1beba35c8a69ee7ae1298f51711995011b5c:/ec.c

diff --git a/ec.c b/ec.c
index 604190b..47c01a9 100644
--- a/ec.c
+++ b/ec.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: ec.c,v 1.1 2001/04/29 18:12:33 mdw Exp $
+ * $Id: ec.c,v 1.4 2003/05/15 23:25:59 mdw Exp $
  *
  * Elliptic curve definitions
  *
@@ -30,6 +30,16 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: ec.c,v $
+ * Revision 1.4  2003/05/15 23:25:59  mdw
+ * Make elliptic curve stuff build.
+ *
+ * Revision 1.3  2002/01/13 13:48:44  mdw
+ * Further progress.
+ *
+ * Revision 1.2  2001/05/07 17:29:44  mdw
+ * Treat projective coordinates as an internal representation.  Various
+ * minor interface changes.
+ *
  * Revision 1.1  2001/04/29 18:12:33  mdw
  * Prototype version.
  *
@@ -38,6 +48,7 @@
 /*----- Header files ------------------------------------------------------*/
 
 #include "ec.h"
+#include "ec-exp.h"
 
 /*----- Trivial wrappers --------------------------------------------------*/
 
@@ -45,13 +56,13 @@
  *
  * Arguments:	@ec *p@ = pointer to an elliptic-curve point
  *
- * Returns:	---
+ * Returns:	The argument @p@.
  *
  * 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 *ec_create(ec *p) { EC_CREATE(p); return (p); }
 
 /* --- @ec_destroy@ --- *
  *
@@ -78,40 +89,41 @@ int ec_atinf(const ec *p) { return (EC_ATINF(p)); }
  *
  * Arguments:	@ec *p@ = pointer to a point
  *
- * Returns:	---
+ * Returns:	The argument @p@.
  *
  * Use:		Sets the given point to be the point %$O$% at infinity.
  */
 
-void ec_setinf(ec *p) { EC_SETINF(p); }
+ec *ec_setinf(ec *p) { EC_SETINF(p); return (p); }
 
 /* --- @ec_copy@ --- *
  *
  * Arguments:	@ec *d@ = pointer to destination point
  *		@const ec *p@ = pointer to source point
  *
- * Returns:	---
+ * Returns:	The destination @d@.
  *
  * Use:		Creates a copy of an elliptic curve point.
  */
 
-void ec_copy(ec *d, const ec *p) { EC_COPY(d, p); }
+ec *ec_copy(ec *d, const ec *p) { EC_COPY(d, p); return (d); }
 
-/*----- Real arithmetic ---------------------------------------------------*/
+/*----- Standard curve operations -----------------------------------------*/
 
-/* --- @ec_denorm@ --- *
+/* --- @ec_idin@, @ec_idout@ --- *
  *
  * Arguments:	@ec_curve *c@ = pointer to an elliptic curve
- *		@ec *d@ = pointer to the destination point
- *		@const ec *p@ = pointer to the source point
+ *		@ec *d@ = pointer to the destination
+ *		@const ec *p@ = pointer to a source point
  *
- * Returns:	---
+ * Returns:	The destination @d@.
  *
- * Use:		Denormalizes the given point, converting to internal
- *		representations and setting the denominator to 1.
+ * Use:		An identity operation if your curve has no internal
+ *		representation.  (The field internal representation is still
+ *		used.)
  */
 
-void ec_denorm(ec_curve *c, ec *d, const ec *p)
+ec *ec_idin(ec_curve *c, ec *d, const ec *p)
 {
   if (EC_ATINF(p))
     EC_SETINF(d);
@@ -119,24 +131,50 @@ void ec_denorm(ec_curve *c, ec *d, const ec *p)
     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);
+    mp_drop(d->z); d->z = 0;
+  }
+  return (d);
+}
+
+ec *ec_idout(ec_curve *c, ec *d, const ec *p)
+{
+  if (EC_ATINF(p))
+    EC_SETINF(d);
+  else {
+    field *f = c->f;
+    d->x = F_OUT(f, d->x, p->x);
+    d->y = F_OUT(f, d->y, p->y);
+    mp_drop(d->z); d->z = 0;
   }
+  return (d);
 }
 
-/* --- @ec_norm@ --- *
+/* --- @ec_projin@, @ec_projout@ --- *
  *
  * Arguments:	@ec_curve *c@ = pointer to an elliptic curve
- *		@ec *d@ = pointer to the destination point
- *		@const ec *p@ = pointer to the source point
+ *		@ec *d@ = pointer to the destination
+ *		@const ec *p@ = pointer to a source point
  *
- * Returns:	---
+ * Returns:	The destination @d@.
  *
- * Use:		Normalizes the given point, by dividing through by the
- *		denominator and returning to external representation.
+ * Use:		Conversion functions if your curve operations use a
+ *		projective representation.
  */
 
-void ec_norm(ec_curve *c, ec *d, const ec *p)
+ec *ec_projin(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);
+  }
+  return (d);
+}
+
+ec *ec_projout(ec_curve *c, ec *d, const ec *p)
 {
   if (EC_ATINF(p))
     EC_SETINF(d);
@@ -152,8 +190,46 @@ void ec_norm(ec_curve *c, ec *d, const ec *p)
     d->y = F_OUT(f, y, y);
     d->z = 0;
   }
+  return (d);
+}
+
+/* --- @ec_stdsub@ --- *
+ *
+ * Arguments:	@ec_curve *c@ = pointer to an elliptic curve
+ *		@ec *d@ = pointer to the destination
+ *		@const ec *p, *q@ = the operand points
+ *
+ * Returns:	The destination @d@.
+ *
+ * Use:		Standard point subtraction operation, in terms of negation
+ *		and addition.  This isn't as efficient as a ready-made
+ *		subtraction operator.
+ */
+
+ec *ec_stdsub(ec_curve *c, ec *d, const ec *p, const ec *q)
+{
+  ec t = EC_INIT;
+  EC_NEG(c, &t, q);
+  EC_ADD(c, d, p, &t);
+  EC_DESTROY(&t);
+  return (d);
 }
 
+/*----- Creating curves ---------------------------------------------------*/
+
+/* --- @ec_destroycurve@ --- *
+ *
+ * Arguments:	@ec_curve *c@ = pointer to an ellptic curve
+ *
+ * Returns:	---
+ *
+ * Use:		Destroys a description of an elliptic curve.
+ */
+
+void ec_destroycurve(ec_curve *c) { c->ops->destroy(c); }
+
+/*----- Real arithmetic ---------------------------------------------------*/
+
 /* --- @ec_find@ --- *
  *
  * Arguments:	@ec_curve *c@ = pointer to an elliptic curve
@@ -165,14 +241,13 @@ void ec_norm(ec_curve *c, ec *d, const ec *p)
  * Use:		Finds a point on an elliptic curve with a given x-coordinate.
  */
 
-void ec_find(ec_curve *c, ec *d, mp *x)
+ec *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);
+  if ((d = EC_FIND(c, d, x)) != 0)
+    EC_OUT(c, d, d);
   mp_drop(x);
-  return (rc);
+  return (d);
 }
 
 /* --- @ec_add@ --- *
@@ -186,15 +261,16 @@ void ec_find(ec_curve *c, ec *d, mp *x)
  * Use:		Adds two points on an elliptic curve.
  */
 
-void ec_add(ec_curve *c, ec *d, const ec *p, const ec *q)
+ec *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_IN(c, &pp, p);
+  EC_IN(c, &qq, q);
   EC_ADD(c, d, &pp, &qq);
-  ec_norm(c, d, d);
+  EC_OUT(c, d, d);
   EC_DESTROY(&pp);
   EC_DESTROY(&qq);
+  return (d);
 }
 
 /* --- @ec_dbl@ --- *
@@ -208,73 +284,50 @@ void ec_add(ec_curve *c, ec *d, const ec *p, const ec *q)
  * Use:		Doubles a point on an elliptic curve.
  */
 
-void ec_dbl(ec_curve *c, ec *d, const ec *p)
+ec *ec_dbl(ec_curve *c, ec *d, const ec *p)
 {
-  ec_denorm(c, d, p);
+  EC_IN(c, d, p);
   EC_DBL(c, d, d);
-  ec_norm(c, d, d);
+  return (EC_OUT(c, d, d));
 }
 
-/* --- @ec_mul@ --- *
+/* --- @ec_imul@, @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:	---
+ * Returns:	The destination @d@.
  *
- * Use:		Multiplies a point by a scalar, returning %$n p$%.
+ * Use:		Multiplies a point by a scalar, returning %$n p$%.  The
+ *		@imul@ variant uses internal representations for argument
+ *		and result.
  */
 
-void ec_mul(ec_curve *c, ec *d, const ec *p, mp *n)
+ec *ec_imul(ec_curve *c, ec *d, const ec *p, mp *n)
 {
-  mpscan sc;
-  ec g = EC_INIT;
-  unsigned sq = 0;
+  ec t = EC_INIT;
 
+  EC_COPY(&t, p);
+  if (t.x && (n->f & MP_BURN))
+    t.x->f |= MP_BURN;
+  MP_SHRINK(n);
   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--;
-  }
+  if (MP_LEN(n) == 0)
+    ;
+  else if (MP_LEN(n) < EXP_THRESH)
+    EXP_SIMPLE(*d, t, n);
+  else
+    EXP_WINDOW(*d, t, n);
+  return (d);
+}
 
-  EC_DESTROY(&g);
-exit:
-  ec_norm(c, d, d);
+ec *ec_mul(ec_curve *c, ec *d, const ec *p, mp *n)
+{
+  EC_IN(c, d, p);
+  ec_imul(c, d, d, n);
+  return (EC_OUT(c, d, d));
 }
 
 /*----- That's all, folks -------------------------------------------------*/