X-Git-Url: https://git.distorted.org.uk/u/mdw/catacomb/blobdiff_plain/b085fd9162fa3ff5b16788ced6d11a71ffe5a5fe..8823192f6413bed15cfa884ed3a3cbbb97885657:/ec.c

diff --git a/ec.c b/ec.c
index ce4e428..a2b229f 100644
--- a/ec.c
+++ b/ec.c
@@ -1,6 +1,6 @@
 /* -*-c-*-
  *
- * $Id: ec.c,v 1.3 2002/01/13 13:48:44 mdw Exp $
+ * $Id: ec.c,v 1.4.4.2 2004/03/20 00:13:31 mdw Exp $
  *
  * Elliptic curve definitions
  *
@@ -30,6 +30,15 @@
 /*----- Revision history --------------------------------------------------* 
  *
  * $Log: ec.c,v $
+ * Revision 1.4.4.2  2004/03/20 00:13:31  mdw
+ * Projective coordinates for prime curves
+ *
+ * Revision 1.4.4.1  2003/06/10 13:43:53  mdw
+ * Simple (non-projective) curves over prime fields now seem to work.
+ *
+ * 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.
  *
@@ -53,13 +62,13 @@
  *
  * 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@ --- *
  *
@@ -86,28 +95,28 @@ 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); }
 
 /*----- Standard curve operations -----------------------------------------*/
 
-/* --- @ec_idin@, @ec_idout@ --- *
+/* --- @ec_idin@, @ec_idout@, @ec_idfix@ --- *
  *
  * Arguments:	@ec_curve *c@ = pointer to an elliptic curve
  *		@ec *d@ = pointer to the destination
@@ -146,6 +155,12 @@ ec *ec_idout(ec_curve *c, ec *d, const ec *p)
   return (d);
 }
 
+ec *ec_idfix(ec_curve *c, ec *d, const ec *p)
+{
+  EC_COPY(d, p);
+  return (d);
+}
+
 /* --- @ec_projin@, @ec_projout@ --- *
  *
  * Arguments:	@ec_curve *c@ = pointer to an elliptic curve
@@ -176,12 +191,15 @@ ec *ec_projout(ec_curve *c, ec *d, const ec *p)
   if (EC_ATINF(p))
     EC_SETINF(d);
   else {
-    mp *x, *y, *z;
+    mp *x, *y, *z, *zz;
     field *f = c->f;
     z = F_INV(f, MP_NEW, p->z);
-    x = F_MUL(f, d->x, p->x, z);
+    zz = F_SQR(f, MP_NEW, z);
+    z = F_MUL(f, z, zz, z);
+    x = F_MUL(f, d->x, p->x, zz);
     y = F_MUL(f, d->y, p->y, z);
     mp_drop(z);
+    mp_drop(zz);
     mp_drop(d->z);
     d->x = F_OUT(f, x, x);
     d->y = F_OUT(f, y, y);
@@ -190,11 +208,33 @@ ec *ec_projout(ec_curve *c, ec *d, const ec *p)
   return (d);
 }
 
+ec *ec_projfix(ec_curve *c, ec *d, const ec *p)
+{
+  if (EC_ATINF(p))
+    EC_SETINF(d);
+  else if (d->z == c->f->one)
+    EC_COPY(d, p);
+  else {
+    mp *z, *zz;
+    field *f = c->f;
+    z = F_INV(f, MP_NEW, p->z);
+    zz = F_SQR(f, MP_NEW, z);
+    z = F_MUL(f, z, zz, z);
+    d->x = F_MUL(f, d->x, p->x, zz);
+    d->y = F_MUL(f, d->y, p->y, z);
+    mp_drop(z);
+    mp_drop(zz);
+    mp_drop(d->z);
+    d->z = MP_COPY(f->one);
+  }
+  return (d);  
+}
+
 /* --- @ec_stdsub@ --- *
  *
  * Arguments:	@ec_curve *c@ = pointer to an elliptic curve
  *		@ec *d@ = pointer to the destination
- *		@const ec *a, *b@ = the operand points
+ *		@const ec *p, *q@ = the operand points
  *
  * Returns:	The destination @d@.
  *
@@ -203,15 +243,29 @@ ec *ec_projout(ec_curve *c, ec *d, const ec *p)
  *		subtraction operator.
  */
 
-ec *ec_stdsub(ec_curve *c, ec *d, const ec *a, const ec *b)
+ec *ec_stdsub(ec_curve *c, ec *d, const ec *p, const ec *q)
 {
   ec t = EC_INIT;
-  EC_NEG(c, &t, b);
-  EC_SUB(c, d, a, &t);
+  EC_NEG(c, &t, q);
+  EC_FIX(c, &t, &t);
+  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@ --- *
@@ -230,10 +284,28 @@ ec *ec_find(ec_curve *c, ec *d, mp *x)
   x = F_IN(c->f, MP_NEW, x);
   if ((d = EC_FIND(c, d, x)) != 0)
     EC_OUT(c, d, d);
-  mp_drop(x);
+  MP_DROP(x);
   return (d);
 }
 
+/* --- @ec_neg@ --- *
+ *
+ * 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:	The destination point.
+ *
+ * Use:		Computes the negation of the given point.
+ */
+
+ec *ec_neg(ec_curve *c, ec *d, const ec *p)
+{
+  EC_IN(c, d, p);
+  EC_NEG(c, d, d);
+  return (EC_OUT(c, d, d));
+}
+
 /* --- @ec_add@ --- *
  *
  * Arguments:	@ec_curve *c@ = pointer to an elliptic curve
@@ -257,6 +329,29 @@ ec *ec_add(ec_curve *c, ec *d, const ec *p, const ec *q)
   return (d);
 }
 
+/* --- @ec_sub@ --- *
+ *
+ * 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:	The destination @d@.
+ *
+ * Use:		Subtracts one point from another on an elliptic curve.
+ */
+
+ec *ec_sub(ec_curve *c, ec *d, const ec *p, const ec *q)
+{
+  ec pp, qq;
+  EC_IN(c, &pp, p);
+  EC_IN(c, &qq, q);
+  EC_SUB(c, d, &qq, &qq);
+  EC_OUT(c, d, d);
+  EC_DESTROY(&pp);
+  EC_DESTROY(&qq);
+  return (d);
+}
+
 /* --- @ec_dbl@ --- *
  *
  * Arguments:	@ec_curve *c@ = pointer to an elliptic curve
@@ -275,6 +370,29 @@ ec *ec_dbl(ec_curve *c, ec *d, const ec *p)
   return (EC_OUT(c, d, d));
 }
 
+/* --- @ec_check@ --- *
+ *
+ * Arguments:	@ec_curve *c@ = pointer to an elliptic curve
+ *		@const ec *p@ = pointer to the point
+ *
+ * Returns:	Zero if OK, nonzero if this is an invalid point.
+ *
+ * Use:		Checks that a point is actually on an elliptic curve.
+ */
+
+int ec_check(ec_curve *c, const ec *p)
+{
+  ec t = EC_INIT;
+  int rc;
+
+  if (EC_ATINF(p))
+    return (0);
+  EC_IN(c, &t, p);
+  rc = EC_CHECK(c, &t);
+  EC_DESTROY(&t);
+  return (rc);
+}
+
 /* --- @ec_imul@, @ec_mul@ --- *
  *
  * Arguments:	@ec_curve *c@ = pointer to an elliptic curve
@@ -300,10 +418,15 @@ ec *ec_imul(ec_curve *c, ec *d, const ec *p, mp *n)
   EC_SETINF(d);
   if (MP_LEN(n) == 0)
     ;
-  else if (MP_LEN(n) < EXP_THRESH)
-    EXP_SIMPLE(&d, t, n);
-  else
-    EXP_WINDOW(&d, t, n);
+  else {
+    if (n->f & MP_NEG)
+      EC_NEG(c, &t, &t);
+    if (MP_LEN(n) < EXP_THRESH)
+      EXP_SIMPLE(*d, t, n);
+    else
+      EXP_WINDOW(*d, t, n);
+  }
+  EC_DESTROY(&t);
   return (d);
 }