3 * $Id: ec.c,v 1.4.4.2 2004/03/20 00:13:31 mdw Exp $
5 * Elliptic curve definitions
7 * (c) 2001 Straylight/Edgeware
10 /*----- Licensing notice --------------------------------------------------*
12 * This file is part of Catacomb.
14 * Catacomb is free software; you can redistribute it and/or modify
15 * it under the terms of the GNU Library General Public License as
16 * published by the Free Software Foundation; either version 2 of the
17 * License, or (at your option) any later version.
19 * Catacomb is distributed in the hope that it will be useful,
20 * but WITHOUT ANY WARRANTY; without even the implied warranty of
21 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
22 * GNU Library General Public License for more details.
24 * You should have received a copy of the GNU Library General Public
25 * License along with Catacomb; if not, write to the Free
26 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
30 /*----- Revision history --------------------------------------------------*
33 * Revision 1.4.4.2 2004/03/20 00:13:31 mdw
34 * Projective coordinates for prime curves
36 * Revision 1.4.4.1 2003/06/10 13:43:53 mdw
37 * Simple (non-projective) curves over prime fields now seem to work.
39 * Revision 1.4 2003/05/15 23:25:59 mdw
40 * Make elliptic curve stuff build.
42 * Revision 1.3 2002/01/13 13:48:44 mdw
45 * Revision 1.2 2001/05/07 17:29:44 mdw
46 * Treat projective coordinates as an internal representation. Various
47 * minor interface changes.
49 * Revision 1.1 2001/04/29 18:12:33 mdw
54 /*----- Header files ------------------------------------------------------*/
59 /*----- Trivial wrappers --------------------------------------------------*/
61 /* --- @ec_create@ --- *
63 * Arguments: @ec *p@ = pointer to an elliptic-curve point
65 * Returns: The argument @p@.
67 * Use: Initializes a new point. The initial value is the additive
68 * identity (which is universal for all curves).
71 ec *ec_create(ec *p) { EC_CREATE(p); return (p); }
73 /* --- @ec_destroy@ --- *
75 * Arguments: @ec *p@ = pointer to an elliptic-curve point
79 * Use: Destroys a point, making it invalid.
82 void ec_destroy(ec *p) { EC_DESTROY(p); }
84 /* --- @ec_atinf@ --- *
86 * Arguments: @const ec *p@ = pointer to a point
88 * Returns: Nonzero if %$p = O$% is the point at infinity, zero
92 int ec_atinf(const ec *p) { return (EC_ATINF(p)); }
94 /* --- @ec_setinf@ --- *
96 * Arguments: @ec *p@ = pointer to a point
98 * Returns: The argument @p@.
100 * Use: Sets the given point to be the point %$O$% at infinity.
103 ec *ec_setinf(ec *p) { EC_SETINF(p); return (p); }
105 /* --- @ec_copy@ --- *
107 * Arguments: @ec *d@ = pointer to destination point
108 * @const ec *p@ = pointer to source point
110 * Returns: The destination @d@.
112 * Use: Creates a copy of an elliptic curve point.
115 ec *ec_copy(ec *d, const ec *p) { EC_COPY(d, p); return (d); }
117 /*----- Standard curve operations -----------------------------------------*/
119 /* --- @ec_idin@, @ec_idout@, @ec_idfix@ --- *
121 * Arguments: @ec_curve *c@ = pointer to an elliptic curve
122 * @ec *d@ = pointer to the destination
123 * @const ec *p@ = pointer to a source point
125 * Returns: The destination @d@.
127 * Use: An identity operation if your curve has no internal
128 * representation. (The field internal representation is still
132 ec *ec_idin(ec_curve *c, ec *d, const ec *p)
138 d->x = F_IN(f, d->x, p->x);
139 d->y = F_IN(f, d->y, p->y);
140 mp_drop(d->z); d->z = 0;
145 ec *ec_idout(ec_curve *c, ec *d, const ec *p)
151 d->x = F_OUT(f, d->x, p->x);
152 d->y = F_OUT(f, d->y, p->y);
153 mp_drop(d->z); d->z = 0;
158 ec *ec_idfix(ec_curve *c, ec *d, const ec *p)
164 /* --- @ec_projin@, @ec_projout@ --- *
166 * Arguments: @ec_curve *c@ = pointer to an elliptic curve
167 * @ec *d@ = pointer to the destination
168 * @const ec *p@ = pointer to a source point
170 * Returns: The destination @d@.
172 * Use: Conversion functions if your curve operations use a
173 * projective representation.
176 ec *ec_projin(ec_curve *c, ec *d, const ec *p)
182 d->x = F_IN(f, d->x, p->x);
183 d->y = F_IN(f, d->y, p->y);
184 mp_drop(d->z); d->z = MP_COPY(f->one);
189 ec *ec_projout(ec_curve *c, ec *d, const ec *p)
196 z = F_INV(f, MP_NEW, p->z);
197 zz = F_SQR(f, MP_NEW, z);
198 z = F_MUL(f, z, zz, z);
199 x = F_MUL(f, d->x, p->x, zz);
200 y = F_MUL(f, d->y, p->y, z);
204 d->x = F_OUT(f, x, x);
205 d->y = F_OUT(f, y, y);
211 ec *ec_projfix(ec_curve *c, ec *d, const ec *p)
215 else if (d->z == c->f->one)
220 z = F_INV(f, MP_NEW, p->z);
221 zz = F_SQR(f, MP_NEW, z);
222 z = F_MUL(f, z, zz, z);
223 d->x = F_MUL(f, d->x, p->x, zz);
224 d->y = F_MUL(f, d->y, p->y, z);
228 d->z = MP_COPY(f->one);
233 /* --- @ec_stdsub@ --- *
235 * Arguments: @ec_curve *c@ = pointer to an elliptic curve
236 * @ec *d@ = pointer to the destination
237 * @const ec *p, *q@ = the operand points
239 * Returns: The destination @d@.
241 * Use: Standard point subtraction operation, in terms of negation
242 * and addition. This isn't as efficient as a ready-made
243 * subtraction operator.
246 ec *ec_stdsub(ec_curve *c, ec *d, const ec *p, const ec *q)
256 /*----- Creating curves ---------------------------------------------------*/
258 /* --- @ec_destroycurve@ --- *
260 * Arguments: @ec_curve *c@ = pointer to an ellptic curve
264 * Use: Destroys a description of an elliptic curve.
267 void ec_destroycurve(ec_curve *c) { c->ops->destroy(c); }
269 /*----- Real arithmetic ---------------------------------------------------*/
271 /* --- @ec_find@ --- *
273 * Arguments: @ec_curve *c@ = pointer to an elliptic curve
274 * @ec *d@ = pointer to the destination point
275 * @mp *x@ = a possible x-coordinate
277 * Returns: Zero if OK, nonzero if there isn't a point there.
279 * Use: Finds a point on an elliptic curve with a given x-coordinate.
282 ec *ec_find(ec_curve *c, ec *d, mp *x)
284 x = F_IN(c->f, MP_NEW, x);
285 if ((d = EC_FIND(c, d, x)) != 0)
291 /* --- @ec_neg@ --- *
293 * Arguments: @ec_curve *c@ = pointer to an elliptic curve
294 * @ec *d@ = pointer to the destination point
295 * @const ec *p@ = pointer to the operand point
297 * Returns: The destination point.
299 * Use: Computes the negation of the given point.
302 ec *ec_neg(ec_curve *c, ec *d, const ec *p)
306 return (EC_OUT(c, d, d));
309 /* --- @ec_add@ --- *
311 * Arguments: @ec_curve *c@ = pointer to an elliptic curve
312 * @ec *d@ = pointer to the destination point
313 * @const ec *p, *q@ = pointers to the operand points
317 * Use: Adds two points on an elliptic curve.
320 ec *ec_add(ec_curve *c, ec *d, const ec *p, const ec *q)
322 ec pp = EC_INIT, qq = EC_INIT;
325 EC_ADD(c, d, &pp, &qq);
332 /* --- @ec_sub@ --- *
334 * Arguments: @ec_curve *c@ = pointer to an elliptic curve
335 * @ec *d@ = pointer to the destination point
336 * @const ec *p, *q@ = pointers to the operand points
338 * Returns: The destination @d@.
340 * Use: Subtracts one point from another on an elliptic curve.
343 ec *ec_sub(ec_curve *c, ec *d, const ec *p, const ec *q)
348 EC_SUB(c, d, &qq, &qq);
355 /* --- @ec_dbl@ --- *
357 * Arguments: @ec_curve *c@ = pointer to an elliptic curve
358 * @ec *d@ = pointer to the destination point
359 * @const ec *p@ = pointer to the operand point
363 * Use: Doubles a point on an elliptic curve.
366 ec *ec_dbl(ec_curve *c, ec *d, const ec *p)
370 return (EC_OUT(c, d, d));
373 /* --- @ec_check@ --- *
375 * Arguments: @ec_curve *c@ = pointer to an elliptic curve
376 * @const ec *p@ = pointer to the point
378 * Returns: Zero if OK, nonzero if this is an invalid point.
380 * Use: Checks that a point is actually on an elliptic curve.
383 int ec_check(ec_curve *c, const ec *p)
391 rc = EC_CHECK(c, &t);
396 /* --- @ec_imul@, @ec_mul@ --- *
398 * Arguments: @ec_curve *c@ = pointer to an elliptic curve
399 * @ec *d@ = pointer to the destination point
400 * @const ec *p@ = pointer to the generator point
401 * @mp *n@ = integer multiplier
403 * Returns: The destination @d@.
405 * Use: Multiplies a point by a scalar, returning %$n p$%. The
406 * @imul@ variant uses internal representations for argument
410 ec *ec_imul(ec_curve *c, ec *d, const ec *p, mp *n)
415 if (t.x && (n->f & MP_BURN))
424 if (MP_LEN(n) < EXP_THRESH)
425 EXP_SIMPLE(*d, t, n);
427 EXP_WINDOW(*d, t, n);
433 ec *ec_mul(ec_curve *c, ec *d, const ec *p, mp *n)
437 return (EC_OUT(c, d, d));
440 /*----- That's all, folks -------------------------------------------------*/