3 * $Id: ec-prime.c,v 1.3.4.2 2004/03/20 00:13:31 mdw Exp $
5 * Elliptic curves over prime fields
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 --------------------------------------------------*
32 * $Log: ec-prime.c,v $
33 * Revision 1.3.4.2 2004/03/20 00:13:31 mdw
34 * Projective coordinates for prime curves
36 * Revision 1.3.4.1 2003/06/10 13:43:53 mdw
37 * Simple (non-projective) curves over prime fields now seem to work.
39 * Revision 1.3 2003/05/15 23:25:59 mdw
40 * Make elliptic curve stuff build.
42 * Revision 1.2 2002/01/13 13:48:44 mdw
45 * Revision 1.1 2001/04/29 18:12:33 mdw
50 /*----- Header files ------------------------------------------------------*/
56 /*----- Data structures ---------------------------------------------------*/
58 typedef struct ecctx {
63 /*----- Simple prime curves -----------------------------------------------*/
65 static const ec_ops ec_primeops, ec_primeprojops, ec_primeprojxops;
67 static ec *ecneg(ec_curve *c, ec *d, const ec *p)
70 d->y = F_NEG(c->f, d->y, d->y);
74 static ec *ecfind(ec_curve *c, ec *d, mp *x)
77 ecctx *cc = (ecctx *)c;
80 q = F_SQR(f, MP_NEW, x);
81 p = F_MUL(f, MP_NEW, x, q);
82 q = F_MUL(f, q, x, cc->a);
83 p = F_ADD(f, p, p, q);
84 p = F_ADD(f, p, p, cc->b);
92 d->z = MP_COPY(f->one);
96 static ec *ecdbl(ec_curve *c, ec *d, const ec *a)
100 else if (F_ZEROP(c->f, a->y))
104 ecctx *cc = (ecctx *)c;
108 dx = F_SQR(f, MP_NEW, a->x); /* %$x^2$% */
109 dy = F_DBL(f, MP_NEW, a->y); /* %$2 y$% */
110 dx = F_TPL(f, dx, dx); /* %$3 x^2$% */
111 dx = F_ADD(f, dx, dx, cc->a); /* %$3 x^2 + A$% */
112 dy = F_INV(f, dy, dy); /* %$(2 y)^{-1}$% */
113 lambda = F_MUL(f, MP_NEW, dx, dy); /* %$\lambda = (3 x^2 + A)/(2 y)$% */
115 dx = F_SQR(f, dx, lambda); /* %$\lambda^2$% */
116 dy = F_DBL(f, dy, a->x); /* %$2 x$% */
117 dx = F_SUB(f, dx, dx, dy); /* %$x' = \lambda^2 - 2 x */
118 dy = F_SUB(f, dy, a->x, dx); /* %$x - x'$% */
119 dy = F_MUL(f, dy, lambda, dy); /* %$\lambda (x - x')$% */
120 dy = F_SUB(f, dy, dy, a->y); /* %$y' = \lambda (x - x') - y$% */
131 static ec *ecprojdbl(ec_curve *c, ec *d, const ec *a)
135 else if (F_ZEROP(c->f, a->y))
139 ecctx *cc = (ecctx *)c;
140 mp *p, *q, *m, *s, *dx, *dy, *dz;
142 p = F_SQR(f, MP_NEW, a->z); /* %$z^2$% */
143 q = F_SQR(f, MP_NEW, p); /* %$z^4$% */
144 p = F_MUL(f, p, q, cc->a); /* %$A z^4$% */
145 m = F_SQR(f, MP_NEW, a->x); /* %$x^2$% */
146 m = F_TPL(f, m, m); /* %$3 x^2$% */
147 m = F_ADD(f, m, m, p); /* %$m = 3 x^2 + A z^4$% */
149 q = F_DBL(f, q, a->y); /* %$2 y$% */
150 dz = F_MUL(f, MP_NEW, q, a->z); /* %$z' = 2 y z$% */
152 p = F_SQR(f, p, q); /* %$4 y^2$% */
153 s = F_MUL(f, MP_NEW, p, a->x); /* %$s = 4 x y^2$% */
154 q = F_SQR(f, q, p); /* %$16 y^4$% */
155 q = F_HLV(f, q, q); /* %$t = 8 y^4$% */
157 p = F_DBL(f, p, s); /* %$2 s$% */
158 dx = F_SQR(f, MP_NEW, m); /* %$m^2$% */
159 dx = F_SUB(f, dx, dx, p); /* %$x' = m^2 - 2 s$% */
161 s = F_SUB(f, s, s, dx); /* %$s - x'$% */
162 dy = F_MUL(f, p, m, s); /* %$m (s - x')$% */
163 dy = F_SUB(f, dy, dy, q); /* %$y' = m (s - x') - t$% */
176 static ec *ecprojxdbl(ec_curve *c, ec *d, const ec *a)
180 else if (F_ZEROP(c->f, a->y))
184 mp *p, *q, *m, *s, *dx, *dy, *dz;
186 m = F_SQR(f, MP_NEW, a->z); /* %$z^2$% */
187 p = F_SUB(f, MP_NEW, a->x, m); /* %$x - z^2$% */
188 q = F_ADD(f, MP_NEW, a->x, m); /* %$x + z^2$% */
189 m = F_MUL(f, m, p, q); /* %$x^2 - z^4$% */
190 m = F_TPL(f, m, m); /* %$m = 3 x^2 - 3 z^4$% */
192 q = F_DBL(f, q, a->y); /* %$2 y$% */
193 dz = F_MUL(f, MP_NEW, q, a->z); /* %$z' = 2 y z$% */
195 p = F_SQR(f, p, q); /* %$4 y^2$% */
196 s = F_MUL(f, MP_NEW, p, a->x); /* %$s = 4 x y^2$% */
197 q = F_SQR(f, q, p); /* %$16 y^4$% */
198 q = F_HLV(f, q, q); /* %$t = 8 y^4$% */
200 p = F_DBL(f, p, s); /* %$2 s$% */
201 dx = F_SQR(f, MP_NEW, m); /* %$m^2$% */
202 dx = F_SUB(f, dx, dx, p); /* %$x' = m^2 - 2 s$% */
204 s = F_SUB(f, s, s, dx); /* %$s - x'$% */
205 dy = F_MUL(f, p, m, s); /* %$m (s - x')$% */
206 dy = F_SUB(f, dy, dy, q); /* %$y' = m (s - x') - t$% */
219 static ec *ecadd(ec_curve *c, ec *d, const ec *a, const ec *b)
223 else if (EC_ATINF(a))
225 else if (EC_ATINF(b))
232 if (!MP_EQ(a->x, b->x)) {
233 dy = F_SUB(f, MP_NEW, a->y, b->y); /* %$y_0 - y_1$% */
234 dx = F_SUB(f, MP_NEW, a->x, b->x); /* %$x_0 - x_1$% */
235 dx = F_INV(f, dx, dx); /* %$(x_0 - x_1)^{-1}$% */
236 lambda = F_MUL(f, MP_NEW, dy, dx);
237 /* %$\lambda = (y_0 - y1)/(x_0 - x_1)$% */
238 } else if (F_ZEROP(c->f, a->y) || !MP_EQ(a->y, b->y)) {
242 ecctx *cc = (ecctx *)c;
243 dx = F_SQR(f, MP_NEW, a->x); /* %$x_0^2$% */
244 dx = F_TPL(f, dx, dx); /* %$3 x_0^2$% */
245 dx = F_ADD(f, dx, dx, cc->a); /* %$3 x_0^2 + A$% */
246 dy = F_DBL(f, MP_NEW, a->y); /* %$2 y_0$% */
247 dy = F_INV(f, dy, dy); /* %$(2 y_0)^{-1}$% */
248 lambda = F_MUL(f, MP_NEW, dx, dy);
249 /* %$\lambda = (3 x_0^2 + A)/(2 y_0)$% */
252 dx = F_SQR(f, dx, lambda); /* %$\lambda^2$% */
253 dx = F_SUB(f, dx, dx, a->x); /* %$\lambda^2 - x_0$% */
254 dx = F_SUB(f, dx, dx, b->x); /* %$x' = \lambda^2 - x_0 - x_1$% */
255 dy = F_SUB(f, dy, b->x, dx); /* %$x_1 - x'$% */
256 dy = F_MUL(f, dy, lambda, dy); /* %$\lambda (x_1 - x')$% */
257 dy = F_SUB(f, dy, dy, b->y);
258 /* %$y' = \lambda (x_1 - x') - y_1$% */
269 static ec *ecprojadd(ec_curve *c, ec *d, const ec *a, const ec *b)
272 c->ops->dbl(c, d, a);
273 else if (EC_ATINF(a))
275 else if (EC_ATINF(b))
279 mp *p, *q, *r, *w, *u, *s, *dx, *dy, *dz;
281 q = F_SQR(f, MP_NEW, a->z); /* %$z_0^2$% */
282 u = F_MUL(f, MP_NEW, q, b->x); /* %$u = x_1 z_0^2$% */
283 p = F_MUL(f, MP_NEW, q, b->y); /* %$y_1 z_0^2$% */
284 s = F_MUL(f, q, p, a->z); /* %$s = y_1 z_0^3$% */
286 w = F_SUB(f, p, a->x, u); /* %$w = x_0 - u$% */
287 r = F_SUB(f, MP_NEW, a->y, s); /* %$r = y_0 - s$% */
294 return (c->ops->dbl(c, d, a));
304 u = F_ADD(f, u, u, a->x); /* %$t = x_0 + u$% */
305 s = F_ADD(f, s, s, a->y); /* %$m = y_0 + r$% */
307 dz = F_MUL(f, MP_NEW, a->z, w); /* %$z' = z_0 w$% */
309 p = F_SQR(f, MP_NEW, w); /* %$w^2$% */
310 q = F_MUL(f, MP_NEW, p, u); /* %$t w^2$% */
311 u = F_MUL(f, u, p, w); /* %$w^3$% */
312 p = F_MUL(f, p, u, s); /* %$m w^3$% */
314 dx = F_SQR(f, u, r); /* %$r^2$% */
315 dx = F_SUB(f, dx, dx, q); /* %$x' = r^2 - t w^2$% */
317 s = F_DBL(f, s, dx); /* %$2 x'$% */
318 q = F_SUB(f, q, q, s); /* %$v = t w^2 - 2 x'$% */
319 dy = F_MUL(f, s, q, r); /* %$v r$% */
320 dy = F_SUB(f, dy, dy, p); /* %$v r - m w^3$% */
321 dy = F_HLV(f, dy, dy); /* %$y' = (v r - m w^3)/2$% */
335 static int eccheck(ec_curve *c, const ec *p)
337 ecctx *cc = (ecctx *)c;
340 mp *l = F_SQR(f, MP_NEW, p->y);
341 mp *x = F_SQR(f, MP_NEW, p->x);
342 mp *r = F_MUL(f, MP_NEW, x, p->x);
343 x = F_MUL(f, x, cc->a, p->x);
344 r = F_ADD(f, r, r, x);
345 r = F_ADD(f, r, r, cc->b);
346 rc = MP_EQ(l, r) ? 0 : -1;
353 static int ecprojcheck(ec_curve *c, const ec *p)
358 c->ops->fix(c, &t, p);
364 static void ecdestroy(ec_curve *c)
366 ecctx *cc = (ecctx *)c;
372 /* --- @ec_prime@, @ec_primeproj@ --- *
374 * Arguments: @field *f@ = the underlying field for this elliptic curve
375 * @mp *a, *b@ = the coefficients for this curve
377 * Returns: A pointer to the curve.
379 * Use: Creates a curve structure for an elliptic curve defined over
380 * a prime field. The @primeproj@ variant uses projective
381 * coordinates, which can be a win.
384 extern ec_curve *ec_prime(field *f, mp *a, mp *b)
386 ecctx *cc = CREATE(ecctx);
387 cc->c.ops = &ec_primeops;
389 cc->a = F_IN(f, MP_NEW, a);
390 cc->b = F_IN(f, MP_NEW, b);
394 extern ec_curve *ec_primeproj(field *f, mp *a, mp *b)
396 ecctx *cc = CREATE(ecctx);
399 ax = mp_add(MP_NEW, a, MP_THREE);
400 ax = F_IN(f, ax, ax);
402 cc->c.ops = &ec_primeprojxops;
404 cc->c.ops = &ec_primeprojops;
407 cc->a = F_IN(f, MP_NEW, a);
408 cc->b = F_IN(f, MP_NEW, b);
412 static const ec_ops ec_primeops = {
413 ecdestroy, ec_idin, ec_idout, ec_idfix,
414 0, ecneg, ecadd, ec_stdsub, ecdbl, eccheck
417 static const ec_ops ec_primeprojops = {
418 ecdestroy, ec_projin, ec_projout, ec_projfix,
419 0, ecneg, ecprojadd, ec_stdsub, ecprojdbl, ecprojcheck
422 static const ec_ops ec_primeprojxops = {
423 ecdestroy, ec_projin, ec_projout, ec_projfix,
424 0, ecneg, ecprojadd, ec_stdsub, ecprojxdbl, ecprojcheck
427 /*----- Test rig ----------------------------------------------------------*/
431 #define MP(x) mp_readstring(MP_NEW, #x, 0, 0)
437 ec g = EC_INIT, d = EC_INIT;
440 printf("ec-prime: ");
443 b = MP(0x64210519e59c80e70fa7e9ab72243049feb8deecc146b9b1);
444 p = MP(6277101735386680763835789423207666416083908700390324961279);
445 r = MP(6277101735386680763835789423176059013767194773182842284080);
448 c = ec_prime(f, a, b);
450 g.x = MP(0x188da80eb03090f67cbf20eb43a18800f4ff0afd82ff1012);
451 g.y = MP(0x07192b95ffc8da78631011ed6b24cdd573f977a11e794811);
453 ec_mul(c, &d, &g, r);
455 fprintf(stderr, "zero too early\n");
458 ec_add(c, &d, &d, &g);
460 fprintf(stderr, "didn't reach zero\n");
461 MP_EPRINT("d.x", d.x);
462 MP_EPRINT("d.y", d.y);
470 MP_DROP(p); MP_DROP(a); MP_DROP(b); MP_DROP(r);
471 assert(!mparena_count(&mparena_global));
478 /*----- That's all, folks -------------------------------------------------*/