3 * $Id: ec-bin.c,v 1.6 2004/04/01 12:50:09 mdw Exp $
5 * Arithmetic for elliptic curves over binary fields
7 * (c) 2004 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 1.6 2004/04/01 12:50:09 mdw
34 * Add cyclic group abstraction, with test code. Separate off exponentation
35 * functions for better static linking. Fix a buttload of bugs on the way.
36 * Generally ensure that negative exponents do inversion correctly. Add
37 * table of standard prime-field subgroups. (Binary field subgroups are
38 * currently unimplemented but easy to add if anyone ever finds a good one.)
40 * Revision 1.5 2004/03/27 17:54:11 mdw
41 * Standard curves and curve checking.
43 * Revision 1.4 2004/03/23 15:19:32 mdw
44 * Test elliptic curves more thoroughly.
46 * Revision 1.3 2004/03/22 02:19:09 mdw
47 * Rationalise the sliding-window threshold. Drop guarantee that right
48 * arguments to EC @add@ are canonical, and fix up projective implementations
51 * Revision 1.2 2004/03/21 22:52:06 mdw
52 * Merge and close elliptic curve branch.
54 * Revision 1.1.2.1 2004/03/21 22:39:46 mdw
55 * Elliptic curves on binary fields work.
59 /*----- Header files ------------------------------------------------------*/
65 /*----- Data structures ---------------------------------------------------*/
67 typedef struct ecctx {
72 /*----- Main code ---------------------------------------------------------*/
74 static const ec_ops ec_binops, ec_binprojops;
76 static ec *ecneg(ec_curve *c, ec *d, const ec *p)
80 d->y = F_ADD(c->f, d->y, d->y, d->x);
84 static ec *ecprojneg(ec_curve *c, ec *d, const ec *p)
88 mp *t = F_MUL(c->f, MP_NEW, d->x, d->z);
89 d->y = F_ADD(c->f, d->y, d->y, t);
95 static ec *ecfind(ec_curve *c, ec *d, mp *x)
101 y = F_SQRT(f, MP_NEW, c->b);
103 u = F_SQR(f, MP_NEW, x); /* %$x^2$% */
104 y = F_MUL(f, MP_NEW, u, c->a); /* %$a x^2$% */
105 y = F_ADD(f, y, y, c->b); /* %$a x^2 + b$% */
106 v = F_MUL(f, MP_NEW, u, x); /* %$x^3$% */
107 y = F_ADD(f, y, y, v); /* %$A = x^3 + a x^2 + b$% */
108 if (!F_ZEROP(f, y)) {
109 u = F_INV(f, u, u); /* %$x^{-2}$% */
110 v = F_MUL(f, v, u, y); /* %$B = A x^{-2} = x + a + b x^{-2}$% */
111 y = F_QUADSOLVE(f, y, v); /* %$z^2 + z = B$% */
112 if (y) y = F_MUL(f, y, y, x); /* %$y = z x$% */
121 d->z = MP_COPY(f->one);
125 static ec *ecdbl(ec_curve *c, ec *d, const ec *a)
127 if (EC_ATINF(a) || F_ZEROP(c->f, a->x))
134 dx = F_INV(f, MP_NEW, a->x); /* %$x^{-1}$% */
135 dy = F_MUL(f, MP_NEW, dx, a->y); /* %$y/x$% */
136 lambda = F_ADD(f, dy, dy, a->x); /* %$\lambda = x + y/x$% */
138 dx = F_SQR(f, dx, lambda); /* %$\lambda^2$% */
139 dx = F_ADD(f, dx, dx, lambda); /* %$\lambda^2 + \lambda$% */
140 dx = F_ADD(f, dx, dx, c->a); /* %$x' = a + \lambda^2 + \lambda$% */
142 dy = F_ADD(f, MP_NEW, a->x, dx); /* %$ x + x' $% */
143 dy = F_MUL(f, dy, dy, lambda); /* %$ (x + x') \lambda$% */
144 dy = F_ADD(f, dy, dy, a->y); /* %$ (x + x') \lambda + y$% */
145 dy = F_ADD(f, dy, dy, dx); /* %$ y' = (x + x') \lambda + y + x'$% */
156 static ec *ecprojdbl(ec_curve *c, ec *d, const ec *a)
158 if (EC_ATINF(a) || F_ZEROP(c->f, a->x))
162 ecctx *cc = (ecctx *)c;
163 mp *dx, *dy, *dz, *u, *v;
165 dy = F_SQR(f, MP_NEW, a->z); /* %$z^2$% */
166 dx = F_MUL(f, MP_NEW, dy, cc->bb); /* %$c z^2$% */
167 dx = F_ADD(f, dx, dx, a->x); /* %$x + c z^2$% */
168 dz = F_SQR(f, MP_NEW, dx); /* %$(x + c z^2)^2$% */
169 dx = F_SQR(f, dx, dz); /* %$x' = (x + c z^2)^4$% */
171 dz = F_MUL(f, dz, dy, a->x); /* %$z' = x z^2$% */
173 dy = F_SQR(f, dy, a->x); /* %$x^2$% */
174 u = F_MUL(f, MP_NEW, a->y, a->z); /* %$y z$% */
175 u = F_ADD(f, u, u, dz); /* %$z' + y z$% */
176 u = F_ADD(f, u, u, dy); /* %$u = z' + x^2 + y z$% */
178 v = F_SQR(f, MP_NEW, dy); /* %$x^4$% */
179 dy = F_MUL(f, dy, v, dz); /* %$x^4 z'$% */
180 v = F_MUL(f, v, u, dx); /* %$u x'$% */
181 dy = F_ADD(f, dy, dy, v); /* %$y' = x^4 z' + u x'$% */
189 assert(!(d->x->f & MP_DESTROYED));
190 assert(!(d->y->f & MP_DESTROYED));
191 assert(!(d->z->f & MP_DESTROYED));
196 static ec *ecadd(ec_curve *c, ec *d, const ec *a, const ec *b)
200 else if (EC_ATINF(a))
202 else if (EC_ATINF(b))
209 if (!MP_EQ(a->x, b->x)) {
210 dx = F_ADD(f, MP_NEW, a->x, b->x); /* %$x_0 + x_1$% */
211 dy = F_INV(f, MP_NEW, dx); /* %$(x_0 + x_1)^{-1}$% */
212 dx = F_ADD(f, dx, a->y, b->y); /* %$y_0 + y_1$% */
213 lambda = F_MUL(f, MP_NEW, dy, dx);
214 /* %$\lambda = (y_0 + y_1)/(x_0 + x_1)$% */
216 dx = F_SQR(f, dx, lambda); /* %$\lambda^2$% */
217 dx = F_ADD(f, dx, dx, lambda); /* %$\lambda^2 + \lambda$% */
218 dx = F_ADD(f, dx, dx, c->a); /* %$a + \lambda^2 + \lambda$% */
219 dx = F_ADD(f, dx, dx, a->x); /* %$a + \lambda^2 + \lambda + x_0$% */
220 dx = F_ADD(f, dx, dx, b->x);
221 /* %$x' = a + \lambda^2 + \lambda + x_0 + x_1$% */
222 } else if (!MP_EQ(a->y, b->y) || F_ZEROP(f, a->x)) {
226 dx = F_INV(f, MP_NEW, a->x); /* %$x^{-1}$% */
227 dy = F_MUL(f, MP_NEW, dx, a->y); /* %$y/x$% */
228 lambda = F_ADD(f, dy, dy, a->x); /* %$\lambda = x + y/x$% */
230 dx = F_SQR(f, dx, lambda); /* %$\lambda^2$% */
231 dx = F_ADD(f, dx, dx, lambda); /* %$\lambda^2 + \lambda$% */
232 dx = F_ADD(f, dx, dx, c->a); /* %$x' = a + \lambda^2 + \lambda$% */
236 dy = F_ADD(f, dy, a->x, dx); /* %$ x + x' $% */
237 dy = F_MUL(f, dy, dy, lambda); /* %$ (x + x') \lambda$% */
238 dy = F_ADD(f, dy, dy, a->y); /* %$ (x + x') \lambda + y$% */
239 dy = F_ADD(f, dy, dy, dx); /* %$ y' = (x + x') \lambda + y + x'$% */
250 static ec *ecprojadd(ec_curve *c, ec *d, const ec *a, const ec *b)
253 c->ops->dbl(c, d, a);
254 else if (EC_ATINF(a))
256 else if (EC_ATINF(b))
260 mp *dx, *dy, *dz, *u, *uu, *v, *t, *s, *ss, *r, *w, *l;
262 dz = F_SQR(f, MP_NEW, b->z); /* %$z_1^2$% */
263 u = F_MUL(f, MP_NEW, dz, a->x); /* %$u_0 = x_0 z_1^2$% */
264 t = F_MUL(f, MP_NEW, dz, b->z); /* %$z_1^3$% */
265 s = F_MUL(f, MP_NEW, t, a->y); /* %$s_0 = y_0 z_1^3$% */
267 dz = F_SQR(f, dz, a->z); /* %$z_0^2$% */
268 uu = F_MUL(f, MP_NEW, dz, b->x); /* %$u_1 = x_1 z_0^2$% */
269 t = F_MUL(f, t, dz, a->z); /* %$z_0^3$% */
270 ss = F_MUL(f, MP_NEW, t, b->y); /* %$s_1 = y_1 z_0^3$% */
272 w = F_ADD(f, u, u, uu); /* %$r = u_0 + u_1$% */
273 r = F_ADD(f, s, s, ss); /* %$w = s_0 + s_1$% */
282 return (c->ops->dbl(c, d, a));
290 l = F_MUL(f, t, a->z, w); /* %$l = z_0 w$% */
292 dz = F_MUL(f, dz, l, b->z); /* %$z' = l z_1$% */
294 ss = F_MUL(f, ss, r, b->x); /* %$r x_1$% */
295 t = F_MUL(f, uu, l, b->y); /* %$l y_1$% */
296 v = F_ADD(f, ss, ss, t); /* %$v = r x_1 + l y_1$% */
298 t = F_ADD(f, t, r, dz); /* %$t = r + z'$% */
300 uu = F_SQR(f, MP_NEW, dz); /* %$z'^2$% */
301 dx = F_MUL(f, MP_NEW, uu, c->a); /* %$a z'^2$% */
302 uu = F_MUL(f, uu, t, r); /* %$t r$% */
303 dx = F_ADD(f, dx, dx, uu); /* %$a z'^2 + t r$% */
304 r = F_SQR(f, r, w); /* %$w^2$% */
305 uu = F_MUL(f, uu, r, w); /* %$w^3$% */
306 dx = F_ADD(f, dx, dx, uu); /* %$x' = a z'^2 + t r + w^3$% */
308 r = F_SQR(f, r, l); /* %$l^2$% */
309 dy = F_MUL(f, uu, v, r); /* %$v l^2$% */
310 l = F_MUL(f, l, t, dx); /* %$t x'$% */
311 dy = F_ADD(f, dy, dy, l); /* %$y' = t x' + v l^2$% */
326 static int eccheck(ec_curve *c, const ec *p)
332 if (EC_ATINF(p)) return (0);
333 v = F_SQR(f, MP_NEW, p->x);
334 u = F_MUL(f, MP_NEW, v, p->x);
335 v = F_MUL(f, v, v, c->a);
336 u = F_ADD(f, u, u, v);
337 u = F_ADD(f, u, u, c->b);
338 v = F_MUL(f, v, p->x, p->y);
339 u = F_ADD(f, u, u, v);
340 v = F_SQR(f, v, p->y);
341 u = F_ADD(f, u, u, v);
342 rc = F_ZEROP(f, u) ? 0 : -1;
348 static int ecprojcheck(ec_curve *c, const ec *p)
353 c->ops->fix(c, &t, p);
359 static void ecdestroy(ec_curve *c)
361 ecctx *cc = (ecctx *)c;
364 if (cc->bb) MP_DROP(cc->bb);
368 /* --- @ec_bin@, @ec_binproj@ --- *
370 * Arguments: @field *f@ = the underlying field for this elliptic curve
371 * @mp *a, *b@ = the coefficients for this curve
373 * Returns: A pointer to the curve.
375 * Use: Creates a curve structure for an elliptic curve defined over
376 * a binary field. The @binproj@ variant uses projective
377 * coordinates, which can be a win.
380 ec_curve *ec_bin(field *f, mp *a, mp *b)
382 ecctx *cc = CREATE(ecctx);
383 cc->c.ops = &ec_binops;
385 cc->c.a = F_IN(f, MP_NEW, a);
386 cc->c.b = F_IN(f, MP_NEW, b);
391 ec_curve *ec_binproj(field *f, mp *a, mp *b)
393 ecctx *cc = CREATE(ecctx);
394 cc->c.ops = &ec_binprojops;
396 cc->c.a = F_IN(f, MP_NEW, a);
397 cc->c.b = F_IN(f, MP_NEW, b);
398 cc->bb = F_SQRT(f, MP_NEW, b);
399 cc->bb = F_SQRT(f, cc->bb, cc->bb);
403 static const ec_ops ec_binops = {
404 ecdestroy, ec_stdsamep, ec_idin, ec_idout, ec_idfix,
405 ecfind, ecneg, ecadd, ec_stdsub, ecdbl, eccheck
408 static const ec_ops ec_binprojops = {
409 ecdestroy, ec_stdsamep, ec_projin, ec_projout, ec_projfix,
410 ecfind, ecprojneg, ecprojadd, ec_stdsub, ecprojdbl, ecprojcheck
413 /*----- Test rig ----------------------------------------------------------*/
417 #define MP(x) mp_readstring(MP_NEW, #x, 0, 0)
419 int main(int argc, char *argv[])
423 ec g = EC_INIT, d = EC_INIT;
425 int i, n = argc == 1 ? 1 : atoi(argv[1]);
430 b = MP(0x021a5c2c8ee9feb5c4b9a753b7b476b7fd6422ef1f3dd674761fa99d6ac27c8a9a197b272822f6cd57a55aa4f50ae317b13545f);
431 p = MP(0x2000000000000000000000000000000000000000000000000000000000000000000000000000000008000000000000000000001);
433 MP(661055968790248598951915308032771039828404682964281219284648798304157774827374805208143723762179110965979867288366567526770);
435 f = field_binpoly(p);
436 c = ec_binproj(f, a, b);
438 g.x = MP(0x15d4860d088ddb3496b0c6064756260441cde4af1771d4db01ffe5b34e59703dc255a868a1180515603aeab60794e54bb7996a7);
439 g.y = MP(0x061b1cfab6be5f32bbfa78324ed106a7636b9c5a7bd198d0158aa4f5488d08f38514f1fdf4b4f40d2181b3681c364ba0273c706);
441 for (i = 0; i < n; i++) {
442 ec_mul(c, &d, &g, r);
444 fprintf(stderr, "zero too early\n");
447 ec_add(c, &d, &d, &g);
449 fprintf(stderr, "didn't reach zero\n");
450 MP_EPRINTX("d.x", d.x);
451 MP_EPRINTX("d.y", d.y);
460 MP_DROP(p); MP_DROP(a); MP_DROP(b); MP_DROP(r);
461 assert(!mparena_count(&mparena_global));
468 /*----- That's all, folks -------------------------------------------------*/