3 * $Id: ec-bin.c,v 1.4 2004/03/23 15:19:32 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 1.4 2004/03/23 15:19:32 mdw
34 * Test elliptic curves more thoroughly.
36 * Revision 1.3 2004/03/22 02:19:09 mdw
37 * Rationalise the sliding-window threshold. Drop guarantee that right
38 * arguments to EC @add@ are canonical, and fix up projective implementations
41 * Revision 1.2 2004/03/21 22:52:06 mdw
42 * Merge and close elliptic curve branch.
44 * Revision 1.1.2.1 2004/03/21 22:39:46 mdw
45 * Elliptic curves on binary fields work.
49 /*----- Header files ------------------------------------------------------*/
55 /*----- Data structures ---------------------------------------------------*/
57 typedef struct ecctx {
63 /*----- Main code ---------------------------------------------------------*/
65 static const ec_ops ec_binops, ec_binprojops;
67 static ec *ecneg(ec_curve *c, ec *d, const ec *p)
71 d->y = F_ADD(c->f, d->y, d->y, d->x);
75 static ec *ecprojneg(ec_curve *c, ec *d, const ec *p)
79 mp *t = F_MUL(c->f, MP_NEW, d->x, d->z);
80 d->y = F_ADD(c->f, d->y, d->y, t);
86 static ec *ecfind(ec_curve *c, ec *d, mp *x)
89 ecctx *cc = (ecctx *)c;
93 y = F_SQRT(f, MP_NEW, cc->b);
95 u = F_SQR(f, MP_NEW, x); /* %$x^2$% */
96 y = F_MUL(f, MP_NEW, u, cc->a); /* %$a x^2$% */
97 y = F_ADD(f, y, y, cc->b); /* %$a x^2 + b$% */
98 v = F_MUL(f, MP_NEW, u, x); /* %$x^3$% */
99 y = F_ADD(f, y, y, v); /* %$A = x^3 + a x^2 + b$% */
100 if (!F_ZEROP(f, y)) {
101 u = F_INV(f, u, u); /* %$x^{-2}$% */
102 v = F_MUL(f, v, u, y); /* %$B = A x^{-2} = x + a + b x^{-2}$% */
103 y = F_QUADSOLVE(f, y, v); /* %$z^2 + z = B$% */
104 if (y) y = F_MUL(f, y, y, x); /* %$y = z x$% */
113 d->z = MP_COPY(f->one);
117 static ec *ecdbl(ec_curve *c, ec *d, const ec *a)
119 if (EC_ATINF(a) || F_ZEROP(c->f, a->x))
123 ecctx *cc = (ecctx *)c;
127 dx = F_INV(f, MP_NEW, a->x); /* %$x^{-1}$% */
128 dy = F_MUL(f, MP_NEW, dx, a->y); /* %$y/x$% */
129 lambda = F_ADD(f, dy, dy, a->x); /* %$\lambda = x + y/x$% */
131 dx = F_SQR(f, dx, lambda); /* %$\lambda^2$% */
132 dx = F_ADD(f, dx, dx, lambda); /* %$\lambda^2 + \lambda$% */
133 dx = F_ADD(f, dx, dx, cc->a); /* %$x' = a + \lambda^2 + \lambda$% */
135 dy = F_ADD(f, MP_NEW, a->x, dx); /* %$ x + x' $% */
136 dy = F_MUL(f, dy, dy, lambda); /* %$ (x + x') \lambda$% */
137 dy = F_ADD(f, dy, dy, a->y); /* %$ (x + x') \lambda + y$% */
138 dy = F_ADD(f, dy, dy, dx); /* %$ y' = (x + x') \lambda + y + x'$% */
149 static ec *ecprojdbl(ec_curve *c, ec *d, const ec *a)
151 if (EC_ATINF(a) || F_ZEROP(c->f, a->x))
155 ecctx *cc = (ecctx *)c;
156 mp *dx, *dy, *dz, *u, *v;
158 dy = F_SQR(f, MP_NEW, a->z); /* %$z^2$% */
159 dx = F_MUL(f, MP_NEW, dy, cc->bb); /* %$c z^2$% */
160 dx = F_ADD(f, dx, dx, a->x); /* %$x + c z^2$% */
161 dz = F_SQR(f, MP_NEW, dx); /* %$(x + c z^2)^2$% */
162 dx = F_SQR(f, dx, dz); /* %$x' = (x + c z^2)^4$% */
164 dz = F_MUL(f, dz, dy, a->x); /* %$z' = x z^2$% */
166 dy = F_SQR(f, dy, a->x); /* %$x^2$% */
167 u = F_MUL(f, MP_NEW, a->y, a->z); /* %$y z$% */
168 u = F_ADD(f, u, u, dz); /* %$z' + y z$% */
169 u = F_ADD(f, u, u, dy); /* %$u = z' + x^2 + y z$% */
171 v = F_SQR(f, MP_NEW, dy); /* %$x^4$% */
172 dy = F_MUL(f, dy, v, dz); /* %$x^4 z'$% */
173 v = F_MUL(f, v, u, dx); /* %$u x'$% */
174 dy = F_ADD(f, dy, dy, v); /* %$y' = x^4 z' + u x'$% */
182 assert(!(d->x->f & MP_DESTROYED));
183 assert(!(d->y->f & MP_DESTROYED));
184 assert(!(d->z->f & MP_DESTROYED));
189 static ec *ecadd(ec_curve *c, ec *d, const ec *a, const ec *b)
193 else if (EC_ATINF(a))
195 else if (EC_ATINF(b))
199 ecctx *cc = (ecctx *)c;
203 if (!MP_EQ(a->x, b->x)) {
204 dx = F_ADD(f, MP_NEW, a->x, b->x); /* %$x_0 + x_1$% */
205 dy = F_INV(f, MP_NEW, dx); /* %$(x_0 + x_1)^{-1}$% */
206 dx = F_ADD(f, dx, a->y, b->y); /* %$y_0 + y_1$% */
207 lambda = F_MUL(f, MP_NEW, dy, dx);
208 /* %$\lambda = (y_0 + y_1)/(x_0 + x_1)$% */
210 dx = F_SQR(f, dx, lambda); /* %$\lambda^2$% */
211 dx = F_ADD(f, dx, dx, lambda); /* %$\lambda^2 + \lambda$% */
212 dx = F_ADD(f, dx, dx, cc->a); /* %$a + \lambda^2 + \lambda$% */
213 dx = F_ADD(f, dx, dx, a->x); /* %$a + \lambda^2 + \lambda + x_0$% */
214 dx = F_ADD(f, dx, dx, b->x);
215 /* %$x' = a + \lambda^2 + \lambda + x_0 + x_1$% */
216 } else if (!MP_EQ(a->y, b->y) || F_ZEROP(f, a->x)) {
220 dx = F_INV(f, MP_NEW, a->x); /* %$x^{-1}$% */
221 dy = F_MUL(f, MP_NEW, dx, a->y); /* %$y/x$% */
222 lambda = F_ADD(f, dy, dy, a->x); /* %$\lambda = x + y/x$% */
224 dx = F_SQR(f, dx, lambda); /* %$\lambda^2$% */
225 dx = F_ADD(f, dx, dx, lambda); /* %$\lambda^2 + \lambda$% */
226 dx = F_ADD(f, dx, dx, cc->a); /* %$x' = a + \lambda^2 + \lambda$% */
230 dy = F_ADD(f, dy, a->x, dx); /* %$ x + x' $% */
231 dy = F_MUL(f, dy, dy, lambda); /* %$ (x + x') \lambda$% */
232 dy = F_ADD(f, dy, dy, a->y); /* %$ (x + x') \lambda + y$% */
233 dy = F_ADD(f, dy, dy, dx); /* %$ y' = (x + x') \lambda + y + x'$% */
244 static ec *ecprojadd(ec_curve *c, ec *d, const ec *a, const ec *b)
247 c->ops->dbl(c, d, a);
248 else if (EC_ATINF(a))
250 else if (EC_ATINF(b))
254 ecctx *cc = (ecctx *)c;
255 mp *dx, *dy, *dz, *u, *uu, *v, *t, *s, *ss, *r, *w, *l;
257 dz = F_SQR(f, MP_NEW, b->z); /* %$z_1^2$% */
258 u = F_MUL(f, MP_NEW, dz, a->x); /* %$u_0 = x_0 z_1^2$% */
259 t = F_MUL(f, MP_NEW, dz, b->z); /* %$z_1^3$% */
260 s = F_MUL(f, MP_NEW, t, a->y); /* %$s_0 = y_0 z_1^3$% */
262 dz = F_SQR(f, dz, a->z); /* %$z_0^2$% */
263 uu = F_MUL(f, MP_NEW, dz, b->x); /* %$u_1 = x_1 z_0^2$% */
264 t = F_MUL(f, t, dz, a->z); /* %$z_0^3$% */
265 ss = F_MUL(f, MP_NEW, t, b->y); /* %$s_1 = y_1 z_0^3$% */
267 w = F_ADD(f, u, u, uu); /* %$r = u_0 + u_1$% */
268 r = F_ADD(f, s, s, ss); /* %$w = s_0 + s_1$% */
277 return (c->ops->dbl(c, d, a));
285 l = F_MUL(f, t, a->z, w); /* %$l = z_0 w$% */
287 dz = F_MUL(f, dz, l, b->z); /* %$z' = l z_1$% */
289 ss = F_MUL(f, ss, r, b->x); /* %$r x_1$% */
290 t = F_MUL(f, uu, l, b->y); /* %$l y_1$% */
291 v = F_ADD(f, ss, ss, t); /* %$v = r x_1 + l y_1$% */
293 t = F_ADD(f, t, r, dz); /* %$t = r + z'$% */
295 uu = F_SQR(f, MP_NEW, dz); /* %$z'^2$% */
296 dx = F_MUL(f, MP_NEW, uu, cc->a); /* %$a z'^2$% */
297 uu = F_MUL(f, uu, t, r); /* %$t r$% */
298 dx = F_ADD(f, dx, dx, uu); /* %$a z'^2 + t r$% */
299 r = F_SQR(f, r, w); /* %$w^2$% */
300 uu = F_MUL(f, uu, r, w); /* %$w^3$% */
301 dx = F_ADD(f, dx, dx, uu); /* %$x' = a z'^2 + t r + w^3$% */
303 r = F_SQR(f, r, l); /* %$l^2$% */
304 dy = F_MUL(f, uu, v, r); /* %$v l^2$% */
305 l = F_MUL(f, l, t, dx); /* %$t x'$% */
306 dy = F_ADD(f, dy, dy, l); /* %$y' = t x' + v l^2$% */
321 static int eccheck(ec_curve *c, const ec *p)
323 ecctx *cc = (ecctx *)c;
328 v = F_SQR(f, MP_NEW, p->x);
329 u = F_MUL(f, MP_NEW, v, p->x);
330 v = F_MUL(f, v, v, cc->a);
331 u = F_ADD(f, u, u, v);
332 u = F_ADD(f, u, u, cc->b);
333 v = F_MUL(f, v, p->x, p->y);
334 u = F_ADD(f, u, u, v);
335 v = F_SQR(f, v, p->y);
336 u = F_ADD(f, u, u, v);
337 rc = F_ZEROP(f, u) ? 0 : -1;
343 static int ecprojcheck(ec_curve *c, const ec *p)
348 c->ops->fix(c, &t, p);
354 static void ecdestroy(ec_curve *c)
356 ecctx *cc = (ecctx *)c;
359 if (cc->bb) MP_DROP(cc->bb);
363 /* --- @ec_bin@, @ec_binproj@ --- *
365 * Arguments: @field *f@ = the underlying field for this elliptic curve
366 * @mp *a, *b@ = the coefficients for this curve
368 * Returns: A pointer to the curve.
370 * Use: Creates a curve structure for an elliptic curve defined over
371 * a binary field. The @binproj@ variant uses projective
372 * coordinates, which can be a win.
375 ec_curve *ec_bin(field *f, mp *a, mp *b)
377 ecctx *cc = CREATE(ecctx);
378 cc->c.ops = &ec_binops;
380 cc->a = F_IN(f, MP_NEW, a);
381 cc->b = F_IN(f, MP_NEW, b);
386 ec_curve *ec_binproj(field *f, mp *a, mp *b)
388 ecctx *cc = CREATE(ecctx);
389 cc->c.ops = &ec_binprojops;
391 cc->a = F_IN(f, MP_NEW, a);
392 cc->b = F_IN(f, MP_NEW, b);
393 cc->bb = F_SQRT(f, MP_NEW, b);
394 cc->bb = F_SQRT(f, cc->bb, cc->bb);
398 static const ec_ops ec_binops = {
399 ecdestroy, ec_idin, ec_idout, ec_idfix,
400 ecfind, ecneg, ecadd, ec_stdsub, ecdbl, eccheck
403 static const ec_ops ec_binprojops = {
404 ecdestroy, ec_projin, ec_projout, ec_projfix,
405 ecfind, ecprojneg, ecprojadd, ec_stdsub, ecprojdbl, ecprojcheck
408 /*----- Test rig ----------------------------------------------------------*/
412 #define MP(x) mp_readstring(MP_NEW, #x, 0, 0)
414 int main(int argc, char *argv[])
418 ec g = EC_INIT, d = EC_INIT;
420 int i, n = argc == 1 ? 1 : atoi(argv[1]);
425 b = MP(0x021a5c2c8ee9feb5c4b9a753b7b476b7fd6422ef1f3dd674761fa99d6ac27c8a9a197b272822f6cd57a55aa4f50ae317b13545f);
426 p = MP(0x2000000000000000000000000000000000000000000000000000000000000000000000000000000008000000000000000000001);
428 MP(661055968790248598951915308032771039828404682964281219284648798304157774827374805208143723762179110965979867288366567526770);
430 f = field_binpoly(p);
431 c = ec_binproj(f, a, b);
433 g.x = MP(0x15d4860d088ddb3496b0c6064756260441cde4af1771d4db01ffe5b34e59703dc255a868a1180515603aeab60794e54bb7996a7);
434 g.y = MP(0x061b1cfab6be5f32bbfa78324ed106a7636b9c5a7bd198d0158aa4f5488d08f38514f1fdf4b4f40d2181b3681c364ba0273c706);
436 for (i = 0; i < n; i++) {
437 ec_mul(c, &d, &g, r);
439 fprintf(stderr, "zero too early\n");
442 ec_add(c, &d, &d, &g);
444 fprintf(stderr, "didn't reach zero\n");
445 MP_EPRINTX("d.x", d.x);
446 MP_EPRINTX("d.y", d.y);
455 MP_DROP(p); MP_DROP(a); MP_DROP(b); MP_DROP(r);
456 assert(!mparena_count(&mparena_global));
463 /*----- That's all, folks -------------------------------------------------*/