3 * Elliptic curves over prime fields
5 * (c) 2001 Straylight/Edgeware
8 /*----- Licensing notice --------------------------------------------------*
10 * This file is part of Catacomb.
12 * Catacomb is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU Library General Public License as
14 * published by the Free Software Foundation; either version 2 of the
15 * License, or (at your option) any later version.
17 * Catacomb is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU Library General Public License for more details.
22 * You should have received a copy of the GNU Library General Public
23 * License along with Catacomb; if not, write to the Free
24 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
28 /*----- Header files ------------------------------------------------------*/
34 /*----- Simple prime curves -----------------------------------------------*/
36 static const ec_ops ec_primeops
, ec_primeprojops
, ec_primeprojxops
;
38 static ec
*ecneg(ec_curve
*c
, ec
*d
, const ec
*p
)
42 d
->y
= F_NEG(c
->f
, d
->y
, d
->y
);
46 static ec
*ecfind(ec_curve
*c
, ec
*d
, mp
*x
)
51 q
= F_SQR(f
, MP_NEW
, x
);
52 p
= F_MUL(f
, MP_NEW
, x
, q
);
53 q
= F_MUL(f
, q
, x
, c
->a
);
54 p
= F_ADD(f
, p
, p
, q
);
55 p
= F_ADD(f
, p
, p
, c
->b
);
63 d
->z
= MP_COPY(f
->one
);
67 static ec
*ecdbl(ec_curve
*c
, ec
*d
, const ec
*a
)
69 if (EC_ATINF(a
) || F_ZEROP(c
->f
, a
->y
))
76 dx
= F_SQR(f
, MP_NEW
, a
->x
); /* %$x^2$% */
77 dy
= F_DBL(f
, MP_NEW
, a
->y
); /* %$2 y$% */
78 dx
= F_TPL(f
, dx
, dx
); /* %$3 x^2$% */
79 dx
= F_ADD(f
, dx
, dx
, c
->a
); /* %$3 x^2 + A$% */
80 dy
= F_INV(f
, dy
, dy
); /* %$(2 y)^{-1}$% */
81 lambda
= F_MUL(f
, MP_NEW
, dx
, dy
); /* %$\lambda = (3 x^2 + A)/(2 y)$% */
83 dx
= F_SQR(f
, dx
, lambda
); /* %$\lambda^2$% */
84 dy
= F_DBL(f
, dy
, a
->x
); /* %$2 x$% */
85 dx
= F_SUB(f
, dx
, dx
, dy
); /* %$x' = \lambda^2 - 2 x */
86 dy
= F_SUB(f
, dy
, a
->x
, dx
); /* %$x - x'$% */
87 dy
= F_MUL(f
, dy
, lambda
, dy
); /* %$\lambda (x - x')$% */
88 dy
= F_SUB(f
, dy
, dy
, a
->y
); /* %$y' = \lambda (x - x') - y$% */
99 static ec
*ecprojdbl(ec_curve
*c
, ec
*d
, const ec
*a
)
101 if (EC_ATINF(a
) || F_ZEROP(c
->f
, a
->y
))
105 mp
*p
, *q
, *m
, *s
, *dx
, *dy
, *dz
;
107 p
= F_SQR(f
, MP_NEW
, a
->z
); /* %$z^2$% */
108 q
= F_SQR(f
, MP_NEW
, p
); /* %$z^4$% */
109 p
= F_MUL(f
, p
, q
, c
->a
); /* %$A z^4$% */
110 m
= F_SQR(f
, MP_NEW
, a
->x
); /* %$x^2$% */
111 m
= F_TPL(f
, m
, m
); /* %$3 x^2$% */
112 m
= F_ADD(f
, m
, m
, p
); /* %$m = 3 x^2 + A z^4$% */
114 q
= F_DBL(f
, q
, a
->y
); /* %$2 y$% */
115 dz
= F_MUL(f
, MP_NEW
, q
, a
->z
); /* %$z' = 2 y z$% */
117 p
= F_SQR(f
, p
, q
); /* %$4 y^2$% */
118 s
= F_MUL(f
, MP_NEW
, p
, a
->x
); /* %$s = 4 x y^2$% */
119 q
= F_SQR(f
, q
, p
); /* %$16 y^4$% */
120 q
= F_HLV(f
, q
, q
); /* %$t = 8 y^4$% */
122 p
= F_DBL(f
, p
, s
); /* %$2 s$% */
123 dx
= F_SQR(f
, MP_NEW
, m
); /* %$m^2$% */
124 dx
= F_SUB(f
, dx
, dx
, p
); /* %$x' = m^2 - 2 s$% */
126 s
= F_SUB(f
, s
, s
, dx
); /* %$s - x'$% */
127 dy
= F_MUL(f
, p
, m
, s
); /* %$m (s - x')$% */
128 dy
= F_SUB(f
, dy
, dy
, q
); /* %$y' = m (s - x') - t$% */
141 static ec
*ecprojxdbl(ec_curve
*c
, ec
*d
, const ec
*a
)
143 if (EC_ATINF(a
) || F_ZEROP(c
->f
, a
->y
))
147 mp
*p
, *q
, *m
, *s
, *dx
, *dy
, *dz
;
149 m
= F_SQR(f
, MP_NEW
, a
->z
); /* %$z^2$% */
150 p
= F_SUB(f
, MP_NEW
, a
->x
, m
); /* %$x - z^2$% */
151 q
= F_ADD(f
, MP_NEW
, a
->x
, m
); /* %$x + z^2$% */
152 m
= F_MUL(f
, m
, p
, q
); /* %$x^2 - z^4$% */
153 m
= F_TPL(f
, m
, m
); /* %$m = 3 x^2 - 3 z^4$% */
155 q
= F_DBL(f
, q
, a
->y
); /* %$2 y$% */
156 dz
= F_MUL(f
, MP_NEW
, q
, a
->z
); /* %$z' = 2 y z$% */
158 p
= F_SQR(f
, p
, q
); /* %$4 y^2$% */
159 s
= F_MUL(f
, MP_NEW
, p
, a
->x
); /* %$s = 4 x y^2$% */
160 q
= F_SQR(f
, q
, p
); /* %$16 y^4$% */
161 q
= F_HLV(f
, q
, q
); /* %$t = 8 y^4$% */
163 p
= F_DBL(f
, p
, s
); /* %$2 s$% */
164 dx
= F_SQR(f
, MP_NEW
, m
); /* %$m^2$% */
165 dx
= F_SUB(f
, dx
, dx
, p
); /* %$x' = m^2 - 2 s$% */
167 s
= F_SUB(f
, s
, s
, dx
); /* %$s - x'$% */
168 dy
= F_MUL(f
, p
, m
, s
); /* %$m (s - x')$% */
169 dy
= F_SUB(f
, dy
, dy
, q
); /* %$y' = m (s - x') - t$% */
182 static ec
*ecadd(ec_curve
*c
, ec
*d
, const ec
*a
, const ec
*b
)
186 else if (EC_ATINF(a
))
188 else if (EC_ATINF(b
))
195 if (!MP_EQ(a
->x
, b
->x
)) {
196 dy
= F_SUB(f
, MP_NEW
, a
->y
, b
->y
); /* %$y_0 - y_1$% */
197 dx
= F_SUB(f
, MP_NEW
, a
->x
, b
->x
); /* %$x_0 - x_1$% */
198 dx
= F_INV(f
, dx
, dx
); /* %$(x_0 - x_1)^{-1}$% */
199 lambda
= F_MUL(f
, MP_NEW
, dy
, dx
);
200 /* %$\lambda = (y_0 - y1)/(x_0 - x_1)$% */
201 } else if (F_ZEROP(c
->f
, a
->y
) || !MP_EQ(a
->y
, b
->y
)) {
205 dx
= F_SQR(f
, MP_NEW
, a
->x
); /* %$x_0^2$% */
206 dx
= F_TPL(f
, dx
, dx
); /* %$3 x_0^2$% */
207 dx
= F_ADD(f
, dx
, dx
, c
->a
); /* %$3 x_0^2 + A$% */
208 dy
= F_DBL(f
, MP_NEW
, a
->y
); /* %$2 y_0$% */
209 dy
= F_INV(f
, dy
, dy
); /* %$(2 y_0)^{-1}$% */
210 lambda
= F_MUL(f
, MP_NEW
, dx
, dy
);
211 /* %$\lambda = (3 x_0^2 + A)/(2 y_0)$% */
214 dx
= F_SQR(f
, dx
, lambda
); /* %$\lambda^2$% */
215 dx
= F_SUB(f
, dx
, dx
, a
->x
); /* %$\lambda^2 - x_0$% */
216 dx
= F_SUB(f
, dx
, dx
, b
->x
); /* %$x' = \lambda^2 - x_0 - x_1$% */
217 dy
= F_SUB(f
, dy
, b
->x
, dx
); /* %$x_1 - x'$% */
218 dy
= F_MUL(f
, dy
, lambda
, dy
); /* %$\lambda (x_1 - x')$% */
219 dy
= F_SUB(f
, dy
, dy
, b
->y
); /* %$y' = \lambda (x_1 - x') - y_1$% */
230 static ec
*ecprojadd(ec_curve
*c
, ec
*d
, const ec
*a
, const ec
*b
)
233 c
->ops
->dbl(c
, d
, a
);
234 else if (EC_ATINF(a
))
236 else if (EC_ATINF(b
))
240 mp
*p
, *q
, *r
, *w
, *u
, *uu
, *s
, *ss
, *dx
, *dy
, *dz
;
242 q
= F_SQR(f
, MP_NEW
, a
->z
); /* %$z_0^2$% */
243 u
= F_MUL(f
, MP_NEW
, q
, b
->x
); /* %$u = x_1 z_0^2$% */
244 p
= F_MUL(f
, MP_NEW
, q
, b
->y
); /* %$y_1 z_0^2$% */
245 s
= F_MUL(f
, q
, p
, a
->z
); /* %$s = y_1 z_0^3$% */
247 q
= F_SQR(f
, MP_NEW
, b
->z
); /* %$z_1^2$% */
248 uu
= F_MUL(f
, MP_NEW
, q
, a
->x
); /* %$uu = x_0 z_1^2$%*/
249 p
= F_MUL(f
, p
, q
, a
->y
); /* %$y_0 z_1^2$% */
250 ss
= F_MUL(f
, q
, p
, b
->z
); /* %$ss = y_0 z_1^3$% */
252 w
= F_SUB(f
, p
, uu
, u
); /* %$w = uu - u$% */
253 r
= F_SUB(f
, MP_NEW
, ss
, s
); /* %$r = ss - s$% */
262 return (c
->ops
->dbl(c
, d
, a
));
269 u
= F_ADD(f
, u
, u
, uu
); /* %$t = uu + u$% */
270 s
= F_ADD(f
, s
, s
, ss
); /* %$m = ss + s$% */
272 uu
= F_MUL(f
, uu
, a
->z
, w
); /* %$z_0 w$% */
273 dz
= F_MUL(f
, ss
, uu
, b
->z
); /* %$z' = z_0 z_1 w$% */
275 p
= F_SQR(f
, uu
, w
); /* %$w^2$% */
276 q
= F_MUL(f
, MP_NEW
, p
, u
); /* %$t w^2$% */
277 u
= F_MUL(f
, u
, p
, w
); /* %$w^3$% */
278 p
= F_MUL(f
, p
, u
, s
); /* %$m w^3$% */
280 dx
= F_SQR(f
, u
, r
); /* %$r^2$% */
281 dx
= F_SUB(f
, dx
, dx
, q
); /* %$x' = r^2 - t w^2$% */
283 s
= F_DBL(f
, s
, dx
); /* %$2 x'$% */
284 q
= F_SUB(f
, q
, q
, s
); /* %$v = t w^2 - 2 x'$% */
285 dy
= F_MUL(f
, s
, q
, r
); /* %$v r$% */
286 dy
= F_SUB(f
, dy
, dy
, p
); /* %$v r - m w^3$% */
287 dy
= F_HLV(f
, dy
, dy
); /* %$y' = (v r - m w^3)/2$% */
301 static int eccheck(ec_curve
*c
, const ec
*p
)
306 if (EC_ATINF(p
)) return (0);
307 l
= F_SQR(f
, MP_NEW
, p
->y
);
308 x
= F_SQR(f
, MP_NEW
, p
->x
);
309 r
= F_MUL(f
, MP_NEW
, x
, p
->x
);
310 x
= F_MUL(f
, x
, c
->a
, p
->x
);
311 r
= F_ADD(f
, r
, r
, x
);
312 r
= F_ADD(f
, r
, r
, c
->b
);
313 rc
= MP_EQ(l
, r
) ?
0 : -1;
320 static int ecprojcheck(ec_curve
*c
, const ec
*p
)
325 c
->ops
->fix(c
, &t
, p
);
331 static void ecdestroy(ec_curve
*c
)
338 /* --- @ec_prime@, @ec_primeproj@ --- *
340 * Arguments: @field *f@ = the underlying field for this elliptic curve
341 * @mp *a, *b@ = the coefficients for this curve
343 * Returns: A pointer to the curve, or null.
345 * Use: Creates a curve structure for an elliptic curve defined over
346 * a prime field. The @primeproj@ variant uses projective
347 * coordinates, which can be a win.
350 extern ec_curve
*ec_prime(field
*f
, mp
*a
, mp
*b
)
352 ec_curve
*c
= CREATE(ec_curve
);
353 c
->ops
= &ec_primeops
;
355 c
->a
= F_IN(f
, MP_NEW
, a
);
356 c
->b
= F_IN(f
, MP_NEW
, b
);
360 extern ec_curve
*ec_primeproj(field
*f
, mp
*a
, mp
*b
)
362 ec_curve
*c
= CREATE(ec_curve
);
365 ax
= mp_add(MP_NEW
, a
, MP_THREE
);
366 ax
= F_IN(f
, ax
, ax
);
368 c
->ops
= &ec_primeprojxops
;
370 c
->ops
= &ec_primeprojops
;
373 c
->a
= F_IN(f
, MP_NEW
, a
);
374 c
->b
= F_IN(f
, MP_NEW
, b
);
378 static const ec_ops ec_primeops
= {
380 ecdestroy
, ec_stdsamep
, ec_idin
, ec_idout
, ec_idfix
,
381 ecfind
, ecneg
, ecadd
, ec_stdsub
, ecdbl
, eccheck
384 static const ec_ops ec_primeprojops
= {
386 ecdestroy
, ec_stdsamep
, ec_projin
, ec_projout
, ec_projfix
,
387 ecfind
, ecneg
, ecprojadd
, ec_stdsub
, ecprojdbl
, ecprojcheck
390 static const ec_ops ec_primeprojxops
= {
392 ecdestroy
, ec_stdsamep
, ec_projin
, ec_projout
, ec_projfix
,
393 ecfind
, ecneg
, ecprojadd
, ec_stdsub
, ecprojxdbl
, ecprojcheck
396 /*----- Test rig ----------------------------------------------------------*/
400 #define MP(x) mp_readstring(MP_NEW, #x, 0, 0)
402 int main(int argc
, char *argv
[])
406 ec g
= EC_INIT
, d
= EC_INIT
;
408 int i
, n
= argc
== 1 ?
1 : atoi(argv
[1]);
410 printf("ec-prime: ");
413 b
= MP(0xb3312fa7e23ee7e4988e056be3f82d19181d9c6efe8141120314088f5013875ac656398d8a2ed19d2a85c8edd3ec2aef);
414 p
= MP(39402006196394479212279040100143613805079739270465446667948293404245721771496870329047266088258938001861606973112319);
415 r
= MP(39402006196394479212279040100143613805079739270465446667946905279627659399113263569398956308152294913554433653942642);
417 f
= field_niceprime(p
);
418 c
= ec_primeproj(f
, a
, b
);
420 g
.x
= MP(0xaa87ca22be8b05378eb1c71ef320ad746e1d3b628ba79b9859f741e082542a385502f25dbf55296c3a545e3872760ab7);
421 g
.y
= MP(0x3617de4a96262c6f5d9e98bf9292dc29f8f41dbd289a147ce9da3113b5f0b8c00a60b1ce1d7e819d7a431d7c90ea0e5f);
423 for (i
= 0; i
< n
; i
++) {
424 ec_mul(c
, &d
, &g
, r
);
426 fprintf(stderr
, "zero too early\n");
429 ec_add(c
, &d
, &d
, &g
);
431 fprintf(stderr
, "didn't reach zero\n");
432 MP_EPRINT("d.x", d
.x
);
433 MP_EPRINT("d.y", d
.y
);
441 MP_DROP(p
); MP_DROP(a
); MP_DROP(b
); MP_DROP(r
);
442 assert(!mparena_count(&mparena_global
));
449 /*----- That's all, folks -------------------------------------------------*/