2 * Copyright 2001-2020 The OpenSSL Project Authors. All Rights Reserved.
3 * Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved
5 * Licensed under the Apache License 2.0 (the "License"). You may not use
6 * this file except in compliance with the License. You can obtain a copy
7 * in the file LICENSE in the source distribution or at
8 * https://www.openssl.org/source/license.html
12 * ECDSA low level APIs are deprecated for public use, but still ok for
15 #include "internal/deprecated.h"
18 #include <openssl/err.h>
20 #include "internal/cryptlib.h"
21 #include "crypto/bn.h"
23 #include "internal/refcount.h"
26 * This file implements the wNAF-based interleaving multi-exponentiation method
28 * http://www.informatik.tu-darmstadt.de/TI/Mitarbeiter/moeller.html#multiexp
29 * You might now find it here:
30 * http://link.springer.com/chapter/10.1007%2F3-540-45537-X_13
31 * http://www.bmoeller.de/pdf/TI-01-08.multiexp.pdf
32 * For multiplication with precomputation, we use wNAF splitting, formerly at:
33 * http://www.informatik.tu-darmstadt.de/TI/Mitarbeiter/moeller.html#fastexp
36 /* structure for precomputed multiples of the generator */
37 struct ec_pre_comp_st {
38 const EC_GROUP *group; /* parent EC_GROUP object */
39 size_t blocksize; /* block size for wNAF splitting */
40 size_t numblocks; /* max. number of blocks for which we have
42 size_t w; /* window size */
43 EC_POINT **points; /* array with pre-calculated multiples of
44 * generator: 'num' pointers to EC_POINT
45 * objects followed by a NULL */
46 size_t num; /* numblocks * 2^(w-1) */
47 CRYPTO_REF_COUNT references;
51 static EC_PRE_COMP *ec_pre_comp_new(const EC_GROUP *group)
53 EC_PRE_COMP *ret = NULL;
58 ret = OPENSSL_zalloc(sizeof(*ret));
60 ECerr(EC_F_EC_PRE_COMP_NEW, ERR_R_MALLOC_FAILURE);
65 ret->blocksize = 8; /* default */
66 ret->w = 4; /* default */
69 ret->lock = CRYPTO_THREAD_lock_new();
70 if (ret->lock == NULL) {
71 ECerr(EC_F_EC_PRE_COMP_NEW, ERR_R_MALLOC_FAILURE);
78 EC_PRE_COMP *EC_ec_pre_comp_dup(EC_PRE_COMP *pre)
82 CRYPTO_UP_REF(&pre->references, &i, pre->lock);
86 void EC_ec_pre_comp_free(EC_PRE_COMP *pre)
93 CRYPTO_DOWN_REF(&pre->references, &i, pre->lock);
94 REF_PRINT_COUNT("EC_ec", pre);
97 REF_ASSERT_ISNT(i < 0);
99 if (pre->points != NULL) {
102 for (pts = pre->points; *pts != NULL; pts++)
104 OPENSSL_free(pre->points);
106 CRYPTO_THREAD_lock_free(pre->lock);
110 #define EC_POINT_BN_set_flags(P, flags) do { \
111 BN_set_flags((P)->X, (flags)); \
112 BN_set_flags((P)->Y, (flags)); \
113 BN_set_flags((P)->Z, (flags)); \
117 * This functions computes a single point multiplication over the EC group,
118 * using, at a high level, a Montgomery ladder with conditional swaps, with
119 * various timing attack defenses.
121 * It performs either a fixed point multiplication
122 * (scalar * generator)
123 * when point is NULL, or a variable point multiplication
125 * when point is not NULL.
127 * `scalar` cannot be NULL and should be in the range [0,n) otherwise all
128 * constant time bets are off (where n is the cardinality of the EC group).
130 * This function expects `group->order` and `group->cardinality` to be well
131 * defined and non-zero: it fails with an error code otherwise.
133 * NB: This says nothing about the constant-timeness of the ladder step
134 * implementation (i.e., the default implementation is based on EC_POINT_add and
135 * EC_POINT_dbl, which of course are not constant time themselves) or the
136 * underlying multiprecision arithmetic.
138 * The product is stored in `r`.
140 * This is an internal function: callers are in charge of ensuring that the
141 * input parameters `group`, `r`, `scalar` and `ctx` are not NULL.
143 * Returns 1 on success, 0 otherwise.
145 int ec_scalar_mul_ladder(const EC_GROUP *group, EC_POINT *r,
146 const BIGNUM *scalar, const EC_POINT *point,
149 int i, cardinality_bits, group_top, kbit, pbit, Z_is_one;
153 BIGNUM *lambda = NULL;
154 BIGNUM *cardinality = NULL;
157 /* early exit if the input point is the point at infinity */
158 if (point != NULL && EC_POINT_is_at_infinity(group, point))
159 return EC_POINT_set_to_infinity(group, r);
161 if (BN_is_zero(group->order)) {
162 ECerr(EC_F_EC_SCALAR_MUL_LADDER, EC_R_UNKNOWN_ORDER);
165 if (BN_is_zero(group->cofactor)) {
166 ECerr(EC_F_EC_SCALAR_MUL_LADDER, EC_R_UNKNOWN_COFACTOR);
172 if (((p = EC_POINT_new(group)) == NULL)
173 || ((s = EC_POINT_new(group)) == NULL)) {
174 ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_MALLOC_FAILURE);
179 if (!EC_POINT_copy(p, group->generator)) {
180 ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_EC_LIB);
184 if (!EC_POINT_copy(p, point)) {
185 ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_EC_LIB);
190 EC_POINT_BN_set_flags(p, BN_FLG_CONSTTIME);
191 EC_POINT_BN_set_flags(r, BN_FLG_CONSTTIME);
192 EC_POINT_BN_set_flags(s, BN_FLG_CONSTTIME);
194 cardinality = BN_CTX_get(ctx);
195 lambda = BN_CTX_get(ctx);
198 ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_MALLOC_FAILURE);
202 if (!BN_mul(cardinality, group->order, group->cofactor, ctx)) {
203 ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_BN_LIB);
208 * Group cardinalities are often on a word boundary.
209 * So when we pad the scalar, some timing diff might
210 * pop if it needs to be expanded due to carries.
211 * So expand ahead of time.
213 cardinality_bits = BN_num_bits(cardinality);
214 group_top = bn_get_top(cardinality);
215 if ((bn_wexpand(k, group_top + 2) == NULL)
216 || (bn_wexpand(lambda, group_top + 2) == NULL)) {
217 ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_BN_LIB);
221 if (!BN_copy(k, scalar)) {
222 ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_BN_LIB);
226 BN_set_flags(k, BN_FLG_CONSTTIME);
228 if ((BN_num_bits(k) > cardinality_bits) || (BN_is_negative(k))) {
230 * this is an unusual input, and we don't guarantee
233 if (!BN_nnmod(k, k, cardinality, ctx)) {
234 ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_BN_LIB);
239 if (!BN_add(lambda, k, cardinality)) {
240 ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_BN_LIB);
243 BN_set_flags(lambda, BN_FLG_CONSTTIME);
244 if (!BN_add(k, lambda, cardinality)) {
245 ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_BN_LIB);
249 * lambda := scalar + cardinality
250 * k := scalar + 2*cardinality
252 kbit = BN_is_bit_set(lambda, cardinality_bits);
253 BN_consttime_swap(kbit, k, lambda, group_top + 2);
255 group_top = bn_get_top(group->field);
256 if ((bn_wexpand(s->X, group_top) == NULL)
257 || (bn_wexpand(s->Y, group_top) == NULL)
258 || (bn_wexpand(s->Z, group_top) == NULL)
259 || (bn_wexpand(r->X, group_top) == NULL)
260 || (bn_wexpand(r->Y, group_top) == NULL)
261 || (bn_wexpand(r->Z, group_top) == NULL)
262 || (bn_wexpand(p->X, group_top) == NULL)
263 || (bn_wexpand(p->Y, group_top) == NULL)
264 || (bn_wexpand(p->Z, group_top) == NULL)) {
265 ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_BN_LIB);
269 /* ensure input point is in affine coords for ladder step efficiency */
270 if (!p->Z_is_one && (group->meth->make_affine == NULL
271 || !group->meth->make_affine(group, p, ctx))) {
272 ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_EC_LIB);
276 /* Initialize the Montgomery ladder */
277 if (!ec_point_ladder_pre(group, r, s, p, ctx)) {
278 ECerr(EC_F_EC_SCALAR_MUL_LADDER, EC_R_LADDER_PRE_FAILURE);
282 /* top bit is a 1, in a fixed pos */
285 #define EC_POINT_CSWAP(c, a, b, w, t) do { \
286 BN_consttime_swap(c, (a)->X, (b)->X, w); \
287 BN_consttime_swap(c, (a)->Y, (b)->Y, w); \
288 BN_consttime_swap(c, (a)->Z, (b)->Z, w); \
289 t = ((a)->Z_is_one ^ (b)->Z_is_one) & (c); \
290 (a)->Z_is_one ^= (t); \
291 (b)->Z_is_one ^= (t); \
295 * The ladder step, with branches, is
297 * k[i] == 0: S = add(R, S), R = dbl(R)
298 * k[i] == 1: R = add(S, R), S = dbl(S)
300 * Swapping R, S conditionally on k[i] leaves you with state
302 * k[i] == 0: T, U = R, S
303 * k[i] == 1: T, U = S, R
305 * Then perform the ECC ops.
310 * Which leaves you with state
312 * k[i] == 0: U = add(R, S), T = dbl(R)
313 * k[i] == 1: U = add(S, R), T = dbl(S)
315 * Swapping T, U conditionally on k[i] leaves you with state
317 * k[i] == 0: R, S = T, U
318 * k[i] == 1: R, S = U, T
320 * Which leaves you with state
322 * k[i] == 0: S = add(R, S), R = dbl(R)
323 * k[i] == 1: R = add(S, R), S = dbl(S)
325 * So we get the same logic, but instead of a branch it's a
326 * conditional swap, followed by ECC ops, then another conditional swap.
328 * Optimization: The end of iteration i and start of i-1 looks like
335 * CSWAP(k[i-1], R, S)
337 * CSWAP(k[i-1], R, S)
340 * So instead of two contiguous swaps, you can merge the condition
341 * bits and do a single swap.
343 * k[i] k[i-1] Outcome
349 * This is XOR. pbit tracks the previous bit of k.
352 for (i = cardinality_bits - 1; i >= 0; i--) {
353 kbit = BN_is_bit_set(k, i) ^ pbit;
354 EC_POINT_CSWAP(kbit, r, s, group_top, Z_is_one);
356 /* Perform a single step of the Montgomery ladder */
357 if (!ec_point_ladder_step(group, r, s, p, ctx)) {
358 ECerr(EC_F_EC_SCALAR_MUL_LADDER, EC_R_LADDER_STEP_FAILURE);
362 * pbit logic merges this cswap with that of the
367 /* one final cswap to move the right value into r */
368 EC_POINT_CSWAP(pbit, r, s, group_top, Z_is_one);
369 #undef EC_POINT_CSWAP
371 /* Finalize ladder (and recover full point coordinates) */
372 if (!ec_point_ladder_post(group, r, s, p, ctx)) {
373 ECerr(EC_F_EC_SCALAR_MUL_LADDER, EC_R_LADDER_POST_FAILURE);
381 EC_POINT_clear_free(s);
387 #undef EC_POINT_BN_set_flags
390 * TODO: table should be optimised for the wNAF-based implementation,
391 * sometimes smaller windows will give better performance (thus the
392 * boundaries should be increased)
394 #define EC_window_bits_for_scalar_size(b) \
405 * \sum scalars[i]*points[i],
408 * in the addition if scalar != NULL
410 int ec_wNAF_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,
411 size_t num, const EC_POINT *points[], const BIGNUM *scalars[],
414 const EC_POINT *generator = NULL;
415 EC_POINT *tmp = NULL;
417 size_t blocksize = 0, numblocks = 0; /* for wNAF splitting */
418 size_t pre_points_per_block = 0;
421 int r_is_inverted = 0;
422 int r_is_at_infinity = 1;
423 size_t *wsize = NULL; /* individual window sizes */
424 signed char **wNAF = NULL; /* individual wNAFs */
425 size_t *wNAF_len = NULL;
428 EC_POINT **val = NULL; /* precomputation */
430 EC_POINT ***val_sub = NULL; /* pointers to sub-arrays of 'val' or
431 * 'pre_comp->points' */
432 const EC_PRE_COMP *pre_comp = NULL;
433 int num_scalar = 0; /* flag: will be set to 1 if 'scalar' must be
434 * treated like other scalars, i.e.
435 * precomputation is not available */
438 if (!BN_is_zero(group->order) && !BN_is_zero(group->cofactor)) {
440 * Handle the common cases where the scalar is secret, enforcing a
441 * scalar multiplication implementation based on a Montgomery ladder,
442 * with various timing attack defenses.
444 if ((scalar != group->order) && (scalar != NULL) && (num == 0)) {
446 * In this case we want to compute scalar * GeneratorPoint: this
447 * codepath is reached most prominently by (ephemeral) key
448 * generation of EC cryptosystems (i.e. ECDSA keygen and sign setup,
449 * ECDH keygen/first half), where the scalar is always secret. This
450 * is why we ignore if BN_FLG_CONSTTIME is actually set and we
451 * always call the ladder version.
453 return ec_scalar_mul_ladder(group, r, scalar, NULL, ctx);
455 if ((scalar == NULL) && (num == 1) && (scalars[0] != group->order)) {
457 * In this case we want to compute scalar * VariablePoint: this
458 * codepath is reached most prominently by the second half of ECDH,
459 * where the secret scalar is multiplied by the peer's public point.
460 * To protect the secret scalar, we ignore if BN_FLG_CONSTTIME is
461 * actually set and we always call the ladder version.
463 return ec_scalar_mul_ladder(group, r, scalars[0], points[0], ctx);
467 if (scalar != NULL) {
468 generator = EC_GROUP_get0_generator(group);
469 if (generator == NULL) {
470 ECerr(EC_F_EC_WNAF_MUL, EC_R_UNDEFINED_GENERATOR);
474 /* look if we can use precomputed multiples of generator */
476 pre_comp = group->pre_comp.ec;
477 if (pre_comp && pre_comp->numblocks
478 && (EC_POINT_cmp(group, generator, pre_comp->points[0], ctx) ==
480 blocksize = pre_comp->blocksize;
483 * determine maximum number of blocks that wNAF splitting may
484 * yield (NB: maximum wNAF length is bit length plus one)
486 numblocks = (BN_num_bits(scalar) / blocksize) + 1;
489 * we cannot use more blocks than we have precomputation for
491 if (numblocks > pre_comp->numblocks)
492 numblocks = pre_comp->numblocks;
494 pre_points_per_block = (size_t)1 << (pre_comp->w - 1);
496 /* check that pre_comp looks sane */
497 if (pre_comp->num != (pre_comp->numblocks * pre_points_per_block)) {
498 ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
502 /* can't use precomputation */
505 num_scalar = 1; /* treat 'scalar' like 'num'-th element of
510 totalnum = num + numblocks;
512 wsize = OPENSSL_malloc(totalnum * sizeof(wsize[0]));
513 wNAF_len = OPENSSL_malloc(totalnum * sizeof(wNAF_len[0]));
514 /* include space for pivot */
515 wNAF = OPENSSL_malloc((totalnum + 1) * sizeof(wNAF[0]));
516 val_sub = OPENSSL_malloc(totalnum * sizeof(val_sub[0]));
518 /* Ensure wNAF is initialised in case we end up going to err */
520 wNAF[0] = NULL; /* preliminary pivot */
522 if (wsize == NULL || wNAF_len == NULL || wNAF == NULL || val_sub == NULL) {
523 ECerr(EC_F_EC_WNAF_MUL, ERR_R_MALLOC_FAILURE);
528 * num_val will be the total number of temporarily precomputed points
532 for (i = 0; i < num + num_scalar; i++) {
535 bits = i < num ? BN_num_bits(scalars[i]) : BN_num_bits(scalar);
536 wsize[i] = EC_window_bits_for_scalar_size(bits);
537 num_val += (size_t)1 << (wsize[i] - 1);
538 wNAF[i + 1] = NULL; /* make sure we always have a pivot */
540 bn_compute_wNAF((i < num ? scalars[i] : scalar), wsize[i],
544 if (wNAF_len[i] > max_len)
545 max_len = wNAF_len[i];
549 /* we go here iff scalar != NULL */
551 if (pre_comp == NULL) {
552 if (num_scalar != 1) {
553 ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
556 /* we have already generated a wNAF for 'scalar' */
558 signed char *tmp_wNAF = NULL;
561 if (num_scalar != 0) {
562 ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
567 * use the window size for which we have precomputation
569 wsize[num] = pre_comp->w;
570 tmp_wNAF = bn_compute_wNAF(scalar, wsize[num], &tmp_len);
574 if (tmp_len <= max_len) {
576 * One of the other wNAFs is at least as long as the wNAF
577 * belonging to the generator, so wNAF splitting will not buy
582 totalnum = num + 1; /* don't use wNAF splitting */
583 wNAF[num] = tmp_wNAF;
584 wNAF[num + 1] = NULL;
585 wNAF_len[num] = tmp_len;
587 * pre_comp->points starts with the points that we need here:
589 val_sub[num] = pre_comp->points;
592 * don't include tmp_wNAF directly into wNAF array - use wNAF
593 * splitting and include the blocks
597 EC_POINT **tmp_points;
599 if (tmp_len < numblocks * blocksize) {
601 * possibly we can do with fewer blocks than estimated
603 numblocks = (tmp_len + blocksize - 1) / blocksize;
604 if (numblocks > pre_comp->numblocks) {
605 ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
606 OPENSSL_free(tmp_wNAF);
609 totalnum = num + numblocks;
612 /* split wNAF in 'numblocks' parts */
614 tmp_points = pre_comp->points;
616 for (i = num; i < totalnum; i++) {
617 if (i < totalnum - 1) {
618 wNAF_len[i] = blocksize;
619 if (tmp_len < blocksize) {
620 ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
621 OPENSSL_free(tmp_wNAF);
624 tmp_len -= blocksize;
627 * last block gets whatever is left (this could be
628 * more or less than 'blocksize'!)
630 wNAF_len[i] = tmp_len;
633 wNAF[i] = OPENSSL_malloc(wNAF_len[i]);
634 if (wNAF[i] == NULL) {
635 ECerr(EC_F_EC_WNAF_MUL, ERR_R_MALLOC_FAILURE);
636 OPENSSL_free(tmp_wNAF);
639 memcpy(wNAF[i], pp, wNAF_len[i]);
640 if (wNAF_len[i] > max_len)
641 max_len = wNAF_len[i];
643 if (*tmp_points == NULL) {
644 ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
645 OPENSSL_free(tmp_wNAF);
648 val_sub[i] = tmp_points;
649 tmp_points += pre_points_per_block;
652 OPENSSL_free(tmp_wNAF);
658 * All points we precompute now go into a single array 'val'.
659 * 'val_sub[i]' is a pointer to the subarray for the i-th point, or to a
660 * subarray of 'pre_comp->points' if we already have precomputation.
662 val = OPENSSL_malloc((num_val + 1) * sizeof(val[0]));
664 ECerr(EC_F_EC_WNAF_MUL, ERR_R_MALLOC_FAILURE);
667 val[num_val] = NULL; /* pivot element */
669 /* allocate points for precomputation */
671 for (i = 0; i < num + num_scalar; i++) {
673 for (j = 0; j < ((size_t)1 << (wsize[i] - 1)); j++) {
674 *v = EC_POINT_new(group);
680 if (!(v == val + num_val)) {
681 ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
685 if ((tmp = EC_POINT_new(group)) == NULL)
689 * prepare precomputed values:
690 * val_sub[i][0] := points[i]
691 * val_sub[i][1] := 3 * points[i]
692 * val_sub[i][2] := 5 * points[i]
695 for (i = 0; i < num + num_scalar; i++) {
697 if (!EC_POINT_copy(val_sub[i][0], points[i]))
700 if (!EC_POINT_copy(val_sub[i][0], generator))
705 if (!EC_POINT_dbl(group, tmp, val_sub[i][0], ctx))
707 for (j = 1; j < ((size_t)1 << (wsize[i] - 1)); j++) {
709 (group, val_sub[i][j], val_sub[i][j - 1], tmp, ctx))
715 if (group->meth->points_make_affine == NULL
716 || !group->meth->points_make_affine(group, num_val, val, ctx))
719 r_is_at_infinity = 1;
721 for (k = max_len - 1; k >= 0; k--) {
722 if (!r_is_at_infinity) {
723 if (!EC_POINT_dbl(group, r, r, ctx))
727 for (i = 0; i < totalnum; i++) {
728 if (wNAF_len[i] > (size_t)k) {
729 int digit = wNAF[i][k];
738 if (is_neg != r_is_inverted) {
739 if (!r_is_at_infinity) {
740 if (!EC_POINT_invert(group, r, ctx))
743 r_is_inverted = !r_is_inverted;
748 if (r_is_at_infinity) {
749 if (!EC_POINT_copy(r, val_sub[i][digit >> 1]))
753 * Apply coordinate blinding for EC_POINT.
755 * The underlying EC_METHOD can optionally implement this function:
756 * ec_point_blind_coordinates() returns 0 in case of errors or 1 on
757 * success or if coordinate blinding is not implemented for this
760 if (!ec_point_blind_coordinates(group, r, ctx)) {
761 ECerr(EC_F_EC_WNAF_MUL, EC_R_POINT_COORDINATES_BLIND_FAILURE);
765 r_is_at_infinity = 0;
768 (group, r, r, val_sub[i][digit >> 1], ctx))
776 if (r_is_at_infinity) {
777 if (!EC_POINT_set_to_infinity(group, r))
781 if (!EC_POINT_invert(group, r, ctx))
790 OPENSSL_free(wNAF_len);
794 for (w = wNAF; *w != NULL; w++)
800 for (v = val; *v != NULL; v++)
801 EC_POINT_clear_free(*v);
805 OPENSSL_free(val_sub);
810 * ec_wNAF_precompute_mult()
811 * creates an EC_PRE_COMP object with preprecomputed multiples of the generator
812 * for use with wNAF splitting as implemented in ec_wNAF_mul().
814 * 'pre_comp->points' is an array of multiples of the generator
815 * of the following form:
816 * points[0] = generator;
817 * points[1] = 3 * generator;
819 * points[2^(w-1)-1] = (2^(w-1)-1) * generator;
820 * points[2^(w-1)] = 2^blocksize * generator;
821 * points[2^(w-1)+1] = 3 * 2^blocksize * generator;
823 * points[2^(w-1)*(numblocks-1)-1] = (2^(w-1)) * 2^(blocksize*(numblocks-2)) * generator
824 * points[2^(w-1)*(numblocks-1)] = 2^(blocksize*(numblocks-1)) * generator
826 * points[2^(w-1)*numblocks-1] = (2^(w-1)) * 2^(blocksize*(numblocks-1)) * generator
827 * points[2^(w-1)*numblocks] = NULL
829 int ec_wNAF_precompute_mult(EC_GROUP *group, BN_CTX *ctx)
831 const EC_POINT *generator;
832 EC_POINT *tmp_point = NULL, *base = NULL, **var;
834 size_t i, bits, w, pre_points_per_block, blocksize, numblocks, num;
835 EC_POINT **points = NULL;
836 EC_PRE_COMP *pre_comp;
839 BN_CTX *new_ctx = NULL;
842 /* if there is an old EC_PRE_COMP object, throw it away */
843 EC_pre_comp_free(group);
844 if ((pre_comp = ec_pre_comp_new(group)) == NULL)
847 generator = EC_GROUP_get0_generator(group);
848 if (generator == NULL) {
849 ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, EC_R_UNDEFINED_GENERATOR);
855 ctx = new_ctx = BN_CTX_new();
862 order = EC_GROUP_get0_order(group);
865 if (BN_is_zero(order)) {
866 ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, EC_R_UNKNOWN_ORDER);
870 bits = BN_num_bits(order);
872 * The following parameters mean we precompute (approximately) one point
873 * per bit. TBD: The combination 8, 4 is perfect for 160 bits; for other
874 * bit lengths, other parameter combinations might provide better
879 if (EC_window_bits_for_scalar_size(bits) > w) {
880 /* let's not make the window too small ... */
881 w = EC_window_bits_for_scalar_size(bits);
884 numblocks = (bits + blocksize - 1) / blocksize; /* max. number of blocks
888 pre_points_per_block = (size_t)1 << (w - 1);
889 num = pre_points_per_block * numblocks; /* number of points to compute
892 points = OPENSSL_malloc(sizeof(*points) * (num + 1));
893 if (points == NULL) {
894 ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, ERR_R_MALLOC_FAILURE);
899 var[num] = NULL; /* pivot */
900 for (i = 0; i < num; i++) {
901 if ((var[i] = EC_POINT_new(group)) == NULL) {
902 ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, ERR_R_MALLOC_FAILURE);
907 if ((tmp_point = EC_POINT_new(group)) == NULL
908 || (base = EC_POINT_new(group)) == NULL) {
909 ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, ERR_R_MALLOC_FAILURE);
913 if (!EC_POINT_copy(base, generator))
916 /* do the precomputation */
917 for (i = 0; i < numblocks; i++) {
920 if (!EC_POINT_dbl(group, tmp_point, base, ctx))
923 if (!EC_POINT_copy(*var++, base))
926 for (j = 1; j < pre_points_per_block; j++, var++) {
928 * calculate odd multiples of the current base point
930 if (!EC_POINT_add(group, *var, tmp_point, *(var - 1), ctx))
934 if (i < numblocks - 1) {
936 * get the next base (multiply current one by 2^blocksize)
940 if (blocksize <= 2) {
941 ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, ERR_R_INTERNAL_ERROR);
945 if (!EC_POINT_dbl(group, base, tmp_point, ctx))
947 for (k = 2; k < blocksize; k++) {
948 if (!EC_POINT_dbl(group, base, base, ctx))
954 if (group->meth->points_make_affine == NULL
955 || !group->meth->points_make_affine(group, num, points, ctx))
958 pre_comp->group = group;
959 pre_comp->blocksize = blocksize;
960 pre_comp->numblocks = numblocks;
962 pre_comp->points = points;
965 SETPRECOMP(group, ec, pre_comp);
972 BN_CTX_free(new_ctx);
974 EC_ec_pre_comp_free(pre_comp);
978 for (p = points; *p != NULL; p++)
980 OPENSSL_free(points);
982 EC_POINT_free(tmp_point);
987 int ec_wNAF_have_precompute_mult(const EC_GROUP *group)
989 return HAVEPRECOMP(group, ec);