1 /* crypto/ec/ec_mult.c */
3 * Originally written by Bodo Moeller and Nils Larsch for the OpenSSL project.
5 /* ====================================================================
6 * Copyright (c) 1998-2018 The OpenSSL Project. All rights reserved.
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in
17 * the documentation and/or other materials provided with the
20 * 3. All advertising materials mentioning features or use of this
21 * software must display the following acknowledgment:
22 * "This product includes software developed by the OpenSSL Project
23 * for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
25 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
26 * endorse or promote products derived from this software without
27 * prior written permission. For written permission, please contact
28 * openssl-core@openssl.org.
30 * 5. Products derived from this software may not be called "OpenSSL"
31 * nor may "OpenSSL" appear in their names without prior written
32 * permission of the OpenSSL Project.
34 * 6. Redistributions of any form whatsoever must retain the following
36 * "This product includes software developed by the OpenSSL Project
37 * for use in the OpenSSL Toolkit (http://www.openssl.org/)"
39 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
40 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
41 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
42 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR
43 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
44 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
45 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
46 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
47 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
48 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
49 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
50 * OF THE POSSIBILITY OF SUCH DAMAGE.
51 * ====================================================================
53 * This product includes cryptographic software written by Eric Young
54 * (eay@cryptsoft.com). This product includes software written by Tim
55 * Hudson (tjh@cryptsoft.com).
58 /* ====================================================================
59 * Copyright 2002 Sun Microsystems, Inc. ALL RIGHTS RESERVED.
60 * Portions of this software developed by SUN MICROSYSTEMS, INC.,
61 * and contributed to the OpenSSL project.
66 #include <openssl/err.h>
71 * This file implements the wNAF-based interleaving multi-exponentiation method
73 * http://www.informatik.tu-darmstadt.de/TI/Mitarbeiter/moeller.html#multiexp
74 * You might now find it here:
75 * http://link.springer.com/chapter/10.1007%2F3-540-45537-X_13
76 * http://www.bmoeller.de/pdf/TI-01-08.multiexp.pdf
77 * For multiplication with precomputation, we use wNAF splitting, formerly at:
78 * http://www.informatik.tu-darmstadt.de/TI/Mitarbeiter/moeller.html#fastexp
81 /* structure for precomputed multiples of the generator */
82 typedef struct ec_pre_comp_st {
83 const EC_GROUP *group; /* parent EC_GROUP object */
84 size_t blocksize; /* block size for wNAF splitting */
85 size_t numblocks; /* max. number of blocks for which we have
87 size_t w; /* window size */
88 EC_POINT **points; /* array with pre-calculated multiples of
89 * generator: 'num' pointers to EC_POINT
90 * objects followed by a NULL */
91 size_t num; /* numblocks * 2^(w-1) */
95 /* functions to manage EC_PRE_COMP within the EC_GROUP extra_data framework */
96 static void *ec_pre_comp_dup(void *);
97 static void ec_pre_comp_free(void *);
98 static void ec_pre_comp_clear_free(void *);
100 static EC_PRE_COMP *ec_pre_comp_new(const EC_GROUP *group)
102 EC_PRE_COMP *ret = NULL;
107 ret = (EC_PRE_COMP *)OPENSSL_malloc(sizeof(EC_PRE_COMP));
109 ECerr(EC_F_EC_PRE_COMP_NEW, ERR_R_MALLOC_FAILURE);
113 ret->blocksize = 8; /* default */
115 ret->w = 4; /* default */
122 static void *ec_pre_comp_dup(void *src_)
124 EC_PRE_COMP *src = src_;
126 /* no need to actually copy, these objects never change! */
128 CRYPTO_add(&src->references, 1, CRYPTO_LOCK_EC_PRE_COMP);
133 static void ec_pre_comp_free(void *pre_)
136 EC_PRE_COMP *pre = pre_;
141 i = CRYPTO_add(&pre->references, -1, CRYPTO_LOCK_EC_PRE_COMP);
148 for (p = pre->points; *p != NULL; p++)
150 OPENSSL_free(pre->points);
155 static void ec_pre_comp_clear_free(void *pre_)
158 EC_PRE_COMP *pre = pre_;
163 i = CRYPTO_add(&pre->references, -1, CRYPTO_LOCK_EC_PRE_COMP);
170 for (p = pre->points; *p != NULL; p++) {
171 EC_POINT_clear_free(*p);
172 OPENSSL_cleanse(p, sizeof(*p));
174 OPENSSL_free(pre->points);
176 OPENSSL_cleanse(pre, sizeof(*pre));
181 * Determine the modified width-(w+1) Non-Adjacent Form (wNAF) of 'scalar'.
182 * This is an array r[] of values that are either zero or odd with an
183 * absolute value less than 2^w satisfying
184 * scalar = \sum_j r[j]*2^j
185 * where at most one of any w+1 consecutive digits is non-zero
186 * with the exception that the most significant digit may be only
187 * w-1 zeros away from that next non-zero digit.
189 static signed char *compute_wNAF(const BIGNUM *scalar, int w, size_t *ret_len)
193 signed char *r = NULL;
195 int bit, next_bit, mask;
198 if (BN_is_zero(scalar)) {
199 r = OPENSSL_malloc(1);
201 ECerr(EC_F_COMPUTE_WNAF, ERR_R_MALLOC_FAILURE);
209 if (w <= 0 || w > 7) { /* 'signed char' can represent integers with
210 * absolute values less than 2^7 */
211 ECerr(EC_F_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR);
214 bit = 1 << w; /* at most 128 */
215 next_bit = bit << 1; /* at most 256 */
216 mask = next_bit - 1; /* at most 255 */
218 if (BN_is_negative(scalar)) {
222 if (scalar->d == NULL || scalar->top == 0) {
223 ECerr(EC_F_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR);
227 len = BN_num_bits(scalar);
228 r = OPENSSL_malloc(len + 1); /* modified wNAF may be one digit longer
229 * than binary representation (*ret_len will
230 * be set to the actual length, i.e. at most
231 * BN_num_bits(scalar) + 1) */
233 ECerr(EC_F_COMPUTE_WNAF, ERR_R_MALLOC_FAILURE);
236 window_val = scalar->d[0] & mask;
238 while ((window_val != 0) || (j + w + 1 < len)) { /* if j+w+1 >= len,
239 * window_val will not
243 /* 0 <= window_val <= 2^(w+1) */
245 if (window_val & 1) {
246 /* 0 < window_val < 2^(w+1) */
248 if (window_val & bit) {
249 digit = window_val - next_bit; /* -2^w < digit < 0 */
251 #if 1 /* modified wNAF */
252 if (j + w + 1 >= len) {
254 * special case for generating modified wNAFs: no new
255 * bits will be added into window_val, so using a
256 * positive digit here will decrease the total length of
260 digit = window_val & (mask >> 1); /* 0 < digit < 2^w */
264 digit = window_val; /* 0 < digit < 2^w */
267 if (digit <= -bit || digit >= bit || !(digit & 1)) {
268 ECerr(EC_F_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR);
275 * now window_val is 0 or 2^(w+1) in standard wNAF generation;
276 * for modified window NAFs, it may also be 2^w
278 if (window_val != 0 && window_val != next_bit
279 && window_val != bit) {
280 ECerr(EC_F_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR);
285 r[j++] = sign * digit;
288 window_val += bit * BN_is_bit_set(scalar, j + w);
290 if (window_val > next_bit) {
291 ECerr(EC_F_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR);
297 ECerr(EC_F_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR);
313 #define EC_POINT_BN_set_flags(P, flags) do { \
314 BN_set_flags(&(P)->X, (flags)); \
315 BN_set_flags(&(P)->Y, (flags)); \
316 BN_set_flags(&(P)->Z, (flags)); \
320 * This functions computes (in constant time) a point multiplication over the
323 * At a high level, it is Montgomery ladder with conditional swaps.
325 * It performs either a fixed scalar point multiplication
326 * (scalar * generator)
327 * when point is NULL, or a generic scalar point multiplication
329 * when point is not NULL.
331 * scalar should be in the range [0,n) otherwise all constant time bets are off.
333 * NB: This says nothing about EC_POINT_add and EC_POINT_dbl,
334 * which of course are not constant time themselves.
336 * The product is stored in r.
338 * Returns 1 on success, 0 otherwise.
340 static int ec_mul_consttime(const EC_GROUP *group, EC_POINT *r,
341 const BIGNUM *scalar, const EC_POINT *point,
344 int i, cardinality_bits, group_top, kbit, pbit, Z_is_one;
347 BIGNUM *lambda = NULL;
348 BIGNUM *cardinality = NULL;
349 BN_CTX *new_ctx = NULL;
352 if (ctx == NULL && (ctx = new_ctx = BN_CTX_new()) == NULL)
357 s = EC_POINT_new(group);
362 if (!EC_POINT_copy(s, group->generator))
365 if (!EC_POINT_copy(s, point))
369 EC_POINT_BN_set_flags(s, BN_FLG_CONSTTIME);
371 cardinality = BN_CTX_get(ctx);
372 lambda = BN_CTX_get(ctx);
374 if (k == NULL || !BN_mul(cardinality, &group->order, &group->cofactor, ctx))
378 * Group cardinalities are often on a word boundary.
379 * So when we pad the scalar, some timing diff might
380 * pop if it needs to be expanded due to carries.
381 * So expand ahead of time.
383 cardinality_bits = BN_num_bits(cardinality);
384 group_top = cardinality->top;
385 if ((bn_wexpand(k, group_top + 2) == NULL)
386 || (bn_wexpand(lambda, group_top + 2) == NULL))
389 if (!BN_copy(k, scalar))
392 BN_set_flags(k, BN_FLG_CONSTTIME);
394 if ((BN_num_bits(k) > cardinality_bits) || (BN_is_negative(k))) {
396 * this is an unusual input, and we don't guarantee
399 if (!BN_nnmod(k, k, cardinality, ctx))
403 if (!BN_add(lambda, k, cardinality))
405 BN_set_flags(lambda, BN_FLG_CONSTTIME);
406 if (!BN_add(k, lambda, cardinality))
409 * lambda := scalar + cardinality
410 * k := scalar + 2*cardinality
412 kbit = BN_is_bit_set(lambda, cardinality_bits);
413 BN_consttime_swap(kbit, k, lambda, group_top + 2);
415 group_top = group->field.top;
416 if ((bn_wexpand(&s->X, group_top) == NULL)
417 || (bn_wexpand(&s->Y, group_top) == NULL)
418 || (bn_wexpand(&s->Z, group_top) == NULL)
419 || (bn_wexpand(&r->X, group_top) == NULL)
420 || (bn_wexpand(&r->Y, group_top) == NULL)
421 || (bn_wexpand(&r->Z, group_top) == NULL))
424 /* top bit is a 1, in a fixed pos */
425 if (!EC_POINT_copy(r, s))
428 EC_POINT_BN_set_flags(r, BN_FLG_CONSTTIME);
430 if (!EC_POINT_dbl(group, s, s, ctx))
435 #define EC_POINT_CSWAP(c, a, b, w, t) do { \
436 BN_consttime_swap(c, &(a)->X, &(b)->X, w); \
437 BN_consttime_swap(c, &(a)->Y, &(b)->Y, w); \
438 BN_consttime_swap(c, &(a)->Z, &(b)->Z, w); \
439 t = ((a)->Z_is_one ^ (b)->Z_is_one) & (c); \
440 (a)->Z_is_one ^= (t); \
441 (b)->Z_is_one ^= (t); \
445 * The ladder step, with branches, is
447 * k[i] == 0: S = add(R, S), R = dbl(R)
448 * k[i] == 1: R = add(S, R), S = dbl(S)
450 * Swapping R, S conditionally on k[i] leaves you with state
452 * k[i] == 0: T, U = R, S
453 * k[i] == 1: T, U = S, R
455 * Then perform the ECC ops.
460 * Which leaves you with state
462 * k[i] == 0: U = add(R, S), T = dbl(R)
463 * k[i] == 1: U = add(S, R), T = dbl(S)
465 * Swapping T, U conditionally on k[i] leaves you with state
467 * k[i] == 0: R, S = T, U
468 * k[i] == 1: R, S = U, T
470 * Which leaves you with state
472 * k[i] == 0: S = add(R, S), R = dbl(R)
473 * k[i] == 1: R = add(S, R), S = dbl(S)
475 * So we get the same logic, but instead of a branch it's a
476 * conditional swap, followed by ECC ops, then another conditional swap.
478 * Optimization: The end of iteration i and start of i-1 looks like
485 * CSWAP(k[i-1], R, S)
487 * CSWAP(k[i-1], R, S)
490 * So instead of two contiguous swaps, you can merge the condition
491 * bits and do a single swap.
493 * k[i] k[i-1] Outcome
499 * This is XOR. pbit tracks the previous bit of k.
502 for (i = cardinality_bits - 1; i >= 0; i--) {
503 kbit = BN_is_bit_set(k, i) ^ pbit;
504 EC_POINT_CSWAP(kbit, r, s, group_top, Z_is_one);
505 if (!EC_POINT_add(group, s, r, s, ctx))
507 if (!EC_POINT_dbl(group, r, r, ctx))
510 * pbit logic merges this cswap with that of the
515 /* one final cswap to move the right value into r */
516 EC_POINT_CSWAP(pbit, r, s, group_top, Z_is_one);
517 #undef EC_POINT_CSWAP
524 BN_CTX_free(new_ctx);
529 #undef EC_POINT_BN_set_flags
532 * TODO: table should be optimised for the wNAF-based implementation,
533 * sometimes smaller windows will give better performance (thus the
534 * boundaries should be increased)
536 #define EC_window_bits_for_scalar_size(b) \
547 * \sum scalars[i]*points[i],
550 * in the addition if scalar != NULL
552 int ec_wNAF_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar,
553 size_t num, const EC_POINT *points[], const BIGNUM *scalars[],
556 BN_CTX *new_ctx = NULL;
557 const EC_POINT *generator = NULL;
558 EC_POINT *tmp = NULL;
560 size_t blocksize = 0, numblocks = 0; /* for wNAF splitting */
561 size_t pre_points_per_block = 0;
564 int r_is_inverted = 0;
565 int r_is_at_infinity = 1;
566 size_t *wsize = NULL; /* individual window sizes */
567 signed char **wNAF = NULL; /* individual wNAFs */
568 size_t *wNAF_len = NULL;
571 EC_POINT **val = NULL; /* precomputation */
573 EC_POINT ***val_sub = NULL; /* pointers to sub-arrays of 'val' or
574 * 'pre_comp->points' */
575 const EC_PRE_COMP *pre_comp = NULL;
576 int num_scalar = 0; /* flag: will be set to 1 if 'scalar' must be
577 * treated like other scalars, i.e.
578 * precomputation is not available */
581 if (group->meth != r->meth) {
582 ECerr(EC_F_EC_WNAF_MUL, EC_R_INCOMPATIBLE_OBJECTS);
586 if ((scalar == NULL) && (num == 0)) {
587 return EC_POINT_set_to_infinity(group, r);
590 if (!BN_is_zero(&group->order) && !BN_is_zero(&group->cofactor)) {
592 * Handle the common cases where the scalar is secret, enforcing a constant
593 * time scalar multiplication algorithm.
595 if ((scalar != NULL) && (num == 0)) {
597 * In this case we want to compute scalar * GeneratorPoint: this
598 * codepath is reached most prominently by (ephemeral) key generation
599 * of EC cryptosystems (i.e. ECDSA keygen and sign setup, ECDH
600 * keygen/first half), where the scalar is always secret. This is why
601 * we ignore if BN_FLG_CONSTTIME is actually set and we always call the
602 * constant time version.
604 return ec_mul_consttime(group, r, scalar, NULL, ctx);
606 if ((scalar == NULL) && (num == 1)) {
608 * In this case we want to compute scalar * GenericPoint: this codepath
609 * is reached most prominently by the second half of ECDH, where the
610 * secret scalar is multiplied by the peer's public point. To protect
611 * the secret scalar, we ignore if BN_FLG_CONSTTIME is actually set and
612 * we always call the constant time version.
614 return ec_mul_consttime(group, r, scalars[0], points[0], ctx);
618 for (i = 0; i < num; i++) {
619 if (group->meth != points[i]->meth) {
620 ECerr(EC_F_EC_WNAF_MUL, EC_R_INCOMPATIBLE_OBJECTS);
626 ctx = new_ctx = BN_CTX_new();
631 if (scalar != NULL) {
632 generator = EC_GROUP_get0_generator(group);
633 if (generator == NULL) {
634 ECerr(EC_F_EC_WNAF_MUL, EC_R_UNDEFINED_GENERATOR);
638 /* look if we can use precomputed multiples of generator */
641 EC_EX_DATA_get_data(group->extra_data, ec_pre_comp_dup,
642 ec_pre_comp_free, ec_pre_comp_clear_free);
644 if (pre_comp && pre_comp->numblocks
645 && (EC_POINT_cmp(group, generator, pre_comp->points[0], ctx) ==
647 blocksize = pre_comp->blocksize;
650 * determine maximum number of blocks that wNAF splitting may
651 * yield (NB: maximum wNAF length is bit length plus one)
653 numblocks = (BN_num_bits(scalar) / blocksize) + 1;
656 * we cannot use more blocks than we have precomputation for
658 if (numblocks > pre_comp->numblocks)
659 numblocks = pre_comp->numblocks;
661 pre_points_per_block = (size_t)1 << (pre_comp->w - 1);
663 /* check that pre_comp looks sane */
664 if (pre_comp->num != (pre_comp->numblocks * pre_points_per_block)) {
665 ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
669 /* can't use precomputation */
672 num_scalar = 1; /* treat 'scalar' like 'num'-th element of
677 totalnum = num + numblocks;
679 wsize = OPENSSL_malloc(totalnum * sizeof(wsize[0]));
680 wNAF_len = OPENSSL_malloc(totalnum * sizeof(wNAF_len[0]));
681 /* include space for pivot */
682 wNAF = OPENSSL_malloc((totalnum + 1) * sizeof(wNAF[0]));
683 val_sub = OPENSSL_malloc(totalnum * sizeof(val_sub[0]));
685 /* Ensure wNAF is initialised in case we end up going to err */
687 wNAF[0] = NULL; /* preliminary pivot */
689 if (!wsize || !wNAF_len || !wNAF || !val_sub) {
690 ECerr(EC_F_EC_WNAF_MUL, ERR_R_MALLOC_FAILURE);
695 * num_val will be the total number of temporarily precomputed points
699 for (i = 0; i < num + num_scalar; i++) {
702 bits = i < num ? BN_num_bits(scalars[i]) : BN_num_bits(scalar);
703 wsize[i] = EC_window_bits_for_scalar_size(bits);
704 num_val += (size_t)1 << (wsize[i] - 1);
705 wNAF[i + 1] = NULL; /* make sure we always have a pivot */
707 compute_wNAF((i < num ? scalars[i] : scalar), wsize[i],
711 if (wNAF_len[i] > max_len)
712 max_len = wNAF_len[i];
716 /* we go here iff scalar != NULL */
718 if (pre_comp == NULL) {
719 if (num_scalar != 1) {
720 ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
723 /* we have already generated a wNAF for 'scalar' */
725 signed char *tmp_wNAF = NULL;
728 if (num_scalar != 0) {
729 ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
734 * use the window size for which we have precomputation
736 wsize[num] = pre_comp->w;
737 tmp_wNAF = compute_wNAF(scalar, wsize[num], &tmp_len);
741 if (tmp_len <= max_len) {
743 * One of the other wNAFs is at least as long as the wNAF
744 * belonging to the generator, so wNAF splitting will not buy
749 totalnum = num + 1; /* don't use wNAF splitting */
750 wNAF[num] = tmp_wNAF;
751 wNAF[num + 1] = NULL;
752 wNAF_len[num] = tmp_len;
753 if (tmp_len > max_len)
756 * pre_comp->points starts with the points that we need here:
758 val_sub[num] = pre_comp->points;
761 * don't include tmp_wNAF directly into wNAF array - use wNAF
762 * splitting and include the blocks
766 EC_POINT **tmp_points;
768 if (tmp_len < numblocks * blocksize) {
770 * possibly we can do with fewer blocks than estimated
772 numblocks = (tmp_len + blocksize - 1) / blocksize;
773 if (numblocks > pre_comp->numblocks) {
774 ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
777 totalnum = num + numblocks;
780 /* split wNAF in 'numblocks' parts */
782 tmp_points = pre_comp->points;
784 for (i = num; i < totalnum; i++) {
785 if (i < totalnum - 1) {
786 wNAF_len[i] = blocksize;
787 if (tmp_len < blocksize) {
788 ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
791 tmp_len -= blocksize;
794 * last block gets whatever is left (this could be
795 * more or less than 'blocksize'!)
797 wNAF_len[i] = tmp_len;
800 wNAF[i] = OPENSSL_malloc(wNAF_len[i]);
801 if (wNAF[i] == NULL) {
802 ECerr(EC_F_EC_WNAF_MUL, ERR_R_MALLOC_FAILURE);
803 OPENSSL_free(tmp_wNAF);
806 memcpy(wNAF[i], pp, wNAF_len[i]);
807 if (wNAF_len[i] > max_len)
808 max_len = wNAF_len[i];
810 if (*tmp_points == NULL) {
811 ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
812 OPENSSL_free(tmp_wNAF);
815 val_sub[i] = tmp_points;
816 tmp_points += pre_points_per_block;
819 OPENSSL_free(tmp_wNAF);
825 * All points we precompute now go into a single array 'val'.
826 * 'val_sub[i]' is a pointer to the subarray for the i-th point, or to a
827 * subarray of 'pre_comp->points' if we already have precomputation.
829 val = OPENSSL_malloc((num_val + 1) * sizeof(val[0]));
831 ECerr(EC_F_EC_WNAF_MUL, ERR_R_MALLOC_FAILURE);
834 val[num_val] = NULL; /* pivot element */
836 /* allocate points for precomputation */
838 for (i = 0; i < num + num_scalar; i++) {
840 for (j = 0; j < ((size_t)1 << (wsize[i] - 1)); j++) {
841 *v = EC_POINT_new(group);
847 if (!(v == val + num_val)) {
848 ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
852 if (!(tmp = EC_POINT_new(group)))
856 * prepare precomputed values:
857 * val_sub[i][0] := points[i]
858 * val_sub[i][1] := 3 * points[i]
859 * val_sub[i][2] := 5 * points[i]
862 for (i = 0; i < num + num_scalar; i++) {
864 if (!EC_POINT_copy(val_sub[i][0], points[i]))
867 if (!EC_POINT_copy(val_sub[i][0], generator))
872 if (!EC_POINT_dbl(group, tmp, val_sub[i][0], ctx))
874 for (j = 1; j < ((size_t)1 << (wsize[i] - 1)); j++) {
876 (group, val_sub[i][j], val_sub[i][j - 1], tmp, ctx))
882 #if 1 /* optional; EC_window_bits_for_scalar_size
883 * assumes we do this step */
884 if (!EC_POINTs_make_affine(group, num_val, val, ctx))
888 r_is_at_infinity = 1;
890 for (k = max_len - 1; k >= 0; k--) {
891 if (!r_is_at_infinity) {
892 if (!EC_POINT_dbl(group, r, r, ctx))
896 for (i = 0; i < totalnum; i++) {
897 if (wNAF_len[i] > (size_t)k) {
898 int digit = wNAF[i][k];
907 if (is_neg != r_is_inverted) {
908 if (!r_is_at_infinity) {
909 if (!EC_POINT_invert(group, r, ctx))
912 r_is_inverted = !r_is_inverted;
917 if (r_is_at_infinity) {
918 if (!EC_POINT_copy(r, val_sub[i][digit >> 1]))
920 r_is_at_infinity = 0;
923 (group, r, r, val_sub[i][digit >> 1], ctx))
931 if (r_is_at_infinity) {
932 if (!EC_POINT_set_to_infinity(group, r))
936 if (!EC_POINT_invert(group, r, ctx))
944 BN_CTX_free(new_ctx);
949 if (wNAF_len != NULL)
950 OPENSSL_free(wNAF_len);
954 for (w = wNAF; *w != NULL; w++)
960 for (v = val; *v != NULL; v++)
961 EC_POINT_clear_free(*v);
965 if (val_sub != NULL) {
966 OPENSSL_free(val_sub);
972 * ec_wNAF_precompute_mult()
973 * creates an EC_PRE_COMP object with preprecomputed multiples of the generator
974 * for use with wNAF splitting as implemented in ec_wNAF_mul().
976 * 'pre_comp->points' is an array of multiples of the generator
977 * of the following form:
978 * points[0] = generator;
979 * points[1] = 3 * generator;
981 * points[2^(w-1)-1] = (2^(w-1)-1) * generator;
982 * points[2^(w-1)] = 2^blocksize * generator;
983 * points[2^(w-1)+1] = 3 * 2^blocksize * generator;
985 * points[2^(w-1)*(numblocks-1)-1] = (2^(w-1)) * 2^(blocksize*(numblocks-2)) * generator
986 * points[2^(w-1)*(numblocks-1)] = 2^(blocksize*(numblocks-1)) * generator
988 * points[2^(w-1)*numblocks-1] = (2^(w-1)) * 2^(blocksize*(numblocks-1)) * generator
989 * points[2^(w-1)*numblocks] = NULL
991 int ec_wNAF_precompute_mult(EC_GROUP *group, BN_CTX *ctx)
993 const EC_POINT *generator;
994 EC_POINT *tmp_point = NULL, *base = NULL, **var;
995 BN_CTX *new_ctx = NULL;
997 size_t i, bits, w, pre_points_per_block, blocksize, numblocks, num;
998 EC_POINT **points = NULL;
999 EC_PRE_COMP *pre_comp;
1002 /* if there is an old EC_PRE_COMP object, throw it away */
1003 EC_EX_DATA_free_data(&group->extra_data, ec_pre_comp_dup,
1004 ec_pre_comp_free, ec_pre_comp_clear_free);
1006 if ((pre_comp = ec_pre_comp_new(group)) == NULL)
1009 generator = EC_GROUP_get0_generator(group);
1010 if (generator == NULL) {
1011 ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, EC_R_UNDEFINED_GENERATOR);
1016 ctx = new_ctx = BN_CTX_new();
1022 order = BN_CTX_get(ctx);
1026 if (!EC_GROUP_get_order(group, order, ctx))
1028 if (BN_is_zero(order)) {
1029 ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, EC_R_UNKNOWN_ORDER);
1033 bits = BN_num_bits(order);
1035 * The following parameters mean we precompute (approximately) one point
1036 * per bit. TBD: The combination 8, 4 is perfect for 160 bits; for other
1037 * bit lengths, other parameter combinations might provide better
1042 if (EC_window_bits_for_scalar_size(bits) > w) {
1043 /* let's not make the window too small ... */
1044 w = EC_window_bits_for_scalar_size(bits);
1047 numblocks = (bits + blocksize - 1) / blocksize; /* max. number of blocks
1051 pre_points_per_block = (size_t)1 << (w - 1);
1052 num = pre_points_per_block * numblocks; /* number of points to compute
1055 points = OPENSSL_malloc(sizeof(EC_POINT *) * (num + 1));
1057 ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, ERR_R_MALLOC_FAILURE);
1062 var[num] = NULL; /* pivot */
1063 for (i = 0; i < num; i++) {
1064 if ((var[i] = EC_POINT_new(group)) == NULL) {
1065 ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, ERR_R_MALLOC_FAILURE);
1070 if (!(tmp_point = EC_POINT_new(group)) || !(base = EC_POINT_new(group))) {
1071 ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, ERR_R_MALLOC_FAILURE);
1075 if (!EC_POINT_copy(base, generator))
1078 /* do the precomputation */
1079 for (i = 0; i < numblocks; i++) {
1082 if (!EC_POINT_dbl(group, tmp_point, base, ctx))
1085 if (!EC_POINT_copy(*var++, base))
1088 for (j = 1; j < pre_points_per_block; j++, var++) {
1090 * calculate odd multiples of the current base point
1092 if (!EC_POINT_add(group, *var, tmp_point, *(var - 1), ctx))
1096 if (i < numblocks - 1) {
1098 * get the next base (multiply current one by 2^blocksize)
1102 if (blocksize <= 2) {
1103 ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, ERR_R_INTERNAL_ERROR);
1107 if (!EC_POINT_dbl(group, base, tmp_point, ctx))
1109 for (k = 2; k < blocksize; k++) {
1110 if (!EC_POINT_dbl(group, base, base, ctx))
1116 if (!EC_POINTs_make_affine(group, num, points, ctx))
1119 pre_comp->group = group;
1120 pre_comp->blocksize = blocksize;
1121 pre_comp->numblocks = numblocks;
1123 pre_comp->points = points;
1125 pre_comp->num = num;
1127 if (!EC_EX_DATA_set_data(&group->extra_data, pre_comp,
1128 ec_pre_comp_dup, ec_pre_comp_free,
1129 ec_pre_comp_clear_free))
1137 if (new_ctx != NULL)
1138 BN_CTX_free(new_ctx);
1140 ec_pre_comp_free(pre_comp);
1144 for (p = points; *p != NULL; p++)
1146 OPENSSL_free(points);
1149 EC_POINT_free(tmp_point);
1151 EC_POINT_free(base);
1155 int ec_wNAF_have_precompute_mult(const EC_GROUP *group)
1157 if (EC_EX_DATA_get_data
1158 (group->extra_data, ec_pre_comp_dup, ec_pre_comp_free,
1159 ec_pre_comp_clear_free) != NULL)