diff options
Diffstat (limited to 'src/crypto/ec/wnaf.c')
| -rw-r--r-- | src/crypto/ec/wnaf.c | 844 |
1 files changed, 844 insertions, 0 deletions
diff --git a/src/crypto/ec/wnaf.c b/src/crypto/ec/wnaf.c new file mode 100644 index 0000000..9016328 --- /dev/null +++ b/src/crypto/ec/wnaf.c @@ -0,0 +1,844 @@ +/* Originally written by Bodo Moeller for the OpenSSL project. + * ==================================================================== + * Copyright (c) 1998-2005 The OpenSSL Project. All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in + * the documentation and/or other materials provided with the + * distribution. + * + * 3. All advertising materials mentioning features or use of this + * software must display the following acknowledgment: + * "This product includes software developed by the OpenSSL Project + * for use in the OpenSSL Toolkit. (http://www.openssl.org/)" + * + * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to + * endorse or promote products derived from this software without + * prior written permission. For written permission, please contact + * openssl-core@openssl.org. + * + * 5. Products derived from this software may not be called "OpenSSL" + * nor may "OpenSSL" appear in their names without prior written + * permission of the OpenSSL Project. + * + * 6. Redistributions of any form whatsoever must retain the following + * acknowledgment: + * "This product includes software developed by the OpenSSL Project + * for use in the OpenSSL Toolkit (http://www.openssl.org/)" + * + * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY + * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE + * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR + * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE OpenSSL PROJECT OR + * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT + * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; + * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) + * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, + * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) + * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED + * OF THE POSSIBILITY OF SUCH DAMAGE. + * ==================================================================== + * + * This product includes cryptographic software written by Eric Young + * (eay@cryptsoft.com). This product includes software written by Tim + * Hudson (tjh@cryptsoft.com). + * + */ +/* ==================================================================== + * Copyright 2002 Sun Microsystems, Inc. ALL RIGHTS RESERVED. + * + * Portions of the attached software ("Contribution") are developed by + * SUN MICROSYSTEMS, INC., and are contributed to the OpenSSL project. + * + * The Contribution is licensed pursuant to the OpenSSL open source + * license provided above. + * + * The elliptic curve binary polynomial software is originally written by + * Sheueling Chang Shantz and Douglas Stebila of Sun Microsystems + * Laboratories. */ + +#include <openssl/ec.h> + +#include <string.h> + +#include <openssl/bn.h> +#include <openssl/err.h> +#include <openssl/mem.h> + +#include "internal.h" + + +/* This file implements the wNAF-based interleaving multi-exponentation method + * (<URL:http://www.informatik.tu-darmstadt.de/TI/Mitarbeiter/moeller.html#multiexp>); + * for multiplication with precomputation, we use wNAF splitting + * (<URL:http://www.informatik.tu-darmstadt.de/TI/Mitarbeiter/moeller.html#fastexp>). + * */ + +/* structure for precomputed multiples of the generator */ +typedef struct ec_pre_comp_st { + const EC_GROUP *group; /* parent EC_GROUP object */ + size_t blocksize; /* block size for wNAF splitting */ + size_t numblocks; /* max. number of blocks for which we have precomputation */ + size_t w; /* window size */ + EC_POINT **points; /* array with pre-calculated multiples of generator: + * 'num' pointers to EC_POINT objects followed by a NULL */ + size_t num; /* numblocks * 2^(w-1) */ + int references; +} EC_PRE_COMP; + +static EC_PRE_COMP *ec_pre_comp_new(const EC_GROUP *group) { + EC_PRE_COMP *ret = NULL; + + if (!group) + return NULL; + + ret = (EC_PRE_COMP *)OPENSSL_malloc(sizeof(EC_PRE_COMP)); + if (!ret) { + OPENSSL_PUT_ERROR(EC, ec_pre_comp_new, ERR_R_MALLOC_FAILURE); + return ret; + } + ret->group = group; + ret->blocksize = 8; /* default */ + ret->numblocks = 0; + ret->w = 4; /* default */ + ret->points = NULL; + ret->num = 0; + ret->references = 1; + return ret; +} + +void *ec_pre_comp_dup(EC_PRE_COMP *pre_comp) { + if (pre_comp == NULL) { + return NULL; + } + + CRYPTO_add(&pre_comp->references, 1, CRYPTO_LOCK_EC_PRE_COMP); + return pre_comp; +} + +void ec_pre_comp_free(EC_PRE_COMP *pre_comp) { + int i; + + if (!pre_comp) { + return; + } + + i = CRYPTO_add(&pre_comp->references, -1, CRYPTO_LOCK_EC_PRE_COMP); + if (i > 0) { + return; + } + + if (pre_comp->points) { + EC_POINT **p; + + for (p = pre_comp->points; *p != NULL; p++) { + EC_POINT_free(*p); + } + OPENSSL_free(pre_comp->points); + } + OPENSSL_free(pre_comp); +} + + +/* Determine the modified width-(w+1) Non-Adjacent Form (wNAF) of 'scalar'. + * This is an array r[] of values that are either zero or odd with an + * absolute value less than 2^w satisfying + * scalar = \sum_j r[j]*2^j + * where at most one of any w+1 consecutive digits is non-zero + * with the exception that the most significant digit may be only + * w-1 zeros away from that next non-zero digit. + */ +static signed char *compute_wNAF(const BIGNUM *scalar, int w, size_t *ret_len) { + int window_val; + int ok = 0; + signed char *r = NULL; + int sign = 1; + int bit, next_bit, mask; + size_t len = 0, j; + + if (BN_is_zero(scalar)) { + r = OPENSSL_malloc(1); + if (!r) { + OPENSSL_PUT_ERROR(EC, compute_wNAF, ERR_R_MALLOC_FAILURE); + goto err; + } + r[0] = 0; + *ret_len = 1; + return r; + } + + if (w <= 0 || w > 7) /* 'signed char' can represent integers with absolute + values less than 2^7 */ + { + OPENSSL_PUT_ERROR(EC, compute_wNAF, ERR_R_INTERNAL_ERROR); + goto err; + } + bit = 1 << w; /* at most 128 */ + next_bit = bit << 1; /* at most 256 */ + mask = next_bit - 1; /* at most 255 */ + + if (BN_is_negative(scalar)) { + sign = -1; + } + + if (scalar->d == NULL || scalar->top == 0) { + OPENSSL_PUT_ERROR(EC, compute_wNAF, ERR_R_INTERNAL_ERROR); + goto err; + } + + len = BN_num_bits(scalar); + r = OPENSSL_malloc( + len + + 1); /* modified wNAF may be one digit longer than binary representation + * (*ret_len will be set to the actual length, i.e. at most + * BN_num_bits(scalar) + 1) */ + if (r == NULL) { + OPENSSL_PUT_ERROR(EC, compute_wNAF, ERR_R_MALLOC_FAILURE); + goto err; + } + window_val = scalar->d[0] & mask; + j = 0; + while ((window_val != 0) || + (j + w + 1 < len)) /* if j+w+1 >= len, window_val will not increase */ + { + int digit = 0; + + /* 0 <= window_val <= 2^(w+1) */ + + if (window_val & 1) { + /* 0 < window_val < 2^(w+1) */ + + if (window_val & bit) { + digit = window_val - next_bit; /* -2^w < digit < 0 */ + +#if 1 /* modified wNAF */ + if (j + w + 1 >= len) { + /* special case for generating modified wNAFs: + * no new bits will be added into window_val, + * so using a positive digit here will decrease + * the total length of the representation */ + + digit = window_val & (mask >> 1); /* 0 < digit < 2^w */ + } +#endif + } else { + digit = window_val; /* 0 < digit < 2^w */ + } + + if (digit <= -bit || digit >= bit || !(digit & 1)) { + OPENSSL_PUT_ERROR(EC, compute_wNAF, ERR_R_INTERNAL_ERROR); + goto err; + } + + window_val -= digit; + + /* now window_val is 0 or 2^(w+1) in standard wNAF generation; + * for modified window NAFs, it may also be 2^w + */ + if (window_val != 0 && window_val != next_bit && window_val != bit) { + OPENSSL_PUT_ERROR(EC, compute_wNAF, ERR_R_INTERNAL_ERROR); + goto err; + } + } + + r[j++] = sign * digit; + + window_val >>= 1; + window_val += bit * BN_is_bit_set(scalar, j + w); + + if (window_val > next_bit) { + OPENSSL_PUT_ERROR(EC, compute_wNAF, ERR_R_INTERNAL_ERROR); + goto err; + } + } + + if (j > len + 1) { + OPENSSL_PUT_ERROR(EC, compute_wNAF, ERR_R_INTERNAL_ERROR); + goto err; + } + len = j; + ok = 1; + +err: + if (!ok) { + OPENSSL_free(r); + r = NULL; + } + if (ok) + *ret_len = len; + return r; +} + + +/* TODO: table should be optimised for the wNAF-based implementation, + * sometimes smaller windows will give better performance + * (thus the boundaries should be increased) + */ +#define EC_window_bits_for_scalar_size(b) \ + ((size_t)((b) >= 2000 ? 6 : (b) >= 800 ? 5 : (b) >= 300 \ + ? 4 \ + : (b) >= 70 ? 3 : (b) >= 20 \ + ? 2 \ + : 1)) + +/* Compute + * \sum scalars[i]*points[i], + * also including + * scalar*generator + * in the addition if scalar != NULL + */ +int ec_wNAF_mul(const EC_GROUP *group, EC_POINT *r, const BIGNUM *scalar, + size_t num, const EC_POINT *points[], const BIGNUM *scalars[], + BN_CTX *ctx) { + BN_CTX *new_ctx = NULL; + const EC_POINT *generator = NULL; + EC_POINT *tmp = NULL; + size_t totalnum; + size_t blocksize = 0, numblocks = 0; /* for wNAF splitting */ + size_t pre_points_per_block = 0; + size_t i, j; + int k; + int r_is_inverted = 0; + int r_is_at_infinity = 1; + size_t *wsize = NULL; /* individual window sizes */ + signed char **wNAF = NULL; /* individual wNAFs */ + size_t *wNAF_len = NULL; + size_t max_len = 0; + size_t num_val; + EC_POINT **val = NULL; /* precomputation */ + EC_POINT **v; + EC_POINT ***val_sub = + NULL; /* pointers to sub-arrays of 'val' or 'pre_comp->points' */ + const EC_PRE_COMP *pre_comp = NULL; + int num_scalar = 0; /* flag: will be set to 1 if 'scalar' must be treated like + * other scalars, + * i.e. precomputation is not available */ + int ret = 0; + + if (group->meth != r->meth) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_mul, EC_R_INCOMPATIBLE_OBJECTS); + return 0; + } + + if ((scalar == NULL) && (num == 0)) { + return EC_POINT_set_to_infinity(group, r); + } + + for (i = 0; i < num; i++) { + if (group->meth != points[i]->meth) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_mul, EC_R_INCOMPATIBLE_OBJECTS); + return 0; + } + } + + if (ctx == NULL) { + ctx = new_ctx = BN_CTX_new(); + if (ctx == NULL) + goto err; + } + + if (scalar != NULL) { + generator = EC_GROUP_get0_generator(group); + if (generator == NULL) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_mul, EC_R_UNDEFINED_GENERATOR); + goto err; + } + + /* look if we can use precomputed multiples of generator */ + + pre_comp = group->pre_comp; + + if (pre_comp && pre_comp->numblocks && + (EC_POINT_cmp(group, generator, pre_comp->points[0], ctx) == 0)) { + blocksize = pre_comp->blocksize; + + /* determine maximum number of blocks that wNAF splitting may yield + * (NB: maximum wNAF length is bit length plus one) */ + numblocks = (BN_num_bits(scalar) / blocksize) + 1; + + /* we cannot use more blocks than we have precomputation for */ + if (numblocks > pre_comp->numblocks) + numblocks = pre_comp->numblocks; + + pre_points_per_block = (size_t)1 << (pre_comp->w - 1); + + /* check that pre_comp looks sane */ + if (pre_comp->num != (pre_comp->numblocks * pre_points_per_block)) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_mul, ERR_R_INTERNAL_ERROR); + goto err; + } + } else { + /* can't use precomputation */ + pre_comp = NULL; + numblocks = 1; + num_scalar = 1; /* treat 'scalar' like 'num'-th element of 'scalars' */ + } + } + + totalnum = num + numblocks; + + wsize = OPENSSL_malloc(totalnum * sizeof wsize[0]); + wNAF_len = OPENSSL_malloc(totalnum * sizeof wNAF_len[0]); + wNAF = OPENSSL_malloc((totalnum + 1) * + sizeof wNAF[0]); /* includes space for pivot */ + val_sub = OPENSSL_malloc(totalnum * sizeof val_sub[0]); + + /* Ensure wNAF is initialised in case we end up going to err. */ + if (wNAF) { + wNAF[0] = NULL; /* preliminary pivot */ + } + + if (!wsize || !wNAF_len || !wNAF || !val_sub) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_mul, ERR_R_MALLOC_FAILURE); + goto err; + } + + /* num_val will be the total number of temporarily precomputed points */ + num_val = 0; + + for (i = 0; i < num + num_scalar; i++) { + size_t bits; + + bits = i < num ? BN_num_bits(scalars[i]) : BN_num_bits(scalar); + wsize[i] = EC_window_bits_for_scalar_size(bits); + num_val += (size_t)1 << (wsize[i] - 1); + wNAF[i + 1] = NULL; /* make sure we always have a pivot */ + wNAF[i] = + compute_wNAF((i < num ? scalars[i] : scalar), wsize[i], &wNAF_len[i]); + if (wNAF[i] == NULL) + goto err; + if (wNAF_len[i] > max_len) + max_len = wNAF_len[i]; + } + + if (numblocks) { + /* we go here iff scalar != NULL */ + + if (pre_comp == NULL) { + if (num_scalar != 1) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_mul, ERR_R_INTERNAL_ERROR); + goto err; + } + /* we have already generated a wNAF for 'scalar' */ + } else { + signed char *tmp_wNAF = NULL; + size_t tmp_len = 0; + + if (num_scalar != 0) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_mul, ERR_R_INTERNAL_ERROR); + goto err; + } + + /* use the window size for which we have precomputation */ + wsize[num] = pre_comp->w; + tmp_wNAF = compute_wNAF(scalar, wsize[num], &tmp_len); + if (!tmp_wNAF) + goto err; + + if (tmp_len <= max_len) { + /* One of the other wNAFs is at least as long + * as the wNAF belonging to the generator, + * so wNAF splitting will not buy us anything. */ + + numblocks = 1; /* don't use wNAF splitting */ + totalnum = num + numblocks; + wNAF[num] = tmp_wNAF; + wNAF[num + 1] = NULL; + wNAF_len[num] = tmp_len; + /* pre_comp->points starts with the points that we need here: */ + val_sub[num] = pre_comp->points; + } else { + /* don't include tmp_wNAF directly into wNAF array + * - use wNAF splitting and include the blocks */ + + signed char *pp; + EC_POINT **tmp_points; + + if (tmp_len < numblocks * blocksize) { + /* possibly we can do with fewer blocks than estimated */ + numblocks = (tmp_len + blocksize - 1) / blocksize; + if (numblocks > pre_comp->numblocks) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_mul, ERR_R_INTERNAL_ERROR); + goto err; + } + totalnum = num + numblocks; + } + + /* split wNAF in 'numblocks' parts */ + pp = tmp_wNAF; + tmp_points = pre_comp->points; + + for (i = num; i < totalnum; i++) { + if (i < totalnum - 1) { + wNAF_len[i] = blocksize; + if (tmp_len < blocksize) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_mul, ERR_R_INTERNAL_ERROR); + goto err; + } + tmp_len -= blocksize; + } else + /* last block gets whatever is left + * (this could be more or less than 'blocksize'!) */ + wNAF_len[i] = tmp_len; + + wNAF[i + 1] = NULL; + wNAF[i] = OPENSSL_malloc(wNAF_len[i]); + if (wNAF[i] == NULL) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_mul, ERR_R_MALLOC_FAILURE); + OPENSSL_free(tmp_wNAF); + goto err; + } + memcpy(wNAF[i], pp, wNAF_len[i]); + if (wNAF_len[i] > max_len) + max_len = wNAF_len[i]; + + if (*tmp_points == NULL) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_mul, ERR_R_INTERNAL_ERROR); + OPENSSL_free(tmp_wNAF); + goto err; + } + val_sub[i] = tmp_points; + tmp_points += pre_points_per_block; + pp += blocksize; + } + OPENSSL_free(tmp_wNAF); + } + } + } + + /* All points we precompute now go into a single array 'val'. + * 'val_sub[i]' is a pointer to the subarray for the i-th point, + * or to a subarray of 'pre_comp->points' if we already have precomputation. + */ + val = OPENSSL_malloc((num_val + 1) * sizeof val[0]); + if (val == NULL) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_mul, ERR_R_MALLOC_FAILURE); + goto err; + } + val[num_val] = NULL; /* pivot element */ + + /* allocate points for precomputation */ + v = val; + for (i = 0; i < num + num_scalar; i++) { + val_sub[i] = v; + for (j = 0; j < ((size_t)1 << (wsize[i] - 1)); j++) { + *v = EC_POINT_new(group); + if (*v == NULL) + goto err; + v++; + } + } + if (!(v == val + num_val)) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_mul, ERR_R_INTERNAL_ERROR); + goto err; + } + + if (!(tmp = EC_POINT_new(group))) + goto err; + + /* prepare precomputed values: + * val_sub[i][0] := points[i] + * val_sub[i][1] := 3 * points[i] + * val_sub[i][2] := 5 * points[i] + * ... + */ + for (i = 0; i < num + num_scalar; i++) { + if (i < num) { + if (!EC_POINT_copy(val_sub[i][0], points[i])) + goto err; + } else { + if (!EC_POINT_copy(val_sub[i][0], generator)) + goto err; + } + + if (wsize[i] > 1) { + if (!EC_POINT_dbl(group, tmp, val_sub[i][0], ctx)) + goto err; + for (j = 1; j < ((size_t)1 << (wsize[i] - 1)); j++) { + if (!EC_POINT_add(group, val_sub[i][j], val_sub[i][j - 1], tmp, ctx)) + goto err; + } + } + } + +#if 1 /* optional; EC_window_bits_for_scalar_size assumes we do this step */ + if (!EC_POINTs_make_affine(group, num_val, val, ctx)) + goto err; +#endif + + r_is_at_infinity = 1; + + for (k = max_len - 1; k >= 0; k--) { + if (!r_is_at_infinity) { + if (!EC_POINT_dbl(group, r, r, ctx)) + goto err; + } + + for (i = 0; i < totalnum; i++) { + if (wNAF_len[i] > (size_t)k) { + int digit = wNAF[i][k]; + int is_neg; + + if (digit) { + is_neg = digit < 0; + + if (is_neg) + digit = -digit; + + if (is_neg != r_is_inverted) { + if (!r_is_at_infinity) { + if (!EC_POINT_invert(group, r, ctx)) + goto err; + } + r_is_inverted = !r_is_inverted; + } + + /* digit > 0 */ + + if (r_is_at_infinity) { + if (!EC_POINT_copy(r, val_sub[i][digit >> 1])) + goto err; + r_is_at_infinity = 0; + } else { + if (!EC_POINT_add(group, r, r, val_sub[i][digit >> 1], ctx)) + goto err; + } + } + } + } + } + + if (r_is_at_infinity) { + if (!EC_POINT_set_to_infinity(group, r)) + goto err; + } else { + if (r_is_inverted) + if (!EC_POINT_invert(group, r, ctx)) + goto err; + } + + ret = 1; + +err: + if (new_ctx != NULL) + BN_CTX_free(new_ctx); + if (tmp != NULL) + EC_POINT_free(tmp); + if (wsize != NULL) + OPENSSL_free(wsize); + if (wNAF_len != NULL) + OPENSSL_free(wNAF_len); + if (wNAF != NULL) { + signed char **w; + + for (w = wNAF; *w != NULL; w++) + OPENSSL_free(*w); + + OPENSSL_free(wNAF); + } + if (val != NULL) { + for (v = val; *v != NULL; v++) + EC_POINT_clear_free(*v); + + OPENSSL_free(val); + } + if (val_sub != NULL) { + OPENSSL_free(val_sub); + } + return ret; +} + + +/* ec_wNAF_precompute_mult() + * creates an EC_PRE_COMP object with preprecomputed multiples of the generator + * for use with wNAF splitting as implemented in ec_wNAF_mul(). + * + * 'pre_comp->points' is an array of multiples of the generator + * of the following form: + * points[0] = generator; + * points[1] = 3 * generator; + * ... + * points[2^(w-1)-1] = (2^(w-1)-1) * generator; + * points[2^(w-1)] = 2^blocksize * generator; + * points[2^(w-1)+1] = 3 * 2^blocksize * generator; + * ... + * points[2^(w-1)*(numblocks-1)-1] = (2^(w-1)) * 2^(blocksize*(numblocks-2)) * + *generator + * points[2^(w-1)*(numblocks-1)] = 2^(blocksize*(numblocks-1)) * + *generator + * ... + * points[2^(w-1)*numblocks-1] = (2^(w-1)) * 2^(blocksize*(numblocks-1)) * + *generator + * points[2^(w-1)*numblocks] = NULL + */ +int ec_wNAF_precompute_mult(EC_GROUP *group, BN_CTX *ctx) { + const EC_POINT *generator; + EC_POINT *tmp_point = NULL, *base = NULL, **var; + BN_CTX *new_ctx = NULL; + BIGNUM *order; + size_t i, bits, w, pre_points_per_block, blocksize, numblocks, num; + EC_POINT **points = NULL; + EC_PRE_COMP *pre_comp; + int ret = 0; + + /* if there is an old EC_PRE_COMP object, throw it away */ + if (group->pre_comp) { + ec_pre_comp_free(group->pre_comp); + group->pre_comp = NULL; + } + + if ((pre_comp = ec_pre_comp_new(group)) == NULL) + return 0; + + generator = EC_GROUP_get0_generator(group); + if (generator == NULL) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_precompute_mult, EC_R_UNDEFINED_GENERATOR); + goto err; + } + + if (ctx == NULL) { + ctx = new_ctx = BN_CTX_new(); + if (ctx == NULL) + goto err; + } + + BN_CTX_start(ctx); + order = BN_CTX_get(ctx); + if (order == NULL) + goto err; + + if (!EC_GROUP_get_order(group, order, ctx)) + goto err; + if (BN_is_zero(order)) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_precompute_mult, EC_R_UNKNOWN_ORDER); + goto err; + } + + bits = BN_num_bits(order); + /* The following parameters mean we precompute (approximately) + * one point per bit. + * + * TBD: The combination 8, 4 is perfect for 160 bits; for other + * bit lengths, other parameter combinations might provide better + * efficiency. + */ + blocksize = 8; + w = 4; + if (EC_window_bits_for_scalar_size(bits) > w) { + /* let's not make the window too small ... */ + w = EC_window_bits_for_scalar_size(bits); + } + + numblocks = (bits + blocksize - 1) / + blocksize; /* max. number of blocks to use for wNAF splitting */ + + pre_points_per_block = (size_t)1 << (w - 1); + num = pre_points_per_block * + numblocks; /* number of points to compute and store */ + + points = OPENSSL_malloc(sizeof(EC_POINT *) * (num + 1)); + if (!points) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_precompute_mult, ERR_R_MALLOC_FAILURE); + goto err; + } + + var = points; + var[num] = NULL; /* pivot */ + for (i = 0; i < num; i++) { + if ((var[i] = EC_POINT_new(group)) == NULL) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_precompute_mult, ERR_R_MALLOC_FAILURE); + goto err; + } + } + + if (!(tmp_point = EC_POINT_new(group)) || !(base = EC_POINT_new(group))) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_precompute_mult, ERR_R_MALLOC_FAILURE); + goto err; + } + + if (!EC_POINT_copy(base, generator)) + goto err; + + /* do the precomputation */ + for (i = 0; i < numblocks; i++) { + size_t j; + + if (!EC_POINT_dbl(group, tmp_point, base, ctx)) + goto err; + + if (!EC_POINT_copy(*var++, base)) + goto err; + + for (j = 1; j < pre_points_per_block; j++, var++) { + /* calculate odd multiples of the current base point */ + if (!EC_POINT_add(group, *var, tmp_point, *(var - 1), ctx)) + goto err; + } + + if (i < numblocks - 1) { + /* get the next base (multiply current one by 2^blocksize) */ + size_t k; + + if (blocksize <= 2) { + OPENSSL_PUT_ERROR(EC, ec_wNAF_precompute_mult, ERR_R_INTERNAL_ERROR); + goto err; + } + + if (!EC_POINT_dbl(group, base, tmp_point, ctx)) + goto err; + for (k = 2; k < blocksize; k++) { + if (!EC_POINT_dbl(group, base, base, ctx)) + goto err; + } + } + } + + if (!EC_POINTs_make_affine(group, num, points, ctx)) + goto err; + + pre_comp->group = group; + pre_comp->blocksize = blocksize; + pre_comp->numblocks = numblocks; + pre_comp->w = w; + pre_comp->points = points; + points = NULL; + pre_comp->num = num; + + group->pre_comp = pre_comp; + pre_comp = NULL; + + ret = 1; + +err: + if (ctx != NULL) + BN_CTX_end(ctx); + if (new_ctx != NULL) + BN_CTX_free(new_ctx); + if (pre_comp) + ec_pre_comp_free(pre_comp); + if (points) { + EC_POINT **p; + + for (p = points; *p != NULL; p++) + EC_POINT_free(*p); + OPENSSL_free(points); + } + if (tmp_point) + EC_POINT_free(tmp_point); + if (base) + EC_POINT_free(base); + return ret; +} + + +int ec_wNAF_have_precompute_mult(const EC_GROUP *group) { + return group->pre_comp != NULL; +} |