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openssl/crypto/ec/ec_mult.c

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v1.1.1t
2023-05-09 22:08:48 +00:00
/*
* Copyright 2001-2020 The OpenSSL Project Authors. All Rights Reserved.
* Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved
*
* Licensed under the OpenSSL license (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#include <string.h>
#include <openssl/err.h>
#include "internal/cryptlib.h"
#include "crypto/bn.h"
#include "ec_local.h"
#include "internal/refcount.h"
/*
* This file implements the wNAF-based interleaving multi-exponentiation method
* Formerly at:
* http://www.informatik.tu-darmstadt.de/TI/Mitarbeiter/moeller.html#multiexp
* You might now find it here:
* http://link.springer.com/chapter/10.1007%2F3-540-45537-X_13
* http://www.bmoeller.de/pdf/TI-01-08.multiexp.pdf
* For multiplication with precomputation, we use wNAF splitting, formerly at:
* http://www.informatik.tu-darmstadt.de/TI/Mitarbeiter/moeller.html#fastexp
*/
/* structure for precomputed multiples of the generator */
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) */
CRYPTO_REF_COUNT references;
CRYPTO_RWLOCK *lock;
};
static EC_PRE_COMP *ec_pre_comp_new(const EC_GROUP *group)
{
EC_PRE_COMP *ret = NULL;
if (!group)
return NULL;
ret = OPENSSL_zalloc(sizeof(*ret));
if (ret == NULL) {
ECerr(EC_F_EC_PRE_COMP_NEW, ERR_R_MALLOC_FAILURE);
return ret;
}
ret->group = group;
ret->blocksize = 8; /* default */
ret->w = 4; /* default */
ret->references = 1;
ret->lock = CRYPTO_THREAD_lock_new();
if (ret->lock == NULL) {
ECerr(EC_F_EC_PRE_COMP_NEW, ERR_R_MALLOC_FAILURE);
OPENSSL_free(ret);
return NULL;
}
return ret;
}
EC_PRE_COMP *EC_ec_pre_comp_dup(EC_PRE_COMP *pre)
{
int i;
if (pre != NULL)
CRYPTO_UP_REF(&pre->references, &i, pre->lock);
return pre;
}
void EC_ec_pre_comp_free(EC_PRE_COMP *pre)
{
int i;
if (pre == NULL)
return;
CRYPTO_DOWN_REF(&pre->references, &i, pre->lock);
REF_PRINT_COUNT("EC_ec", pre);
if (i > 0)
return;
REF_ASSERT_ISNT(i < 0);
if (pre->points != NULL) {
EC_POINT **pts;
for (pts = pre->points; *pts != NULL; pts++)
EC_POINT_free(*pts);
OPENSSL_free(pre->points);
}
CRYPTO_THREAD_lock_free(pre->lock);
OPENSSL_free(pre);
}
#define EC_POINT_BN_set_flags(P, flags) do { \
BN_set_flags((P)->X, (flags)); \
BN_set_flags((P)->Y, (flags)); \
BN_set_flags((P)->Z, (flags)); \
} while(0)
/*-
* This functions computes a single point multiplication over the EC group,
* using, at a high level, a Montgomery ladder with conditional swaps, with
* various timing attack defenses.
*
* It performs either a fixed point multiplication
* (scalar * generator)
* when point is NULL, or a variable point multiplication
* (scalar * point)
* when point is not NULL.
*
* `scalar` cannot be NULL and should be in the range [0,n) otherwise all
* constant time bets are off (where n is the cardinality of the EC group).
*
* This function expects `group->order` and `group->cardinality` to be well
* defined and non-zero: it fails with an error code otherwise.
*
* NB: This says nothing about the constant-timeness of the ladder step
* implementation (i.e., the default implementation is based on EC_POINT_add and
* EC_POINT_dbl, which of course are not constant time themselves) or the
* underlying multiprecision arithmetic.
*
* The product is stored in `r`.
*
* This is an internal function: callers are in charge of ensuring that the
* input parameters `group`, `r`, `scalar` and `ctx` are not NULL.
*
* Returns 1 on success, 0 otherwise.
*/
int ec_scalar_mul_ladder(const EC_GROUP *group, EC_POINT *r,
const BIGNUM *scalar, const EC_POINT *point,
BN_CTX *ctx)
{
int i, cardinality_bits, group_top, kbit, pbit, Z_is_one;
EC_POINT *p = NULL;
EC_POINT *s = NULL;
BIGNUM *k = NULL;
BIGNUM *lambda = NULL;
BIGNUM *cardinality = NULL;
int ret = 0;
/* early exit if the input point is the point at infinity */
if (point != NULL && EC_POINT_is_at_infinity(group, point))
return EC_POINT_set_to_infinity(group, r);
if (BN_is_zero(group->order)) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, EC_R_UNKNOWN_ORDER);
return 0;
}
if (BN_is_zero(group->cofactor)) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, EC_R_UNKNOWN_COFACTOR);
return 0;
}
BN_CTX_start(ctx);
if (((p = EC_POINT_new(group)) == NULL)
|| ((s = EC_POINT_new(group)) == NULL)) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_MALLOC_FAILURE);
goto err;
}
if (point == NULL) {
if (!EC_POINT_copy(p, group->generator)) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_EC_LIB);
goto err;
}
} else {
if (!EC_POINT_copy(p, point)) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_EC_LIB);
goto err;
}
}
EC_POINT_BN_set_flags(p, BN_FLG_CONSTTIME);
EC_POINT_BN_set_flags(r, BN_FLG_CONSTTIME);
EC_POINT_BN_set_flags(s, BN_FLG_CONSTTIME);
cardinality = BN_CTX_get(ctx);
lambda = BN_CTX_get(ctx);
k = BN_CTX_get(ctx);
if (k == NULL) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_MALLOC_FAILURE);
goto err;
}
if (!BN_mul(cardinality, group->order, group->cofactor, ctx)) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_BN_LIB);
goto err;
}
/*
* Group cardinalities are often on a word boundary.
* So when we pad the scalar, some timing diff might
* pop if it needs to be expanded due to carries.
* So expand ahead of time.
*/
cardinality_bits = BN_num_bits(cardinality);
group_top = bn_get_top(cardinality);
if ((bn_wexpand(k, group_top + 2) == NULL)
|| (bn_wexpand(lambda, group_top + 2) == NULL)) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_BN_LIB);
goto err;
}
if (!BN_copy(k, scalar)) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_BN_LIB);
goto err;
}
BN_set_flags(k, BN_FLG_CONSTTIME);
if ((BN_num_bits(k) > cardinality_bits) || (BN_is_negative(k))) {
/*-
* this is an unusual input, and we don't guarantee
* constant-timeness
*/
if (!BN_nnmod(k, k, cardinality, ctx)) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_BN_LIB);
goto err;
}
}
if (!BN_add(lambda, k, cardinality)) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_BN_LIB);
goto err;
}
BN_set_flags(lambda, BN_FLG_CONSTTIME);
if (!BN_add(k, lambda, cardinality)) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_BN_LIB);
goto err;
}
/*
* lambda := scalar + cardinality
* k := scalar + 2*cardinality
*/
kbit = BN_is_bit_set(lambda, cardinality_bits);
BN_consttime_swap(kbit, k, lambda, group_top + 2);
group_top = bn_get_top(group->field);
if ((bn_wexpand(s->X, group_top) == NULL)
|| (bn_wexpand(s->Y, group_top) == NULL)
|| (bn_wexpand(s->Z, group_top) == NULL)
|| (bn_wexpand(r->X, group_top) == NULL)
|| (bn_wexpand(r->Y, group_top) == NULL)
|| (bn_wexpand(r->Z, group_top) == NULL)
|| (bn_wexpand(p->X, group_top) == NULL)
|| (bn_wexpand(p->Y, group_top) == NULL)
|| (bn_wexpand(p->Z, group_top) == NULL)) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_BN_LIB);
goto err;
}
/* ensure input point is in affine coords for ladder step efficiency */
if (!p->Z_is_one && !EC_POINT_make_affine(group, p, ctx)) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, ERR_R_EC_LIB);
goto err;
}
/* Initialize the Montgomery ladder */
if (!ec_point_ladder_pre(group, r, s, p, ctx)) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, EC_R_LADDER_PRE_FAILURE);
goto err;
}
/* top bit is a 1, in a fixed pos */
pbit = 1;
#define EC_POINT_CSWAP(c, a, b, w, t) do { \
BN_consttime_swap(c, (a)->X, (b)->X, w); \
BN_consttime_swap(c, (a)->Y, (b)->Y, w); \
BN_consttime_swap(c, (a)->Z, (b)->Z, w); \
t = ((a)->Z_is_one ^ (b)->Z_is_one) & (c); \
(a)->Z_is_one ^= (t); \
(b)->Z_is_one ^= (t); \
} while(0)
/*-
* The ladder step, with branches, is
*
* k[i] == 0: S = add(R, S), R = dbl(R)
* k[i] == 1: R = add(S, R), S = dbl(S)
*
* Swapping R, S conditionally on k[i] leaves you with state
*
* k[i] == 0: T, U = R, S
* k[i] == 1: T, U = S, R
*
* Then perform the ECC ops.
*
* U = add(T, U)
* T = dbl(T)
*
* Which leaves you with state
*
* k[i] == 0: U = add(R, S), T = dbl(R)
* k[i] == 1: U = add(S, R), T = dbl(S)
*
* Swapping T, U conditionally on k[i] leaves you with state
*
* k[i] == 0: R, S = T, U
* k[i] == 1: R, S = U, T
*
* Which leaves you with state
*
* k[i] == 0: S = add(R, S), R = dbl(R)
* k[i] == 1: R = add(S, R), S = dbl(S)
*
* So we get the same logic, but instead of a branch it's a
* conditional swap, followed by ECC ops, then another conditional swap.
*
* Optimization: The end of iteration i and start of i-1 looks like
*
* ...
* CSWAP(k[i], R, S)
* ECC
* CSWAP(k[i], R, S)
* (next iteration)
* CSWAP(k[i-1], R, S)
* ECC
* CSWAP(k[i-1], R, S)
* ...
*
* So instead of two contiguous swaps, you can merge the condition
* bits and do a single swap.
*
* k[i] k[i-1] Outcome
* 0 0 No Swap
* 0 1 Swap
* 1 0 Swap
* 1 1 No Swap
*
* This is XOR. pbit tracks the previous bit of k.
*/
for (i = cardinality_bits - 1; i >= 0; i--) {
kbit = BN_is_bit_set(k, i) ^ pbit;
EC_POINT_CSWAP(kbit, r, s, group_top, Z_is_one);
/* Perform a single step of the Montgomery ladder */
if (!ec_point_ladder_step(group, r, s, p, ctx)) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, EC_R_LADDER_STEP_FAILURE);
goto err;
}
/*
* pbit logic merges this cswap with that of the
* next iteration
*/
pbit ^= kbit;
}
/* one final cswap to move the right value into r */
EC_POINT_CSWAP(pbit, r, s, group_top, Z_is_one);
#undef EC_POINT_CSWAP
/* Finalize ladder (and recover full point coordinates) */
if (!ec_point_ladder_post(group, r, s, p, ctx)) {
ECerr(EC_F_EC_SCALAR_MUL_LADDER, EC_R_LADDER_POST_FAILURE);
goto err;
}
ret = 1;
err:
EC_POINT_free(p);
EC_POINT_clear_free(s);
BN_CTX_end(ctx);
return ret;
}
#undef EC_POINT_BN_set_flags
/*
* 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)
{
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 (!BN_is_zero(group->order) && !BN_is_zero(group->cofactor)) {
/*-
* Handle the common cases where the scalar is secret, enforcing a
* scalar multiplication implementation based on a Montgomery ladder,
* with various timing attack defenses.
*/
if ((scalar != group->order) && (scalar != NULL) && (num == 0)) {
/*-
* In this case we want to compute scalar * GeneratorPoint: this
* codepath is reached most prominently by (ephemeral) key
* generation of EC cryptosystems (i.e. ECDSA keygen and sign setup,
* ECDH keygen/first half), where the scalar is always secret. This
* is why we ignore if BN_FLG_CONSTTIME is actually set and we
* always call the ladder version.
*/
return ec_scalar_mul_ladder(group, r, scalar, NULL, ctx);
}
if ((scalar == NULL) && (num == 1) && (scalars[0] != group->order)) {
/*-
* In this case we want to compute scalar * VariablePoint: this
* codepath is reached most prominently by the second half of ECDH,
* where the secret scalar is multiplied by the peer's public point.
* To protect the secret scalar, we ignore if BN_FLG_CONSTTIME is
* actually set and we always call the ladder version.
*/
return ec_scalar_mul_ladder(group, r, scalars[0], points[0], ctx);
}
}
if (scalar != NULL) {
generator = EC_GROUP_get0_generator(group);
if (generator == NULL) {
ECerr(EC_F_EC_WNAF_MUL, EC_R_UNDEFINED_GENERATOR);
goto err;
}
/* look if we can use precomputed multiples of generator */
pre_comp = group->pre_comp.ec;
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)) {
ECerr(EC_F_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]));
/* include space for pivot */
wNAF = OPENSSL_malloc((totalnum + 1) * sizeof(wNAF[0]));
val_sub = OPENSSL_malloc(totalnum * sizeof(val_sub[0]));
/* Ensure wNAF is initialised in case we end up going to err */
if (wNAF != NULL)
wNAF[0] = NULL; /* preliminary pivot */
if (wsize == NULL || wNAF_len == NULL || wNAF == NULL || val_sub == NULL) {
ECerr(EC_F_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] =
bn_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) {
ECerr(EC_F_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) {
ECerr(EC_F_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 = bn_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;
totalnum = num + 1; /* don't use wNAF splitting */
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) {
ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
OPENSSL_free(tmp_wNAF);
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) {
ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
OPENSSL_free(tmp_wNAF);
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) {
ECerr(EC_F_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) {
ECerr(EC_F_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) {
ECerr(EC_F_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)) {
ECerr(EC_F_EC_WNAF_MUL, ERR_R_INTERNAL_ERROR);
goto err;
}
if ((tmp = EC_POINT_new(group)) == NULL)
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 (!EC_POINTs_make_affine(group, num_val, val, ctx))
goto err;
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;
/*-
* Apply coordinate blinding for EC_POINT.
*
* The underlying EC_METHOD can optionally implement this function:
* ec_point_blind_coordinates() returns 0 in case of errors or 1 on
* success or if coordinate blinding is not implemented for this
* group.
*/
if (!ec_point_blind_coordinates(group, r, ctx)) {
ECerr(EC_F_EC_WNAF_MUL, EC_R_POINT_COORDINATES_BLIND_FAILURE);
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:
EC_POINT_free(tmp);
OPENSSL_free(wsize);
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);
}
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;
const 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 */
EC_pre_comp_free(group);
if ((pre_comp = ec_pre_comp_new(group)) == NULL)
return 0;
generator = EC_GROUP_get0_generator(group);
if (generator == NULL) {
ECerr(EC_F_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 = EC_GROUP_get0_order(group);
if (order == NULL)
goto err;
if (BN_is_zero(order)) {
ECerr(EC_F_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(*points) * (num + 1));
if (points == NULL) {
ECerr(EC_F_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) {
ECerr(EC_F_EC_WNAF_PRECOMPUTE_MULT, ERR_R_MALLOC_FAILURE);
goto err;
}
}
if ((tmp_point = EC_POINT_new(group)) == NULL
|| (base = EC_POINT_new(group)) == NULL) {
ECerr(EC_F_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) {
ECerr(EC_F_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;
SETPRECOMP(group, ec, pre_comp);
pre_comp = NULL;
ret = 1;
err:
BN_CTX_end(ctx);
BN_CTX_free(new_ctx);
EC_ec_pre_comp_free(pre_comp);
if (points) {
EC_POINT **p;
for (p = points; *p != NULL; p++)
EC_POINT_free(*p);
OPENSSL_free(points);
}
EC_POINT_free(tmp_point);
EC_POINT_free(base);
return ret;
}
int ec_wNAF_have_precompute_mult(const EC_GROUP *group)
{
return HAVEPRECOMP(group, ec);
}