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/*
* Copyright 2014-2018 The OpenSSL Project Authors. 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 "internal/cryptlib.h"
#include "bn_lcl.h"
/*
* 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.
*/
signed char *bn_compute_wNAF(const BIGNUM *scalar, int w, size_t *ret_len)
{
int window_val;
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 == NULL) {
BNerr(BN_F_BN_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 */
BNerr(BN_F_BN_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) {
BNerr(BN_F_BN_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) {
BNerr(BN_F_BN_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)) {
BNerr(BN_F_BN_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) {
BNerr(BN_F_BN_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) {
BNerr(BN_F_BN_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR);
goto err;
}
}
if (j > len + 1) {
BNerr(BN_F_BN_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR);
goto err;
}
*ret_len = j;
return r;
err:
OPENSSL_free(r);
return NULL;
}
int bn_get_top(const BIGNUM *a)
{
return a->top;
}
int bn_get_dmax(const BIGNUM *a)
{
return a->dmax;
}
void bn_set_all_zero(BIGNUM *a)
{
int i;
for (i = a->top; i < a->dmax; i++)
a->d[i] = 0;
}
int bn_copy_words(BN_ULONG *out, const BIGNUM *in, int size)
{
if (in->top > size)
return 0;
memset(out, 0, sizeof(*out) * size);
if (in->d != NULL)
memcpy(out, in->d, sizeof(*out) * in->top);
return 1;
}
BN_ULONG *bn_get_words(const BIGNUM *a)
{
return a->d;
}
void bn_set_static_words(BIGNUM *a, const BN_ULONG *words, int size)
{
/*
* |const| qualifier omission is compensated by BN_FLG_STATIC_DATA
* flag, which effectively means "read-only data".
*/
a->d = (BN_ULONG *)words;
a->dmax = a->top = size;
a->neg = 0;
a->flags |= BN_FLG_STATIC_DATA;
bn_correct_top(a);
}
int bn_set_words(BIGNUM *a, const BN_ULONG *words, int num_words)
{
if (bn_wexpand(a, num_words) == NULL) {
BNerr(BN_F_BN_SET_WORDS, ERR_R_MALLOC_FAILURE);
return 0;
}
memcpy(a->d, words, sizeof(BN_ULONG) * num_words);
a->top = num_words;
bn_correct_top(a);
return 1;
}
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