2 * Copyright 2014-2018 The OpenSSL Project Authors. All Rights Reserved.
4 * Licensed under the OpenSSL license (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
10 #include "internal/cryptlib.h"
14 * Determine the modified width-(w+1) Non-Adjacent Form (wNAF) of 'scalar'.
15 * This is an array r[] of values that are either zero or odd with an
16 * absolute value less than 2^w satisfying
17 * scalar = \sum_j r[j]*2^j
18 * where at most one of any w+1 consecutive digits is non-zero
19 * with the exception that the most significant digit may be only
20 * w-1 zeros away from that next non-zero digit.
22 signed char *bn_compute_wNAF(const BIGNUM *scalar, int w, size_t *ret_len)
25 signed char *r = NULL;
27 int bit, next_bit, mask;
30 if (BN_is_zero(scalar)) {
31 r = OPENSSL_malloc(1);
33 BNerr(BN_F_BN_COMPUTE_WNAF, ERR_R_MALLOC_FAILURE);
41 if (w <= 0 || w > 7) { /* 'signed char' can represent integers with
42 * absolute values less than 2^7 */
43 BNerr(BN_F_BN_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR);
46 bit = 1 << w; /* at most 128 */
47 next_bit = bit << 1; /* at most 256 */
48 mask = next_bit - 1; /* at most 255 */
50 if (BN_is_negative(scalar)) {
54 if (scalar->d == NULL || scalar->top == 0) {
55 BNerr(BN_F_BN_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR);
59 len = BN_num_bits(scalar);
60 r = OPENSSL_malloc(len + 1); /*
61 * Modified wNAF may be one digit longer than binary representation
62 * (*ret_len will be set to the actual length, i.e. at most
63 * BN_num_bits(scalar) + 1)
66 BNerr(BN_F_BN_COMPUTE_WNAF, ERR_R_MALLOC_FAILURE);
69 window_val = scalar->d[0] & mask;
71 while ((window_val != 0) || (j + w + 1 < len)) { /* if j+w+1 >= len,
76 /* 0 <= window_val <= 2^(w+1) */
79 /* 0 < window_val < 2^(w+1) */
81 if (window_val & bit) {
82 digit = window_val - next_bit; /* -2^w < digit < 0 */
84 #if 1 /* modified wNAF */
85 if (j + w + 1 >= len) {
87 * Special case for generating modified wNAFs:
88 * no new bits will be added into window_val,
89 * so using a positive digit here will decrease
90 * the total length of the representation
93 digit = window_val & (mask >> 1); /* 0 < digit < 2^w */
97 digit = window_val; /* 0 < digit < 2^w */
100 if (digit <= -bit || digit >= bit || !(digit & 1)) {
101 BNerr(BN_F_BN_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR);
108 * now window_val is 0 or 2^(w+1) in standard wNAF generation;
109 * for modified window NAFs, it may also be 2^w
111 if (window_val != 0 && window_val != next_bit
112 && window_val != bit) {
113 BNerr(BN_F_BN_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR);
118 r[j++] = sign * digit;
121 window_val += bit * BN_is_bit_set(scalar, j + w);
123 if (window_val > next_bit) {
124 BNerr(BN_F_BN_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR);
130 BNerr(BN_F_BN_COMPUTE_WNAF, ERR_R_INTERNAL_ERROR);
141 int bn_get_top(const BIGNUM *a)
146 int bn_get_dmax(const BIGNUM *a)
151 void bn_set_all_zero(BIGNUM *a)
155 for (i = a->top; i < a->dmax; i++)
159 int bn_copy_words(BN_ULONG *out, const BIGNUM *in, int size)
164 memset(out, 0, sizeof(*out) * size);
166 memcpy(out, in->d, sizeof(*out) * in->top);
170 BN_ULONG *bn_get_words(const BIGNUM *a)
175 void bn_set_static_words(BIGNUM *a, const BN_ULONG *words, int size)
178 * |const| qualifier omission is compensated by BN_FLG_STATIC_DATA
179 * flag, which effectively means "read-only data".
181 a->d = (BN_ULONG *)words;
182 a->dmax = a->top = size;
184 a->flags |= BN_FLG_STATIC_DATA;
188 int bn_set_words(BIGNUM *a, const BN_ULONG *words, int num_words)
190 if (bn_wexpand(a, num_words) == NULL) {
191 BNerr(BN_F_BN_SET_WORDS, ERR_R_MALLOC_FAILURE);
195 memcpy(a->d, words, sizeof(BN_ULONG) * num_words);