1 /*
2 * Copyright 2014-2020 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the Apache License 2.0 (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
8 */
9
10 #include "internal/cryptlib.h"
11 #include "bn_local.h"
12
13 /*
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.
21 */
bn_compute_wNAF(const BIGNUM * scalar,int w,size_t * ret_len)22 signed char *bn_compute_wNAF(const BIGNUM *scalar, int w, size_t *ret_len)
23 {
24 int window_val;
25 signed char *r = NULL;
26 int sign = 1;
27 int bit, next_bit, mask;
28 size_t len = 0, j;
29
30 if (BN_is_zero(scalar)) {
31 r = OPENSSL_malloc(1);
32 if (r == NULL) {
33 ERR_raise(ERR_LIB_BN, ERR_R_MALLOC_FAILURE);
34 goto err;
35 }
36 r[0] = 0;
37 *ret_len = 1;
38 return r;
39 }
40
41 if (w <= 0 || w > 7) { /* 'signed char' can represent integers with
42 * absolute values less than 2^7 */
43 ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR);
44 goto err;
45 }
46 bit = 1 << w; /* at most 128 */
47 next_bit = bit << 1; /* at most 256 */
48 mask = next_bit - 1; /* at most 255 */
49
50 if (BN_is_negative(scalar)) {
51 sign = -1;
52 }
53
54 if (scalar->d == NULL || scalar->top == 0) {
55 ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR);
56 goto err;
57 }
58
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)
64 */
65 if (r == NULL) {
66 ERR_raise(ERR_LIB_BN, ERR_R_MALLOC_FAILURE);
67 goto err;
68 }
69 window_val = scalar->d[0] & mask;
70 j = 0;
71 while ((window_val != 0) || (j + w + 1 < len)) { /* if j+w+1 >= len,
72 * window_val will not
73 * increase */
74 int digit = 0;
75
76 /* 0 <= window_val <= 2^(w+1) */
77
78 if (window_val & 1) {
79 /* 0 < window_val < 2^(w+1) */
80
81 if (window_val & bit) {
82 digit = window_val - next_bit; /* -2^w < digit < 0 */
83
84 #if 1 /* modified wNAF */
85 if (j + w + 1 >= len) {
86 /*
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
91 */
92
93 digit = window_val & (mask >> 1); /* 0 < digit < 2^w */
94 }
95 #endif
96 } else {
97 digit = window_val; /* 0 < digit < 2^w */
98 }
99
100 if (digit <= -bit || digit >= bit || !(digit & 1)) {
101 ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR);
102 goto err;
103 }
104
105 window_val -= digit;
106
107 /*
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
110 */
111 if (window_val != 0 && window_val != next_bit
112 && window_val != bit) {
113 ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR);
114 goto err;
115 }
116 }
117
118 r[j++] = sign * digit;
119
120 window_val >>= 1;
121 window_val += bit * BN_is_bit_set(scalar, j + w);
122
123 if (window_val > next_bit) {
124 ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR);
125 goto err;
126 }
127 }
128
129 if (j > len + 1) {
130 ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR);
131 goto err;
132 }
133 *ret_len = j;
134 return r;
135
136 err:
137 OPENSSL_free(r);
138 return NULL;
139 }
140
bn_get_top(const BIGNUM * a)141 int bn_get_top(const BIGNUM *a)
142 {
143 return a->top;
144 }
145
bn_get_dmax(const BIGNUM * a)146 int bn_get_dmax(const BIGNUM *a)
147 {
148 return a->dmax;
149 }
150
bn_set_all_zero(BIGNUM * a)151 void bn_set_all_zero(BIGNUM *a)
152 {
153 int i;
154
155 for (i = a->top; i < a->dmax; i++)
156 a->d[i] = 0;
157 }
158
bn_copy_words(BN_ULONG * out,const BIGNUM * in,int size)159 int bn_copy_words(BN_ULONG *out, const BIGNUM *in, int size)
160 {
161 if (in->top > size)
162 return 0;
163
164 memset(out, 0, sizeof(*out) * size);
165 if (in->d != NULL)
166 memcpy(out, in->d, sizeof(*out) * in->top);
167 return 1;
168 }
169
bn_get_words(const BIGNUM * a)170 BN_ULONG *bn_get_words(const BIGNUM *a)
171 {
172 return a->d;
173 }
174
bn_set_static_words(BIGNUM * a,const BN_ULONG * words,int size)175 void bn_set_static_words(BIGNUM *a, const BN_ULONG *words, int size)
176 {
177 /*
178 * |const| qualifier omission is compensated by BN_FLG_STATIC_DATA
179 * flag, which effectively means "read-only data".
180 */
181 a->d = (BN_ULONG *)words;
182 a->dmax = a->top = size;
183 a->neg = 0;
184 a->flags |= BN_FLG_STATIC_DATA;
185 bn_correct_top(a);
186 }
187
bn_set_words(BIGNUM * a,const BN_ULONG * words,int num_words)188 int bn_set_words(BIGNUM *a, const BN_ULONG *words, int num_words)
189 {
190 if (bn_wexpand(a, num_words) == NULL) {
191 ERR_raise(ERR_LIB_BN, ERR_R_MALLOC_FAILURE);
192 return 0;
193 }
194
195 memcpy(a->d, words, sizeof(BN_ULONG) * num_words);
196 a->top = num_words;
197 bn_correct_top(a);
198 return 1;
199 }
200