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 */ 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 goto err; 34 r[0] = 0; 35 *ret_len = 1; 36 return r; 37 } 38 39 if (w <= 0 || w > 7) { /* 'signed char' can represent integers with 40 * absolute values less than 2^7 */ 41 ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR); 42 goto err; 43 } 44 bit = 1 << w; /* at most 128 */ 45 next_bit = bit << 1; /* at most 256 */ 46 mask = next_bit - 1; /* at most 255 */ 47 48 if (BN_is_negative(scalar)) { 49 sign = -1; 50 } 51 52 if (scalar->d == NULL || scalar->top == 0) { 53 ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR); 54 goto err; 55 } 56 57 len = BN_num_bits(scalar); 58 r = OPENSSL_malloc(len + 1); /* 59 * Modified wNAF may be one digit longer than binary representation 60 * (*ret_len will be set to the actual length, i.e. at most 61 * BN_num_bits(scalar) + 1) 62 */ 63 if (r == NULL) 64 goto err; 65 window_val = scalar->d[0] & mask; 66 j = 0; 67 while ((window_val != 0) || (j + w + 1 < len)) { /* if j+w+1 >= len, 68 * window_val will not 69 * increase */ 70 int digit = 0; 71 72 /* 0 <= window_val <= 2^(w+1) */ 73 74 if (window_val & 1) { 75 /* 0 < window_val < 2^(w+1) */ 76 77 if (window_val & bit) { 78 digit = window_val - next_bit; /* -2^w < digit < 0 */ 79 80 #if 1 /* modified wNAF */ 81 if (j + w + 1 >= len) { 82 /* 83 * Special case for generating modified wNAFs: 84 * no new bits will be added into window_val, 85 * so using a positive digit here will decrease 86 * the total length of the representation 87 */ 88 89 digit = window_val & (mask >> 1); /* 0 < digit < 2^w */ 90 } 91 #endif 92 } else { 93 digit = window_val; /* 0 < digit < 2^w */ 94 } 95 96 if (digit <= -bit || digit >= bit || !(digit & 1)) { 97 ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR); 98 goto err; 99 } 100 101 window_val -= digit; 102 103 /* 104 * now window_val is 0 or 2^(w+1) in standard wNAF generation; 105 * for modified window NAFs, it may also be 2^w 106 */ 107 if (window_val != 0 && window_val != next_bit 108 && window_val != bit) { 109 ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR); 110 goto err; 111 } 112 } 113 114 r[j++] = sign * digit; 115 116 window_val >>= 1; 117 window_val += bit * BN_is_bit_set(scalar, j + w); 118 119 if (window_val > next_bit) { 120 ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR); 121 goto err; 122 } 123 } 124 125 if (j > len + 1) { 126 ERR_raise(ERR_LIB_BN, ERR_R_INTERNAL_ERROR); 127 goto err; 128 } 129 *ret_len = j; 130 return r; 131 132 err: 133 OPENSSL_free(r); 134 return NULL; 135 } 136 137 int bn_get_top(const BIGNUM *a) 138 { 139 return a->top; 140 } 141 142 int bn_get_dmax(const BIGNUM *a) 143 { 144 return a->dmax; 145 } 146 147 void bn_set_all_zero(BIGNUM *a) 148 { 149 int i; 150 151 for (i = a->top; i < a->dmax; i++) 152 a->d[i] = 0; 153 } 154 155 int bn_copy_words(BN_ULONG *out, const BIGNUM *in, int size) 156 { 157 if (in->top > size) 158 return 0; 159 160 memset(out, 0, sizeof(*out) * size); 161 if (in->d != NULL) 162 memcpy(out, in->d, sizeof(*out) * in->top); 163 return 1; 164 } 165 166 BN_ULONG *bn_get_words(const BIGNUM *a) 167 { 168 return a->d; 169 } 170 171 void bn_set_static_words(BIGNUM *a, const BN_ULONG *words, int size) 172 { 173 /* 174 * |const| qualifier omission is compensated by BN_FLG_STATIC_DATA 175 * flag, which effectively means "read-only data". 176 */ 177 a->d = (BN_ULONG *)words; 178 a->dmax = a->top = size; 179 a->neg = 0; 180 a->flags |= BN_FLG_STATIC_DATA; 181 bn_correct_top(a); 182 } 183 184 int bn_set_words(BIGNUM *a, const BN_ULONG *words, int num_words) 185 { 186 if (bn_wexpand(a, num_words) == NULL) { 187 ERR_raise(ERR_LIB_BN, ERR_R_BN_LIB); 188 return 0; 189 } 190 191 memcpy(a->d, words, sizeof(BN_ULONG) * num_words); 192 a->top = num_words; 193 bn_correct_top(a); 194 return 1; 195 } 196