openssl/crypto/bn/bn_intern.c

/* ====================================================================
 * Copyright (c) 1998-2014 The OpenSSL Project.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. All advertising materials mentioning features or use of this
 *    software must display the following acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
 *
 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
 *    endorse or promote products derived from this software without
 *    prior written permission. For written permission, please contact
 *    openssl-core@openssl.org.
 *
 * 5. Products derived from this software may not be called "OpenSSL"
 *    nor may "OpenSSL" appear in their names without prior written
 *    permission of the OpenSSL Project.
 *
 * 6. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by the OpenSSL Project
 *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
 *
 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 * ====================================================================
 *
 * This product includes cryptographic software written by Eric Young
 * (eay@cryptsoft.com).  This product includes software written by Tim
 * Hudson (tjh@cryptsoft.com).
 *
 */

#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) {
            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;
}

void bn_set_top(BIGNUM *a, int top)
{
    a->top = 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);
    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, BN_ULONG *words, int size)
{
    a->d = 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, 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;
}

size_t bn_sizeof_BIGNUM(void)
{
    return sizeof(BIGNUM);
}

BIGNUM *bn_array_el(BIGNUM *base, int el)
{
    return &base[el];
}