/* $OpenBSD: bn_exp2.c,v 1.13 2022/02/07 19:49:56 tb Exp $ */

/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)

 * All rights reserved.

 *

 * This package is an SSL implementation written

 * by Eric Young (eay@cryptsoft.com).

 * The implementation was written so as to conform with Netscapes SSL.

 *

 * This library is free for commercial and non-commercial use as long as

 * the following conditions are aheared to.  The following conditions

 * apply to all code found in this distribution, be it the RC4, RSA,

 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation

 * included with this distribution is covered by the same copyright terms

 * except that the holder is Tim Hudson (tjh@cryptsoft.com).

 *

 * Copyright remains Eric Young's, and as such any Copyright notices in

 * the code are not to be removed.

 * If this package is used in a product, Eric Young should be given attribution

 * as the author of the parts of the library used.

 * This can be in the form of a textual message at program startup or

 * in documentation (online or textual) provided with the package.

 *

 * 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 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 acknowledgement:

 *    "This product includes cryptographic software written by

 *     Eric Young (eay@cryptsoft.com)"

 *    The word 'cryptographic' can be left out if the rouines from the library

 *    being used are not cryptographic related :-).

 * 4. If you include any Windows specific code (or a derivative thereof) from

 *    the apps directory (application code) you must include an acknowledgement:

 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"

 *

 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND

 * ANY EXPRESS 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 AUTHOR OR 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.

 *

 * The licence and distribution terms for any publically available version or

 * derivative of this code cannot be changed.  i.e. this code cannot simply be

 * copied and put under another distribution licence

 * [including the GNU Public Licence.]

 */

/* ====================================================================

 * Copyright (c) 1998-2000 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 <stdio.h>

#include <openssl/err.h>

#include "bn_lcl.h"

#define TABLE_SIZE  32

int

BN_mod_exp2_mont(BIGNUM *rr, const BIGNUM *a1, const BIGNUM *p1,

    const BIGNUM *a2, const BIGNUM *p2, const BIGNUM *m, BN_CTX *ctx,

    BN_MONT_CTX *in_mont)

{

  int i, j, bits, b, bits1, bits2, ret = 0, wpos1, wpos2, window1, window2, wvalue1, wvalue2;

  int r_is_one = 1;

  BIGNUM *d, *r;

  const BIGNUM *a_mod_m;

  /* Tables of variables obtained from 'ctx' */

  BIGNUM *val1[TABLE_SIZE], *val2[TABLE_SIZE];

  BN_MONT_CTX *mont = NULL;

  bn_check_top(a1);

  bn_check_top(p1);

  bn_check_top(a2);

  bn_check_top(p2);

  bn_check_top(m);

  if (!BN_is_odd(m)) {

    BNerror(BN_R_CALLED_WITH_EVEN_MODULUS);

    return (0);

  }

  bits1 = BN_num_bits(p1);

  bits2 = BN_num_bits(p2);

  if ((bits1 == 0) && (bits2 == 0)) {

    ret = BN_one(rr);

    return ret;

  }

  bits = (bits1 > bits2) ? bits1 : bits2;

  BN_CTX_start(ctx);

  if ((d = BN_CTX_get(ctx)) == NULL)

    goto err;

  if ((r = BN_CTX_get(ctx)) == NULL)

    goto err;

  if ((val1[0] = BN_CTX_get(ctx)) == NULL)

    goto err;

  if ((val2[0] = BN_CTX_get(ctx)) == NULL)

    goto err;

  if (in_mont != NULL)

    mont = in_mont;

  else {

    if ((mont = BN_MONT_CTX_new()) == NULL)

      goto err;

    if (!BN_MONT_CTX_set(mont, m, ctx))

      goto err;

  }

  window1 = BN_window_bits_for_exponent_size(bits1);

  window2 = BN_window_bits_for_exponent_size(bits2);

  /*

   * Build table for a1:   val1[i] := a1^(2*i + 1) mod m  for i = 0 .. 2^(window1-1)

   */

  if (a1->neg || BN_ucmp(a1, m) >= 0) {

    if (!BN_mod_ct(val1[0], a1, m, ctx))

      goto err;

    a_mod_m = val1[0];

  } else

    a_mod_m = a1;

  if (BN_is_zero(a_mod_m)) {

    BN_zero(rr);

    ret = 1;

    goto err;

  }

  if (!BN_to_montgomery(val1[0], a_mod_m, mont, ctx))

    goto err;

  if (window1 > 1) {

    if (!BN_mod_mul_montgomery(d, val1[0], val1[0], mont, ctx))

      goto err;

    j = 1 << (window1 - 1);

    for (i = 1; i < j; i++) {

      if (((val1[i] = BN_CTX_get(ctx)) == NULL) ||

          !BN_mod_mul_montgomery(val1[i], val1[i - 1],

          d, mont, ctx))

        goto err;

    }

  }

  /*

   * Build table for a2:   val2[i] := a2^(2*i + 1) mod m  for i = 0 .. 2^(window2-1)

   */

  if (a2->neg || BN_ucmp(a2, m) >= 0) {

    if (!BN_mod_ct(val2[0], a2, m, ctx))

      goto err;

    a_mod_m = val2[0];

  } else

    a_mod_m = a2;

  if (BN_is_zero(a_mod_m)) {

    BN_zero(rr);

    ret = 1;

    goto err;

  }

  if (!BN_to_montgomery(val2[0], a_mod_m, mont, ctx))

    goto err;

  if (window2 > 1) {

    if (!BN_mod_mul_montgomery(d, val2[0], val2[0], mont, ctx))

      goto err;

    j = 1 << (window2 - 1);

    for (i = 1; i < j; i++) {

      if (((val2[i] = BN_CTX_get(ctx)) == NULL) ||

          !BN_mod_mul_montgomery(val2[i], val2[i - 1],

          d, mont, ctx))

        goto err;

    }

  }

  /* Now compute the power product, using independent windows. */

  r_is_one = 1;

  wvalue1 = 0;  /* The 'value' of the first window */

  wvalue2 = 0;  /* The 'value' of the second window */

  wpos1 = 0;    /* If wvalue1 > 0, the bottom bit of the first window */

  wpos2 = 0;    /* If wvalue2 > 0, the bottom bit of the second window */

  if (!BN_to_montgomery(r, BN_value_one(), mont, ctx))

    goto err;

  for (b = bits - 1; b >= 0; b--) {

    if (!r_is_one) {

      if (!BN_mod_mul_montgomery(r, r,r, mont, ctx))

        goto err;

    }

    if (!wvalue1)

      if (BN_is_bit_set(p1, b)) {

      /* consider bits b-window1+1 .. b for this window */

      i = b - window1 + 1;

      while (!BN_is_bit_set(p1, i)) /* works for i<0 */

        i++;

      wpos1 = i;

      wvalue1 = 1;

      for (i = b - 1; i >= wpos1; i--) {

        wvalue1 <<= 1;

        if (BN_is_bit_set(p1, i))

          wvalue1++;

      }

    }

    if (!wvalue2)

      if (BN_is_bit_set(p2, b)) {

      /* consider bits b-window2+1 .. b for this window */

      i = b - window2 + 1;

      while (!BN_is_bit_set(p2, i))

        i++;

      wpos2 = i;

      wvalue2 = 1;

      for (i = b - 1; i >= wpos2; i--) {

        wvalue2 <<= 1;

        if (BN_is_bit_set(p2, i))

          wvalue2++;

      }

    }

    if (wvalue1 && b == wpos1) {

      /* wvalue1 is odd and < 2^window1 */

      if (!BN_mod_mul_montgomery(r, r, val1[wvalue1 >> 1],

          mont, ctx))

        goto err;

      wvalue1 = 0;

      r_is_one = 0;

    }

    if (wvalue2 && b == wpos2) {

      /* wvalue2 is odd and < 2^window2 */

      if (!BN_mod_mul_montgomery(r, r, val2[wvalue2 >> 1],

          mont, ctx))

        goto err;

      wvalue2 = 0;

      r_is_one = 0;

    }

  }

  if (!BN_from_montgomery(rr, r,mont, ctx))

    goto err;

  ret = 1;

err:

  if ((in_mont == NULL) && (mont != NULL))

    BN_MONT_CTX_free(mont);

  BN_CTX_end(ctx);

  bn_check_top(rr);

  return (ret);

}