text: // SPDX-License-Identifier: BSD-2-Clause
  /*
   * Copyright (c) 2001-2007, Tom St Denis
   * 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.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 COPYRIGHT HOLDER 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.
   */
  
  /* LibTomCrypt, modular cryptographic library -- Tom St Denis
   *
   * LibTomCrypt is a library that provides various cryptographic
   * algorithms in a highly modular and flexible manner.
   *
   * The library is free for all purposes without any express
   * guarantee it works.
   *
   * Tom St Denis, tomstdenis@gmail.com, http://libtom.org
   */
  
  /* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b
   *
   * All curves taken from NIST recommendation paper of July 1999
   * Available at http://csrc.nist.gov/cryptval/dss.htm
   */
  #include "tomcrypt.h"
  
  /**
    @file ltc_ecc_map.c
    ECC Crypto, Tom St Denis
  */  
  
  #ifdef LTC_MECC
  
  /**
    Map a projective jacbobian point back to affine space
    @param P        [in/out] The point to map
    @param modulus  The modulus of the field the ECC curve is in
    @param mp       The "b" value from montgomery_setup()
    @return CRYPT_OK on success
  */
  int ltc_ecc_map(ecc_point *P, void *modulus, void *mp)
  {
     void *t1, *t2;
     int   err;
  
     LTC_ARGCHK(P       != NULL);
     LTC_ARGCHK(modulus != NULL);
     LTC_ARGCHK(mp      != NULL);
  
     if ((err = mp_init_multi(&t1, &t2, NULL)) != CRYPT_OK) {
        return CRYPT_MEM;
     }
  
     /* first map z back to normal */
     if ((err = mp_montgomery_reduce(P->z, modulus, mp)) != CRYPT_OK)           { goto done; }
  
     /* get 1/z */
     if ((err = mp_invmod(P->z, modulus, t1)) != CRYPT_OK)                      { goto done; }
   
     /* get 1/z^2 and 1/z^3 */
     if ((err = mp_sqr(t1, t2)) != CRYPT_OK)                                    { goto done; }
     if ((err = mp_mod(t2, modulus, t2)) != CRYPT_OK)                           { goto done; }
     if ((err = mp_mul(t1, t2, t1)) != CRYPT_OK)                                { goto done; }
     if ((err = mp_mod(t1, modulus, t1)) != CRYPT_OK)                           { goto done; }
  
     /* multiply against x/y */
     if ((err = mp_mul(P->x, t2, P->x)) != CRYPT_OK)                            { goto done; }
     if ((err = mp_montgomery_reduce(P->x, modulus, mp)) != CRYPT_OK)           { goto done; }
     if ((err = mp_mul(P->y, t1, P->y)) != CRYPT_OK)                            { goto done; }
     if ((err = mp_montgomery_reduce(P->y, modulus, mp)) != CRYPT_OK)           { goto done; }
     if ((err = mp_set(P->z, 1)) != CRYPT_OK)                                   { goto done; }
  
     err = CRYPT_OK;
  done:
     mp_clear_multi(t1, t2, NULL);
     return err;
  }
  
  #endif
  
  /* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ltc_ecc_map.c,v $ */
  /* $Revision: 1.7 $ */
  /* $Date: 2007/05/12 14:32:35 $ */
  