text: /* 
   * ***** BEGIN LICENSE BLOCK *****
   * Version: MPL 1.1/GPL 2.0/LGPL 2.1
   *
   * The contents of this file are subject to the Mozilla Public License Version
   * 1.1 (the "License"); you may not use this file except in compliance with
   * the License. You may obtain a copy of the License at
   * http://www.mozilla.org/MPL/
   *
   * Software distributed under the License is distributed on an "AS IS" basis,
   * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
   * for the specific language governing rights and limitations under the
   * License.
   *
   * The Original Code is the elliptic curve math library for prime field curves.
   *
   * The Initial Developer of the Original Code is
   * Sun Microsystems, Inc.
   * Portions created by the Initial Developer are Copyright (C) 2003
   * the Initial Developer. All Rights Reserved.
   *
   * Contributor(s):
   *   Douglas Stebila <douglas@stebila.ca>
   *
   * Alternatively, the contents of this file may be used under the terms of
   * either the GNU General Public License Version 2 or later (the "GPL"), or
   * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
   * in which case the provisions of the GPL or the LGPL are applicable instead
   * of those above. If you wish to allow use of your version of this file only
   * under the terms of either the GPL or the LGPL, and not to allow others to
   * use your version of this file under the terms of the MPL, indicate your
   * decision by deleting the provisions above and replace them with the notice
   * and other provisions required by the GPL or the LGPL. If you do not delete
   * the provisions above, a recipient may use your version of this file under
   * the terms of any one of the MPL, the GPL or the LGPL.
   *
   * ***** END LICENSE BLOCK ***** */
  /*
   * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
   * Use is subject to license terms.
   *
   * Sun elects to use this software under the MPL license.
   */
  
  #pragma ident	"%Z%%M%	%I%	%E% SMI"
  
  #include "ecp.h"
  #include "mpi.h"
  #include "mplogic.h"
  #include "mpi-priv.h"
  #ifndef _KERNEL
  #include <stdlib.h>
  #endif
  
  #define ECP521_DIGITS ECL_CURVE_DIGITS(521)
  
  /* Fast modular reduction for p521 = 2^521 - 1.  a can be r. Uses
   * algorithm 2.31 from Hankerson, Menezes, Vanstone. Guide to 
   * Elliptic Curve Cryptography. */
  mp_err
  ec_GFp_nistp521_mod(const mp_int *a, mp_int *r, const GFMethod *meth)
  {
  	mp_err res = MP_OKAY;
  	int a_bits = mpl_significant_bits(a);
  	int i;
  
  	/* m1, m2 are statically-allocated mp_int of exactly the size we need */
  	mp_int m1;
  
  	mp_digit s1[ECP521_DIGITS] = { 0 };
  
  	MP_SIGN(&m1) = MP_ZPOS;
  	MP_ALLOC(&m1) = ECP521_DIGITS;
  	MP_USED(&m1) = ECP521_DIGITS;
  	MP_DIGITS(&m1) = s1;
  
  	if (a_bits < 521) {
  		if (a==r) return MP_OKAY;
  		return mp_copy(a, r);
  	}
  	/* for polynomials larger than twice the field size or polynomials 
  	 * not using all words, use regular reduction */
  	if (a_bits > (521*2)) {
  		MP_CHECKOK(mp_mod(a, &meth->irr, r));
  	} else {
  #define FIRST_DIGIT (ECP521_DIGITS-1)
  		for (i = FIRST_DIGIT; i < MP_USED(a)-1; i++) {
  			s1[i-FIRST_DIGIT] = (MP_DIGIT(a, i) >> 9) 
  				| (MP_DIGIT(a, 1+i) << (MP_DIGIT_BIT-9));
  		}
  		s1[i-FIRST_DIGIT] = MP_DIGIT(a, i) >> 9;
  
  		if ( a != r ) {
  			MP_CHECKOK(s_mp_pad(r,ECP521_DIGITS));
  			for (i = 0; i < ECP521_DIGITS; i++) {
  				MP_DIGIT(r,i) = MP_DIGIT(a, i);
  			}
  		}
  		MP_USED(r) = ECP521_DIGITS;
  		MP_DIGIT(r,FIRST_DIGIT) &=  0x1FF;
  
  		MP_CHECKOK(s_mp_add(r, &m1));
  		if (MP_DIGIT(r, FIRST_DIGIT) & 0x200) {
  			MP_CHECKOK(s_mp_add_d(r,1));
  			MP_DIGIT(r,FIRST_DIGIT) &=  0x1FF;
  		}
  		s_mp_clamp(r);
  	}
  
    CLEANUP:
  	return res;
  }
  
  /* Compute the square of polynomial a, reduce modulo p521. Store the
   * result in r.  r could be a.  Uses optimized modular reduction for p521. 
   */
  mp_err
  ec_GFp_nistp521_sqr(const mp_int *a, mp_int *r, const GFMethod *meth)
  {
  	mp_err res = MP_OKAY;
  
  	MP_CHECKOK(mp_sqr(a, r));
  	MP_CHECKOK(ec_GFp_nistp521_mod(r, r, meth));
    CLEANUP:
  	return res;
  }
  
  /* Compute the product of two polynomials a and b, reduce modulo p521.
   * Store the result in r.  r could be a or b; a could be b.  Uses
   * optimized modular reduction for p521. */
  mp_err
  ec_GFp_nistp521_mul(const mp_int *a, const mp_int *b, mp_int *r,
  					const GFMethod *meth)
  {
  	mp_err res = MP_OKAY;
  
  	MP_CHECKOK(mp_mul(a, b, r));
  	MP_CHECKOK(ec_GFp_nistp521_mod(r, r, meth));
    CLEANUP:
  	return res;
  }
  
  /* Divides two field elements. If a is NULL, then returns the inverse of
   * b. */
  mp_err
  ec_GFp_nistp521_div(const mp_int *a, const mp_int *b, mp_int *r,
  		   const GFMethod *meth)
  {
  	mp_err res = MP_OKAY;
  	mp_int t;
  
  	/* If a is NULL, then return the inverse of b, otherwise return a/b. */
  	if (a == NULL) {
  		return mp_invmod(b, &meth->irr, r);
  	} else {
  		/* MPI doesn't support divmod, so we implement it using invmod and 
  		 * mulmod. */
  		MP_CHECKOK(mp_init(&t, FLAG(b)));
  		MP_CHECKOK(mp_invmod(b, &meth->irr, &t));
  		MP_CHECKOK(mp_mul(a, &t, r));
  		MP_CHECKOK(ec_GFp_nistp521_mod(r, r, meth));
  	  CLEANUP:
  		mp_clear(&t);
  		return res;
  	}
  }
  
  /* Wire in fast field arithmetic and precomputation of base point for
   * named curves. */
  mp_err
  ec_group_set_gfp521(ECGroup *group, ECCurveName name)
  {
  	if (name == ECCurve_NIST_P521) {
  		group->meth->field_mod = &ec_GFp_nistp521_mod;
  		group->meth->field_mul = &ec_GFp_nistp521_mul;
  		group->meth->field_sqr = &ec_GFp_nistp521_sqr;
  		group->meth->field_div = &ec_GFp_nistp521_div;
  	}
  	return MP_OKAY;
  }
  