*

 *

 *

 *

 * The Original Code is the elliptic curve math library.

 *

 * 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>, Sun Microsystems Laboratories

 *

 *********************************************************************** */

/* Uses Montgomery reduction for field arithmetic.  See mpi/mpmontg.c for

 * code implementation. */

#include "mpi.h"

#include "mplogic.h"

#include "mpi-priv.h"

#include "ecl-priv.h"

#include "ecp.h"

#ifndef _KERNEL

#include <stdlib.h>

#include <stdio.h>

#endif

/* Construct a generic GFMethod for arithmetic over prime fields with

 * irreducible irr. */

GFMethod *

GFMethod_consGFp_mont(const mp_int *irr)

{

        mp_err res = MP_OKAY;

        int i;

        GFMethod *meth = NULL;

        mp_mont_modulus *mmm;

        meth = GFMethod_consGFp(irr);

        if (meth == NULL)

                return NULL;

#ifdef _KERNEL

        mmm = (mp_mont_modulus *) kmem_alloc(sizeof(mp_mont_modulus),

            FLAG(irr));

#else

        mmm = (mp_mont_modulus *) malloc(sizeof(mp_mont_modulus));

#endif

        if (mmm == NULL) {

                res = MP_MEM;

                goto CLEANUP;

        }

        meth->field_mul = &ec_GFp_mul_mont;

        meth->field_sqr = &ec_GFp_sqr_mont;

        meth->field_div = &ec_GFp_div_mont;

        meth->field_enc = &ec_GFp_enc_mont;

        meth->field_dec = &ec_GFp_dec_mont;

        meth->extra1 = mmm;

        meth->extra2 = NULL;

        meth->extra_free = &ec_GFp_extra_free_mont;

        mmm->N = meth->irr;

        i = mpl_significant_bits(&meth->irr);

        i += MP_DIGIT_BIT - 1;

        mmm->b = i - i % MP_DIGIT_BIT;

        mmm->n0prime = 0 - s_mp_invmod_radix(MP_DIGIT(&meth->irr, 0));

  CLEANUP:

        if (res != MP_OKAY) {

                GFMethod_free(meth);

                return NULL;

        }

        return meth;

}

/* Wrapper functions for generic prime field arithmetic. */

/* Field multiplication using Montgomery reduction. */

mp_err

ec_GFp_mul_mont(const mp_int *a, const mp_int *b, mp_int *r,

                                const GFMethod *meth)

{

        mp_err res = MP_OKAY;

#ifdef MP_MONT_USE_MP_MUL

        /* if MP_MONT_USE_MP_MUL is defined, then the function s_mp_mul_mont

         * is not implemented and we have to use mp_mul and s_mp_redc directly

         */

        MP_CHECKOK(mp_mul(a, b, r));

        MP_CHECKOK(s_mp_redc(r, (mp_mont_modulus *) meth->extra1));

#else

        mp_int s;

        MP_DIGITS(&s) = 0;

        /* s_mp_mul_mont doesn't allow source and destination to be the same */

        if ((a == r) || (b == r)) {

                MP_CHECKOK(mp_init(&s, FLAG(a)));

                MP_CHECKOK(s_mp_mul_mont

                                   (a, b, &s, (mp_mont_modulus *) meth->extra1));

                MP_CHECKOK(mp_copy(&s, r));

                mp_clear(&s);

        } else {

                return s_mp_mul_mont(a, b, r, (mp_mont_modulus *) meth->extra1);

        }

#endif

  CLEANUP:

        return res;

}

/* Field squaring using Montgomery reduction. */

mp_err

ec_GFp_sqr_mont(const mp_int *a, mp_int *r, const GFMethod *meth)

{

        return ec_GFp_mul_mont(a, a, r, meth);

}

/* Field division using Montgomery reduction. */

mp_err

ec_GFp_div_mont(const mp_int *a, const mp_int *b, mp_int *r,

                                const GFMethod *meth)

{

        mp_err res = MP_OKAY;

        /* if A=aZ represents a encoded in montgomery coordinates with Z and #

         * and \ respectively represent multiplication and division in

         * montgomery coordinates, then A\B = (a/b)Z = (A/B)Z and Binv =

         * (1/b)Z = (1/B)(Z^2) where B # Binv = Z */

        MP_CHECKOK(ec_GFp_div(a, b, r, meth));

        MP_CHECKOK(ec_GFp_enc_mont(r, r, meth));

        if (a == NULL) {

                MP_CHECKOK(ec_GFp_enc_mont(r, r, meth));

        }

  CLEANUP:

        return res;

}

/* Encode a field element in Montgomery form. See s_mp_to_mont in

 * mpi/mpmontg.c */

mp_err

ec_GFp_enc_mont(const mp_int *a, mp_int *r, const GFMethod *meth)

{

        mp_mont_modulus *mmm;

        mp_err res = MP_OKAY;

        mmm = (mp_mont_modulus *) meth->extra1;

        MP_CHECKOK(mpl_lsh(a, r, mmm->b));

        MP_CHECKOK(mp_mod(r, &mmm->N, r));

  CLEANUP:

        return res;

}

/* Decode a field element from Montgomery form. */

mp_err

ec_GFp_dec_mont(const mp_int *a, mp_int *r, const GFMethod *meth)

{

        mp_err res = MP_OKAY;

        if (a != r) {

                MP_CHECKOK(mp_copy(a, r));

        }

        MP_CHECKOK(s_mp_redc(r, (mp_mont_modulus *) meth->extra1));

  CLEANUP:

        return res;

}

/* Free the memory allocated to the extra fields of Montgomery GFMethod

 * object. */

void

ec_GFp_extra_free_mont(GFMethod *meth)

{

        if (meth->extra1 != NULL) {

#ifdef _KERNEL

                kmem_free(meth->extra1, sizeof(mp_mont_modulus));

#else

                free(meth->extra1);

#endif

                meth->extra1 = NULL;

        }

}