michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: /* Uses Montgomery reduction for field arithmetic.  See mpi/mpmontg.c for
michael@0:  * code implementation. */
michael@0: 
michael@0: #include "mpi.h"
michael@0: #include "mplogic.h"
michael@0: #include "mpi-priv.h"
michael@0: #include "ecl-priv.h"
michael@0: #include "ecp.h"
michael@0: #include <stdlib.h>
michael@0: #include <stdio.h>
michael@0: 
michael@0: /* Construct a generic GFMethod for arithmetic over prime fields with
michael@0:  * irreducible irr. */
michael@0: GFMethod *
michael@0: GFMethod_consGFp_mont(const mp_int *irr)
michael@0: {
michael@0: 	mp_err res = MP_OKAY;
michael@0: 	GFMethod *meth = NULL;
michael@0: 	mp_mont_modulus *mmm;
michael@0: 
michael@0: 	meth = GFMethod_consGFp(irr);
michael@0: 	if (meth == NULL)
michael@0: 		return NULL;
michael@0: 
michael@0: 	mmm = (mp_mont_modulus *) malloc(sizeof(mp_mont_modulus));
michael@0: 	if (mmm == NULL) {
michael@0: 		res = MP_MEM;
michael@0: 		goto CLEANUP;
michael@0: 	}
michael@0: 
michael@0: 	meth->field_mul = &ec_GFp_mul_mont;
michael@0: 	meth->field_sqr = &ec_GFp_sqr_mont;
michael@0: 	meth->field_div = &ec_GFp_div_mont;
michael@0: 	meth->field_enc = &ec_GFp_enc_mont;
michael@0: 	meth->field_dec = &ec_GFp_dec_mont;
michael@0: 	meth->extra1 = mmm;
michael@0: 	meth->extra2 = NULL;
michael@0: 	meth->extra_free = &ec_GFp_extra_free_mont;
michael@0: 
michael@0: 	mmm->N = meth->irr;
michael@0: 	mmm->n0prime = 0 - s_mp_invmod_radix(MP_DIGIT(&meth->irr, 0));
michael@0: 
michael@0:   CLEANUP:
michael@0: 	if (res != MP_OKAY) {
michael@0: 		GFMethod_free(meth);
michael@0: 		return NULL;
michael@0: 	}
michael@0: 	return meth;
michael@0: }
michael@0: 
michael@0: /* Wrapper functions for generic prime field arithmetic. */
michael@0: 
michael@0: /* Field multiplication using Montgomery reduction. */
michael@0: mp_err
michael@0: ec_GFp_mul_mont(const mp_int *a, const mp_int *b, mp_int *r,
michael@0: 				const GFMethod *meth)
michael@0: {
michael@0: 	mp_err res = MP_OKAY;
michael@0: 
michael@0: #ifdef MP_MONT_USE_MP_MUL
michael@0: 	/* if MP_MONT_USE_MP_MUL is defined, then the function s_mp_mul_mont
michael@0: 	 * is not implemented and we have to use mp_mul and s_mp_redc directly 
michael@0: 	 */
michael@0: 	MP_CHECKOK(mp_mul(a, b, r));
michael@0: 	MP_CHECKOK(s_mp_redc(r, (mp_mont_modulus *) meth->extra1));
michael@0: #else
michael@0: 	mp_int s;
michael@0: 
michael@0: 	MP_DIGITS(&s) = 0;
michael@0: 	/* s_mp_mul_mont doesn't allow source and destination to be the same */
michael@0: 	if ((a == r) || (b == r)) {
michael@0: 		MP_CHECKOK(mp_init(&s));
michael@0: 		MP_CHECKOK(s_mp_mul_mont
michael@0: 				   (a, b, &s, (mp_mont_modulus *) meth->extra1));
michael@0: 		MP_CHECKOK(mp_copy(&s, r));
michael@0: 		mp_clear(&s);
michael@0: 	} else {
michael@0: 		return s_mp_mul_mont(a, b, r, (mp_mont_modulus *) meth->extra1);
michael@0: 	}
michael@0: #endif
michael@0:   CLEANUP:
michael@0: 	return res;
michael@0: }
michael@0: 
michael@0: /* Field squaring using Montgomery reduction. */
michael@0: mp_err
michael@0: ec_GFp_sqr_mont(const mp_int *a, mp_int *r, const GFMethod *meth)
michael@0: {
michael@0: 	return ec_GFp_mul_mont(a, a, r, meth);
michael@0: }
michael@0: 
michael@0: /* Field division using Montgomery reduction. */
michael@0: mp_err
michael@0: ec_GFp_div_mont(const mp_int *a, const mp_int *b, mp_int *r,
michael@0: 				const GFMethod *meth)
michael@0: {
michael@0: 	mp_err res = MP_OKAY;
michael@0: 
michael@0: 	/* if A=aZ represents a encoded in montgomery coordinates with Z and # 
michael@0: 	 * and \ respectively represent multiplication and division in
michael@0: 	 * montgomery coordinates, then A\B = (a/b)Z = (A/B)Z and Binv =
michael@0: 	 * (1/b)Z = (1/B)(Z^2) where B # Binv = Z */
michael@0: 	MP_CHECKOK(ec_GFp_div(a, b, r, meth));
michael@0: 	MP_CHECKOK(ec_GFp_enc_mont(r, r, meth));
michael@0: 	if (a == NULL) {
michael@0: 		MP_CHECKOK(ec_GFp_enc_mont(r, r, meth));
michael@0: 	}
michael@0:   CLEANUP:
michael@0: 	return res;
michael@0: }
michael@0: 
michael@0: /* Encode a field element in Montgomery form. See s_mp_to_mont in
michael@0:  * mpi/mpmontg.c */
michael@0: mp_err
michael@0: ec_GFp_enc_mont(const mp_int *a, mp_int *r, const GFMethod *meth)
michael@0: {
michael@0: 	mp_mont_modulus *mmm;
michael@0: 	mp_err res = MP_OKAY;
michael@0: 
michael@0: 	mmm = (mp_mont_modulus *) meth->extra1;
michael@0: 	MP_CHECKOK(mp_copy(a, r));
michael@0: 	MP_CHECKOK(s_mp_lshd(r, MP_USED(&mmm->N)));
michael@0: 	MP_CHECKOK(mp_mod(r, &mmm->N, r));
michael@0:   CLEANUP:
michael@0: 	return res;
michael@0: }
michael@0: 
michael@0: /* Decode a field element from Montgomery form. */
michael@0: mp_err
michael@0: ec_GFp_dec_mont(const mp_int *a, mp_int *r, const GFMethod *meth)
michael@0: {
michael@0: 	mp_err res = MP_OKAY;
michael@0: 
michael@0: 	if (a != r) {
michael@0: 		MP_CHECKOK(mp_copy(a, r));
michael@0: 	}
michael@0: 	MP_CHECKOK(s_mp_redc(r, (mp_mont_modulus *) meth->extra1));
michael@0:   CLEANUP:
michael@0: 	return res;
michael@0: }
michael@0: 
michael@0: /* Free the memory allocated to the extra fields of Montgomery GFMethod
michael@0:  * object. */
michael@0: void
michael@0: ec_GFp_extra_free_mont(GFMethod *meth)
michael@0: {
michael@0: 	if (meth->extra1 != NULL) {
michael@0: 		free(meth->extra1);
michael@0: 		meth->extra1 = NULL;
michael@0: 	}
michael@0: }