1/*
2 * ***** BEGIN LICENSE BLOCK *****
3 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
4 *
5 * The contents of this file are subject to the Mozilla Public License Version
6 * 1.1 (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 * http://www.mozilla.org/MPL/
9 *
10 * Software distributed under the License is distributed on an "AS IS" basis,
11 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
12 * for the specific language governing rights and limitations under the
13 * License.
14 *
15 * The Original Code is the elliptic curve math library for prime field curves.
16 *
17 * The Initial Developer of the Original Code is
18 * Sun Microsystems, Inc.
19 * Portions created by the Initial Developer are Copyright (C) 2003
20 * the Initial Developer. All Rights Reserved.
21 *
22 * Contributor(s):
23 *   Douglas Stebila <douglas@stebila.ca>
24 *
25 * Alternatively, the contents of this file may be used under the terms of
26 * either the GNU General Public License Version 2 or later (the "GPL"), or
27 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
28 * in which case the provisions of the GPL or the LGPL are applicable instead
29 * of those above. If you wish to allow use of your version of this file only
30 * under the terms of either the GPL or the LGPL, and not to allow others to
31 * use your version of this file under the terms of the MPL, indicate your
32 * decision by deleting the provisions above and replace them with the notice
33 * and other provisions required by the GPL or the LGPL. If you do not delete
34 * the provisions above, a recipient may use your version of this file under
35 * the terms of any one of the MPL, the GPL or the LGPL.
36 *
37 * ***** END LICENSE BLOCK ***** */
38/*
39 * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
40 * Use is subject to license terms.
41 *
42 * Sun elects to use this software under the MPL license.
43 */
44
45#pragma ident	"%Z%%M%	%I%	%E% SMI"
46
47#include "ecp.h"
48#include "mpi.h"
49#include "mplogic.h"
50#include "mpi-priv.h"
51#ifndef _KERNEL
52#include <stdlib.h>
53#endif
54
55#define ECP521_DIGITS ECL_CURVE_DIGITS(521)
56
57/* Fast modular reduction for p521 = 2^521 - 1.  a can be r. Uses
58 * algorithm 2.31 from Hankerson, Menezes, Vanstone. Guide to
59 * Elliptic Curve Cryptography. */
60mp_err
61ec_GFp_nistp521_mod(const mp_int *a, mp_int *r, const GFMethod *meth)
62{
63	mp_err res = MP_OKAY;
64	int a_bits = mpl_significant_bits(a);
65	int i;
66
67	/* m1, m2 are statically-allocated mp_int of exactly the size we need */
68	mp_int m1;
69
70	mp_digit s1[ECP521_DIGITS] = { 0 };
71
72	MP_SIGN(&m1) = MP_ZPOS;
73	MP_ALLOC(&m1) = ECP521_DIGITS;
74	MP_USED(&m1) = ECP521_DIGITS;
75	MP_DIGITS(&m1) = s1;
76
77	if (a_bits < 521) {
78		if (a==r) return MP_OKAY;
79		return mp_copy(a, r);
80	}
81	/* for polynomials larger than twice the field size or polynomials
82	 * not using all words, use regular reduction */
83	if (a_bits > (521*2)) {
84		MP_CHECKOK(mp_mod(a, &meth->irr, r));
85	} else {
86#define FIRST_DIGIT (ECP521_DIGITS-1)
87		for (i = FIRST_DIGIT; i < MP_USED(a)-1; i++) {
88			s1[i-FIRST_DIGIT] = (MP_DIGIT(a, i) >> 9)
89				| (MP_DIGIT(a, 1+i) << (MP_DIGIT_BIT-9));
90		}
91		s1[i-FIRST_DIGIT] = MP_DIGIT(a, i) >> 9;
92
93		if ( a != r ) {
94			MP_CHECKOK(s_mp_pad(r,ECP521_DIGITS));
95			for (i = 0; i < ECP521_DIGITS; i++) {
96				MP_DIGIT(r,i) = MP_DIGIT(a, i);
97			}
98		}
99		MP_USED(r) = ECP521_DIGITS;
100		MP_DIGIT(r,FIRST_DIGIT) &=  0x1FF;
101
102		MP_CHECKOK(s_mp_add(r, &m1));
103		if (MP_DIGIT(r, FIRST_DIGIT) & 0x200) {
104			MP_CHECKOK(s_mp_add_d(r,1));
105			MP_DIGIT(r,FIRST_DIGIT) &=  0x1FF;
106		}
107		s_mp_clamp(r);
108	}
109
110  CLEANUP:
111	return res;
112}
113
114/* Compute the square of polynomial a, reduce modulo p521. Store the
115 * result in r.  r could be a.  Uses optimized modular reduction for p521.
116 */
117mp_err
118ec_GFp_nistp521_sqr(const mp_int *a, mp_int *r, const GFMethod *meth)
119{
120	mp_err res = MP_OKAY;
121
122	MP_CHECKOK(mp_sqr(a, r));
123	MP_CHECKOK(ec_GFp_nistp521_mod(r, r, meth));
124  CLEANUP:
125	return res;
126}
127
128/* Compute the product of two polynomials a and b, reduce modulo p521.
129 * Store the result in r.  r could be a or b; a could be b.  Uses
130 * optimized modular reduction for p521. */
131mp_err
132ec_GFp_nistp521_mul(const mp_int *a, const mp_int *b, mp_int *r,
133					const GFMethod *meth)
134{
135	mp_err res = MP_OKAY;
136
137	MP_CHECKOK(mp_mul(a, b, r));
138	MP_CHECKOK(ec_GFp_nistp521_mod(r, r, meth));
139  CLEANUP:
140	return res;
141}
142
143/* Divides two field elements. If a is NULL, then returns the inverse of
144 * b. */
145mp_err
146ec_GFp_nistp521_div(const mp_int *a, const mp_int *b, mp_int *r,
147		   const GFMethod *meth)
148{
149	mp_err res = MP_OKAY;
150	mp_int t;
151
152	/* If a is NULL, then return the inverse of b, otherwise return a/b. */
153	if (a == NULL) {
154		return mp_invmod(b, &meth->irr, r);
155	} else {
156		/* MPI doesn't support divmod, so we implement it using invmod and
157		 * mulmod. */
158		MP_CHECKOK(mp_init(&t, FLAG(b)));
159		MP_CHECKOK(mp_invmod(b, &meth->irr, &t));
160		MP_CHECKOK(mp_mul(a, &t, r));
161		MP_CHECKOK(ec_GFp_nistp521_mod(r, r, meth));
162	  CLEANUP:
163		mp_clear(&t);
164		return res;
165	}
166}
167
168/* Wire in fast field arithmetic and precomputation of base point for
169 * named curves. */
170mp_err
171ec_group_set_gfp521(ECGroup *group, ECCurveName name)
172{
173	if (name == ECCurve_NIST_P521) {
174		group->meth->field_mod = &ec_GFp_nistp521_mod;
175		group->meth->field_mul = &ec_GFp_nistp521_mul;
176		group->meth->field_sqr = &ec_GFp_nistp521_sqr;
177		group->meth->field_div = &ec_GFp_nistp521_div;
178	}
179	return MP_OKAY;
180}
181