ec2_oct.c revision 392aa7cc7d2b122614c5393c3e357da07fd07af3 
1/* crypto/ec/ec2_oct.c */
2/* ====================================================================
3 * Copyright 2002 Sun Microsystems, Inc. ALL RIGHTS RESERVED.
4 *
5 * The Elliptic Curve Public-Key Crypto Library (ECC Code) included
6 * herein is developed by SUN MICROSYSTEMS, INC., and is contributed
7 * to the OpenSSL project.
8 *
9 * The ECC Code is licensed pursuant to the OpenSSL open source
10 * license provided below.
11 *
12 * The software is originally written by Sheueling Chang Shantz and
13 * Douglas Stebila of Sun Microsystems Laboratories.
14 *
15 */
16/* ====================================================================
17 * Copyright (c) 1998-2005 The OpenSSL Project.  All rights reserved.
18 *
19 * Redistribution and use in source and binary forms, with or without
20 * modification, are permitted provided that the following conditions
21 * are met:
22 *
23 * 1. Redistributions of source code must retain the above copyright
24 *    notice, this list of conditions and the following disclaimer.
25 *
26 * 2. Redistributions in binary form must reproduce the above copyright
27 *    notice, this list of conditions and the following disclaimer in
28 *    the documentation and/or other materials provided with the
29 *    distribution.
30 *
31 * 3. All advertising materials mentioning features or use of this
32 *    software must display the following acknowledgment:
33 *    "This product includes software developed by the OpenSSL Project
34 *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
35 *
36 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
37 *    endorse or promote products derived from this software without
38 *    prior written permission. For written permission, please contact
39 *    openssl-core@openssl.org.
40 *
41 * 5. Products derived from this software may not be called "OpenSSL"
42 *    nor may "OpenSSL" appear in their names without prior written
43 *    permission of the OpenSSL Project.
44 *
45 * 6. Redistributions of any form whatsoever must retain the following
46 *    acknowledgment:
47 *    "This product includes software developed by the OpenSSL Project
48 *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
49 *
50 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
51 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
52 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
53 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
54 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
55 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
56 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
57 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
58 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
59 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
60 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
61 * OF THE POSSIBILITY OF SUCH DAMAGE.
62 * ====================================================================
63 *
64 * This product includes cryptographic software written by Eric Young
65 * (eay@cryptsoft.com).  This product includes software written by Tim
66 * Hudson (tjh@cryptsoft.com).
67 *
68 */
69
70#include <openssl/err.h>
71
72#include "ec_lcl.h"
73
74#ifndef OPENSSL_NO_EC2M
75
76/* Calculates and sets the affine coordinates of an EC_POINT from the given
77 * compressed coordinates.  Uses algorithm 2.3.4 of SEC 1.
78 * Note that the simple implementation only uses affine coordinates.
79 *
80 * The method is from the following publication:
81 *
82 *     Harper, Menezes, Vanstone:
83 *     "Public-Key Cryptosystems with Very Small Key Lengths",
84 *     EUROCRYPT '92, Springer-Verlag LNCS 658,
85 *     published February 1993
86 *
87 * US Patents 6,141,420 and 6,618,483 (Vanstone, Mullin, Agnew) describe
88 * the same method, but claim no priority date earlier than July 29, 1994
89 * (and additionally fail to cite the EUROCRYPT '92 publication as prior art).
90 */
91int ec_GF2m_simple_set_compressed_coordinates(const EC_GROUP *group, EC_POINT *point,
92	const BIGNUM *x_, int y_bit, BN_CTX *ctx)
93	{
94	BN_CTX *new_ctx = NULL;
95	BIGNUM *tmp, *x, *y, *z;
96	int ret = 0, z0;
97
98	/* clear error queue */
99	ERR_clear_error();
100
101	if (ctx == NULL)
102		{
103		ctx = new_ctx = BN_CTX_new();
104		if (ctx == NULL)
105			return 0;
106		}
107
108	y_bit = (y_bit != 0) ? 1 : 0;
109
110	BN_CTX_start(ctx);
111	tmp = BN_CTX_get(ctx);
112	x = BN_CTX_get(ctx);
113	y = BN_CTX_get(ctx);
114	z = BN_CTX_get(ctx);
115	if (z == NULL) goto err;
116
117	if (!BN_GF2m_mod_arr(x, x_, group->poly)) goto err;
118	if (BN_is_zero(x))
119		{
120		if (!BN_GF2m_mod_sqrt_arr(y, &group->b, group->poly, ctx)) goto err;
121		}
122	else
123		{
124		if (!group->meth->field_sqr(group, tmp, x, ctx)) goto err;
125		if (!group->meth->field_div(group, tmp, &group->b, tmp, ctx)) goto err;
126		if (!BN_GF2m_add(tmp, &group->a, tmp)) goto err;
127		if (!BN_GF2m_add(tmp, x, tmp)) goto err;
128		if (!BN_GF2m_mod_solve_quad_arr(z, tmp, group->poly, ctx))
129			{
130			unsigned long err = ERR_peek_last_error();
131
132			if (ERR_GET_LIB(err) == ERR_LIB_BN && ERR_GET_REASON(err) == BN_R_NO_SOLUTION)
133				{
134				ERR_clear_error();
135				ECerr(EC_F_EC_GF2M_SIMPLE_SET_COMPRESSED_COORDINATES, EC_R_INVALID_COMPRESSED_POINT);
136				}
137			else
138				ECerr(EC_F_EC_GF2M_SIMPLE_SET_COMPRESSED_COORDINATES, ERR_R_BN_LIB);
139			goto err;
140			}
141		z0 = (BN_is_odd(z)) ? 1 : 0;
142		if (!group->meth->field_mul(group, y, x, z, ctx)) goto err;
143		if (z0 != y_bit)
144			{
145			if (!BN_GF2m_add(y, y, x)) goto err;
146			}
147		}
148
149	if (!EC_POINT_set_affine_coordinates_GF2m(group, point, x, y, ctx)) goto err;
150
151	ret = 1;
152
153 err:
154	BN_CTX_end(ctx);
155	if (new_ctx != NULL)
156		BN_CTX_free(new_ctx);
157	return ret;
158	}
159
160
161/* Converts an EC_POINT to an octet string.
162 * If buf is NULL, the encoded length will be returned.
163 * If the length len of buf is smaller than required an error will be returned.
164 */
165size_t ec_GF2m_simple_point2oct(const EC_GROUP *group, const EC_POINT *point, point_conversion_form_t form,
166	unsigned char *buf, size_t len, BN_CTX *ctx)
167	{
168	size_t ret;
169	BN_CTX *new_ctx = NULL;
170	int used_ctx = 0;
171	BIGNUM *x, *y, *yxi;
172	size_t field_len, i, skip;
173
174	if ((form != POINT_CONVERSION_COMPRESSED)
175		&& (form != POINT_CONVERSION_UNCOMPRESSED)
176		&& (form != POINT_CONVERSION_HYBRID))
177		{
178		ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_INVALID_FORM);
179		goto err;
180		}
181
182	if (EC_POINT_is_at_infinity(group, point))
183		{
184		/* encodes to a single 0 octet */
185		if (buf != NULL)
186			{
187			if (len < 1)
188				{
189				ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_BUFFER_TOO_SMALL);
190				return 0;
191				}
192			buf[0] = 0;
193			}
194		return 1;
195		}
196
197
198	/* ret := required output buffer length */
199	field_len = (EC_GROUP_get_degree(group) + 7) / 8;
200	ret = (form == POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2*field_len;
201
202	/* if 'buf' is NULL, just return required length */
203	if (buf != NULL)
204		{
205		if (len < ret)
206			{
207			ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, EC_R_BUFFER_TOO_SMALL);
208			goto err;
209			}
210
211		if (ctx == NULL)
212			{
213			ctx = new_ctx = BN_CTX_new();
214			if (ctx == NULL)
215				return 0;
216			}
217
218		BN_CTX_start(ctx);
219		used_ctx = 1;
220		x = BN_CTX_get(ctx);
221		y = BN_CTX_get(ctx);
222		yxi = BN_CTX_get(ctx);
223		if (yxi == NULL) goto err;
224
225		if (!EC_POINT_get_affine_coordinates_GF2m(group, point, x, y, ctx)) goto err;
226
227		buf[0] = form;
228		if ((form != POINT_CONVERSION_UNCOMPRESSED) && !BN_is_zero(x))
229			{
230			if (!group->meth->field_div(group, yxi, y, x, ctx)) goto err;
231			if (BN_is_odd(yxi)) buf[0]++;
232			}
233
234		i = 1;
235
236		skip = field_len - BN_num_bytes(x);
237		if (skip > field_len)
238			{
239			ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
240			goto err;
241			}
242		while (skip > 0)
243			{
244			buf[i++] = 0;
245			skip--;
246			}
247		skip = BN_bn2bin(x, buf + i);
248		i += skip;
249		if (i != 1 + field_len)
250			{
251			ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
252			goto err;
253			}
254
255		if (form == POINT_CONVERSION_UNCOMPRESSED || form == POINT_CONVERSION_HYBRID)
256			{
257			skip = field_len - BN_num_bytes(y);
258			if (skip > field_len)
259				{
260				ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
261				goto err;
262				}
263			while (skip > 0)
264				{
265				buf[i++] = 0;
266				skip--;
267				}
268			skip = BN_bn2bin(y, buf + i);
269			i += skip;
270			}
271
272		if (i != ret)
273			{
274			ECerr(EC_F_EC_GF2M_SIMPLE_POINT2OCT, ERR_R_INTERNAL_ERROR);
275			goto err;
276			}
277		}
278
279	if (used_ctx)
280		BN_CTX_end(ctx);
281	if (new_ctx != NULL)
282		BN_CTX_free(new_ctx);
283	return ret;
284
285 err:
286	if (used_ctx)
287		BN_CTX_end(ctx);
288	if (new_ctx != NULL)
289		BN_CTX_free(new_ctx);
290	return 0;
291	}
292
293
294/* Converts an octet string representation to an EC_POINT.
295 * Note that the simple implementation only uses affine coordinates.
296 */
297int ec_GF2m_simple_oct2point(const EC_GROUP *group, EC_POINT *point,
298	const unsigned char *buf, size_t len, BN_CTX *ctx)
299	{
300	point_conversion_form_t form;
301	int y_bit;
302	BN_CTX *new_ctx = NULL;
303	BIGNUM *x, *y, *yxi;
304	size_t field_len, enc_len;
305	int ret = 0;
306
307	if (len == 0)
308		{
309		ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_BUFFER_TOO_SMALL);
310		return 0;
311		}
312	form = buf[0];
313	y_bit = form & 1;
314	form = form & ~1U;
315	if ((form != 0)	&& (form != POINT_CONVERSION_COMPRESSED)
316		&& (form != POINT_CONVERSION_UNCOMPRESSED)
317		&& (form != POINT_CONVERSION_HYBRID))
318		{
319		ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
320		return 0;
321		}
322	if ((form == 0 || form == POINT_CONVERSION_UNCOMPRESSED) && y_bit)
323		{
324		ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
325		return 0;
326		}
327
328	if (form == 0)
329		{
330		if (len != 1)
331			{
332			ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
333			return 0;
334			}
335
336		return EC_POINT_set_to_infinity(group, point);
337		}
338
339	field_len = (EC_GROUP_get_degree(group) + 7) / 8;
340	enc_len = (form == POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2*field_len;
341
342	if (len != enc_len)
343		{
344		ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
345		return 0;
346		}
347
348	if (ctx == NULL)
349		{
350		ctx = new_ctx = BN_CTX_new();
351		if (ctx == NULL)
352			return 0;
353		}
354
355	BN_CTX_start(ctx);
356	x = BN_CTX_get(ctx);
357	y = BN_CTX_get(ctx);
358	yxi = BN_CTX_get(ctx);
359	if (yxi == NULL) goto err;
360
361	if (!BN_bin2bn(buf + 1, field_len, x)) goto err;
362	if (BN_ucmp(x, &group->field) >= 0)
363		{
364		ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
365		goto err;
366		}
367
368	if (form == POINT_CONVERSION_COMPRESSED)
369		{
370		if (!EC_POINT_set_compressed_coordinates_GF2m(group, point, x, y_bit, ctx)) goto err;
371		}
372	else
373		{
374		if (!BN_bin2bn(buf + 1 + field_len, field_len, y)) goto err;
375		if (BN_ucmp(y, &group->field) >= 0)
376			{
377			ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
378			goto err;
379			}
380		if (form == POINT_CONVERSION_HYBRID)
381			{
382			if (!group->meth->field_div(group, yxi, y, x, ctx)) goto err;
383			if (y_bit != BN_is_odd(yxi))
384				{
385				ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_INVALID_ENCODING);
386				goto err;
387				}
388			}
389
390		if (!EC_POINT_set_affine_coordinates_GF2m(group, point, x, y, ctx)) goto err;
391		}
392
393	if (!EC_POINT_is_on_curve(group, point, ctx)) /* test required by X9.62 */
394		{
395		ECerr(EC_F_EC_GF2M_SIMPLE_OCT2POINT, EC_R_POINT_IS_NOT_ON_CURVE);
396		goto err;
397		}
398
399	ret = 1;
400
401 err:
402	BN_CTX_end(ctx);
403	if (new_ctx != NULL)
404		BN_CTX_free(new_ctx);
405	return ret;
406	}
407#endif
408