ecp_oct.c revision 1.19 
1/* $OpenBSD: ecp_oct.c,v 1.19 2022/11/26 16:08:52 tb Exp $ */
2/* Includes code written by Lenka Fibikova <fibikova@exp-math.uni-essen.de>
3 * for the OpenSSL project.
4 * Includes code written by Bodo Moeller for the OpenSSL project.
5*/
6/* ====================================================================
7 * Copyright (c) 1998-2002 The OpenSSL Project.  All rights reserved.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 *
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 *
16 * 2. Redistributions in binary form must reproduce the above copyright
17 *    notice, this list of conditions and the following disclaimer in
18 *    the documentation and/or other materials provided with the
19 *    distribution.
20 *
21 * 3. All advertising materials mentioning features or use of this
22 *    software must display the following acknowledgment:
23 *    "This product includes software developed by the OpenSSL Project
24 *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
25 *
26 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
27 *    endorse or promote products derived from this software without
28 *    prior written permission. For written permission, please contact
29 *    openssl-core@openssl.org.
30 *
31 * 5. Products derived from this software may not be called "OpenSSL"
32 *    nor may "OpenSSL" appear in their names without prior written
33 *    permission of the OpenSSL Project.
34 *
35 * 6. Redistributions of any form whatsoever must retain the following
36 *    acknowledgment:
37 *    "This product includes software developed by the OpenSSL Project
38 *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
39 *
40 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
41 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
42 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
43 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
44 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
45 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
46 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
47 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
48 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
49 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
50 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
51 * OF THE POSSIBILITY OF SUCH DAMAGE.
52 * ====================================================================
53 *
54 * This product includes cryptographic software written by Eric Young
55 * (eay@cryptsoft.com).  This product includes software written by Tim
56 * Hudson (tjh@cryptsoft.com).
57 *
58 */
59/* ====================================================================
60 * Copyright 2002 Sun Microsystems, Inc. ALL RIGHTS RESERVED.
61 * Portions of this software developed by SUN MICROSYSTEMS, INC.,
62 * and contributed to the OpenSSL project.
63 */
64
65#include <openssl/err.h>
66
67#include "ec_local.h"
68
69int
70ec_GFp_simple_set_compressed_coordinates(const EC_GROUP *group,
71    EC_POINT *point, const BIGNUM *x_, int y_bit, BN_CTX *ctx)
72{
73	BN_CTX *new_ctx = NULL;
74	BIGNUM *tmp1, *tmp2, *x, *y;
75	int ret = 0;
76
77	/* clear error queue */
78	ERR_clear_error();
79
80	if (ctx == NULL) {
81		ctx = new_ctx = BN_CTX_new();
82		if (ctx == NULL)
83			return 0;
84	}
85	y_bit = (y_bit != 0);
86
87	BN_CTX_start(ctx);
88	if ((tmp1 = BN_CTX_get(ctx)) == NULL)
89		goto err;
90	if ((tmp2 = BN_CTX_get(ctx)) == NULL)
91		goto err;
92	if ((x = BN_CTX_get(ctx)) == NULL)
93		goto err;
94	if ((y = BN_CTX_get(ctx)) == NULL)
95		goto err;
96
97	/*
98	 * Recover y.  We have a Weierstrass equation y^2 = x^3 + a*x + b, so
99	 * y  is one of the square roots of  x^3 + a*x + b.
100	 */
101
102	/* tmp1 := x^3 */
103	if (!BN_nnmod(x, x_, &group->field, ctx))
104		goto err;
105	if (group->meth->field_decode == 0) {
106		/* field_{sqr,mul} work on standard representation */
107		if (!group->meth->field_sqr(group, tmp2, x_, ctx))
108			goto err;
109		if (!group->meth->field_mul(group, tmp1, tmp2, x_, ctx))
110			goto err;
111	} else {
112		if (!BN_mod_sqr(tmp2, x_, &group->field, ctx))
113			goto err;
114		if (!BN_mod_mul(tmp1, tmp2, x_, &group->field, ctx))
115			goto err;
116	}
117
118	/* tmp1 := tmp1 + a*x */
119	if (group->a_is_minus3) {
120		if (!BN_mod_lshift1_quick(tmp2, x, &group->field))
121			goto err;
122		if (!BN_mod_add_quick(tmp2, tmp2, x, &group->field))
123			goto err;
124		if (!BN_mod_sub_quick(tmp1, tmp1, tmp2, &group->field))
125			goto err;
126	} else {
127		if (group->meth->field_decode) {
128			if (!group->meth->field_decode(group, tmp2, &group->a, ctx))
129				goto err;
130			if (!BN_mod_mul(tmp2, tmp2, x, &group->field, ctx))
131				goto err;
132		} else {
133			/* field_mul works on standard representation */
134			if (!group->meth->field_mul(group, tmp2, &group->a, x, ctx))
135				goto err;
136		}
137
138		if (!BN_mod_add_quick(tmp1, tmp1, tmp2, &group->field))
139			goto err;
140	}
141
142	/* tmp1 := tmp1 + b */
143	if (group->meth->field_decode) {
144		if (!group->meth->field_decode(group, tmp2, &group->b, ctx))
145			goto err;
146		if (!BN_mod_add_quick(tmp1, tmp1, tmp2, &group->field))
147			goto err;
148	} else {
149		if (!BN_mod_add_quick(tmp1, tmp1, &group->b, &group->field))
150			goto err;
151	}
152
153	if (!BN_mod_sqrt(y, tmp1, &group->field, ctx)) {
154		unsigned long err = ERR_peek_last_error();
155
156		if (ERR_GET_LIB(err) == ERR_LIB_BN && ERR_GET_REASON(err) == BN_R_NOT_A_SQUARE) {
157			ERR_clear_error();
158			ECerror(EC_R_INVALID_COMPRESSED_POINT);
159		} else
160			ECerror(ERR_R_BN_LIB);
161		goto err;
162	}
163	if (y_bit != BN_is_odd(y)) {
164		if (BN_is_zero(y)) {
165			ECerror(EC_R_INVALID_COMPRESSION_BIT);
166			goto err;
167		}
168		if (!BN_usub(y, &group->field, y))
169			goto err;
170		if (y_bit != BN_is_odd(y)) {
171			ECerror(ERR_R_INTERNAL_ERROR);
172			goto err;
173		}
174	}
175	if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
176		goto err;
177
178	ret = 1;
179
180 err:
181	BN_CTX_end(ctx);
182	BN_CTX_free(new_ctx);
183	return ret;
184}
185
186
187size_t
188ec_GFp_simple_point2oct(const EC_GROUP *group, const EC_POINT *point, point_conversion_form_t form,
189    unsigned char *buf, size_t len, BN_CTX *ctx)
190{
191	size_t ret;
192	BN_CTX *new_ctx = NULL;
193	int used_ctx = 0;
194	BIGNUM *x, *y;
195	size_t field_len, i, skip;
196
197	if ((form != POINT_CONVERSION_COMPRESSED)
198	    && (form != POINT_CONVERSION_UNCOMPRESSED)
199	    && (form != POINT_CONVERSION_HYBRID)) {
200		ECerror(EC_R_INVALID_FORM);
201		goto err;
202	}
203	if (EC_POINT_is_at_infinity(group, point) > 0) {
204		/* encodes to a single 0 octet */
205		if (buf != NULL) {
206			if (len < 1) {
207				ECerror(EC_R_BUFFER_TOO_SMALL);
208				return 0;
209			}
210			buf[0] = 0;
211		}
212		return 1;
213	}
214	/* ret := required output buffer length */
215	field_len = BN_num_bytes(&group->field);
216	ret = (form == POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
217
218	/* if 'buf' is NULL, just return required length */
219	if (buf != NULL) {
220		if (len < ret) {
221			ECerror(EC_R_BUFFER_TOO_SMALL);
222			goto err;
223		}
224		if (ctx == NULL) {
225			ctx = new_ctx = BN_CTX_new();
226			if (ctx == NULL)
227				return 0;
228		}
229		BN_CTX_start(ctx);
230		used_ctx = 1;
231		if ((x = BN_CTX_get(ctx)) == NULL)
232			goto err;
233		if ((y = BN_CTX_get(ctx)) == NULL)
234			goto err;
235
236		if (!EC_POINT_get_affine_coordinates(group, point, x, y, ctx))
237			goto err;
238
239		if ((form == POINT_CONVERSION_COMPRESSED || form == POINT_CONVERSION_HYBRID) && BN_is_odd(y))
240			buf[0] = form + 1;
241		else
242			buf[0] = form;
243
244		i = 1;
245
246		skip = field_len - BN_num_bytes(x);
247		if (skip > field_len) {
248			ECerror(ERR_R_INTERNAL_ERROR);
249			goto err;
250		}
251		while (skip > 0) {
252			buf[i++] = 0;
253			skip--;
254		}
255		skip = BN_bn2bin(x, buf + i);
256		i += skip;
257		if (i != 1 + field_len) {
258			ECerror(ERR_R_INTERNAL_ERROR);
259			goto err;
260		}
261		if (form == POINT_CONVERSION_UNCOMPRESSED || form == POINT_CONVERSION_HYBRID) {
262			skip = field_len - BN_num_bytes(y);
263			if (skip > field_len) {
264				ECerror(ERR_R_INTERNAL_ERROR);
265				goto err;
266			}
267			while (skip > 0) {
268				buf[i++] = 0;
269				skip--;
270			}
271			skip = BN_bn2bin(y, buf + i);
272			i += skip;
273		}
274		if (i != ret) {
275			ECerror(ERR_R_INTERNAL_ERROR);
276			goto err;
277		}
278	}
279	if (used_ctx)
280		BN_CTX_end(ctx);
281	BN_CTX_free(new_ctx);
282	return ret;
283
284 err:
285	if (used_ctx)
286		BN_CTX_end(ctx);
287	BN_CTX_free(new_ctx);
288	return 0;
289}
290
291
292int
293ec_GFp_simple_oct2point(const EC_GROUP *group, EC_POINT *point,
294    const unsigned char *buf, size_t len, BN_CTX *ctx)
295{
296	point_conversion_form_t form;
297	int y_bit;
298	BN_CTX *new_ctx = NULL;
299	BIGNUM *x, *y;
300	size_t field_len, enc_len;
301	int ret = 0;
302
303	if (len == 0) {
304		ECerror(EC_R_BUFFER_TOO_SMALL);
305		return 0;
306	}
307	form = buf[0];
308	y_bit = form & 1;
309	form = form & ~1U;
310	if ((form != 0) && (form != POINT_CONVERSION_COMPRESSED)
311	    && (form != POINT_CONVERSION_UNCOMPRESSED)
312	    && (form != POINT_CONVERSION_HYBRID)) {
313		ECerror(EC_R_INVALID_ENCODING);
314		return 0;
315	}
316	if ((form == 0 || form == POINT_CONVERSION_UNCOMPRESSED) && y_bit) {
317		ECerror(EC_R_INVALID_ENCODING);
318		return 0;
319	}
320	if (form == 0) {
321		if (len != 1) {
322			ECerror(EC_R_INVALID_ENCODING);
323			return 0;
324		}
325		return EC_POINT_set_to_infinity(group, point);
326	}
327	field_len = BN_num_bytes(&group->field);
328	enc_len = (form == POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
329
330	if (len != enc_len) {
331		ECerror(EC_R_INVALID_ENCODING);
332		return 0;
333	}
334	if (ctx == NULL) {
335		ctx = new_ctx = BN_CTX_new();
336		if (ctx == NULL)
337			return 0;
338	}
339	BN_CTX_start(ctx);
340	if ((x = BN_CTX_get(ctx)) == NULL)
341		goto err;
342	if ((y = BN_CTX_get(ctx)) == NULL)
343		goto err;
344
345	if (!BN_bin2bn(buf + 1, field_len, x))
346		goto err;
347	if (BN_ucmp(x, &group->field) >= 0) {
348		ECerror(EC_R_INVALID_ENCODING);
349		goto err;
350	}
351	if (form == POINT_CONVERSION_COMPRESSED) {
352		/*
353		 * EC_POINT_set_compressed_coordinates checks that the point
354		 * is on the curve as required by X9.62.
355		 */
356		if (!EC_POINT_set_compressed_coordinates(group, point, x, y_bit, ctx))
357			goto err;
358	} else {
359		if (!BN_bin2bn(buf + 1 + field_len, field_len, y))
360			goto err;
361		if (BN_ucmp(y, &group->field) >= 0) {
362			ECerror(EC_R_INVALID_ENCODING);
363			goto err;
364		}
365		if (form == POINT_CONVERSION_HYBRID) {
366			if (y_bit != BN_is_odd(y)) {
367				ECerror(EC_R_INVALID_ENCODING);
368				goto err;
369			}
370		}
371		/*
372		 * EC_POINT_set_affine_coordinates checks that the point is
373		 * on the curve as required by X9.62.
374		 */
375		if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
376			goto err;
377	}
378
379	ret = 1;
380
381 err:
382	BN_CTX_end(ctx);
383	BN_CTX_free(new_ctx);
384	return ret;
385}
386