ecp_oct.c revision 1.16 
1/* $OpenBSD: ecp_oct.c,v 1.16 2022/11/19 07:29:29 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_lcl.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			int kron;
166
167			kron = BN_kronecker(x, &group->field, ctx);
168			if (kron == -2)
169				goto err;
170
171			if (kron == 1)
172				ECerror(EC_R_INVALID_COMPRESSION_BIT);
173			else
174				/*
175				 * BN_mod_sqrt() should have cought this
176				 * error (not a square)
177				 */
178				ECerror(EC_R_INVALID_COMPRESSED_POINT);
179			goto err;
180		}
181		if (!BN_usub(y, &group->field, y))
182			goto err;
183	}
184	if (y_bit != BN_is_odd(y)) {
185		ECerror(ERR_R_INTERNAL_ERROR);
186		goto err;
187	}
188	if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
189		goto err;
190
191	ret = 1;
192
193 err:
194	BN_CTX_end(ctx);
195	BN_CTX_free(new_ctx);
196	return ret;
197}
198
199
200size_t
201ec_GFp_simple_point2oct(const EC_GROUP *group, const EC_POINT *point, point_conversion_form_t form,
202    unsigned char *buf, size_t len, BN_CTX *ctx)
203{
204	size_t ret;
205	BN_CTX *new_ctx = NULL;
206	int used_ctx = 0;
207	BIGNUM *x, *y;
208	size_t field_len, i, skip;
209
210	if ((form != POINT_CONVERSION_COMPRESSED)
211	    && (form != POINT_CONVERSION_UNCOMPRESSED)
212	    && (form != POINT_CONVERSION_HYBRID)) {
213		ECerror(EC_R_INVALID_FORM);
214		goto err;
215	}
216	if (EC_POINT_is_at_infinity(group, point) > 0) {
217		/* encodes to a single 0 octet */
218		if (buf != NULL) {
219			if (len < 1) {
220				ECerror(EC_R_BUFFER_TOO_SMALL);
221				return 0;
222			}
223			buf[0] = 0;
224		}
225		return 1;
226	}
227	/* ret := required output buffer length */
228	field_len = BN_num_bytes(&group->field);
229	ret = (form == POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
230
231	/* if 'buf' is NULL, just return required length */
232	if (buf != NULL) {
233		if (len < ret) {
234			ECerror(EC_R_BUFFER_TOO_SMALL);
235			goto err;
236		}
237		if (ctx == NULL) {
238			ctx = new_ctx = BN_CTX_new();
239			if (ctx == NULL)
240				return 0;
241		}
242		BN_CTX_start(ctx);
243		used_ctx = 1;
244		if ((x = BN_CTX_get(ctx)) == NULL)
245			goto err;
246		if ((y = BN_CTX_get(ctx)) == NULL)
247			goto err;
248
249		if (!EC_POINT_get_affine_coordinates(group, point, x, y, ctx))
250			goto err;
251
252		if ((form == POINT_CONVERSION_COMPRESSED || form == POINT_CONVERSION_HYBRID) && BN_is_odd(y))
253			buf[0] = form + 1;
254		else
255			buf[0] = form;
256
257		i = 1;
258
259		skip = field_len - BN_num_bytes(x);
260		if (skip > field_len) {
261			ECerror(ERR_R_INTERNAL_ERROR);
262			goto err;
263		}
264		while (skip > 0) {
265			buf[i++] = 0;
266			skip--;
267		}
268		skip = BN_bn2bin(x, buf + i);
269		i += skip;
270		if (i != 1 + field_len) {
271			ECerror(ERR_R_INTERNAL_ERROR);
272			goto err;
273		}
274		if (form == POINT_CONVERSION_UNCOMPRESSED || form == POINT_CONVERSION_HYBRID) {
275			skip = field_len - BN_num_bytes(y);
276			if (skip > field_len) {
277				ECerror(ERR_R_INTERNAL_ERROR);
278				goto err;
279			}
280			while (skip > 0) {
281				buf[i++] = 0;
282				skip--;
283			}
284			skip = BN_bn2bin(y, buf + i);
285			i += skip;
286		}
287		if (i != ret) {
288			ECerror(ERR_R_INTERNAL_ERROR);
289			goto err;
290		}
291	}
292	if (used_ctx)
293		BN_CTX_end(ctx);
294	BN_CTX_free(new_ctx);
295	return ret;
296
297 err:
298	if (used_ctx)
299		BN_CTX_end(ctx);
300	BN_CTX_free(new_ctx);
301	return 0;
302}
303
304
305int
306ec_GFp_simple_oct2point(const EC_GROUP *group, EC_POINT *point,
307    const unsigned char *buf, size_t len, BN_CTX *ctx)
308{
309	point_conversion_form_t form;
310	int y_bit;
311	BN_CTX *new_ctx = NULL;
312	BIGNUM *x, *y;
313	size_t field_len, enc_len;
314	int ret = 0;
315
316	if (len == 0) {
317		ECerror(EC_R_BUFFER_TOO_SMALL);
318		return 0;
319	}
320	form = buf[0];
321	y_bit = form & 1;
322	form = form & ~1U;
323	if ((form != 0) && (form != POINT_CONVERSION_COMPRESSED)
324	    && (form != POINT_CONVERSION_UNCOMPRESSED)
325	    && (form != POINT_CONVERSION_HYBRID)) {
326		ECerror(EC_R_INVALID_ENCODING);
327		return 0;
328	}
329	if ((form == 0 || form == POINT_CONVERSION_UNCOMPRESSED) && y_bit) {
330		ECerror(EC_R_INVALID_ENCODING);
331		return 0;
332	}
333	if (form == 0) {
334		if (len != 1) {
335			ECerror(EC_R_INVALID_ENCODING);
336			return 0;
337		}
338		return EC_POINT_set_to_infinity(group, point);
339	}
340	field_len = BN_num_bytes(&group->field);
341	enc_len = (form == POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
342
343	if (len != enc_len) {
344		ECerror(EC_R_INVALID_ENCODING);
345		return 0;
346	}
347	if (ctx == NULL) {
348		ctx = new_ctx = BN_CTX_new();
349		if (ctx == NULL)
350			return 0;
351	}
352	BN_CTX_start(ctx);
353	if ((x = BN_CTX_get(ctx)) == NULL)
354		goto err;
355	if ((y = BN_CTX_get(ctx)) == NULL)
356		goto err;
357
358	if (!BN_bin2bn(buf + 1, field_len, x))
359		goto err;
360	if (BN_ucmp(x, &group->field) >= 0) {
361		ECerror(EC_R_INVALID_ENCODING);
362		goto err;
363	}
364	if (form == POINT_CONVERSION_COMPRESSED) {
365		/*
366		 * EC_POINT_set_compressed_coordinates checks that the point
367		 * is on the curve as required by X9.62.
368		 */
369		if (!EC_POINT_set_compressed_coordinates(group, point, x, y_bit, ctx))
370			goto err;
371	} else {
372		if (!BN_bin2bn(buf + 1 + field_len, field_len, y))
373			goto err;
374		if (BN_ucmp(y, &group->field) >= 0) {
375			ECerror(EC_R_INVALID_ENCODING);
376			goto err;
377		}
378		if (form == POINT_CONVERSION_HYBRID) {
379			if (y_bit != BN_is_odd(y)) {
380				ECerror(EC_R_INVALID_ENCODING);
381				goto err;
382			}
383		}
384		/*
385		 * EC_POINT_set_affine_coordinates checks that the point is
386		 * on the curve as required by X9.62.
387		 */
388		if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
389			goto err;
390	}
391
392	ret = 1;
393
394 err:
395	BN_CTX_end(ctx);
396	BN_CTX_free(new_ctx);
397	return ret;
398}
399