1 /*
2 * Copyright 2011-2022 The OpenSSL Project Authors. All Rights Reserved.
3 * Copyright (c) 2002, Oracle and/or its affiliates. All rights reserved
4 *
5 * Licensed under the Apache License 2.0 (the "License"). You may not use
6 * this file except in compliance with the License. You can obtain a copy
7 * in the file LICENSE in the source distribution or at
8 * https://www.openssl.org/source/license.html
9 */
10
11 /*
12 * ECDSA low level APIs are deprecated for public use, but still ok for
13 * internal use.
14 */
15 #include "internal/deprecated.h"
16
17 #include <openssl/err.h>
18
19 #include "ec_local.h"
20
21 #ifndef OPENSSL_NO_EC2M
22
23 /*-
24 * Calculates and sets the affine coordinates of an EC_POINT from the given
25 * compressed coordinates. Uses algorithm 2.3.4 of SEC 1.
26 * Note that the simple implementation only uses affine coordinates.
27 *
28 * The method is from the following publication:
29 *
30 * Harper, Menezes, Vanstone:
31 * "Public-Key Cryptosystems with Very Small Key Lengths",
32 * EUROCRYPT '92, Springer-Verlag LNCS 658,
33 * published February 1993
34 *
35 * US Patents 6,141,420 and 6,618,483 (Vanstone, Mullin, Agnew) describe
36 * the same method, but claim no priority date earlier than July 29, 1994
37 * (and additionally fail to cite the EUROCRYPT '92 publication as prior art).
38 */
ossl_ec_GF2m_simple_set_compressed_coordinates(const EC_GROUP * group,EC_POINT * point,const BIGNUM * x_,int y_bit,BN_CTX * ctx)39 int ossl_ec_GF2m_simple_set_compressed_coordinates(const EC_GROUP *group,
40 EC_POINT *point,
41 const BIGNUM *x_, int y_bit,
42 BN_CTX *ctx)
43 {
44 BIGNUM *tmp, *x, *y, *z;
45 int ret = 0, z0;
46 #ifndef FIPS_MODULE
47 BN_CTX *new_ctx = NULL;
48
49 if (ctx == NULL) {
50 ctx = new_ctx = BN_CTX_new();
51 if (ctx == NULL)
52 return 0;
53 }
54 #endif
55
56 y_bit = (y_bit != 0) ? 1 : 0;
57
58 BN_CTX_start(ctx);
59 tmp = BN_CTX_get(ctx);
60 x = BN_CTX_get(ctx);
61 y = BN_CTX_get(ctx);
62 z = BN_CTX_get(ctx);
63 if (z == NULL)
64 goto err;
65
66 if (!BN_GF2m_mod_arr(x, x_, group->poly))
67 goto err;
68 if (BN_is_zero(x)) {
69 if (!BN_GF2m_mod_sqrt_arr(y, group->b, group->poly, ctx))
70 goto err;
71 } else {
72 if (!group->meth->field_sqr(group, tmp, x, ctx))
73 goto err;
74 if (!group->meth->field_div(group, tmp, group->b, tmp, ctx))
75 goto err;
76 if (!BN_GF2m_add(tmp, group->a, tmp))
77 goto err;
78 if (!BN_GF2m_add(tmp, x, tmp))
79 goto err;
80 ERR_set_mark();
81 if (!BN_GF2m_mod_solve_quad_arr(z, tmp, group->poly, ctx)) {
82 #ifndef FIPS_MODULE
83 unsigned long err = ERR_peek_last_error();
84
85 if (ERR_GET_LIB(err) == ERR_LIB_BN
86 && ERR_GET_REASON(err) == BN_R_NO_SOLUTION) {
87 ERR_pop_to_mark();
88 ERR_raise(ERR_LIB_EC, EC_R_INVALID_COMPRESSED_POINT);
89 } else
90 #endif
91 {
92 ERR_clear_last_mark();
93 ERR_raise(ERR_LIB_EC, ERR_R_BN_LIB);
94 }
95 goto err;
96 }
97 ERR_clear_last_mark();
98 z0 = (BN_is_odd(z)) ? 1 : 0;
99 if (!group->meth->field_mul(group, y, x, z, ctx))
100 goto err;
101 if (z0 != y_bit) {
102 if (!BN_GF2m_add(y, y, x))
103 goto err;
104 }
105 }
106
107 if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
108 goto err;
109
110 ret = 1;
111
112 err:
113 BN_CTX_end(ctx);
114 #ifndef FIPS_MODULE
115 BN_CTX_free(new_ctx);
116 #endif
117 return ret;
118 }
119
120 /*
121 * Converts an EC_POINT to an octet string. If buf is NULL, the encoded
122 * length will be returned. If the length len of buf is smaller than required
123 * an error will be returned.
124 */
ossl_ec_GF2m_simple_point2oct(const EC_GROUP * group,const EC_POINT * point,point_conversion_form_t form,unsigned char * buf,size_t len,BN_CTX * ctx)125 size_t ossl_ec_GF2m_simple_point2oct(const EC_GROUP *group,
126 const EC_POINT *point,
127 point_conversion_form_t form,
128 unsigned char *buf, size_t len, BN_CTX *ctx)
129 {
130 size_t ret;
131 int used_ctx = 0;
132 BIGNUM *x, *y, *yxi;
133 size_t field_len, i, skip;
134 #ifndef FIPS_MODULE
135 BN_CTX *new_ctx = NULL;
136 #endif
137
138 if ((form != POINT_CONVERSION_COMPRESSED)
139 && (form != POINT_CONVERSION_UNCOMPRESSED)
140 && (form != POINT_CONVERSION_HYBRID)) {
141 ERR_raise(ERR_LIB_EC, EC_R_INVALID_FORM);
142 goto err;
143 }
144
145 if (EC_POINT_is_at_infinity(group, point)) {
146 /* encodes to a single 0 octet */
147 if (buf != NULL) {
148 if (len < 1) {
149 ERR_raise(ERR_LIB_EC, EC_R_BUFFER_TOO_SMALL);
150 return 0;
151 }
152 buf[0] = 0;
153 }
154 return 1;
155 }
156
157 /* ret := required output buffer length */
158 field_len = (EC_GROUP_get_degree(group) + 7) / 8;
159 ret =
160 (form ==
161 POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
162
163 /* if 'buf' is NULL, just return required length */
164 if (buf != NULL) {
165 if (len < ret) {
166 ERR_raise(ERR_LIB_EC, EC_R_BUFFER_TOO_SMALL);
167 goto err;
168 }
169
170 #ifndef FIPS_MODULE
171 if (ctx == NULL) {
172 ctx = new_ctx = BN_CTX_new();
173 if (ctx == NULL)
174 return 0;
175 }
176 #endif
177
178 BN_CTX_start(ctx);
179 used_ctx = 1;
180 x = BN_CTX_get(ctx);
181 y = BN_CTX_get(ctx);
182 yxi = BN_CTX_get(ctx);
183 if (yxi == NULL)
184 goto err;
185
186 if (!EC_POINT_get_affine_coordinates(group, point, x, y, ctx))
187 goto err;
188
189 buf[0] = form;
190 if ((form != POINT_CONVERSION_UNCOMPRESSED) && !BN_is_zero(x)) {
191 if (!group->meth->field_div(group, yxi, y, x, ctx))
192 goto err;
193 if (BN_is_odd(yxi))
194 buf[0]++;
195 }
196
197 i = 1;
198
199 skip = field_len - BN_num_bytes(x);
200 if (skip > field_len) {
201 ERR_raise(ERR_LIB_EC, ERR_R_INTERNAL_ERROR);
202 goto err;
203 }
204 while (skip > 0) {
205 buf[i++] = 0;
206 skip--;
207 }
208 skip = BN_bn2bin(x, buf + i);
209 i += skip;
210 if (i != 1 + field_len) {
211 ERR_raise(ERR_LIB_EC, ERR_R_INTERNAL_ERROR);
212 goto err;
213 }
214
215 if (form == POINT_CONVERSION_UNCOMPRESSED
216 || form == POINT_CONVERSION_HYBRID) {
217 skip = field_len - BN_num_bytes(y);
218 if (skip > field_len) {
219 ERR_raise(ERR_LIB_EC, ERR_R_INTERNAL_ERROR);
220 goto err;
221 }
222 while (skip > 0) {
223 buf[i++] = 0;
224 skip--;
225 }
226 skip = BN_bn2bin(y, buf + i);
227 i += skip;
228 }
229
230 if (i != ret) {
231 ERR_raise(ERR_LIB_EC, ERR_R_INTERNAL_ERROR);
232 goto err;
233 }
234 }
235
236 if (used_ctx)
237 BN_CTX_end(ctx);
238 #ifndef FIPS_MODULE
239 BN_CTX_free(new_ctx);
240 #endif
241 return ret;
242
243 err:
244 if (used_ctx)
245 BN_CTX_end(ctx);
246 #ifndef FIPS_MODULE
247 BN_CTX_free(new_ctx);
248 #endif
249 return 0;
250 }
251
252 /*
253 * Converts an octet string representation to an EC_POINT. Note that the
254 * simple implementation only uses affine coordinates.
255 */
ossl_ec_GF2m_simple_oct2point(const EC_GROUP * group,EC_POINT * point,const unsigned char * buf,size_t len,BN_CTX * ctx)256 int ossl_ec_GF2m_simple_oct2point(const EC_GROUP *group, EC_POINT *point,
257 const unsigned char *buf, size_t len,
258 BN_CTX *ctx)
259 {
260 point_conversion_form_t form;
261 int y_bit, m;
262 BIGNUM *x, *y, *yxi;
263 size_t field_len, enc_len;
264 int ret = 0;
265 #ifndef FIPS_MODULE
266 BN_CTX *new_ctx = NULL;
267 #endif
268
269 if (len == 0) {
270 ERR_raise(ERR_LIB_EC, EC_R_BUFFER_TOO_SMALL);
271 return 0;
272 }
273
274 /*
275 * The first octet is the point conversion octet PC, see X9.62, page 4
276 * and section 4.4.2. It must be:
277 * 0x00 for the point at infinity
278 * 0x02 or 0x03 for compressed form
279 * 0x04 for uncompressed form
280 * 0x06 or 0x07 for hybrid form.
281 * For compressed or hybrid forms, we store the last bit of buf[0] as
282 * y_bit and clear it from buf[0] so as to obtain a POINT_CONVERSION_*.
283 * We error if buf[0] contains any but the above values.
284 */
285 y_bit = buf[0] & 1;
286 form = buf[0] & ~1U;
287
288 if ((form != 0) && (form != POINT_CONVERSION_COMPRESSED)
289 && (form != POINT_CONVERSION_UNCOMPRESSED)
290 && (form != POINT_CONVERSION_HYBRID)) {
291 ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
292 return 0;
293 }
294 if ((form == 0 || form == POINT_CONVERSION_UNCOMPRESSED) && y_bit) {
295 ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
296 return 0;
297 }
298
299 /* The point at infinity is represented by a single zero octet. */
300 if (form == 0) {
301 if (len != 1) {
302 ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
303 return 0;
304 }
305
306 return EC_POINT_set_to_infinity(group, point);
307 }
308
309 m = EC_GROUP_get_degree(group);
310 field_len = (m + 7) / 8;
311 enc_len =
312 (form ==
313 POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
314
315 if (len != enc_len) {
316 ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
317 return 0;
318 }
319
320 #ifndef FIPS_MODULE
321 if (ctx == NULL) {
322 ctx = new_ctx = BN_CTX_new();
323 if (ctx == NULL)
324 return 0;
325 }
326 #endif
327
328 BN_CTX_start(ctx);
329 x = BN_CTX_get(ctx);
330 y = BN_CTX_get(ctx);
331 yxi = BN_CTX_get(ctx);
332 if (yxi == NULL)
333 goto err;
334
335 if (!BN_bin2bn(buf + 1, field_len, x))
336 goto err;
337 if (BN_num_bits(x) > m) {
338 ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
339 goto err;
340 }
341
342 if (form == POINT_CONVERSION_COMPRESSED) {
343 if (!EC_POINT_set_compressed_coordinates(group, point, x, y_bit, ctx))
344 goto err;
345 } else {
346 if (!BN_bin2bn(buf + 1 + field_len, field_len, y))
347 goto err;
348 if (BN_num_bits(y) > m) {
349 ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
350 goto err;
351 }
352 if (form == POINT_CONVERSION_HYBRID) {
353 /*
354 * Check that the form in the encoding was set correctly
355 * according to X9.62 4.4.2.a, 4(c), see also first paragraph
356 * of X9.62, 4.4.1.b.
357 */
358 if (BN_is_zero(x)) {
359 if (y_bit != 0) {
360 ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
361 goto err;
362 }
363 } else {
364 if (!group->meth->field_div(group, yxi, y, x, ctx))
365 goto err;
366 if (y_bit != BN_is_odd(yxi)) {
367 ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
368 goto err;
369 }
370 }
371 }
372
373 /*
374 * EC_POINT_set_affine_coordinates is responsible for checking that
375 * the point is on the curve.
376 */
377 if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
378 goto err;
379 }
380
381 ret = 1;
382
383 err:
384 BN_CTX_end(ctx);
385 #ifndef FIPS_MODULE
386 BN_CTX_free(new_ctx);
387 #endif
388 return ret;
389 }
390 #endif
391
