xref: /openssl/crypto/ec/ec2_oct.c (revision fecb3aae)
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