xref: /openssl/crypto/ec/ecp_oct.c (revision afecd85d)
1 /*
2  * Copyright 2011-2021 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 #include <openssl/symhacks.h>
19 
20 #include "ec_local.h"
21 
ossl_ec_GFp_simple_set_compressed_coordinates(const EC_GROUP * group,EC_POINT * point,const BIGNUM * x_,int y_bit,BN_CTX * ctx)22 int ossl_ec_GFp_simple_set_compressed_coordinates(const EC_GROUP *group,
23                                                   EC_POINT *point,
24                                                   const BIGNUM *x_, int y_bit,
25                                                   BN_CTX *ctx)
26 {
27     BN_CTX *new_ctx = NULL;
28     BIGNUM *tmp1, *tmp2, *x, *y;
29     int ret = 0;
30 
31     if (ctx == NULL) {
32         ctx = new_ctx = BN_CTX_new_ex(group->libctx);
33         if (ctx == NULL)
34             return 0;
35     }
36 
37     y_bit = (y_bit != 0);
38 
39     BN_CTX_start(ctx);
40     tmp1 = BN_CTX_get(ctx);
41     tmp2 = BN_CTX_get(ctx);
42     x = BN_CTX_get(ctx);
43     y = BN_CTX_get(ctx);
44     if (y == NULL)
45         goto err;
46 
47     /*-
48      * Recover y.  We have a Weierstrass equation
49      *     y^2 = x^3 + a*x + b,
50      * so  y  is one of the square roots of  x^3 + a*x + b.
51      */
52 
53     /* tmp1 := x^3 */
54     if (!BN_nnmod(x, x_, group->field, ctx))
55         goto err;
56     if (group->meth->field_decode == 0) {
57         /* field_{sqr,mul} work on standard representation */
58         if (!group->meth->field_sqr(group, tmp2, x_, ctx))
59             goto err;
60         if (!group->meth->field_mul(group, tmp1, tmp2, x_, ctx))
61             goto err;
62     } else {
63         if (!BN_mod_sqr(tmp2, x_, group->field, ctx))
64             goto err;
65         if (!BN_mod_mul(tmp1, tmp2, x_, group->field, ctx))
66             goto err;
67     }
68 
69     /* tmp1 := tmp1 + a*x */
70     if (group->a_is_minus3) {
71         if (!BN_mod_lshift1_quick(tmp2, x, group->field))
72             goto err;
73         if (!BN_mod_add_quick(tmp2, tmp2, x, group->field))
74             goto err;
75         if (!BN_mod_sub_quick(tmp1, tmp1, tmp2, group->field))
76             goto err;
77     } else {
78         if (group->meth->field_decode) {
79             if (!group->meth->field_decode(group, tmp2, group->a, ctx))
80                 goto err;
81             if (!BN_mod_mul(tmp2, tmp2, x, group->field, ctx))
82                 goto err;
83         } else {
84             /* field_mul works on standard representation */
85             if (!group->meth->field_mul(group, tmp2, group->a, x, ctx))
86                 goto err;
87         }
88 
89         if (!BN_mod_add_quick(tmp1, tmp1, tmp2, group->field))
90             goto err;
91     }
92 
93     /* tmp1 := tmp1 + b */
94     if (group->meth->field_decode) {
95         if (!group->meth->field_decode(group, tmp2, group->b, ctx))
96             goto err;
97         if (!BN_mod_add_quick(tmp1, tmp1, tmp2, group->field))
98             goto err;
99     } else {
100         if (!BN_mod_add_quick(tmp1, tmp1, group->b, group->field))
101             goto err;
102     }
103 
104     ERR_set_mark();
105     if (!BN_mod_sqrt(y, tmp1, group->field, ctx)) {
106 #ifndef FIPS_MODULE
107         unsigned long err = ERR_peek_last_error();
108 
109         if (ERR_GET_LIB(err) == ERR_LIB_BN
110             && ERR_GET_REASON(err) == BN_R_NOT_A_SQUARE) {
111             ERR_pop_to_mark();
112             ERR_raise(ERR_LIB_EC, EC_R_INVALID_COMPRESSED_POINT);
113         } else
114 #endif
115         {
116             ERR_clear_last_mark();
117             ERR_raise(ERR_LIB_EC, ERR_R_BN_LIB);
118         }
119         goto err;
120     }
121     ERR_clear_last_mark();
122 
123     if (y_bit != BN_is_odd(y)) {
124         if (BN_is_zero(y)) {
125             int kron;
126 
127             kron = BN_kronecker(x, group->field, ctx);
128             if (kron == -2)
129                 goto err;
130 
131             if (kron == 1)
132                 ERR_raise(ERR_LIB_EC, EC_R_INVALID_COMPRESSION_BIT);
133             else
134                 /*
135                  * BN_mod_sqrt() should have caught this error (not a square)
136                  */
137                 ERR_raise(ERR_LIB_EC, EC_R_INVALID_COMPRESSED_POINT);
138             goto err;
139         }
140         if (!BN_usub(y, group->field, y))
141             goto err;
142     }
143     if (y_bit != BN_is_odd(y)) {
144         ERR_raise(ERR_LIB_EC, ERR_R_INTERNAL_ERROR);
145         goto err;
146     }
147 
148     if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
149         goto err;
150 
151     ret = 1;
152 
153  err:
154     BN_CTX_end(ctx);
155     BN_CTX_free(new_ctx);
156     return ret;
157 }
158 
ossl_ec_GFp_simple_point2oct(const EC_GROUP * group,const EC_POINT * point,point_conversion_form_t form,unsigned char * buf,size_t len,BN_CTX * ctx)159 size_t ossl_ec_GFp_simple_point2oct(const EC_GROUP *group, const EC_POINT *point,
160                                     point_conversion_form_t form,
161                                     unsigned char *buf, size_t len, BN_CTX *ctx)
162 {
163     size_t ret;
164     BN_CTX *new_ctx = NULL;
165     int used_ctx = 0;
166     BIGNUM *x, *y;
167     size_t field_len, i, skip;
168 
169     if ((form != POINT_CONVERSION_COMPRESSED)
170         && (form != POINT_CONVERSION_UNCOMPRESSED)
171         && (form != POINT_CONVERSION_HYBRID)) {
172         ERR_raise(ERR_LIB_EC, EC_R_INVALID_FORM);
173         goto err;
174     }
175 
176     if (EC_POINT_is_at_infinity(group, point)) {
177         /* encodes to a single 0 octet */
178         if (buf != NULL) {
179             if (len < 1) {
180                 ERR_raise(ERR_LIB_EC, EC_R_BUFFER_TOO_SMALL);
181                 return 0;
182             }
183             buf[0] = 0;
184         }
185         return 1;
186     }
187 
188     /* ret := required output buffer length */
189     field_len = BN_num_bytes(group->field);
190     ret =
191         (form ==
192          POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
193 
194     /* if 'buf' is NULL, just return required length */
195     if (buf != NULL) {
196         if (len < ret) {
197             ERR_raise(ERR_LIB_EC, EC_R_BUFFER_TOO_SMALL);
198             goto err;
199         }
200 
201         if (ctx == NULL) {
202             ctx = new_ctx = BN_CTX_new_ex(group->libctx);
203             if (ctx == NULL)
204                 return 0;
205         }
206 
207         BN_CTX_start(ctx);
208         used_ctx = 1;
209         x = BN_CTX_get(ctx);
210         y = BN_CTX_get(ctx);
211         if (y == NULL)
212             goto err;
213 
214         if (!EC_POINT_get_affine_coordinates(group, point, x, y, ctx))
215             goto err;
216 
217         if ((form == POINT_CONVERSION_COMPRESSED
218              || form == POINT_CONVERSION_HYBRID) && BN_is_odd(y))
219             buf[0] = form + 1;
220         else
221             buf[0] = form;
222 
223         i = 1;
224 
225         skip = field_len - BN_num_bytes(x);
226         if (skip > field_len) {
227             ERR_raise(ERR_LIB_EC, ERR_R_INTERNAL_ERROR);
228             goto err;
229         }
230         while (skip > 0) {
231             buf[i++] = 0;
232             skip--;
233         }
234         skip = BN_bn2bin(x, buf + i);
235         i += skip;
236         if (i != 1 + field_len) {
237             ERR_raise(ERR_LIB_EC, ERR_R_INTERNAL_ERROR);
238             goto err;
239         }
240 
241         if (form == POINT_CONVERSION_UNCOMPRESSED
242             || form == POINT_CONVERSION_HYBRID) {
243             skip = field_len - BN_num_bytes(y);
244             if (skip > field_len) {
245                 ERR_raise(ERR_LIB_EC, ERR_R_INTERNAL_ERROR);
246                 goto err;
247             }
248             while (skip > 0) {
249                 buf[i++] = 0;
250                 skip--;
251             }
252             skip = BN_bn2bin(y, buf + i);
253             i += skip;
254         }
255 
256         if (i != ret) {
257             ERR_raise(ERR_LIB_EC, ERR_R_INTERNAL_ERROR);
258             goto err;
259         }
260     }
261 
262     if (used_ctx)
263         BN_CTX_end(ctx);
264     BN_CTX_free(new_ctx);
265     return ret;
266 
267  err:
268     if (used_ctx)
269         BN_CTX_end(ctx);
270     BN_CTX_free(new_ctx);
271     return 0;
272 }
273 
ossl_ec_GFp_simple_oct2point(const EC_GROUP * group,EC_POINT * point,const unsigned char * buf,size_t len,BN_CTX * ctx)274 int ossl_ec_GFp_simple_oct2point(const EC_GROUP *group, EC_POINT *point,
275                                  const unsigned char *buf, size_t len,
276                                  BN_CTX *ctx)
277 {
278     point_conversion_form_t form;
279     int y_bit;
280     BN_CTX *new_ctx = NULL;
281     BIGNUM *x, *y;
282     size_t field_len, enc_len;
283     int ret = 0;
284 
285     if (len == 0) {
286         ERR_raise(ERR_LIB_EC, EC_R_BUFFER_TOO_SMALL);
287         return 0;
288     }
289     form = buf[0];
290     y_bit = form & 1;
291     form = form & ~1U;
292     if ((form != 0) && (form != POINT_CONVERSION_COMPRESSED)
293         && (form != POINT_CONVERSION_UNCOMPRESSED)
294         && (form != POINT_CONVERSION_HYBRID)) {
295         ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
296         return 0;
297     }
298     if ((form == 0 || form == POINT_CONVERSION_UNCOMPRESSED) && y_bit) {
299         ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
300         return 0;
301     }
302 
303     if (form == 0) {
304         if (len != 1) {
305             ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
306             return 0;
307         }
308 
309         return EC_POINT_set_to_infinity(group, point);
310     }
311 
312     field_len = BN_num_bytes(group->field);
313     enc_len =
314         (form ==
315          POINT_CONVERSION_COMPRESSED) ? 1 + field_len : 1 + 2 * field_len;
316 
317     if (len != enc_len) {
318         ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
319         return 0;
320     }
321 
322     if (ctx == NULL) {
323         ctx = new_ctx = BN_CTX_new_ex(group->libctx);
324         if (ctx == NULL)
325             return 0;
326     }
327 
328     BN_CTX_start(ctx);
329     x = BN_CTX_get(ctx);
330     y = BN_CTX_get(ctx);
331     if (y == NULL)
332         goto err;
333 
334     if (!BN_bin2bn(buf + 1, field_len, x))
335         goto err;
336     if (BN_ucmp(x, group->field) >= 0) {
337         ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
338         goto err;
339     }
340 
341     if (form == POINT_CONVERSION_COMPRESSED) {
342         if (!EC_POINT_set_compressed_coordinates(group, point, x, y_bit, ctx))
343             goto err;
344     } else {
345         if (!BN_bin2bn(buf + 1 + field_len, field_len, y))
346             goto err;
347         if (BN_ucmp(y, group->field) >= 0) {
348             ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
349             goto err;
350         }
351         if (form == POINT_CONVERSION_HYBRID) {
352             if (y_bit != BN_is_odd(y)) {
353                 ERR_raise(ERR_LIB_EC, EC_R_INVALID_ENCODING);
354                 goto err;
355             }
356         }
357 
358         /*
359          * EC_POINT_set_affine_coordinates is responsible for checking that
360          * the point is on the curve.
361          */
362         if (!EC_POINT_set_affine_coordinates(group, point, x, y, ctx))
363             goto err;
364     }
365 
366     ret = 1;
367 
368  err:
369     BN_CTX_end(ctx);
370     BN_CTX_free(new_ctx);
371     return ret;
372 }
373