xref: /openssl/crypto/sm2/sm2_sign.c (revision 7ed6de99)
1 /*
2  * Copyright 2017-2024 The OpenSSL Project Authors. All Rights Reserved.
3  * Copyright 2017 Ribose Inc. All Rights Reserved.
4  * Ported from Ribose contributions from Botan.
5  *
6  * Licensed under the Apache License 2.0 (the "License").  You may not use
7  * this file except in compliance with the License.  You can obtain a copy
8  * in the file LICENSE in the source distribution or at
9  * https://www.openssl.org/source/license.html
10  */
11 
12 #include "internal/deprecated.h"
13 
14 #include "crypto/sm2.h"
15 #include "crypto/sm2err.h"
16 #include "crypto/ec.h" /* ossl_ec_group_do_inverse_ord() */
17 #include "internal/numbers.h"
18 #include <openssl/err.h>
19 #include <openssl/evp.h>
20 #include <openssl/bn.h>
21 #include <string.h>
22 
ossl_sm2_compute_z_digest(uint8_t * out,const EVP_MD * digest,const uint8_t * id,const size_t id_len,const EC_KEY * key)23 int ossl_sm2_compute_z_digest(uint8_t *out,
24                               const EVP_MD *digest,
25                               const uint8_t *id,
26                               const size_t id_len,
27                               const EC_KEY *key)
28 {
29     int rc = 0;
30     const EC_GROUP *group = EC_KEY_get0_group(key);
31     const EC_POINT *pubkey = EC_KEY_get0_public_key(key);
32     BN_CTX *ctx = NULL;
33     EVP_MD_CTX *hash = NULL;
34     BIGNUM *p = NULL;
35     BIGNUM *a = NULL;
36     BIGNUM *b = NULL;
37     BIGNUM *xG = NULL;
38     BIGNUM *yG = NULL;
39     BIGNUM *xA = NULL;
40     BIGNUM *yA = NULL;
41     int p_bytes = 0;
42     uint8_t *buf = NULL;
43     uint16_t entl = 0;
44     uint8_t e_byte = 0;
45 
46     /* SM2 Signatures require a public key, check for it */
47     if (pubkey == NULL) {
48         ERR_raise(ERR_LIB_SM2, ERR_R_PASSED_NULL_PARAMETER);
49         goto done;
50     }
51 
52     hash = EVP_MD_CTX_new();
53     if (hash == NULL) {
54         ERR_raise(ERR_LIB_SM2, ERR_R_EVP_LIB);
55         goto done;
56     }
57     ctx = BN_CTX_new_ex(ossl_ec_key_get_libctx(key));
58     if (ctx == NULL) {
59         ERR_raise(ERR_LIB_SM2, ERR_R_BN_LIB);
60         goto done;
61     }
62 
63     p = BN_CTX_get(ctx);
64     a = BN_CTX_get(ctx);
65     b = BN_CTX_get(ctx);
66     xG = BN_CTX_get(ctx);
67     yG = BN_CTX_get(ctx);
68     xA = BN_CTX_get(ctx);
69     yA = BN_CTX_get(ctx);
70 
71     if (yA == NULL) {
72         ERR_raise(ERR_LIB_SM2, ERR_R_BN_LIB);
73         goto done;
74     }
75 
76     if (!EVP_DigestInit(hash, digest)) {
77         ERR_raise(ERR_LIB_SM2, ERR_R_EVP_LIB);
78         goto done;
79     }
80 
81     /* Z = h(ENTL || ID || a || b || xG || yG || xA || yA) */
82 
83     if (id_len >= (UINT16_MAX / 8)) {
84         /* too large */
85         ERR_raise(ERR_LIB_SM2, SM2_R_ID_TOO_LARGE);
86         goto done;
87     }
88 
89     entl = (uint16_t)(8 * id_len);
90 
91     e_byte = entl >> 8;
92     if (!EVP_DigestUpdate(hash, &e_byte, 1)) {
93         ERR_raise(ERR_LIB_SM2, ERR_R_EVP_LIB);
94         goto done;
95     }
96     e_byte = entl & 0xFF;
97     if (!EVP_DigestUpdate(hash, &e_byte, 1)) {
98         ERR_raise(ERR_LIB_SM2, ERR_R_EVP_LIB);
99         goto done;
100     }
101 
102     if (id_len > 0 && !EVP_DigestUpdate(hash, id, id_len)) {
103         ERR_raise(ERR_LIB_SM2, ERR_R_EVP_LIB);
104         goto done;
105     }
106 
107     if (!EC_GROUP_get_curve(group, p, a, b, ctx)) {
108         ERR_raise(ERR_LIB_SM2, ERR_R_EC_LIB);
109         goto done;
110     }
111 
112     p_bytes = BN_num_bytes(p);
113     buf = OPENSSL_zalloc(p_bytes);
114     if (buf == NULL)
115         goto done;
116 
117     if (BN_bn2binpad(a, buf, p_bytes) < 0
118             || !EVP_DigestUpdate(hash, buf, p_bytes)
119             || BN_bn2binpad(b, buf, p_bytes) < 0
120             || !EVP_DigestUpdate(hash, buf, p_bytes)
121             || !EC_POINT_get_affine_coordinates(group,
122                                                 EC_GROUP_get0_generator(group),
123                                                 xG, yG, ctx)
124             || BN_bn2binpad(xG, buf, p_bytes) < 0
125             || !EVP_DigestUpdate(hash, buf, p_bytes)
126             || BN_bn2binpad(yG, buf, p_bytes) < 0
127             || !EVP_DigestUpdate(hash, buf, p_bytes)
128             || !EC_POINT_get_affine_coordinates(group,
129                                                 pubkey,
130                                                 xA, yA, ctx)
131             || BN_bn2binpad(xA, buf, p_bytes) < 0
132             || !EVP_DigestUpdate(hash, buf, p_bytes)
133             || BN_bn2binpad(yA, buf, p_bytes) < 0
134             || !EVP_DigestUpdate(hash, buf, p_bytes)
135             || !EVP_DigestFinal(hash, out, NULL)) {
136         ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
137         goto done;
138     }
139 
140     rc = 1;
141 
142  done:
143     OPENSSL_free(buf);
144     BN_CTX_free(ctx);
145     EVP_MD_CTX_free(hash);
146     return rc;
147 }
148 
sm2_compute_msg_hash(const EVP_MD * digest,const EC_KEY * key,const uint8_t * id,const size_t id_len,const uint8_t * msg,size_t msg_len)149 static BIGNUM *sm2_compute_msg_hash(const EVP_MD *digest,
150                                     const EC_KEY *key,
151                                     const uint8_t *id,
152                                     const size_t id_len,
153                                     const uint8_t *msg, size_t msg_len)
154 {
155     EVP_MD_CTX *hash = EVP_MD_CTX_new();
156     const int md_size = EVP_MD_get_size(digest);
157     uint8_t *z = NULL;
158     BIGNUM *e = NULL;
159     EVP_MD *fetched_digest = NULL;
160     OSSL_LIB_CTX *libctx = ossl_ec_key_get_libctx(key);
161     const char *propq = ossl_ec_key_get0_propq(key);
162 
163     if (md_size <= 0) {
164         ERR_raise(ERR_LIB_SM2, SM2_R_INVALID_DIGEST);
165         goto done;
166     }
167     if (hash == NULL) {
168         ERR_raise(ERR_LIB_SM2, ERR_R_EVP_LIB);
169         goto done;
170     }
171 
172     z = OPENSSL_zalloc(md_size);
173     if (z == NULL)
174         goto done;
175 
176     fetched_digest = EVP_MD_fetch(libctx, EVP_MD_get0_name(digest), propq);
177     if (fetched_digest == NULL) {
178         ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
179         goto done;
180     }
181 
182     if (!ossl_sm2_compute_z_digest(z, fetched_digest, id, id_len, key)) {
183         /* SM2err already called */
184         goto done;
185     }
186 
187     if (!EVP_DigestInit(hash, fetched_digest)
188             || !EVP_DigestUpdate(hash, z, md_size)
189             || !EVP_DigestUpdate(hash, msg, msg_len)
190                /* reuse z buffer to hold H(Z || M) */
191             || !EVP_DigestFinal(hash, z, NULL)) {
192         ERR_raise(ERR_LIB_SM2, ERR_R_EVP_LIB);
193         goto done;
194     }
195 
196     e = BN_bin2bn(z, md_size, NULL);
197     if (e == NULL)
198         ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
199 
200  done:
201     EVP_MD_free(fetched_digest);
202     OPENSSL_free(z);
203     EVP_MD_CTX_free(hash);
204     return e;
205 }
206 
sm2_sig_gen(const EC_KEY * key,const BIGNUM * e)207 static ECDSA_SIG *sm2_sig_gen(const EC_KEY *key, const BIGNUM *e)
208 {
209     const BIGNUM *dA = EC_KEY_get0_private_key(key);
210     const EC_GROUP *group = EC_KEY_get0_group(key);
211     const BIGNUM *order = EC_GROUP_get0_order(group);
212     ECDSA_SIG *sig = NULL;
213     EC_POINT *kG = NULL;
214     BN_CTX *ctx = NULL;
215     BIGNUM *k = NULL;
216     BIGNUM *rk = NULL;
217     BIGNUM *r = NULL;
218     BIGNUM *s = NULL;
219     BIGNUM *x1 = NULL;
220     BIGNUM *tmp = NULL;
221     OSSL_LIB_CTX *libctx = ossl_ec_key_get_libctx(key);
222 
223     kG = EC_POINT_new(group);
224     if (kG == NULL) {
225         ERR_raise(ERR_LIB_SM2, ERR_R_EC_LIB);
226         goto done;
227     }
228     ctx = BN_CTX_new_ex(libctx);
229     if (ctx == NULL) {
230         ERR_raise(ERR_LIB_SM2, ERR_R_BN_LIB);
231         goto done;
232     }
233 
234     BN_CTX_start(ctx);
235     k = BN_CTX_get(ctx);
236     rk = BN_CTX_get(ctx);
237     x1 = BN_CTX_get(ctx);
238     tmp = BN_CTX_get(ctx);
239     if (tmp == NULL) {
240         ERR_raise(ERR_LIB_SM2, ERR_R_BN_LIB);
241         goto done;
242     }
243 
244     /*
245      * These values are returned and so should not be allocated out of the
246      * context
247      */
248     r = BN_new();
249     s = BN_new();
250 
251     if (r == NULL || s == NULL) {
252         ERR_raise(ERR_LIB_SM2, ERR_R_BN_LIB);
253         goto done;
254     }
255 
256     /*
257      * A3: Generate a random number k in [1,n-1] using random number generators;
258      * A4: Compute (x1,y1)=[k]G, and convert the type of data x1 to be integer
259      *     as specified in clause 4.2.8 of GM/T 0003.1-2012;
260      * A5: Compute r=(e+x1) mod n. If r=0 or r+k=n, then go to A3;
261      * A6: Compute s=(1/(1+dA)*(k-r*dA)) mod n. If s=0, then go to A3;
262      * A7: Convert the type of data (r,s) to be bit strings according to the details
263      *     in clause 4.2.2 of GM/T 0003.1-2012. Then the signature of message M is (r,s).
264      */
265     for (;;) {
266         if (!BN_priv_rand_range_ex(k, order, 0, ctx)) {
267             ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
268             goto done;
269         }
270 
271         if (!EC_POINT_mul(group, kG, k, NULL, NULL, ctx)
272                 || !EC_POINT_get_affine_coordinates(group, kG, x1, NULL,
273                                                     ctx)
274                 || !BN_mod_add(r, e, x1, order, ctx)) {
275             ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
276             goto done;
277         }
278 
279         /* try again if r == 0 or r+k == n */
280         if (BN_is_zero(r))
281             continue;
282 
283         if (!BN_add(rk, r, k)) {
284             ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
285             goto done;
286         }
287 
288         if (BN_cmp(rk, order) == 0)
289             continue;
290 
291         if (!BN_add(s, dA, BN_value_one())
292                 || !ossl_ec_group_do_inverse_ord(group, s, s, ctx)
293                 || !BN_mod_mul(tmp, dA, r, order, ctx)
294                 || !BN_sub(tmp, k, tmp)
295                 || !BN_mod_mul(s, s, tmp, order, ctx)) {
296             ERR_raise(ERR_LIB_SM2, ERR_R_BN_LIB);
297             goto done;
298         }
299 
300         /* try again if s == 0 */
301         if (BN_is_zero(s))
302             continue;
303 
304         sig = ECDSA_SIG_new();
305         if (sig == NULL) {
306             ERR_raise(ERR_LIB_SM2, ERR_R_ECDSA_LIB);
307             goto done;
308         }
309 
310          /* takes ownership of r and s */
311         ECDSA_SIG_set0(sig, r, s);
312         break;
313     }
314 
315  done:
316     if (sig == NULL) {
317         BN_free(r);
318         BN_free(s);
319     }
320 
321     BN_CTX_free(ctx);
322     EC_POINT_free(kG);
323     return sig;
324 }
325 
sm2_sig_verify(const EC_KEY * key,const ECDSA_SIG * sig,const BIGNUM * e)326 static int sm2_sig_verify(const EC_KEY *key, const ECDSA_SIG *sig,
327                           const BIGNUM *e)
328 {
329     int ret = 0;
330     const EC_GROUP *group = EC_KEY_get0_group(key);
331     const BIGNUM *order = EC_GROUP_get0_order(group);
332     BN_CTX *ctx = NULL;
333     EC_POINT *pt = NULL;
334     BIGNUM *t = NULL;
335     BIGNUM *x1 = NULL;
336     const BIGNUM *r = NULL;
337     const BIGNUM *s = NULL;
338     OSSL_LIB_CTX *libctx = ossl_ec_key_get_libctx(key);
339 
340     ctx = BN_CTX_new_ex(libctx);
341     pt = EC_POINT_new(group);
342     if (ctx == NULL || pt == NULL) {
343         ERR_raise(ERR_LIB_SM2, ERR_R_EC_LIB);
344         goto done;
345     }
346 
347     BN_CTX_start(ctx);
348     t = BN_CTX_get(ctx);
349     x1 = BN_CTX_get(ctx);
350     if (x1 == NULL) {
351         ERR_raise(ERR_LIB_SM2, ERR_R_BN_LIB);
352         goto done;
353     }
354 
355     /*
356      * B1: verify whether r' in [1,n-1], verification failed if not
357      * B2: verify whether s' in [1,n-1], verification failed if not
358      * B3: set M'~=ZA || M'
359      * B4: calculate e'=Hv(M'~)
360      * B5: calculate t = (r' + s') modn, verification failed if t=0
361      * B6: calculate the point (x1', y1')=[s']G + [t]PA
362      * B7: calculate R=(e'+x1') modn, verification pass if yes, otherwise failed
363      */
364 
365     ECDSA_SIG_get0(sig, &r, &s);
366 
367     if (BN_cmp(r, BN_value_one()) < 0
368             || BN_cmp(s, BN_value_one()) < 0
369             || BN_cmp(order, r) <= 0
370             || BN_cmp(order, s) <= 0) {
371         ERR_raise(ERR_LIB_SM2, SM2_R_BAD_SIGNATURE);
372         goto done;
373     }
374 
375     if (!BN_mod_add(t, r, s, order, ctx)) {
376         ERR_raise(ERR_LIB_SM2, ERR_R_BN_LIB);
377         goto done;
378     }
379 
380     if (BN_is_zero(t)) {
381         ERR_raise(ERR_LIB_SM2, SM2_R_BAD_SIGNATURE);
382         goto done;
383     }
384 
385     if (!EC_POINT_mul(group, pt, s, EC_KEY_get0_public_key(key), t, ctx)
386             || !EC_POINT_get_affine_coordinates(group, pt, x1, NULL, ctx)) {
387         ERR_raise(ERR_LIB_SM2, ERR_R_EC_LIB);
388         goto done;
389     }
390 
391     if (!BN_mod_add(t, e, x1, order, ctx)) {
392         ERR_raise(ERR_LIB_SM2, ERR_R_BN_LIB);
393         goto done;
394     }
395 
396     if (BN_cmp(r, t) == 0)
397         ret = 1;
398 
399  done:
400     BN_CTX_end(ctx);
401     EC_POINT_free(pt);
402     BN_CTX_free(ctx);
403     return ret;
404 }
405 
ossl_sm2_do_sign(const EC_KEY * key,const EVP_MD * digest,const uint8_t * id,const size_t id_len,const uint8_t * msg,size_t msg_len)406 ECDSA_SIG *ossl_sm2_do_sign(const EC_KEY *key,
407                             const EVP_MD *digest,
408                             const uint8_t *id,
409                             const size_t id_len,
410                             const uint8_t *msg, size_t msg_len)
411 {
412     BIGNUM *e = NULL;
413     ECDSA_SIG *sig = NULL;
414 
415     e = sm2_compute_msg_hash(digest, key, id, id_len, msg, msg_len);
416     if (e == NULL) {
417         /* SM2err already called */
418         goto done;
419     }
420 
421     sig = sm2_sig_gen(key, e);
422 
423  done:
424     BN_free(e);
425     return sig;
426 }
427 
ossl_sm2_do_verify(const EC_KEY * key,const EVP_MD * digest,const ECDSA_SIG * sig,const uint8_t * id,const size_t id_len,const uint8_t * msg,size_t msg_len)428 int ossl_sm2_do_verify(const EC_KEY *key,
429                        const EVP_MD *digest,
430                        const ECDSA_SIG *sig,
431                        const uint8_t *id,
432                        const size_t id_len,
433                        const uint8_t *msg, size_t msg_len)
434 {
435     BIGNUM *e = NULL;
436     int ret = 0;
437 
438     e = sm2_compute_msg_hash(digest, key, id, id_len, msg, msg_len);
439     if (e == NULL) {
440         /* SM2err already called */
441         goto done;
442     }
443 
444     ret = sm2_sig_verify(key, sig, e);
445 
446  done:
447     BN_free(e);
448     return ret;
449 }
450 
ossl_sm2_internal_sign(const unsigned char * dgst,int dgstlen,unsigned char * sig,unsigned int * siglen,EC_KEY * eckey)451 int ossl_sm2_internal_sign(const unsigned char *dgst, int dgstlen,
452                            unsigned char *sig, unsigned int *siglen,
453                            EC_KEY *eckey)
454 {
455     BIGNUM *e = NULL;
456     ECDSA_SIG *s = NULL;
457     int sigleni;
458     int ret = -1;
459 
460     if (sig == NULL) {
461         ERR_raise(ERR_LIB_SM2, ERR_R_PASSED_NULL_PARAMETER);
462         goto done;
463     }
464 
465     e = BN_bin2bn(dgst, dgstlen, NULL);
466     if (e == NULL) {
467        ERR_raise(ERR_LIB_SM2, ERR_R_BN_LIB);
468        goto done;
469     }
470 
471     s = sm2_sig_gen(eckey, e);
472     if (s == NULL) {
473         ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
474         goto done;
475     }
476 
477     sigleni = i2d_ECDSA_SIG(s, &sig);
478     if (sigleni < 0) {
479        ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
480        goto done;
481     }
482     *siglen = (unsigned int)sigleni;
483 
484     ret = 1;
485 
486  done:
487     ECDSA_SIG_free(s);
488     BN_free(e);
489     return ret;
490 }
491 
ossl_sm2_internal_verify(const unsigned char * dgst,int dgstlen,const unsigned char * sig,int sig_len,EC_KEY * eckey)492 int ossl_sm2_internal_verify(const unsigned char *dgst, int dgstlen,
493                              const unsigned char *sig, int sig_len,
494                              EC_KEY *eckey)
495 {
496     ECDSA_SIG *s = NULL;
497     BIGNUM *e = NULL;
498     const unsigned char *p = sig;
499     unsigned char *der = NULL;
500     int derlen = -1;
501     int ret = -1;
502 
503     s = ECDSA_SIG_new();
504     if (s == NULL) {
505         ERR_raise(ERR_LIB_SM2, ERR_R_ECDSA_LIB);
506         goto done;
507     }
508     if (d2i_ECDSA_SIG(&s, &p, sig_len) == NULL) {
509         ERR_raise(ERR_LIB_SM2, SM2_R_INVALID_ENCODING);
510         goto done;
511     }
512     /* Ensure signature uses DER and doesn't have trailing garbage */
513     derlen = i2d_ECDSA_SIG(s, &der);
514     if (derlen != sig_len || memcmp(sig, der, derlen) != 0) {
515         ERR_raise(ERR_LIB_SM2, SM2_R_INVALID_ENCODING);
516         goto done;
517     }
518 
519     e = BN_bin2bn(dgst, dgstlen, NULL);
520     if (e == NULL) {
521         ERR_raise(ERR_LIB_SM2, ERR_R_BN_LIB);
522         goto done;
523     }
524 
525     ret = sm2_sig_verify(eckey, s, e);
526 
527  done:
528     OPENSSL_free(der);
529     BN_free(e);
530     ECDSA_SIG_free(s);
531     return ret;
532 }
533