crypto/sm2/sm2_crypt.c

   1 /*
   2  * Copyright 2017-2021 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 /*
  13  * ECDSA low level APIs are deprecated for public use, but still ok for
  14  * internal use.
  15  */
  16 #include "internal/deprecated.h"
  17
  18 #include "crypto/sm2.h"
  19 #include "crypto/sm2err.h"
  20 #include "crypto/ec.h" /* ossl_ecdh_kdf_X9_63() */
  21 #include <openssl/err.h>
  22 #include <openssl/evp.h>
  23 #include <openssl/bn.h>
  24 #include <openssl/asn1.h>
  25 #include <openssl/asn1t.h>
  26 #include <string.h>
  27
  28 typedef struct SM2_Ciphertext_st SM2_Ciphertext;
  29 DECLARE_ASN1_FUNCTIONS(SM2_Ciphertext)
  30
  31 struct SM2_Ciphertext_st {
  32     BIGNUM *C1x;
  33     BIGNUM *C1y;
  34     ASN1_OCTET_STRING *C3;
  35     ASN1_OCTET_STRING *C2;
  36 };
  37
  38 ASN1_SEQUENCE(SM2_Ciphertext) = {
  39     ASN1_SIMPLE(SM2_Ciphertext, C1x, BIGNUM),
  40     ASN1_SIMPLE(SM2_Ciphertext, C1y, BIGNUM),
  41     ASN1_SIMPLE(SM2_Ciphertext, C3, ASN1_OCTET_STRING),
  42     ASN1_SIMPLE(SM2_Ciphertext, C2, ASN1_OCTET_STRING),
  43 } ASN1_SEQUENCE_END(SM2_Ciphertext)
  44
  45 IMPLEMENT_ASN1_FUNCTIONS(SM2_Ciphertext)
  46
  47 static size_t ec_field_size(const EC_GROUP *group)
  48 {
  49     /* Is there some simpler way to do this? */
  50     BIGNUM *p = BN_new();
  51     BIGNUM *a = BN_new();
  52     BIGNUM *b = BN_new();
  53     size_t field_size = 0;
  54
  55     if (p == NULL || a == NULL || b == NULL)
  56        goto done;
  57
  58     if (!EC_GROUP_get_curve(group, p, a, b, NULL))
  59         goto done;
  60     field_size = (BN_num_bits(p) + 7) / 8;
  61
  62  done:
  63     BN_free(p);
  64     BN_free(a);
  65     BN_free(b);
  66
  67     return field_size;
  68 }
  69
  70 int ossl_sm2_plaintext_size(const unsigned char *ct, size_t ct_size,
  71                             size_t *pt_size)
  72 {
  73     struct SM2_Ciphertext_st *sm2_ctext = NULL;
  74
  75     sm2_ctext = d2i_SM2_Ciphertext(NULL, &ct, ct_size);
  76
  77     if (sm2_ctext == NULL) {
  78         ERR_raise(ERR_LIB_SM2, SM2_R_INVALID_ENCODING);
  79         return 0;
  80     }
  81
  82     *pt_size = sm2_ctext->C2->length;
  83     SM2_Ciphertext_free(sm2_ctext);
  84
  85     return 1;
  86 }
  87
  88 int ossl_sm2_ciphertext_size(const EC_KEY *key, const EVP_MD *digest,
  89                              size_t msg_len, size_t *ct_size)
  90 {
  91     const size_t field_size = ec_field_size(EC_KEY_get0_group(key));
  92     const int md_size = EVP_MD_get_size(digest);
  93     size_t sz;
  94
  95     if (field_size == 0 || md_size < 0)
  96         return 0;
  97
  98     /* Integer and string are simple type; set constructed = 0, means primitive and definite length encoding. */
  99     sz = 2 * ASN1_object_size(0, field_size + 1, V_ASN1_INTEGER)
 100          + ASN1_object_size(0, md_size, V_ASN1_OCTET_STRING)
 101          + ASN1_object_size(0, msg_len, V_ASN1_OCTET_STRING);
 102     /* Sequence is structured type; set constructed = 1, means constructed and definite length encoding. */
 103     *ct_size = ASN1_object_size(1, sz, V_ASN1_SEQUENCE);
 104
 105     return 1;
 106 }
 107
 108 int ossl_sm2_encrypt(const EC_KEY *key,
 109                      const EVP_MD *digest,
 110                      const uint8_t *msg, size_t msg_len,
 111                      uint8_t *ciphertext_buf, size_t *ciphertext_len)
 112 {
 113     int rc = 0, ciphertext_leni;
 114     size_t i;
 115     BN_CTX *ctx = NULL;
 116     BIGNUM *k = NULL;
 117     BIGNUM *x1 = NULL;
 118     BIGNUM *y1 = NULL;
 119     BIGNUM *x2 = NULL;
 120     BIGNUM *y2 = NULL;
 121     EVP_MD_CTX *hash = EVP_MD_CTX_new();
 122     struct SM2_Ciphertext_st ctext_struct;
 123     const EC_GROUP *group = EC_KEY_get0_group(key);
 124     const BIGNUM *order = EC_GROUP_get0_order(group);
 125     const EC_POINT *P = EC_KEY_get0_public_key(key);
 126     EC_POINT *kG = NULL;
 127     EC_POINT *kP = NULL;
 128     uint8_t *msg_mask = NULL;
 129     uint8_t *x2y2 = NULL;
 130     uint8_t *C3 = NULL;
 131     size_t field_size;
 132     const int C3_size = EVP_MD_get_size(digest);
 133     EVP_MD *fetched_digest = NULL;
 134     OSSL_LIB_CTX *libctx = ossl_ec_key_get_libctx(key);
 135     const char *propq = ossl_ec_key_get0_propq(key);
 136
 137     /* NULL these before any "goto done" */
 138     ctext_struct.C2 = NULL;
 139     ctext_struct.C3 = NULL;
 140
 141     if (hash == NULL || C3_size <= 0) {
 142         ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
 143         goto done;
 144     }
 145
 146     field_size = ec_field_size(group);
 147     if (field_size == 0) {
 148         ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
 149         goto done;
 150     }
 151
 152     kG = EC_POINT_new(group);
 153     kP = EC_POINT_new(group);
 154     ctx = BN_CTX_new_ex(libctx);
 155     if (kG == NULL || kP == NULL || ctx == NULL) {
 156         ERR_raise(ERR_LIB_SM2, ERR_R_MALLOC_FAILURE);
 157         goto done;
 158     }
 159
 160     BN_CTX_start(ctx);
 161     k = BN_CTX_get(ctx);
 162     x1 = BN_CTX_get(ctx);
 163     x2 = BN_CTX_get(ctx);
 164     y1 = BN_CTX_get(ctx);
 165     y2 = BN_CTX_get(ctx);
 166
 167     if (y2 == NULL) {
 168         ERR_raise(ERR_LIB_SM2, ERR_R_BN_LIB);
 169         goto done;
 170     }
 171
 172     x2y2 = OPENSSL_zalloc(2 * field_size);
 173     C3 = OPENSSL_zalloc(C3_size);
 174
 175     if (x2y2 == NULL || C3 == NULL) {
 176         ERR_raise(ERR_LIB_SM2, ERR_R_MALLOC_FAILURE);
 177         goto done;
 178     }
 179
 180     memset(ciphertext_buf, 0, *ciphertext_len);
 181
 182     if (!BN_priv_rand_range_ex(k, order, 0, ctx)) {
 183         ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
 184         goto done;
 185     }
 186
 187     if (!EC_POINT_mul(group, kG, k, NULL, NULL, ctx)
 188             || !EC_POINT_get_affine_coordinates(group, kG, x1, y1, ctx)
 189             || !EC_POINT_mul(group, kP, NULL, P, k, ctx)
 190             || !EC_POINT_get_affine_coordinates(group, kP, x2, y2, ctx)) {
 191         ERR_raise(ERR_LIB_SM2, ERR_R_EC_LIB);
 192         goto done;
 193     }
 194
 195     if (BN_bn2binpad(x2, x2y2, field_size) < 0
 196             || BN_bn2binpad(y2, x2y2 + field_size, field_size) < 0) {
 197         ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
 198         goto done;
 199     }
 200
 201     msg_mask = OPENSSL_zalloc(msg_len);
 202     if (msg_mask == NULL) {
 203        ERR_raise(ERR_LIB_SM2, ERR_R_MALLOC_FAILURE);
 204        goto done;
 205    }
 206
 207     /* X9.63 with no salt happens to match the KDF used in SM2 */
 208     if (!ossl_ecdh_kdf_X9_63(msg_mask, msg_len, x2y2, 2 * field_size, NULL, 0,
 209                              digest, libctx, propq)) {
 210         ERR_raise(ERR_LIB_SM2, ERR_R_EVP_LIB);
 211         goto done;
 212     }
 213
 214     for (i = 0; i != msg_len; ++i)
 215         msg_mask[i] ^= msg[i];
 216
 217     fetched_digest = EVP_MD_fetch(libctx, EVP_MD_get0_name(digest), propq);
 218     if (fetched_digest == NULL) {
 219         ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
 220         goto done;
 221     }
 222     if (EVP_DigestInit(hash, fetched_digest) == 0
 223             || EVP_DigestUpdate(hash, x2y2, field_size) == 0
 224             || EVP_DigestUpdate(hash, msg, msg_len) == 0
 225             || EVP_DigestUpdate(hash, x2y2 + field_size, field_size) == 0
 226             || EVP_DigestFinal(hash, C3, NULL) == 0) {
 227         ERR_raise(ERR_LIB_SM2, ERR_R_EVP_LIB);
 228         goto done;
 229     }
 230
 231     ctext_struct.C1x = x1;
 232     ctext_struct.C1y = y1;
 233     ctext_struct.C3 = ASN1_OCTET_STRING_new();
 234     ctext_struct.C2 = ASN1_OCTET_STRING_new();
 235
 236     if (ctext_struct.C3 == NULL || ctext_struct.C2 == NULL) {
 237        ERR_raise(ERR_LIB_SM2, ERR_R_MALLOC_FAILURE);
 238        goto done;
 239     }
 240     if (!ASN1_OCTET_STRING_set(ctext_struct.C3, C3, C3_size)
 241             || !ASN1_OCTET_STRING_set(ctext_struct.C2, msg_mask, msg_len)) {
 242         ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
 243         goto done;
 244     }
 245
 246     ciphertext_leni = i2d_SM2_Ciphertext(&ctext_struct, &ciphertext_buf);
 247     /* Ensure cast to size_t is safe */
 248     if (ciphertext_leni < 0) {
 249         ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
 250         goto done;
 251     }
 252     *ciphertext_len = (size_t)ciphertext_leni;
 253
 254     rc = 1;
 255
 256  done:
 257     EVP_MD_free(fetched_digest);
 258     ASN1_OCTET_STRING_free(ctext_struct.C2);
 259     ASN1_OCTET_STRING_free(ctext_struct.C3);
 260     OPENSSL_free(msg_mask);
 261     OPENSSL_free(x2y2);
 262     OPENSSL_free(C3);
 263     EVP_MD_CTX_free(hash);
 264     BN_CTX_free(ctx);
 265     EC_POINT_free(kG);
 266     EC_POINT_free(kP);
 267     return rc;
 268 }
 269
 270 int ossl_sm2_decrypt(const EC_KEY *key,
 271                      const EVP_MD *digest,
 272                      const uint8_t *ciphertext, size_t ciphertext_len,
 273                      uint8_t *ptext_buf, size_t *ptext_len)
 274 {
 275     int rc = 0;
 276     int i;
 277     BN_CTX *ctx = NULL;
 278     const EC_GROUP *group = EC_KEY_get0_group(key);
 279     EC_POINT *C1 = NULL;
 280     struct SM2_Ciphertext_st *sm2_ctext = NULL;
 281     BIGNUM *x2 = NULL;
 282     BIGNUM *y2 = NULL;
 283     uint8_t *x2y2 = NULL;
 284     uint8_t *computed_C3 = NULL;
 285     const size_t field_size = ec_field_size(group);
 286     const int hash_size = EVP_MD_get_size(digest);
 287     uint8_t *msg_mask = NULL;
 288     const uint8_t *C2 = NULL;
 289     const uint8_t *C3 = NULL;
 290     int msg_len = 0;
 291     EVP_MD_CTX *hash = NULL;
 292     OSSL_LIB_CTX *libctx = ossl_ec_key_get_libctx(key);
 293     const char *propq = ossl_ec_key_get0_propq(key);
 294
 295     if (field_size == 0 || hash_size <= 0)
 296        goto done;
 297
 298     memset(ptext_buf, 0xFF, *ptext_len);
 299
 300     sm2_ctext = d2i_SM2_Ciphertext(NULL, &ciphertext, ciphertext_len);
 301
 302     if (sm2_ctext == NULL) {
 303         ERR_raise(ERR_LIB_SM2, SM2_R_ASN1_ERROR);
 304         goto done;
 305     }
 306
 307     if (sm2_ctext->C3->length != hash_size) {
 308         ERR_raise(ERR_LIB_SM2, SM2_R_INVALID_ENCODING);
 309         goto done;
 310     }
 311
 312     C2 = sm2_ctext->C2->data;
 313     C3 = sm2_ctext->C3->data;
 314     msg_len = sm2_ctext->C2->length;
 315
 316     ctx = BN_CTX_new_ex(libctx);
 317     if (ctx == NULL) {
 318         ERR_raise(ERR_LIB_SM2, ERR_R_MALLOC_FAILURE);
 319         goto done;
 320     }
 321
 322     BN_CTX_start(ctx);
 323     x2 = BN_CTX_get(ctx);
 324     y2 = BN_CTX_get(ctx);
 325
 326     if (y2 == NULL) {
 327         ERR_raise(ERR_LIB_SM2, ERR_R_BN_LIB);
 328         goto done;
 329     }
 330
 331     msg_mask = OPENSSL_zalloc(msg_len);
 332     x2y2 = OPENSSL_zalloc(2 * field_size);
 333     computed_C3 = OPENSSL_zalloc(hash_size);
 334
 335     if (msg_mask == NULL || x2y2 == NULL || computed_C3 == NULL) {
 336         ERR_raise(ERR_LIB_SM2, ERR_R_MALLOC_FAILURE);
 337         goto done;
 338     }
 339
 340     C1 = EC_POINT_new(group);
 341     if (C1 == NULL) {
 342         ERR_raise(ERR_LIB_SM2, ERR_R_MALLOC_FAILURE);
 343         goto done;
 344     }
 345
 346     if (!EC_POINT_set_affine_coordinates(group, C1, sm2_ctext->C1x,
 347                                          sm2_ctext->C1y, ctx)
 348             || !EC_POINT_mul(group, C1, NULL, C1, EC_KEY_get0_private_key(key),
 349                              ctx)
 350             || !EC_POINT_get_affine_coordinates(group, C1, x2, y2, ctx)) {
 351         ERR_raise(ERR_LIB_SM2, ERR_R_EC_LIB);
 352         goto done;
 353     }
 354
 355     if (BN_bn2binpad(x2, x2y2, field_size) < 0
 356             || BN_bn2binpad(y2, x2y2 + field_size, field_size) < 0
 357             || !ossl_ecdh_kdf_X9_63(msg_mask, msg_len, x2y2, 2 * field_size,
 358                                     NULL, 0, digest, libctx, propq)) {
 359         ERR_raise(ERR_LIB_SM2, ERR_R_INTERNAL_ERROR);
 360         goto done;
 361     }
 362
 363     for (i = 0; i != msg_len; ++i)
 364         ptext_buf[i] = C2[i] ^ msg_mask[i];
 365
 366     hash = EVP_MD_CTX_new();
 367     if (hash == NULL) {
 368         ERR_raise(ERR_LIB_SM2, ERR_R_MALLOC_FAILURE);
 369         goto done;
 370     }
 371
 372     if (!EVP_DigestInit(hash, digest)
 373             || !EVP_DigestUpdate(hash, x2y2, field_size)
 374             || !EVP_DigestUpdate(hash, ptext_buf, msg_len)
 375             || !EVP_DigestUpdate(hash, x2y2 + field_size, field_size)
 376             || !EVP_DigestFinal(hash, computed_C3, NULL)) {
 377         ERR_raise(ERR_LIB_SM2, ERR_R_EVP_LIB);
 378         goto done;
 379     }
 380
 381     if (CRYPTO_memcmp(computed_C3, C3, hash_size) != 0) {
 382         ERR_raise(ERR_LIB_SM2, SM2_R_INVALID_DIGEST);
 383         goto done;
 384     }
 385
 386     rc = 1;
 387     *ptext_len = msg_len;
 388
 389  done:
 390     if (rc == 0)
 391         memset(ptext_buf, 0, *ptext_len);
 392
 393     OPENSSL_free(msg_mask);
 394     OPENSSL_free(x2y2);
 395     OPENSSL_free(computed_C3);
 396     EC_POINT_free(C1);
 397     BN_CTX_free(ctx);
 398     SM2_Ciphertext_free(sm2_ctext);
 399     EVP_MD_CTX_free(hash);
 400
 401     return rc;
 402 }