crypto/sm2/sm2_crypt.c

   1 /*
   2  * Copyright 2017-2018 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 OpenSSL license (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/sm2.h"
  13 #include "internal/sm2err.h"
  14 #include <openssl/err.h>
  15 #include <openssl/evp.h>
  16 #include <openssl/bn.h>
  17 #include <openssl/asn1.h>
  18 #include <openssl/asn1t.h>
  19 #include <string.h>
  20
  21 typedef struct SM2_Ciphertext_st SM2_Ciphertext;
  22 DECLARE_ASN1_FUNCTIONS(SM2_Ciphertext)
  23
  24 struct SM2_Ciphertext_st {
  25     BIGNUM *C1x;
  26     BIGNUM *C1y;
  27     ASN1_OCTET_STRING *C3;
  28     ASN1_OCTET_STRING *C2;
  29 };
  30
  31 ASN1_SEQUENCE(SM2_Ciphertext) = {
  32     ASN1_SIMPLE(SM2_Ciphertext, C1x, BIGNUM),
  33     ASN1_SIMPLE(SM2_Ciphertext, C1y, BIGNUM),
  34     ASN1_SIMPLE(SM2_Ciphertext, C3, ASN1_OCTET_STRING),
  35     ASN1_SIMPLE(SM2_Ciphertext, C2, ASN1_OCTET_STRING),
  36 } ASN1_SEQUENCE_END(SM2_Ciphertext)
  37
  38 IMPLEMENT_ASN1_FUNCTIONS(SM2_Ciphertext)
  39
  40 static size_t EC_field_size(const EC_GROUP *group)
  41 {
  42     /* Is there some simpler way to do this? */
  43     BIGNUM *p = BN_new();
  44     BIGNUM *a = BN_new();
  45     BIGNUM *b = BN_new();
  46     size_t field_size = 0;
  47
  48     if (p == NULL || a == NULL || b == NULL)
  49        goto done;
  50
  51     EC_GROUP_get_curve_GFp(group, p, a, b, NULL);
  52     field_size = (BN_num_bits(p) + 7) / 8;
  53
  54  done:
  55     BN_free(p);
  56     BN_free(a);
  57     BN_free(b);
  58
  59     return field_size;
  60 }
  61
  62 int SM2_plaintext_size(const EC_KEY *key, const EVP_MD *digest, size_t msg_len,
  63                        size_t *pt_size)
  64 {
  65     const size_t field_size = EC_field_size(EC_KEY_get0_group(key));
  66     const int md_size = EVP_MD_size(digest);
  67     size_t overhead;
  68
  69     if (md_size < 0) {
  70         SM2err(SM2_F_SM2_PLAINTEXT_SIZE, SM2_R_INVALID_DIGEST);
  71         return 0;
  72     }
  73     if (field_size == 0) {
  74         SM2err(SM2_F_SM2_PLAINTEXT_SIZE, SM2_R_INVALID_FIELD);
  75         return 0;
  76     }
  77
  78     overhead = 10 + 2 * field_size + (size_t)md_size;
  79     if (msg_len <= overhead) {
  80         SM2err(SM2_F_SM2_PLAINTEXT_SIZE, SM2_R_INVALID_ENCODING);
  81         return 0;
  82     }
  83
  84     *pt_size = msg_len - overhead;
  85     return 1;
  86 }
  87
  88 int SM2_ciphertext_size(const EC_KEY *key, const EVP_MD *digest, size_t msg_len,
  89                         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_size(digest);
  93
  94     if (field_size == 0 || md_size < 0)
  95         return 0;
  96
  97     *ct_size = 10 + 2 * field_size + (size_t)md_size + msg_len;
  98     return 1;
  99 }
 100
 101 int SM2_encrypt(const EC_KEY *key,
 102                 const EVP_MD *digest,
 103                 const uint8_t *msg,
 104                 size_t msg_len, uint8_t *ciphertext_buf, size_t *ciphertext_len)
 105 {
 106     int rc = 0, ciphertext_leni;
 107     size_t i;
 108     BN_CTX *ctx = NULL;
 109     BIGNUM *k = NULL;
 110     BIGNUM *x1 = NULL;
 111     BIGNUM *y1 = NULL;
 112     BIGNUM *x2 = NULL;
 113     BIGNUM *y2 = NULL;
 114     EVP_MD_CTX *hash = EVP_MD_CTX_new();
 115     struct SM2_Ciphertext_st ctext_struct;
 116     const EC_GROUP *group = EC_KEY_get0_group(key);
 117     const BIGNUM *order = EC_GROUP_get0_order(group);
 118     const EC_POINT *P = EC_KEY_get0_public_key(key);
 119     EC_POINT *kG = NULL;
 120     EC_POINT *kP = NULL;
 121     uint8_t *msg_mask = NULL;
 122     uint8_t *x2y2 = NULL;
 123     uint8_t *C3 = NULL;
 124     const size_t field_size = EC_field_size(group);
 125     const size_t C3_size = EVP_MD_size(digest);
 126
 127     /* NULL these before any "goto done" */
 128     ctext_struct.C2 = NULL;
 129     ctext_struct.C3 = NULL;
 130
 131     if (hash == NULL
 132             || group == NULL
 133             || order == NULL
 134             || P == NULL
 135             || field_size == 0
 136             || C3_size == 0) {
 137         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);
 138         goto done;
 139     }
 140
 141     kG = EC_POINT_new(group);
 142     kP = EC_POINT_new(group);
 143     ctx = BN_CTX_new();
 144     if (kG == NULL || kP == NULL || ctx == NULL) {
 145         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_MALLOC_FAILURE);
 146         goto done;
 147     }
 148
 149     BN_CTX_start(ctx);
 150     k = BN_CTX_get(ctx);
 151     x1 = BN_CTX_get(ctx);
 152     x2 = BN_CTX_get(ctx);
 153     y1 = BN_CTX_get(ctx);
 154     y2 = BN_CTX_get(ctx);
 155
 156     if (y2 == NULL) {
 157         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_BN_LIB);
 158         goto done;
 159     }
 160
 161     x2y2 = OPENSSL_zalloc(2 * field_size);
 162     C3 = OPENSSL_zalloc(C3_size);
 163
 164     if (x2y2 == NULL || C3 == NULL) {
 165         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_MALLOC_FAILURE);
 166         goto done;
 167     }
 168
 169     memset(ciphertext_buf, 0, *ciphertext_len);
 170
 171     if (!BN_priv_rand_range(k, order)) {
 172         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);
 173         goto done;
 174     }
 175
 176     if (!EC_POINT_mul(group, kG, k, NULL, NULL, ctx)
 177             || !EC_POINT_get_affine_coordinates_GFp(group, kG, x1, y1, ctx)
 178             || !EC_POINT_mul(group, kP, NULL, P, k, ctx)
 179             || !EC_POINT_get_affine_coordinates_GFp(group, kP, x2, y2, ctx)) {
 180         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_EC_LIB);
 181         goto done;
 182     }
 183
 184     if (BN_bn2binpad(x2, x2y2, field_size) < 0
 185             || BN_bn2binpad(y2, x2y2 + field_size, field_size) < 0) {
 186         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);
 187         goto done;
 188     }
 189
 190     msg_mask = OPENSSL_zalloc(msg_len);
 191     if (msg_mask == NULL) {
 192        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_MALLOC_FAILURE);
 193        goto done;
 194    }
 195
 196     /* X9.63 with no salt happens to match the KDF used in SM2 */
 197     if (!ECDH_KDF_X9_62(msg_mask, msg_len, x2y2, 2 * field_size, NULL, 0,
 198                         digest)) {
 199         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_EVP_LIB);
 200         goto done;
 201     }
 202
 203     for (i = 0; i != msg_len; ++i)
 204         msg_mask[i] ^= msg[i];
 205
 206     if (EVP_DigestInit(hash, digest) == 0
 207             || EVP_DigestUpdate(hash, x2y2, field_size) == 0
 208             || EVP_DigestUpdate(hash, msg, msg_len) == 0
 209             || EVP_DigestUpdate(hash, x2y2 + field_size, field_size) == 0
 210             || EVP_DigestFinal(hash, C3, NULL) == 0) {
 211         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_EVP_LIB);
 212         goto done;
 213     }
 214
 215     ctext_struct.C1x = x1;
 216     ctext_struct.C1y = y1;
 217     ctext_struct.C3 = ASN1_OCTET_STRING_new();
 218     ctext_struct.C2 = ASN1_OCTET_STRING_new();
 219
 220     if (ctext_struct.C3 == NULL || ctext_struct.C2 == NULL) {
 221        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_MALLOC_FAILURE);
 222        goto done;
 223     }
 224     if (!ASN1_OCTET_STRING_set(ctext_struct.C3, C3, C3_size)
 225             || !ASN1_OCTET_STRING_set(ctext_struct.C2, msg_mask, msg_len)) {
 226         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);
 227         goto done;
 228     }
 229
 230     ciphertext_leni = i2d_SM2_Ciphertext(&ctext_struct, &ciphertext_buf);
 231     /* Ensure cast to size_t is safe */
 232     if (ciphertext_leni < 0) {
 233         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);
 234         goto done;
 235     }
 236     *ciphertext_len = (size_t)ciphertext_leni;
 237
 238     rc = 1;
 239
 240  done:
 241     ASN1_OCTET_STRING_free(ctext_struct.C2);
 242     ASN1_OCTET_STRING_free(ctext_struct.C3);
 243     OPENSSL_free(msg_mask);
 244     OPENSSL_free(x2y2);
 245     OPENSSL_free(C3);
 246     EVP_MD_CTX_free(hash);
 247     BN_CTX_free(ctx);
 248     EC_POINT_free(kG);
 249     EC_POINT_free(kP);
 250     return rc;
 251 }
 252
 253 int SM2_decrypt(const EC_KEY *key,
 254                 const EVP_MD *digest,
 255                 const uint8_t *ciphertext,
 256                 size_t ciphertext_len, uint8_t *ptext_buf, size_t *ptext_len)
 257 {
 258     int rc = 0;
 259     int i;
 260     BN_CTX *ctx = NULL;
 261     const EC_GROUP *group = EC_KEY_get0_group(key);
 262     EC_POINT *C1 = NULL;
 263     struct SM2_Ciphertext_st *sm2_ctext = NULL;
 264     BIGNUM *x2 = NULL;
 265     BIGNUM *y2 = NULL;
 266     uint8_t *x2y2 = NULL;
 267     uint8_t *computed_C3 = NULL;
 268     const size_t field_size = EC_field_size(group);
 269     const int hash_size = EVP_MD_size(digest);
 270     uint8_t *msg_mask = NULL;
 271     const uint8_t *C2 = NULL;
 272     const uint8_t *C3 = NULL;
 273     int msg_len = 0;
 274     EVP_MD_CTX *hash = NULL;
 275
 276     if (field_size == 0 || hash_size == 0)
 277        goto done;
 278
 279     memset(ptext_buf, 0xFF, *ptext_len);
 280
 281     sm2_ctext = d2i_SM2_Ciphertext(NULL, &ciphertext, ciphertext_len);
 282
 283     if (sm2_ctext == NULL) {
 284         SM2err(SM2_F_SM2_DECRYPT, SM2_R_ASN1_ERROR);
 285         goto done;
 286     }
 287
 288     if (sm2_ctext->C3->length != hash_size) {
 289         SM2err(SM2_F_SM2_DECRYPT, SM2_R_INVALID_ENCODING);
 290         goto done;
 291     }
 292
 293     C2 = sm2_ctext->C2->data;
 294     C3 = sm2_ctext->C3->data;
 295     msg_len = sm2_ctext->C2->length;
 296
 297     ctx = BN_CTX_new();
 298     if (ctx == NULL) {
 299         SM2err(SM2_F_SM2_DECRYPT, ERR_R_MALLOC_FAILURE);
 300         goto done;
 301     }
 302
 303     BN_CTX_start(ctx);
 304     x2 = BN_CTX_get(ctx);
 305     y2 = BN_CTX_get(ctx);
 306
 307     if (y2 == NULL) {
 308         SM2err(SM2_F_SM2_DECRYPT, ERR_R_BN_LIB);
 309         goto done;
 310     }
 311
 312     msg_mask = OPENSSL_zalloc(msg_len);
 313     x2y2 = OPENSSL_zalloc(2 * field_size);
 314     computed_C3 = OPENSSL_zalloc(hash_size);
 315
 316     if (msg_mask == NULL || x2y2 == NULL || computed_C3 == NULL) {
 317         SM2err(SM2_F_SM2_DECRYPT, ERR_R_MALLOC_FAILURE);
 318         goto done;
 319     }
 320
 321     C1 = EC_POINT_new(group);
 322     if (C1 == NULL) {
 323         SM2err(SM2_F_SM2_DECRYPT, ERR_R_MALLOC_FAILURE);
 324         goto done;
 325     }
 326
 327     if (!EC_POINT_set_affine_coordinates_GFp(group, C1, sm2_ctext->C1x,
 328                                             sm2_ctext->C1y, ctx)
 329             || !EC_POINT_mul(group, C1, NULL, C1, EC_KEY_get0_private_key(key),
 330                              ctx)
 331             || !EC_POINT_get_affine_coordinates_GFp(group, C1, x2, y2, ctx)) {
 332         SM2err(SM2_F_SM2_DECRYPT, ERR_R_EC_LIB);
 333         goto done;
 334     }
 335
 336     if (BN_bn2binpad(x2, x2y2, field_size) < 0
 337             || BN_bn2binpad(y2, x2y2 + field_size, field_size) < 0
 338             || !ECDH_KDF_X9_62(msg_mask, msg_len, x2y2, 2 * field_size, NULL, 0,
 339                                digest)) {
 340         SM2err(SM2_F_SM2_DECRYPT, ERR_R_INTERNAL_ERROR);
 341         goto done;
 342     }
 343
 344     for (i = 0; i != msg_len; ++i)
 345         ptext_buf[i] = C2[i] ^ msg_mask[i];
 346
 347     hash = EVP_MD_CTX_new();
 348     if (hash == NULL) {
 349         SM2err(SM2_F_SM2_DECRYPT, ERR_R_MALLOC_FAILURE);
 350         goto done;
 351     }
 352
 353     if (!EVP_DigestInit(hash, digest)
 354             || !EVP_DigestUpdate(hash, x2y2, field_size)
 355             || !EVP_DigestUpdate(hash, ptext_buf, msg_len)
 356             || !EVP_DigestUpdate(hash, x2y2 + field_size, field_size)
 357             || !EVP_DigestFinal(hash, computed_C3, NULL)) {
 358         SM2err(SM2_F_SM2_DECRYPT, ERR_R_EVP_LIB);
 359         goto done;
 360     }
 361
 362     if (CRYPTO_memcmp(computed_C3, C3, hash_size) != 0) {
 363         SM2err(SM2_F_SM2_DECRYPT, SM2_R_INVALID_DIGEST);
 364         goto done;
 365     }
 366
 367     rc = 1;
 368     *ptext_len = msg_len;
 369
 370  done:
 371     if (rc == 0)
 372         memset(ptext_buf, 0, *ptext_len);
 373
 374     OPENSSL_free(msg_mask);
 375     OPENSSL_free(x2y2);
 376     OPENSSL_free(computed_C3);
 377     EC_POINT_free(C1);
 378     BN_CTX_free(ctx);
 379     SM2_Ciphertext_free(sm2_ctext);
 380     EVP_MD_CTX_free(hash);
 381
 382     return rc;
 383 }