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 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" /* 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 sm2_plaintext_size(const EC_KEY *key, const EVP_MD *digest, size_t msg_len,
  71                        size_t *pt_size)
  72 {
  73     const size_t field_size = ec_field_size(EC_KEY_get0_group(key));
  74     const int md_size = EVP_MD_size(digest);
  75     size_t overhead;
  76
  77     if (md_size < 0) {
  78         SM2err(SM2_F_SM2_PLAINTEXT_SIZE, SM2_R_INVALID_DIGEST);
  79         return 0;
  80     }
  81     if (field_size == 0) {
  82         SM2err(SM2_F_SM2_PLAINTEXT_SIZE, SM2_R_INVALID_FIELD);
  83         return 0;
  84     }
  85
  86     overhead = 10 + 2 * field_size + (size_t)md_size;
  87     if (msg_len <= overhead) {
  88         SM2err(SM2_F_SM2_PLAINTEXT_SIZE, SM2_R_INVALID_ENCODING);
  89         return 0;
  90     }
  91
  92     *pt_size = msg_len - overhead;
  93     return 1;
  94 }
  95
  96 int sm2_ciphertext_size(const EC_KEY *key, const EVP_MD *digest, size_t msg_len,
  97                         size_t *ct_size)
  98 {
  99     const size_t field_size = ec_field_size(EC_KEY_get0_group(key));
 100     const int md_size = EVP_MD_size(digest);
 101     size_t sz;
 102
 103     if (field_size == 0 || md_size < 0)
 104         return 0;
 105
 106     /* Integer and string are simple type; set constructed = 0, means primitive and definite length encoding. */
 107     sz = 2 * ASN1_object_size(0, field_size + 1, V_ASN1_INTEGER)
 108          + ASN1_object_size(0, md_size, V_ASN1_OCTET_STRING)
 109          + ASN1_object_size(0, msg_len, V_ASN1_OCTET_STRING);
 110     /* Sequence is structured type; set constructed = 1, means constructed and definite length encoding. */
 111     *ct_size = ASN1_object_size(1, sz, V_ASN1_SEQUENCE);
 112
 113     return 1;
 114 }
 115
 116 int sm2_encrypt(const EC_KEY *key,
 117                 const EVP_MD *digest,
 118                 const uint8_t *msg,
 119                 size_t msg_len, uint8_t *ciphertext_buf, size_t *ciphertext_len)
 120 {
 121     int rc = 0, ciphertext_leni;
 122     size_t i;
 123     BN_CTX *ctx = NULL;
 124     BIGNUM *k = NULL;
 125     BIGNUM *x1 = NULL;
 126     BIGNUM *y1 = NULL;
 127     BIGNUM *x2 = NULL;
 128     BIGNUM *y2 = NULL;
 129     EVP_MD_CTX *hash = EVP_MD_CTX_new();
 130     struct SM2_Ciphertext_st ctext_struct;
 131     const EC_GROUP *group = EC_KEY_get0_group(key);
 132     const BIGNUM *order = EC_GROUP_get0_order(group);
 133     const EC_POINT *P = EC_KEY_get0_public_key(key);
 134     EC_POINT *kG = NULL;
 135     EC_POINT *kP = NULL;
 136     uint8_t *msg_mask = NULL;
 137     uint8_t *x2y2 = NULL;
 138     uint8_t *C3 = NULL;
 139     size_t field_size;
 140     const int C3_size = EVP_MD_size(digest);
 141
 142     /* NULL these before any "goto done" */
 143     ctext_struct.C2 = NULL;
 144     ctext_struct.C3 = NULL;
 145
 146     if (hash == NULL || C3_size <= 0) {
 147         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);
 148         goto done;
 149     }
 150
 151     field_size = ec_field_size(group);
 152     if (field_size == 0) {
 153         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);
 154         goto done;
 155     }
 156
 157     kG = EC_POINT_new(group);
 158     kP = EC_POINT_new(group);
 159     ctx = BN_CTX_new();
 160     if (kG == NULL || kP == NULL || ctx == NULL) {
 161         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_MALLOC_FAILURE);
 162         goto done;
 163     }
 164
 165     BN_CTX_start(ctx);
 166     k = BN_CTX_get(ctx);
 167     x1 = BN_CTX_get(ctx);
 168     x2 = BN_CTX_get(ctx);
 169     y1 = BN_CTX_get(ctx);
 170     y2 = BN_CTX_get(ctx);
 171
 172     if (y2 == NULL) {
 173         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_BN_LIB);
 174         goto done;
 175     }
 176
 177     x2y2 = OPENSSL_zalloc(2 * field_size);
 178     C3 = OPENSSL_zalloc(C3_size);
 179
 180     if (x2y2 == NULL || C3 == NULL) {
 181         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_MALLOC_FAILURE);
 182         goto done;
 183     }
 184
 185     memset(ciphertext_buf, 0, *ciphertext_len);
 186
 187     if (!BN_priv_rand_range(k, order)) {
 188         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);
 189         goto done;
 190     }
 191
 192     if (!EC_POINT_mul(group, kG, k, NULL, NULL, ctx)
 193             || !EC_POINT_get_affine_coordinates(group, kG, x1, y1, ctx)
 194             || !EC_POINT_mul(group, kP, NULL, P, k, ctx)
 195             || !EC_POINT_get_affine_coordinates(group, kP, x2, y2, ctx)) {
 196         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_EC_LIB);
 197         goto done;
 198     }
 199
 200     if (BN_bn2binpad(x2, x2y2, field_size) < 0
 201             || BN_bn2binpad(y2, x2y2 + field_size, field_size) < 0) {
 202         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);
 203         goto done;
 204     }
 205
 206     msg_mask = OPENSSL_zalloc(msg_len);
 207     if (msg_mask == NULL) {
 208        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_MALLOC_FAILURE);
 209        goto done;
 210    }
 211
 212     /* X9.63 with no salt happens to match the KDF used in SM2 */
 213     if (!ecdh_KDF_X9_63(msg_mask, msg_len, x2y2, 2 * field_size, NULL, 0,
 214                         digest)) {
 215         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_EVP_LIB);
 216         goto done;
 217     }
 218
 219     for (i = 0; i != msg_len; ++i)
 220         msg_mask[i] ^= msg[i];
 221
 222     if (EVP_DigestInit(hash, 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         SM2err(SM2_F_SM2_ENCRYPT, 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        SM2err(SM2_F_SM2_ENCRYPT, 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         SM2err(SM2_F_SM2_ENCRYPT, 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         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);
 250         goto done;
 251     }
 252     *ciphertext_len = (size_t)ciphertext_leni;
 253
 254     rc = 1;
 255
 256  done:
 257     ASN1_OCTET_STRING_free(ctext_struct.C2);
 258     ASN1_OCTET_STRING_free(ctext_struct.C3);
 259     OPENSSL_free(msg_mask);
 260     OPENSSL_free(x2y2);
 261     OPENSSL_free(C3);
 262     EVP_MD_CTX_free(hash);
 263     BN_CTX_free(ctx);
 264     EC_POINT_free(kG);
 265     EC_POINT_free(kP);
 266     return rc;
 267 }
 268
 269 int sm2_decrypt(const EC_KEY *key,
 270                 const EVP_MD *digest,
 271                 const uint8_t *ciphertext,
 272                 size_t ciphertext_len, uint8_t *ptext_buf, size_t *ptext_len)
 273 {
 274     int rc = 0;
 275     int i;
 276     BN_CTX *ctx = NULL;
 277     const EC_GROUP *group = EC_KEY_get0_group(key);
 278     EC_POINT *C1 = NULL;
 279     struct SM2_Ciphertext_st *sm2_ctext = NULL;
 280     BIGNUM *x2 = NULL;
 281     BIGNUM *y2 = NULL;
 282     uint8_t *x2y2 = NULL;
 283     uint8_t *computed_C3 = NULL;
 284     const size_t field_size = ec_field_size(group);
 285     const int hash_size = EVP_MD_size(digest);
 286     uint8_t *msg_mask = NULL;
 287     const uint8_t *C2 = NULL;
 288     const uint8_t *C3 = NULL;
 289     int msg_len = 0;
 290     EVP_MD_CTX *hash = NULL;
 291
 292     if (field_size == 0 || hash_size <= 0)
 293        goto done;
 294
 295     memset(ptext_buf, 0xFF, *ptext_len);
 296
 297     sm2_ctext = d2i_SM2_Ciphertext(NULL, &ciphertext, ciphertext_len);
 298
 299     if (sm2_ctext == NULL) {
 300         SM2err(SM2_F_SM2_DECRYPT, SM2_R_ASN1_ERROR);
 301         goto done;
 302     }
 303
 304     if (sm2_ctext->C3->length != hash_size) {
 305         SM2err(SM2_F_SM2_DECRYPT, SM2_R_INVALID_ENCODING);
 306         goto done;
 307     }
 308
 309     C2 = sm2_ctext->C2->data;
 310     C3 = sm2_ctext->C3->data;
 311     msg_len = sm2_ctext->C2->length;
 312
 313     ctx = BN_CTX_new();
 314     if (ctx == NULL) {
 315         SM2err(SM2_F_SM2_DECRYPT, ERR_R_MALLOC_FAILURE);
 316         goto done;
 317     }
 318
 319     BN_CTX_start(ctx);
 320     x2 = BN_CTX_get(ctx);
 321     y2 = BN_CTX_get(ctx);
 322
 323     if (y2 == NULL) {
 324         SM2err(SM2_F_SM2_DECRYPT, ERR_R_BN_LIB);
 325         goto done;
 326     }
 327
 328     msg_mask = OPENSSL_zalloc(msg_len);
 329     x2y2 = OPENSSL_zalloc(2 * field_size);
 330     computed_C3 = OPENSSL_zalloc(hash_size);
 331
 332     if (msg_mask == NULL || x2y2 == NULL || computed_C3 == NULL) {
 333         SM2err(SM2_F_SM2_DECRYPT, ERR_R_MALLOC_FAILURE);
 334         goto done;
 335     }
 336
 337     C1 = EC_POINT_new(group);
 338     if (C1 == NULL) {
 339         SM2err(SM2_F_SM2_DECRYPT, ERR_R_MALLOC_FAILURE);
 340         goto done;
 341     }
 342
 343     if (!EC_POINT_set_affine_coordinates(group, C1, sm2_ctext->C1x,
 344                                          sm2_ctext->C1y, ctx)
 345             || !EC_POINT_mul(group, C1, NULL, C1, EC_KEY_get0_private_key(key),
 346                              ctx)
 347             || !EC_POINT_get_affine_coordinates(group, C1, x2, y2, ctx)) {
 348         SM2err(SM2_F_SM2_DECRYPT, ERR_R_EC_LIB);
 349         goto done;
 350     }
 351
 352     if (BN_bn2binpad(x2, x2y2, field_size) < 0
 353             || BN_bn2binpad(y2, x2y2 + field_size, field_size) < 0
 354             || !ecdh_KDF_X9_63(msg_mask, msg_len, x2y2, 2 * field_size, NULL, 0,
 355                                digest)) {
 356         SM2err(SM2_F_SM2_DECRYPT, ERR_R_INTERNAL_ERROR);
 357         goto done;
 358     }
 359
 360     for (i = 0; i != msg_len; ++i)
 361         ptext_buf[i] = C2[i] ^ msg_mask[i];
 362
 363     hash = EVP_MD_CTX_new();
 364     if (hash == NULL) {
 365         SM2err(SM2_F_SM2_DECRYPT, ERR_R_MALLOC_FAILURE);
 366         goto done;
 367     }
 368
 369     if (!EVP_DigestInit(hash, digest)
 370             || !EVP_DigestUpdate(hash, x2y2, field_size)
 371             || !EVP_DigestUpdate(hash, ptext_buf, msg_len)
 372             || !EVP_DigestUpdate(hash, x2y2 + field_size, field_size)
 373             || !EVP_DigestFinal(hash, computed_C3, NULL)) {
 374         SM2err(SM2_F_SM2_DECRYPT, ERR_R_EVP_LIB);
 375         goto done;
 376     }
 377
 378     if (CRYPTO_memcmp(computed_C3, C3, hash_size) != 0) {
 379         SM2err(SM2_F_SM2_DECRYPT, SM2_R_INVALID_DIGEST);
 380         goto done;
 381     }
 382
 383     rc = 1;
 384     *ptext_len = msg_len;
 385
 386  done:
 387     if (rc == 0)
 388         memset(ptext_buf, 0, *ptext_len);
 389
 390     OPENSSL_free(msg_mask);
 391     OPENSSL_free(x2y2);
 392     OPENSSL_free(computed_C3);
 393     EC_POINT_free(C1);
 394     BN_CTX_free(ctx);
 395     SM2_Ciphertext_free(sm2_ctext);
 396     EVP_MD_CTX_free(hash);
 397
 398     return rc;
 399 }