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 <openssl/evp.h>
  14 #include <openssl/bn.h>
  15 #include <openssl/asn1.h>
  16 #include <openssl/asn1t.h>
  17 #include <string.h>
  18
  19 typedef struct SM2_Ciphertext_st SM2_Ciphertext;
  20 DECLARE_ASN1_FUNCTIONS(SM2_Ciphertext)
  21
  22 struct SM2_Ciphertext_st {
  23     BIGNUM *C1x;
  24     BIGNUM *C1y;
  25     ASN1_OCTET_STRING *C3;
  26     ASN1_OCTET_STRING *C2;
  27 };
  28
  29 ASN1_SEQUENCE(SM2_Ciphertext) = {
  30     ASN1_SIMPLE(SM2_Ciphertext, C1x, BIGNUM),
  31     ASN1_SIMPLE(SM2_Ciphertext, C1y, BIGNUM),
  32     ASN1_SIMPLE(SM2_Ciphertext, C3, ASN1_OCTET_STRING),
  33     ASN1_SIMPLE(SM2_Ciphertext, C2, ASN1_OCTET_STRING),
  34 } ASN1_SEQUENCE_END(SM2_Ciphertext)
  35
  36 IMPLEMENT_ASN1_FUNCTIONS(SM2_Ciphertext)
  37
  38 static size_t EC_field_size(const EC_GROUP *group)
  39 {
  40     /* Is there some simpler way to do this? */
  41     BIGNUM *p = BN_new();
  42     BIGNUM *a = BN_new();
  43     BIGNUM *b = BN_new();
  44     size_t field_size = 0;
  45
  46     if (p == NULL || a == NULL || b == NULL)
  47        goto done;
  48
  49     EC_GROUP_get_curve_GFp(group, p, a, b, NULL);
  50     field_size = (BN_num_bits(p) + 7) / 8;
  51
  52  done:
  53     BN_free(p);
  54     BN_free(a);
  55     BN_free(b);
  56
  57     return field_size;
  58 }
  59
  60 size_t SM2_plaintext_size(const EC_KEY *key, const EVP_MD *digest, size_t msg_len)
  61 {
  62     const size_t field_size = EC_field_size(EC_KEY_get0_group(key));
  63     const size_t md_size = EVP_MD_size(digest);
  64
  65     const size_t overhead = 10 + 2 * field_size + md_size;
  66     if(msg_len <= overhead)
  67        return 0;
  68
  69     return msg_len - overhead;
  70 }
  71
  72 size_t SM2_ciphertext_size(const EC_KEY *key, const EVP_MD *digest, size_t msg_len)
  73 {
  74     const size_t field_size = EC_field_size(EC_KEY_get0_group(key));
  75     const size_t md_size = EVP_MD_size(digest);
  76     return 10 + 2 * field_size + md_size + msg_len;
  77 }
  78
  79 int SM2_encrypt(const EC_KEY *key,
  80                 const EVP_MD *digest,
  81                 const uint8_t *msg,
  82                 size_t msg_len, uint8_t *ciphertext_buf, size_t *ciphertext_len)
  83 {
  84     int rc = 0;
  85     size_t i;
  86     BN_CTX *ctx = NULL;
  87     BIGNUM *k = NULL;
  88     BIGNUM *x1 = NULL;
  89     BIGNUM *y1 = NULL;
  90     BIGNUM *x2 = NULL;
  91     BIGNUM *y2 = NULL;
  92
  93     EVP_MD_CTX *hash = EVP_MD_CTX_new();
  94
  95     struct SM2_Ciphertext_st ctext_struct;
  96     const EC_GROUP *group = EC_KEY_get0_group(key);
  97     const BIGNUM *order = EC_GROUP_get0_order(group);
  98     const EC_POINT *P = EC_KEY_get0_public_key(key);
  99     EC_POINT *kG = NULL;
 100     EC_POINT *kP = NULL;
 101     uint8_t *msg_mask = NULL;
 102
 103     uint8_t *x2y2 = NULL;
 104     uint8_t *C3 = NULL;
 105
 106     const size_t field_size = EC_field_size(group);
 107     const size_t C3_size = EVP_MD_size(digest);
 108
 109     if (field_size == 0 || C3_size == 0)
 110        goto done;
 111
 112     kG = EC_POINT_new(group);
 113     kP = EC_POINT_new(group);
 114     if (kG == NULL || kP == NULL)
 115        goto done;
 116
 117     ctx = BN_CTX_new();
 118     if (ctx == NULL)
 119        goto done;
 120
 121     BN_CTX_start(ctx);
 122     k = BN_CTX_get(ctx);
 123     x1 = BN_CTX_get(ctx);
 124     x2 = BN_CTX_get(ctx);
 125     y1 = BN_CTX_get(ctx);
 126     y2 = BN_CTX_get(ctx);
 127
 128     if (y2 == NULL)
 129        goto done;
 130
 131     x2y2 = OPENSSL_zalloc(2 * field_size);
 132     C3 = OPENSSL_zalloc(C3_size);
 133
 134     if (x2y2 == NULL || C3 == NULL)
 135        goto done;
 136
 137     memset(ciphertext_buf, 0, *ciphertext_len);
 138
 139     BN_priv_rand_range(k, order);
 140
 141     if (EC_POINT_mul(group, kG, k, NULL, NULL, ctx) == 0)
 142         goto done;
 143
 144     if (EC_POINT_get_affine_coordinates_GFp(group, kG, x1, y1, ctx) == 0)
 145         goto done;
 146
 147     if (EC_POINT_mul(group, kP, NULL, P, k, ctx) == 0)
 148         goto done;
 149
 150     if (EC_POINT_get_affine_coordinates_GFp(group, kP, x2, y2, ctx) == 0)
 151         goto done;
 152
 153     BN_bn2binpad(x2, x2y2, field_size);
 154     BN_bn2binpad(y2, x2y2 + field_size, field_size);
 155
 156     msg_mask = OPENSSL_zalloc(msg_len);
 157     if (msg_mask == NULL)
 158        goto done;
 159
 160     /* X9.63 with no salt happens to match the KDF used in SM2 */
 161     if (ECDH_KDF_X9_62(msg_mask, msg_len, x2y2, 2 * field_size, NULL, 0, digest)
 162         == 0)
 163         goto done;
 164
 165     for (i = 0; i != msg_len; ++i)
 166         msg_mask[i] ^= msg[i];
 167
 168     if (EVP_DigestInit(hash, digest) == 0)
 169         goto done;
 170
 171     if (EVP_DigestUpdate(hash, x2y2, field_size) == 0)
 172         goto done;
 173
 174     if (EVP_DigestUpdate(hash, msg, msg_len) == 0)
 175         goto done;
 176
 177     if (EVP_DigestUpdate(hash, x2y2 + field_size, field_size) == 0)
 178         goto done;
 179
 180     if (EVP_DigestFinal(hash, C3, NULL) == 0)
 181         goto done;
 182
 183     ctext_struct.C1x = x1;
 184     ctext_struct.C1y = y1;
 185     ctext_struct.C3 = ASN1_OCTET_STRING_new();
 186     ASN1_OCTET_STRING_set(ctext_struct.C3, C3, C3_size);
 187     ctext_struct.C2 = ASN1_OCTET_STRING_new();
 188     ASN1_OCTET_STRING_set(ctext_struct.C2, msg_mask, msg_len);
 189
 190     *ciphertext_len = i2d_SM2_Ciphertext(&ctext_struct, &ciphertext_buf);
 191
 192     ASN1_OCTET_STRING_free(ctext_struct.C2);
 193     ASN1_OCTET_STRING_free(ctext_struct.C3);
 194
 195     rc = 1;
 196
 197  done:
 198     OPENSSL_free(msg_mask);
 199     OPENSSL_free(x2y2);
 200     OPENSSL_free(C3);
 201     EVP_MD_CTX_free(hash);
 202     BN_CTX_free(ctx);
 203     EC_POINT_free(kG);
 204     EC_POINT_free(kP);
 205     return rc;
 206 }
 207
 208 int SM2_decrypt(const EC_KEY *key,
 209                 const EVP_MD *digest,
 210                 const uint8_t *ciphertext,
 211                 size_t ciphertext_len, uint8_t *ptext_buf, size_t *ptext_len)
 212 {
 213     int rc = 0;
 214     int i;
 215
 216     BN_CTX *ctx = NULL;
 217     const EC_GROUP *group = EC_KEY_get0_group(key);
 218     EC_POINT *C1 = NULL;
 219     struct SM2_Ciphertext_st *sm2_ctext = NULL;
 220     BIGNUM *x2 = NULL;
 221     BIGNUM *y2 = NULL;
 222
 223     uint8_t *x2y2 = NULL;
 224     uint8_t *computed_C3 = NULL;
 225
 226     const size_t field_size = EC_field_size(group);
 227     const int hash_size = EVP_MD_size(digest);
 228
 229     uint8_t *msg_mask = NULL;
 230     const uint8_t *C2 = NULL;
 231     const uint8_t *C3 = NULL;
 232     int msg_len = 0;
 233     EVP_MD_CTX *hash = NULL;
 234
 235     if (field_size == 0 || hash_size == 0)
 236        goto done;
 237
 238     memset(ptext_buf, 0xFF, *ptext_len);
 239
 240     sm2_ctext = d2i_SM2_Ciphertext(NULL, &ciphertext, ciphertext_len);
 241
 242     if (sm2_ctext == NULL)
 243         goto done;
 244
 245     if (sm2_ctext->C3->length != hash_size)
 246         goto done;
 247
 248     C2 = sm2_ctext->C2->data;
 249     C3 = sm2_ctext->C3->data;
 250     msg_len = sm2_ctext->C2->length;
 251
 252     ctx = BN_CTX_new();
 253     if (ctx == NULL)
 254        goto done;
 255
 256     BN_CTX_start(ctx);
 257     x2 = BN_CTX_get(ctx);
 258     y2 = BN_CTX_get(ctx);
 259
 260     if(y2 == NULL)
 261        goto done;
 262
 263     msg_mask = OPENSSL_zalloc(msg_len);
 264     x2y2 = OPENSSL_zalloc(2 * field_size);
 265     computed_C3 = OPENSSL_zalloc(hash_size);
 266
 267     if(msg_mask == NULL || x2y2 == NULL || computed_C3 == NULL)
 268        goto done;
 269
 270     C1 = EC_POINT_new(group);
 271     if (C1 == NULL)
 272         goto done;
 273
 274     if (EC_POINT_set_affine_coordinates_GFp
 275         (group, C1, sm2_ctext->C1x, sm2_ctext->C1y, ctx) == 0)
 276         goto done;
 277
 278     if (EC_POINT_mul(group, C1, NULL, C1, EC_KEY_get0_private_key(key), ctx) ==
 279         0)
 280         goto done;
 281
 282     if (EC_POINT_get_affine_coordinates_GFp(group, C1, x2, y2, ctx) == 0)
 283         goto done;
 284
 285     BN_bn2binpad(x2, x2y2, field_size);
 286     BN_bn2binpad(y2, x2y2 + field_size, field_size);
 287
 288     if (ECDH_KDF_X9_62(msg_mask, msg_len, x2y2, 2 * field_size, NULL, 0, digest)
 289         == 0)
 290         goto done;
 291
 292     for (i = 0; i != msg_len; ++i)
 293         ptext_buf[i] = C2[i] ^ msg_mask[i];
 294
 295     hash = EVP_MD_CTX_new();
 296
 297     if (hash == NULL)
 298        goto done;
 299
 300     if (EVP_DigestInit(hash, digest) == 0)
 301         goto done;
 302
 303     if (EVP_DigestUpdate(hash, x2y2, field_size) == 0)
 304         goto done;
 305
 306     if (EVP_DigestUpdate(hash, ptext_buf, msg_len) == 0)
 307         goto done;
 308
 309     if (EVP_DigestUpdate(hash, x2y2 + field_size, field_size) == 0)
 310         goto done;
 311
 312     if (EVP_DigestFinal(hash, computed_C3, NULL) == 0)
 313         goto done;
 314
 315     if (memcmp(computed_C3, C3, hash_size) != 0)
 316         goto done;
 317
 318     rc = 1;
 319     *ptext_len = msg_len;
 320
 321  done:
 322
 323     if (rc == 0)
 324         memset(ptext_buf, 0, *ptext_len);
 325
 326     OPENSSL_free(msg_mask);
 327     OPENSSL_free(x2y2);
 328     OPENSSL_free(computed_C3);
 329     EC_POINT_free(C1);
 330     BN_CTX_free(ctx);
 331     SM2_Ciphertext_free(sm2_ctext);
 332     EVP_MD_CTX_free(hash);
 333
 334     return rc;
 335 }