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 "internal/ec_int.h" /* ecdh_KDF_X9_63() */
  15 #include <openssl/err.h>
  16 #include <openssl/evp.h>
  17 #include <openssl/bn.h>
  18 #include <openssl/asn1.h>
  19 #include <openssl/asn1t.h>
  20 #include <string.h>
  21
  22 typedef struct SM2_Ciphertext_st SM2_Ciphertext;
  23 DECLARE_ASN1_FUNCTIONS(SM2_Ciphertext)
  24
  25 struct SM2_Ciphertext_st {
  26     BIGNUM *C1x;
  27     BIGNUM *C1y;
  28     ASN1_OCTET_STRING *C3;
  29     ASN1_OCTET_STRING *C2;
  30 };
  31
  32 ASN1_SEQUENCE(SM2_Ciphertext) = {
  33     ASN1_SIMPLE(SM2_Ciphertext, C1x, BIGNUM),
  34     ASN1_SIMPLE(SM2_Ciphertext, C1y, BIGNUM),
  35     ASN1_SIMPLE(SM2_Ciphertext, C3, ASN1_OCTET_STRING),
  36     ASN1_SIMPLE(SM2_Ciphertext, C2, ASN1_OCTET_STRING),
  37 } ASN1_SEQUENCE_END(SM2_Ciphertext)
  38
  39 IMPLEMENT_ASN1_FUNCTIONS(SM2_Ciphertext)
  40
  41 static size_t ec_field_size(const EC_GROUP *group)
  42 {
  43     /* Is there some simpler way to do this? */
  44     BIGNUM *p = BN_new();
  45     BIGNUM *a = BN_new();
  46     BIGNUM *b = BN_new();
  47     size_t field_size = 0;
  48
  49     if (p == NULL || a == NULL || b == NULL)
  50        goto done;
  51
  52     if (!EC_GROUP_get_curve(group, p, a, b, NULL))
  53         goto done;
  54     field_size = (BN_num_bits(p) + 7) / 8;
  55
  56  done:
  57     BN_free(p);
  58     BN_free(a);
  59     BN_free(b);
  60
  61     return field_size;
  62 }
  63
  64 int sm2_plaintext_size(const EC_KEY *key, const EVP_MD *digest, size_t msg_len,
  65                        size_t *pt_size)
  66 {
  67     const size_t field_size = ec_field_size(EC_KEY_get0_group(key));
  68     const int md_size = EVP_MD_size(digest);
  69     size_t overhead;
  70
  71     if (md_size < 0) {
  72         SM2err(SM2_F_SM2_PLAINTEXT_SIZE, SM2_R_INVALID_DIGEST);
  73         return 0;
  74     }
  75     if (field_size == 0) {
  76         SM2err(SM2_F_SM2_PLAINTEXT_SIZE, SM2_R_INVALID_FIELD);
  77         return 0;
  78     }
  79
  80     overhead = 10 + 2 * field_size + (size_t)md_size;
  81     if (msg_len <= overhead) {
  82         SM2err(SM2_F_SM2_PLAINTEXT_SIZE, SM2_R_INVALID_ENCODING);
  83         return 0;
  84     }
  85
  86     *pt_size = msg_len - overhead;
  87     return 1;
  88 }
  89
  90 int sm2_ciphertext_size(const EC_KEY *key, const EVP_MD *digest, size_t msg_len,
  91                         size_t *ct_size)
  92 {
  93     const size_t field_size = ec_field_size(EC_KEY_get0_group(key));
  94     const int md_size = EVP_MD_size(digest);
  95     size_t sz;
  96
  97     if (field_size == 0 || md_size < 0)
  98         return 0;
  99
 100     /* Integer and string are simple type; set constructed = 0, means primitive and definite length encoding. */
 101     sz = 2 * ASN1_object_size(0, field_size + 1, V_ASN1_INTEGER)
 102          + ASN1_object_size(0, md_size, V_ASN1_OCTET_STRING)
 103          + ASN1_object_size(0, msg_len, V_ASN1_OCTET_STRING);
 104     /* Sequence is structured type; set constructed = 1, means constructed and definite length encoding. */
 105     *ct_size = ASN1_object_size(1, sz, V_ASN1_SEQUENCE);
 106
 107     return 1;
 108 }
 109
 110 int sm2_encrypt(const EC_KEY *key,
 111                 const EVP_MD *digest,
 112                 const uint8_t *msg,
 113                 size_t msg_len, uint8_t *ciphertext_buf, size_t *ciphertext_len)
 114 {
 115     int rc = 0, ciphertext_leni;
 116     size_t i;
 117     BN_CTX *ctx = NULL;
 118     BIGNUM *k = NULL;
 119     BIGNUM *x1 = NULL;
 120     BIGNUM *y1 = NULL;
 121     BIGNUM *x2 = NULL;
 122     BIGNUM *y2 = NULL;
 123     EVP_MD_CTX *hash = EVP_MD_CTX_new();
 124     struct SM2_Ciphertext_st ctext_struct;
 125     const EC_GROUP *group = EC_KEY_get0_group(key);
 126     const BIGNUM *order = EC_GROUP_get0_order(group);
 127     const EC_POINT *P = EC_KEY_get0_public_key(key);
 128     EC_POINT *kG = NULL;
 129     EC_POINT *kP = NULL;
 130     uint8_t *msg_mask = NULL;
 131     uint8_t *x2y2 = NULL;
 132     uint8_t *C3 = NULL;
 133     size_t field_size;
 134     const int C3_size = EVP_MD_size(digest);
 135
 136     /* NULL these before any "goto done" */
 137     ctext_struct.C2 = NULL;
 138     ctext_struct.C3 = NULL;
 139
 140     if (hash == NULL || C3_size <= 0) {
 141         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);
 142         goto done;
 143     }
 144
 145     field_size = ec_field_size(group);
 146     if (field_size == 0) {
 147         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);
 148         goto done;
 149     }
 150
 151     kG = EC_POINT_new(group);
 152     kP = EC_POINT_new(group);
 153     ctx = BN_CTX_new();
 154     if (kG == NULL || kP == NULL || ctx == NULL) {
 155         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_MALLOC_FAILURE);
 156         goto done;
 157     }
 158
 159     BN_CTX_start(ctx);
 160     k = BN_CTX_get(ctx);
 161     x1 = BN_CTX_get(ctx);
 162     x2 = BN_CTX_get(ctx);
 163     y1 = BN_CTX_get(ctx);
 164     y2 = BN_CTX_get(ctx);
 165
 166     if (y2 == NULL) {
 167         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_BN_LIB);
 168         goto done;
 169     }
 170
 171     x2y2 = OPENSSL_zalloc(2 * field_size);
 172     C3 = OPENSSL_zalloc(C3_size);
 173
 174     if (x2y2 == NULL || C3 == NULL) {
 175         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_MALLOC_FAILURE);
 176         goto done;
 177     }
 178
 179     memset(ciphertext_buf, 0, *ciphertext_len);
 180
 181     if (!BN_priv_rand_range(k, order)) {
 182         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);
 183         goto done;
 184     }
 185
 186     if (!EC_POINT_mul(group, kG, k, NULL, NULL, ctx)
 187             || !EC_POINT_get_affine_coordinates(group, kG, x1, y1, ctx)
 188             || !EC_POINT_mul(group, kP, NULL, P, k, ctx)
 189             || !EC_POINT_get_affine_coordinates(group, kP, x2, y2, ctx)) {
 190         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_EC_LIB);
 191         goto done;
 192     }
 193
 194     if (BN_bn2binpad(x2, x2y2, field_size) < 0
 195             || BN_bn2binpad(y2, x2y2 + field_size, field_size) < 0) {
 196         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);
 197         goto done;
 198     }
 199
 200     msg_mask = OPENSSL_zalloc(msg_len);
 201     if (msg_mask == NULL) {
 202        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_MALLOC_FAILURE);
 203        goto done;
 204    }
 205
 206     /* X9.63 with no salt happens to match the KDF used in SM2 */
 207     if (!ecdh_KDF_X9_63(msg_mask, msg_len, x2y2, 2 * field_size, NULL, 0,
 208                         digest)) {
 209         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_EVP_LIB);
 210         goto done;
 211     }
 212
 213     for (i = 0; i != msg_len; ++i)
 214         msg_mask[i] ^= msg[i];
 215
 216     if (EVP_DigestInit(hash, digest) == 0
 217             || EVP_DigestUpdate(hash, x2y2, field_size) == 0
 218             || EVP_DigestUpdate(hash, msg, msg_len) == 0
 219             || EVP_DigestUpdate(hash, x2y2 + field_size, field_size) == 0
 220             || EVP_DigestFinal(hash, C3, NULL) == 0) {
 221         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_EVP_LIB);
 222         goto done;
 223     }
 224
 225     ctext_struct.C1x = x1;
 226     ctext_struct.C1y = y1;
 227     ctext_struct.C3 = ASN1_OCTET_STRING_new();
 228     ctext_struct.C2 = ASN1_OCTET_STRING_new();
 229
 230     if (ctext_struct.C3 == NULL || ctext_struct.C2 == NULL) {
 231        SM2err(SM2_F_SM2_ENCRYPT, ERR_R_MALLOC_FAILURE);
 232        goto done;
 233     }
 234     if (!ASN1_OCTET_STRING_set(ctext_struct.C3, C3, C3_size)
 235             || !ASN1_OCTET_STRING_set(ctext_struct.C2, msg_mask, msg_len)) {
 236         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);
 237         goto done;
 238     }
 239
 240     ciphertext_leni = i2d_SM2_Ciphertext(&ctext_struct, &ciphertext_buf);
 241     /* Ensure cast to size_t is safe */
 242     if (ciphertext_leni < 0) {
 243         SM2err(SM2_F_SM2_ENCRYPT, ERR_R_INTERNAL_ERROR);
 244         goto done;
 245     }
 246     *ciphertext_len = (size_t)ciphertext_leni;
 247
 248     rc = 1;
 249
 250  done:
 251     ASN1_OCTET_STRING_free(ctext_struct.C2);
 252     ASN1_OCTET_STRING_free(ctext_struct.C3);
 253     OPENSSL_free(msg_mask);
 254     OPENSSL_free(x2y2);
 255     OPENSSL_free(C3);
 256     EVP_MD_CTX_free(hash);
 257     BN_CTX_free(ctx);
 258     EC_POINT_free(kG);
 259     EC_POINT_free(kP);
 260     return rc;
 261 }
 262
 263 int sm2_decrypt(const EC_KEY *key,
 264                 const EVP_MD *digest,
 265                 const uint8_t *ciphertext,
 266                 size_t ciphertext_len, uint8_t *ptext_buf, size_t *ptext_len)
 267 {
 268     int rc = 0;
 269     int i;
 270     BN_CTX *ctx = NULL;
 271     const EC_GROUP *group = EC_KEY_get0_group(key);
 272     EC_POINT *C1 = NULL;
 273     struct SM2_Ciphertext_st *sm2_ctext = NULL;
 274     BIGNUM *x2 = NULL;
 275     BIGNUM *y2 = NULL;
 276     uint8_t *x2y2 = NULL;
 277     uint8_t *computed_C3 = NULL;
 278     const size_t field_size = ec_field_size(group);
 279     const int hash_size = EVP_MD_size(digest);
 280     uint8_t *msg_mask = NULL;
 281     const uint8_t *C2 = NULL;
 282     const uint8_t *C3 = NULL;
 283     int msg_len = 0;
 284     EVP_MD_CTX *hash = NULL;
 285
 286     if (field_size == 0 || hash_size <= 0)
 287        goto done;
 288
 289     memset(ptext_buf, 0xFF, *ptext_len);
 290
 291     sm2_ctext = d2i_SM2_Ciphertext(NULL, &ciphertext, ciphertext_len);
 292
 293     if (sm2_ctext == NULL) {
 294         SM2err(SM2_F_SM2_DECRYPT, SM2_R_ASN1_ERROR);
 295         goto done;
 296     }
 297
 298     if (sm2_ctext->C3->length != hash_size) {
 299         SM2err(SM2_F_SM2_DECRYPT, SM2_R_INVALID_ENCODING);
 300         goto done;
 301     }
 302
 303     C2 = sm2_ctext->C2->data;
 304     C3 = sm2_ctext->C3->data;
 305     msg_len = sm2_ctext->C2->length;
 306
 307     ctx = BN_CTX_new();
 308     if (ctx == NULL) {
 309         SM2err(SM2_F_SM2_DECRYPT, ERR_R_MALLOC_FAILURE);
 310         goto done;
 311     }
 312
 313     BN_CTX_start(ctx);
 314     x2 = BN_CTX_get(ctx);
 315     y2 = BN_CTX_get(ctx);
 316
 317     if (y2 == NULL) {
 318         SM2err(SM2_F_SM2_DECRYPT, ERR_R_BN_LIB);
 319         goto done;
 320     }
 321
 322     msg_mask = OPENSSL_zalloc(msg_len);
 323     x2y2 = OPENSSL_zalloc(2 * field_size);
 324     computed_C3 = OPENSSL_zalloc(hash_size);
 325
 326     if (msg_mask == NULL || x2y2 == NULL || computed_C3 == NULL) {
 327         SM2err(SM2_F_SM2_DECRYPT, ERR_R_MALLOC_FAILURE);
 328         goto done;
 329     }
 330
 331     C1 = EC_POINT_new(group);
 332     if (C1 == NULL) {
 333         SM2err(SM2_F_SM2_DECRYPT, ERR_R_MALLOC_FAILURE);
 334         goto done;
 335     }
 336
 337     if (!EC_POINT_set_affine_coordinates(group, C1, sm2_ctext->C1x,
 338                                          sm2_ctext->C1y, ctx)
 339             || !EC_POINT_mul(group, C1, NULL, C1, EC_KEY_get0_private_key(key),
 340                              ctx)
 341             || !EC_POINT_get_affine_coordinates(group, C1, x2, y2, ctx)) {
 342         SM2err(SM2_F_SM2_DECRYPT, ERR_R_EC_LIB);
 343         goto done;
 344     }
 345
 346     if (BN_bn2binpad(x2, x2y2, field_size) < 0
 347             || BN_bn2binpad(y2, x2y2 + field_size, field_size) < 0
 348             || !ecdh_KDF_X9_63(msg_mask, msg_len, x2y2, 2 * field_size, NULL, 0,
 349                                digest)) {
 350         SM2err(SM2_F_SM2_DECRYPT, ERR_R_INTERNAL_ERROR);
 351         goto done;
 352     }
 353
 354     for (i = 0; i != msg_len; ++i)
 355         ptext_buf[i] = C2[i] ^ msg_mask[i];
 356
 357     hash = EVP_MD_CTX_new();
 358     if (hash == NULL) {
 359         SM2err(SM2_F_SM2_DECRYPT, ERR_R_MALLOC_FAILURE);
 360         goto done;
 361     }
 362
 363     if (!EVP_DigestInit(hash, digest)
 364             || !EVP_DigestUpdate(hash, x2y2, field_size)
 365             || !EVP_DigestUpdate(hash, ptext_buf, msg_len)
 366             || !EVP_DigestUpdate(hash, x2y2 + field_size, field_size)
 367             || !EVP_DigestFinal(hash, computed_C3, NULL)) {
 368         SM2err(SM2_F_SM2_DECRYPT, ERR_R_EVP_LIB);
 369         goto done;
 370     }
 371
 372     if (CRYPTO_memcmp(computed_C3, C3, hash_size) != 0) {
 373         SM2err(SM2_F_SM2_DECRYPT, SM2_R_INVALID_DIGEST);
 374         goto done;
 375     }
 376
 377     rc = 1;
 378     *ptext_len = msg_len;
 379
 380  done:
 381     if (rc == 0)
 382         memset(ptext_buf, 0, *ptext_len);
 383
 384     OPENSSL_free(msg_mask);
 385     OPENSSL_free(x2y2);
 386     OPENSSL_free(computed_C3);
 387     EC_POINT_free(C1);
 388     BN_CTX_free(ctx);
 389     SM2_Ciphertext_free(sm2_ctext);
 390     EVP_MD_CTX_free(hash);
 391
 392     return rc;
 393 }