sm2_crypt.c
/*
* Copyright 2017-2018 The OpenSSL Project Authors. All Rights Reserved.
* Copyright 2017 Ribose Inc. All Rights Reserved.
* Ported from Ribose contributions from Botan.
*
* Licensed under the OpenSSL license (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#include <openssl/sm2.h>
#include <openssl/evp.h>
#include <openssl/bn.h>
#include <openssl/asn1.h>
#include <openssl/asn1t.h>
#include <string.h>
typedef struct SM2_Ciphertext_st SM2_Ciphertext;
DECLARE_ASN1_FUNCTIONS(SM2_Ciphertext)
struct SM2_Ciphertext_st {
BIGNUM *C1x;
BIGNUM *C1y;
ASN1_OCTET_STRING *C3;
ASN1_OCTET_STRING *C2;
};
ASN1_SEQUENCE(SM2_Ciphertext) = {
ASN1_SIMPLE(SM2_Ciphertext, C1x, BIGNUM),
ASN1_SIMPLE(SM2_Ciphertext, C1y, BIGNUM),
ASN1_SIMPLE(SM2_Ciphertext, C3, ASN1_OCTET_STRING),
ASN1_SIMPLE(SM2_Ciphertext, C2, ASN1_OCTET_STRING),
} ASN1_SEQUENCE_END(SM2_Ciphertext)
IMPLEMENT_ASN1_FUNCTIONS(SM2_Ciphertext)
static size_t EC_field_size(const EC_GROUP *group)
{
/* Is there some simpler way to do this? */
BIGNUM *p = BN_new();
BIGNUM *a = BN_new();
BIGNUM *b = BN_new();
size_t field_size = 0;
if (p == NULL || a == NULL || b == NULL)
goto done;
EC_GROUP_get_curve_GFp(group, p, a, b, NULL);
field_size = (BN_num_bits(p) + 7) / 8;
done:
BN_free(p);
BN_free(a);
BN_free(b);
return field_size;
}
size_t SM2_plaintext_size(const EC_KEY *key, const EVP_MD *digest, size_t msg_len)
{
const size_t field_size = EC_field_size(EC_KEY_get0_group(key));
const size_t md_size = EVP_MD_size(digest);
const size_t overhead = 10 + 2 * field_size + md_size;
if(msg_len <= overhead)
return 0;
return msg_len - overhead;
}
size_t SM2_ciphertext_size(const EC_KEY *key, const EVP_MD *digest, size_t msg_len)
{
const size_t field_size = EC_field_size(EC_KEY_get0_group(key));
const size_t md_size = EVP_MD_size(digest);
return 10 + 2 * field_size + md_size + msg_len;
}
int SM2_encrypt(const EC_KEY *key,
const EVP_MD *digest,
const uint8_t *msg,
size_t msg_len, uint8_t *ciphertext_buf, size_t *ciphertext_len)
{
int rc = 0;
size_t i;
BN_CTX *ctx = NULL;
BIGNUM *k = NULL;
BIGNUM *x1 = NULL;
BIGNUM *y1 = NULL;
BIGNUM *x2 = NULL;
BIGNUM *y2 = NULL;
EVP_MD_CTX *hash = EVP_MD_CTX_new();
struct SM2_Ciphertext_st ctext_struct;
const EC_GROUP *group = EC_KEY_get0_group(key);
const BIGNUM *order = EC_GROUP_get0_order(group);
const EC_POINT *P = EC_KEY_get0_public_key(key);
EC_POINT *kG = NULL;
EC_POINT *kP = NULL;
uint8_t *msg_mask = NULL;
uint8_t *x2y2 = NULL;
uint8_t *C3 = NULL;
const size_t field_size = EC_field_size(group);
const size_t C3_size = EVP_MD_size(digest);
if (field_size == 0 || C3_size == 0)
goto done;
kG = EC_POINT_new(group);
kP = EC_POINT_new(group);
if (kG == NULL || kP == NULL)
goto done;
ctx = BN_CTX_new();
if (ctx == NULL)
goto done;
BN_CTX_start(ctx);
k = BN_CTX_get(ctx);
x1 = BN_CTX_get(ctx);
x2 = BN_CTX_get(ctx);
y1 = BN_CTX_get(ctx);
y2 = BN_CTX_get(ctx);
if (y2 == NULL)
goto done;
x2y2 = OPENSSL_zalloc(2 * field_size);
C3 = OPENSSL_zalloc(C3_size);
if (x2y2 == NULL || C3 == NULL)
goto done;
memset(ciphertext_buf, 0, *ciphertext_len);
BN_priv_rand_range(k, order);
if (EC_POINT_mul(group, kG, k, NULL, NULL, ctx) == 0)
goto done;
if (EC_POINT_get_affine_coordinates_GFp(group, kG, x1, y1, ctx) == 0)
goto done;
if (EC_POINT_mul(group, kP, NULL, P, k, ctx) == 0)
goto done;
if (EC_POINT_get_affine_coordinates_GFp(group, kP, x2, y2, ctx) == 0)
goto done;
BN_bn2binpad(x2, x2y2, field_size);
BN_bn2binpad(y2, x2y2 + field_size, field_size);
msg_mask = OPENSSL_zalloc(msg_len);
if (msg_mask == NULL)
goto done;
/* X9.63 with no salt happens to match the KDF used in SM2 */
if (ECDH_KDF_X9_62(msg_mask, msg_len, x2y2, 2 * field_size, NULL, 0, digest)
== 0)
goto done;
for (i = 0; i != msg_len; ++i)
msg_mask[i] ^= msg[i];
if (EVP_DigestInit(hash, digest) == 0)
goto done;
if (EVP_DigestUpdate(hash, x2y2, field_size) == 0)
goto done;
if (EVP_DigestUpdate(hash, msg, msg_len) == 0)
goto done;
if (EVP_DigestUpdate(hash, x2y2 + field_size, field_size) == 0)
goto done;
if (EVP_DigestFinal(hash, C3, NULL) == 0)
goto done;
ctext_struct.C1x = x1;
ctext_struct.C1y = y1;
ctext_struct.C3 = ASN1_OCTET_STRING_new();
ASN1_OCTET_STRING_set(ctext_struct.C3, C3, C3_size);
ctext_struct.C2 = ASN1_OCTET_STRING_new();
ASN1_OCTET_STRING_set(ctext_struct.C2, msg_mask, msg_len);
*ciphertext_len = i2d_SM2_Ciphertext(&ctext_struct, &ciphertext_buf);
ASN1_OCTET_STRING_free(ctext_struct.C2);
ASN1_OCTET_STRING_free(ctext_struct.C3);
rc = 1;
done:
OPENSSL_free(msg_mask);
OPENSSL_free(x2y2);
OPENSSL_free(C3);
EVP_MD_CTX_free(hash);
BN_CTX_free(ctx);
EC_POINT_free(kG);
EC_POINT_free(kP);
return rc;
}
int SM2_decrypt(const EC_KEY *key,
const EVP_MD *digest,
const uint8_t *ciphertext,
size_t ciphertext_len, uint8_t *ptext_buf, size_t *ptext_len)
{
int rc = 0;
int i;
BN_CTX *ctx = NULL;
const EC_GROUP *group = EC_KEY_get0_group(key);
EC_POINT *C1 = NULL;
struct SM2_Ciphertext_st *sm2_ctext = NULL;
BIGNUM *x2 = NULL;
BIGNUM *y2 = NULL;
uint8_t *x2y2 = NULL;
uint8_t *computed_C3 = NULL;
const size_t field_size = EC_field_size(group);
const int hash_size = EVP_MD_size(digest);
uint8_t *msg_mask = NULL;
const uint8_t *C2 = NULL;
const uint8_t *C3 = NULL;
int msg_len = 0;
EVP_MD_CTX *hash = NULL;
if (field_size == 0 || hash_size == 0)
goto done;
memset(ptext_buf, 0xFF, *ptext_len);
sm2_ctext = d2i_SM2_Ciphertext(NULL, &ciphertext, ciphertext_len);
if (sm2_ctext == NULL)
goto done;
if (sm2_ctext->C3->length != hash_size)
goto done;
C2 = sm2_ctext->C2->data;
C3 = sm2_ctext->C3->data;
msg_len = sm2_ctext->C2->length;
ctx = BN_CTX_new();
if (ctx == NULL)
goto done;
BN_CTX_start(ctx);
x2 = BN_CTX_get(ctx);
y2 = BN_CTX_get(ctx);
if(y2 == NULL)
goto done;
msg_mask = OPENSSL_zalloc(msg_len);
x2y2 = OPENSSL_zalloc(2 * field_size);
computed_C3 = OPENSSL_zalloc(hash_size);
if(msg_mask == NULL || x2y2 == NULL || computed_C3 == NULL)
goto done;
C1 = EC_POINT_new(group);
if (C1 == NULL)
goto done;
if (EC_POINT_set_affine_coordinates_GFp
(group, C1, sm2_ctext->C1x, sm2_ctext->C1y, ctx) == 0)
goto done;
if (EC_POINT_mul(group, C1, NULL, C1, EC_KEY_get0_private_key(key), ctx) ==
0)
goto done;
if (EC_POINT_get_affine_coordinates_GFp(group, C1, x2, y2, ctx) == 0)
goto done;
BN_bn2binpad(x2, x2y2, field_size);
BN_bn2binpad(y2, x2y2 + field_size, field_size);
if (ECDH_KDF_X9_62(msg_mask, msg_len, x2y2, 2 * field_size, NULL, 0, digest)
== 0)
goto done;
for (i = 0; i != msg_len; ++i)
ptext_buf[i] = C2[i] ^ msg_mask[i];
hash = EVP_MD_CTX_new();
if (hash == NULL)
goto done;
if (EVP_DigestInit(hash, digest) == 0)
goto done;
if (EVP_DigestUpdate(hash, x2y2, field_size) == 0)
goto done;
if (EVP_DigestUpdate(hash, ptext_buf, msg_len) == 0)
goto done;
if (EVP_DigestUpdate(hash, x2y2 + field_size, field_size) == 0)
goto done;
if (EVP_DigestFinal(hash, computed_C3, NULL) == 0)
goto done;
if (memcmp(computed_C3, C3, hash_size) != 0)
goto done;
rc = 1;
*ptext_len = msg_len;
done:
if (rc == 0)
memset(ptext_buf, 0, *ptext_len);
OPENSSL_free(msg_mask);
OPENSSL_free(x2y2);
OPENSSL_free(computed_C3);
EC_POINT_free(C1);
BN_CTX_free(ctx);
SM2_Ciphertext_free(sm2_ctext);
EVP_MD_CTX_free(hash);
return rc;
}
