sgx decryption

int envelope_open(EVP_PKEY *evp_pkey, unsigned char *ciphertext,
                  int ciphertext_len, unsigned char *encrypted_key,
                  int encrypted_key_len, unsigned char *iv,
                  unsigned char **plaintext, int *plaintext_len, unsigned char *tag) {
    EVP_CIPHER_CTX *ctx;
    const EVP_CIPHER *type = EVP_aes_256_gcm();
    int len, ret = 0;
    unsigned char *tmpptxt = nullptr;
    if ((ctx = EVP_CIPHER_CTX_new()) == nullptr){
        printf("%s\n", ERR_error_string(ERR_get_error(), nullptr));
        return 0;
    }
    if ((tmpptxt = (unsigned char *)malloc(ciphertext_len)) == nullptr){
        printf("%s\n", ERR_error_string(ERR_get_error(), nullptr));
        ret = 0;
        goto err;
    }    

    if (EVP_OpenInit(ctx, type, encrypted_key, EVP_PKEY_size(evp_pkey),
                     iv, evp_pkey) != 1){
        printf("%s\n", ERR_error_string(ERR_get_error(), nullptr));
        ret = 0;
        goto err;
    }

    if (EVP_OpenUpdate(ctx, tmpptxt, &len, ciphertext, ciphertext_len) != 1){
        printf("%s\n", ERR_error_string(ERR_get_error(), nullptr));   
        ret = 0;
        goto err;
    }

    *plaintext_len = len;

    /* Set expected tag value. Works in OpenSSL 1.0.1d and later     */
    if (!EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, 16, tag)){
        printf("%s\n", ERR_error_string(ERR_get_error(), nullptr));
        ret = 0;
        goto err;
    }

    if (EVP_OpenFinal(ctx, tmpptxt + len, &len) != 1){
        printf("%s\n", ERR_error_string(ERR_get_error(), nullptr));
        ret = 0;
        goto err;
    }

    *plaintext_len += len;

    *plaintext = tmpptxt;
    tmpptxt = nullptr;
    ret = 1;
err:
    EVP_CIPHER_CTX_free(ctx);
    if(ret == 0){
        free(tmpptxt);
    }
    return ret;
}