/* Аутентификация */
    {
        int b = recv(s, id, sizeof(id)-1, 0);
        if(b == SOCKET_ERROR)
            goto end0;

        send(s, Z, strlen(Z), 0);

        b = recv(s, buf, sizeof(buf)-1, 0);
        if(b == SOCKET_ERROR)
            goto end0;

        {
            char out[1024];
            char tid[21];
            char tZ[20];

            if(get_key(id, key) == -1)
                goto end0;

            dvigenere(buf, key, strlen(key), out, b);

            sscanf(buf, "%20s %19s", tid, tZ);

            if(strcmp(id, tid) != 0 || strcmp(Z, tZ) != 0)
                goto end0;
        }
    }