silc_hmac_init_with_key(sha1hmac, keymat, 16);
silc_hmac_update(sha1hmac, enc->data, data_len);
silc_buffer_pull(enc, data_len);
silc_hmac_init_with_key(sha1hmac, keymat, 16);
silc_hmac_update(sha1hmac, enc->data, data_len);
silc_buffer_pull(enc, data_len);