return Observable.defer(() -> {
            int nonce = calculateFreshNonce();
            return login(api, secret, String.valueOf(nonce));
        })
        .map(infoTradeResponse -> {
            if (infoTradeResponse.getResponseStatus() == BaseTradeResponse.ERROR_STATUS && infoTradeResponse.getResponseError().equals(Constants.NONCE_ERROR)) {
                Log.d(TAG, "KeysNonceError");
                throw new KeysNonceError();
            }
            else {
                if (infoTradeResponse.getResponseStatus() == BaseTradeResponse.SUCCESS_STATUS)
                    return true;
                else return false;
            }
        })
        .retryWhen(error -> {
            int[] count = { 0 };
            return error
                    .takeWhile(v -> count[0]++ <= Constants.MAX_RETRY)
                    .delay(count[0] * 100, TimeUnit.MILLISECONDS);
        });