This disclosure provides methods, devices and systems for improving the security of secure long training field (LTF) transmissions. In some implementations, a transmitting device may perform windowing on a secure LTF, in the frequency domain, so that the resulting time-domain LTF signal is difficult, if not impossible, to predict by any device that observes a portion of the LTF signal. In some aspects, the transmitting device may negotiate the windowing of secure LTFs with a receiving device based on fine timing measurement (FTM) negotiation frames exchanged at the start of an FTM procedure. In some other aspects, the transmitting device may dynamically or adaptively perform windowing on secure LTFs. In such aspects, the transmitting device may indicate whether windowing is performed on a secure LTF based on information carried in a signal field of a physical layer convergence protocol (PLCP) protocol data unit (PPDU) that includes the secure LTF.