This disclosure provides methods, devices and systems for generating a secure long training field (LTF). In some implementations, the secure LTF may include a randomized bit sequence that is difficult, if not impossible, to replicate by any device other than the transmitting device and the intended receiving device. For example, the transmitting device may use a block cipher or stream cipher to generate a pseudorandom bit sequence and may select a subset of bits of the pseudorandom bit sequence to be mapped to a sequence of modulation symbols representing an LTF symbol of the secure LTF. More specifically, each of the modulation symbols is mapped to a respective one of a number of subcarriers spanning a bandwidth of the secure LTF. The transmitting device may further transmit a physical layer convergence protocol (PLCP) protocol data unit (PPDU) that includes the secure LTF to the receiving device.