  Wireless communication has been a broadcast system since its inception, which
violates security and privacy issues at the physical layer between the intended
transmit and receive pairs. As we move towards advanced spectrum sharing
methodologies involving billions of devices connected over wireless networks,
it is essential to secure the wireless signal such that only the intended
receiver can realize the properties of the signal. In this paper, we propose
Rand-OFDM, a new waveform, secured with a shared secret key, where the signal
properties can be recovered only at the expected receiver. We achieve the
signal level security by modifying the OFDM signal in time-domain, thus erasing
the OFDM properties and in turn obfuscating the signal properties to an
eavesdropper. We introduce a key-based secured training signal for channel
estimation, which can be used only at the intended receiver with prior
knowledge of the key. As a final step for the recovery of the signal, we use a
clustering-based technique to correct the phase of the received signal. Our
cryptanalysis shows that Rand-OFDM is especially useful in future wideband
signals. Extensive simulation and over-the-air experiments show that the
performance of Rand-OFDM is comparable to legacy OFDM and SNR penalty due to
the secured waveform varies between 1-4dB. In all these scenarios, Rand-OFDM
remains unrecognized by the adversary even at the highest possible SNR.
