  We outline an approach to physical-layer steganography where the transmitted
low-power stego messages are statistically indistinguishable from the Gaussian
component of the channel noise (e.g. the thermal noise) observed in the same
spectral band, and thus the channel noise itself serves as an effective cover
signal. We also demonstrate how the apparent spectral and temporal properties
of transmitted additional, higher-power cover signals (including those using
the existing communication protocols) can be made to match those of the
low-power stego payload and the Gaussian noise, providing extra layers of
obfuscation for both the cover and the stego messages. We further illustrate
how a specific combination of linear and nonlinear filtering can be used for
effective separation of the cover, payload, and/or "friendly jamming" signals
even when all transmissions have essentially the same spectral characteristics
as well as temporal and amplitude structures, and when there are no explicit
differences in the spectral and/or temporal allocations for the cover and the
stego messages.
