Although conventional cryptographic security mechanisms are essential to the overall problem of securing wireless networks, these techniques do not directly leverage the unique properties of the wireless domain to address security threats. The properties of the wireless medium are a powerful source of domain-specific information that can complement and enhance traditional security mechanisms. In this paper, we propose to utilize the fact that the radio channel decorrelates rapidly in space, time and frequency in order to to establish new forms of authentication and confidentiality that operate at the physical layer and can be used to facilitate cross-layer security paradigms. Specifically, for authentication services, we illustrate two channel probing techniques that can be used to verify the authenticity of a transmitter. Similarly, for confidentiality, we examine several strategies for establishing shared secrets/keys between two communicators using the wireless medium. These strategies range from extracting keys from channel state information, to utilizing the channel variability to secretly disseminate keys. We then validate the feasibility of using physical layer techniques for securing wireless systems by presenting results from experiments involving the USRP/GNURadio software defined radio platform.