Recently, chaos based cryptography has attracted significant attraction of the researchers due to their simplicity ofimplementation, complex behavior and extreme sensitivity to initial conditions. In this paper an efficient technique to introduce security at physical (PHY) layer is proposed in 802.11i design to provide security in Medium Access Control. Since it does not emphasize on availability, several denial ofservice (DoS) attacks are possible. The DoS attacks are easy to mount because management and controlframes are unprotected and so are MAC headers. This paper proposes a security scheme at PHY layer by scrambling OFDMconstellation symbols to encrypt data transmission to resist against these malicious attacks. In addition, it can also acts as random interleaver. Analysis shows that, it has good random interleaver properties and also memory efficient. The scrambling matrix is based on a key derived from a one dimensional chaotic nonlinear dynamical system using logistic map. The initial condition of the map acting as the derived key is dependent on the external key. The scrambling is completely reversible with the use of appropriate key. However, use of a wrong initial condition even at 4 th decimal point produces entirely different sequence resulting in erroneous constellations with equal probability. ©2008 IEEE.