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This intentional interference with wireless transmissions can be used as a launchpad for mounting Denial-of-Service attacks on wireless networks. Typically, jamming has been addressed under an external threat model. This paper considers the problem of an attacker disrupting an encrypted victim wireless ad hoc network through jamming. Jamming is broken down into layers and this paper focuses on jamming at the Transport/Network layer. Jamming at this layer exploits AODV and TCP protocols and is shown to be very effective in simulated and real networks when it can sense victim packet types, but the encryption is assumed to mask the entire header and contents of the packet so that only packet size, timing, and sequence is available to the attacker for sensing. A sensor is developed that consists of four components. The first is a probabilistic model of the sizes and interpacket timing of different packet types. The second is a historical method for detecting known protocol sequences that is used to develop the probabilistic models, the third is an active jamming mechanism to force the victim network to produce know sequences for the historical analyzer, and the fourth is the online classifier that makes packet type classification decisions. The ratio of the jamming pulses duration to the transmission duration can be as low as 10-4. We investigate and analyze the performance of combining a cryptographic interleaver with various coding schemes to improve the robustness of wireless LANs for IP packets transmission.