This paper will consider the use of nonlinear dynamic forecasting techniques to extract message signals from a six-dimensional, message-modulated hyperchaotic communication scheme. It will be shown that a variety of messages can be successfully extracted using only a three-dimensional reconstruction. Further, the robustness of the signal extraction is demonstrated by extracting a speech message with the speech amplitude varied by over an order of magnitude. In all cases intelligible speech was extracted, so security was not greatly improved by going to a hyperchaotic system or larger amplitude signals. ͓S1063-651X͑98͒12207-9͔ PACS number͑s͒: 05.45.ϩb, 89.70.ϩc FIG. 4. Extracted speech.

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