Method and apparatus for security systems are provided to protect electronic designs from unauthorized usage. An obfuscation system is provided for creating secure simulation models of IP cores that allow efficient evaluation of an electronic design incorporating an IP core but do not allow practical implementation of the IP core. The obfuscation system identifies regions for obfuscation within an IP core. Logic obfuscation is inserted into these regions. Examples of obfuscation include additional circuitry that produces time dilatation, space dilatation, or a combination of the two in the circuitry of an IP core. Typically, the inserted obfuscation does not change the ultimate behavior of the internal signals, but is complicated enough to make an electronic design so slow and/or so large that it cannot be implemented practically. Further, the inserted obfuscation should be of a type is not normally removed by that normal logic optimizations such as synthesis.