A steganographic method to prevent the execution of malicious code and mitigate software piracy. The method uses invariant portions of machine instructions to create an executable watermark within unmodified code. This watermark can be verified at any stage of the software lifecycle, including dynamically and continuously during execution, to detect foreign code by verifying the integrity of the watermark prior to execution. In addition, the watermark may serve as a steganographic covert channel concealing additional information. Code invariants are not altered by binding operations such as loading and linking on different machines, and thus may be employed to consistently and repeatedly identify an unmodified instantiation of a particular program. The use of opcodes and register references as invariants avoids trivial register substitution as a means of program differentiation that eludes detection.. The split key structure of the resulting cipher implies that knowledge of only the code (first key) or the cipher table (second key) alone is insufficient to derive the message.
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