Request: tamper-proofing executables

I would appreciate any pointers to documents, source code or programs that deal with using cryptographic techniques to detect or prevent modification of executable code. I am looking for something that uses either a signature or a one-way hash to detect modifications at run time. Of particular interest is information on signing a file that includes the signature as part of the file. Is this possible with any of the common algorithms? Thanks! Dan -- Dan Marner dmarner@mis.nu.edu Network Weasel National University "Not on MY network!"