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Practical Programming in Tcl & Tk, Third Edition by Brent B. Welch

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Security Policies

A security policy defines what a safe interpreter can do. Designing security policies that are secure is difficult. If you design your own, make sure to have your colleagues review the code. Give out prizes to folks who can break your policy. Good policy implementations are proven with lots of review and trial attacks. The good news is that Safe-Tcl security policies can be implemented in relatively small amounts of Tcl code. This makes them easier to analyze and get correct. Here are a number of rules of thumb:

  • Small policies are better than big, complex policies. If you do a lot of complex processing to allow or disallow access to resources, chances are there are holes in your policy. Keep it simple.

  • Never eval arguments to ...

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