Here are some hints on defensive programming techniques to avoid creating security problems. Many of these techniques also improve general quality of code, because almost any major bug can be potentially used by a cracker for a Denial of Service or other attack.
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- One of the most common problems is unchecked use of constant-size structures and functions for dynamic-size data (the buffer overflow problem). This is especially common for string data in C.
- Never make your code more complex than necessary. Complexity breeds bugs, including security problems.
- Either leave your code available to everyone on the Net (see Free software)
- If possible, reuse code instead of writing from scratch.
- Encrypt all important data that flows the Net.
- All data is important until proved otherwise.
- All code is unsecure until proven otherwise.
- Never make your program setuid unless you're really sure it's secure.
- If you check data for correctness, check if it's correct, not if it is incorrect.
- William R. Cheswick and Steven M. Bellovin, Firewalls and Internet Security: Repelling the Wily Hacker ISBN 0201633574 http://www.wilyhacker.com/