Defensive Design

Defensive Design

1. Defensive Design helps to ensure programs Function Properly

   • When programs are functioning correctly , they should never break and never produce errors.
   • Programmers try to protect their programs through defensive design:
     • Anticipate how users might misuse their program, then attempt to prevent it from happeneing.
     • Ensure their code is well-maintained
     • Reduce the number of errors in the code through testing.

2. Make sure the Inputs can't be Exploited

   • The easiest way for a user to accidentally or intentionally misuse a program is when entering data.
   • There are two ways that you can prevent users from entering something you don't want them to:
     • INPUT SANITISATION - removing any unwanted characters before passing data through the program
     • INPUT VALIDATION - checking if any data meets certain criteria before passing it into the program. E.g. checking that and email address contains an @ symbol and has a suitable ending (.com, .co.uk, etc)
   • Sanitisation and Validation are often done using whitelists and blacklists. Whitelists ten to be more secure, however they can take a long time to set up and can be too restrictive.
     • A whitelist is a list of all data that a program should accept - any data that isn't on the whitelist will be rejected.
     • A blacklist is a list of all the data that a program should reject - any fata that isn't on the blacklist will be accepted.

3. Authentication can help Protect your programs

   • Authentication can confirm the identity of a user before they're allowed to access certain pieces of data or features of the program.
   • Password are usually associated with a username. When someone tries to access a protected part of the program, it should ask them for their password to check that they are who they claim to be.
   • Here are some common wats to increate the security of a password-based authentication system:
     • Force users to use strong passwords and get them to change their passwords regularly.
     • Limit the number of failed authentication attempts before access to an account is lost.
     • Ask for a random selection of characters from the password on each authentication.

4. Your program should be Easy To Maintain

   • As part of the defensive design of a program, programmers should make sure that it is well-maintained.
   • The following features can improve the maintainability of source code:
     • Comments are useful for explaining what the key features of a program do.
     • Indentation can be used to separate different statements in a program. This allows other programmers to see the flow of the program more clearly and pick out the different features.
     • Variables and sub programs should be named so that they refer to what they actually are.
     • Only use global variables when necessary as they could affect the rest of your code.