defensive design

defensive design

1. helps to ensure programs function properly.

2. programmers try to protect their programs through defensive design.

   • they might try to: anticipate how users might misuse their program, ensure the code is well maintained or reduce the number of errors in the code.

3. input sanitisation- removing any unwanted characters before passing data through the program.

4. input validation- checking of data meets certain criteria before passing it through the program, e.g. checking if an email address contains an @ symbol, etc.

5. authentication can confirm the identity of a user before they're allowed to access certain pieces of data or features of the program. a common that programs do this is through passwords.

   • common ways to increase the security of a password-based authentication system: force user to use strong passwords and get them to change it regularly, limit the number of failed authentication attempts, ask for a random selection of characters from the password on each authentication.

6. a whitelist is a list of data the program should accept.

7. a blacklist is a list of data that the program should reject.

8. your program should be easy to maintain.

   • comments are useful to explain what the key features of the program do
   • identation can be used to separate different statements in a program.
   • 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 the code.

9. syntax errors- when the complier or interpreter doesn't understand something you've typed because it doesn't follow the rules or grammar of the programming language.

10. logic errors- when the complier or interpreter is able to run the program, but the program does something unexpected.

11. programs should be tested before being released.

    • performance test- tests how quickly certain features run and their impact on computer resources.
    • usability test- tests how user friendly the interface and features are.
    • security test- tests vunerability to attacks and how securely data is stored
    • load/stress test- tests how it copes under extreme conditions.

12. computer languages can be high or low level.

    • high level language is easy for humans to write, but computers need to translate it into machine code.
    • low level language is tricky for humans to read and write but are easier for a computer to run, e.g binary etc.

13. translators convert programming languages into machine code.

    • there are three types of translators: assemblers, compliers, interpreters.

14. an integrated development environment (IDE'S) is a piece of software that provides features to help a programmer to develop their program.