Defensive Design

Defensive Design

1. Defensive Design help to ensure that programms are working properly

   • 1. Anticipate how users might misuse their programs and then try to prevent this from happening
   • Ensure their code is well maintained
   • Reduce the number of errors in the code through testing

2. There are 2 ways that you can prevent users from entering something you don't want to:

   • Input Sanitisation: Removing any unwanted characters before passing data through the program
   • Input Validation: Checking if data meets certain criteria before passing it through the program.

3. Authenitication can help protect your programs

   • Authentication can confirm the identity of a user before they're allowed to access certain pieces of the program
   • Passwords 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
   • Common ways to increase security:
     • Force users to use strong password and get them to change their password 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. Programs can be easily maintained by:

   • Comments are useful for explaining what the key features of a program do - well written and clear comments are fundamental for helping other programmers understand you rprogram
   • Indentation can be used to separate different statements in the program. This allows other programmers to see the flow of the program more clearly and pick out the different features
   • Variables and subprograms should be named so that they refer to what they actually are. This helps programmers to keep track and recognise what the variables are and are all the way through your program

5. Testing is the way to make sure that that a program is working correctly

   • There are 2 types of different errors:
     • LOGIC errors - when the compiler or interpreter is able to run the program but the program does something unexpected
     • SYNTAX errors - when the computer or interpreter doesn't understand something you've typed because it does not follow the rules or grammar of the programming language
   • Functionality Testing is an essential part of the development process and a good way to spot LOGIC errors
     • Performance Test - Tests how quickly certain features run and their impact on computer resources
     • Usability Test - Tests how user-friendly the interface and their impact on computer resources
     • Security Test - Tests vulnerability to attacks and securely data is stored
     • Load/Stress Test - Tests how it copes under extreme conditions. e.g. lots of users at the same time
   • There are 2 types of testing:
     • Final Testing - the program only goes through the development cycle once. All the required features of the program are added at the same time. The program is tested against the initial requirements of the customer - if it meets them then the program is signed off. The customer will get what they asked for, but it won't necessarily be what the really want.
     • Iterative Testing - the program will go through the development a few times. The idea is to try and get the program to match what the customer really wants. The requirements in the first cycle might only include the main features of the program. At the start of each new cycle the requirements will be adjusted.