Defensive Design

• Defensive design considerations:

  • Anticipating misuse
  • Authentication
• Authentication

  The process used to test that a person is who they claim to be.
• Anticipating misuse

  Every possible input, however incorrect or creative should be anticipated.
• Input validation

  Validation is the checking of data, on input, to ensure that it is sensible or reasonable. It cannot guarantee that the data is correct.
• Common methods of input validation:

  • Range check
  • Type check
  • Length check
  • Presence check
  • Format check
• Range check

  checks a number or date is within an allowed range
• Type check

  checks data is the right type such as integer, character or text string
• Length check

  checks text entered is not too long or too short- for example, a password is greater than 8 characters
• Presence check

  checks that data has been entered i.e. that a field has not been left blank
• Format check

  checks that the format of, for example, a postcode or email address is appropriate
• Maintainability

  A characteristic of defensive design that helps programmers modify and repair programs
• Things that can improve the maintainability of a program:

  • Use of sub programs- can make it easier for other programmers to see how different parts of a program works
  • Naming conventions- naming a variables, sub programs and parameters to refer to what they are to makes it easier to keep track of them
  • Indentation- can be used to separate different statements in a program
  • Commenting- are used for explaining what the key feature of a program do

  These all help other programmers understand the program better