Authentication & Contingencies
Computer Science: OCR GCSE, topic 2.3.3
Authentication and Contingencies
Two very important elements of defensive design are authentication and contingency planning.
Authentication
- Authentication is the process of checking that a person or system is authorised to use a system.
- The most common form of authentication is to require users to enter a username and password.
- Once a user has authenticated themselves, they should be able to see data relevant to themselves and no one else.
Contingency planning
- It is impossible to predict all possible cases of misuse, but there are ways to help reduce errors. For example:
- Providing helpful prompt messages.
- Providing error-recovery routes (e.g. an undo feature).
- Preventing access from certain parts of the system.
- Using exception handling.
Exceptions
Rather than leaving the program to crash when an error happens, exceptions give us a chance to handle the error more gracefully.
Exceptions
- When an error arises in a program, the program is said to 'throw' an exception.
- An exception is a description of the error that arose.
- Exceptions can be 'caught' or handled rather than allowing the program to crash.
Handling exceptions
- If an exception can be dealt with internally, then we can catch the exception and continue with the program.
- This is done using a structure as below:
- try: ---
- except: ---
- The code within the try block will be executed.
- If an exception is thrown inside the try block, then the except block will be run to 'clean up' after the exception.
Test yourself on Authentication & Contingencies
The most common form of authentication requires what data from the user?
Once a user is authenticated, what should they see?
Which of these is a common error-recovery route?
What is it called when an error arises in a program?
What is the purpose of the 'except' block of a try-except structure?