Computer Security coursework 1

1. Computer Securitycoursework 1 Dr Alexei Vernitski

2. Aims of the coursework • Learn more about: • bits and bytes • bit operations (also known as Boolean operations) • files • arrays of bytes • codes (such as ASCII) • digital steganography • All this is useful not only for understanding computer security, but for any career in information technology

3. A picture with hidden text (download the picture file from the module’s web site)

4. Where is the text hidden? • In the original text, each character (for example, a letter) occupies one byte • I split the text into fragments of 4 bits each • I took a picture of a flower • I placed each 4-bit fragment of the text in 4 least significant bits of each byte of the picture file (excluding the header of the file)

5. Your task • Extract the text hidden in the picture

6. What to submit? • Submit just one file with your source code • It will help me if you include your name and registration number in a comment within the code

7. What does your code need to do exactly? • Read everything from the picture file • Ignore the header of the file • Extract the last four bits from each byte • Reassemble the four-bit fragments into bytes of the hidden text • Output the text (either print it on the screen or save it to a text file, whichever is easier)

8. How shall I mark? • I shall run your code and see if it extracts correctly the text that I have hidden in the file. If it does, you get 100%. • If it does not, I shall look at the code and allocate some partial marks according to the list on the previous slide.

9. Programming (as recommended) • I attempted the coursework and wrote my solution in Python • My complete code contains less than 15 lines • It took me approximately 20 minutes to write it • You may need up to 4 hours to complete the assignment if you need to learn how to open files in Python, how to perform bitwise operations in Python etc.

10. Labs • Before the submission date of each piece of coursework, we shall have a lab on Thursday • The purpose of the lab is: • to help you to write your code, in case you have any difficulties • to give you an opportunity to demonstrate your code to me

11. Programming (as not recommended) • If you use any other programming language except Python, you must demonstrate to me that your code works (preferably during the lab), because I may not be able to compile and run it on my office PC • You may find that if you use a language such as Java or C++, you will have to write a much longer code, and debugging it will be much more difficult.

12. Collaboration: you may work in pairs • For this (and only this) assignment, you may collaborate with one more student. In other words, you may work in pairs. • If you are confident enough to write the assignment on your own, do it by yourself; you do not have to collaborate. • To prevent confusion, if you work in a pair, only submit one copy of the assignment, indicating clearly which two students collaborated on it.