Computer Security coursework 1 Dr Alexei Vernitski

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

A picture with hidden text Download the picture file from the module’s web site The text is a poem about a ship (not a complete poem, but as many characters of it as have fitted within the picture).

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 2 bits each I took a picture of a flower I placed each 2-bit fragment of the text in 2 least significant bits of each byte of the picture file (excluding the header of the file)

Your task Extract the text hidden in the picture

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

What does your code need to do exactly? 1.Read everything from the picture file 2.Ignore the header of the file 3.Extract the last two bits from each byte 4.Reassemble the two-bit fragments into bytes of the hidden text 5.Output the text (either print it on the screen or save it to a text file, whichever is easier)

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.

Programming 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.

Labs Before the submission date of each piece of coursework, we shall have a lab on Monday 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

No collaboration This is an individual assignment I shall look for signs of collaboration and plagiarism