Reference no: EM132494172

Let's see how files are stored on a computer. Windows users should go to https://www.hexworkshop.com/ and download the latest demo version of Hex Workshop. Mac and Linux users should go to https://www.sweetscape.com/010editor/ and download the free trial version of the 010 Editor. Install the software on your computer. Open the hex editor. The left panel will contain addresses, the middle panel contains the bit values stored (in hexadecimal) and the next panel contains possible character values for the bits stored. See the clip on Hex Workshop on Blackboard. If you are using the 010 Editor, please be sure that in the top left-hand side of the panel "Edit As: Hex" is selected. If you see "Edit As: Text", use the drop-down arrow to change it.

a. Most files have signatures so that the computer knows what kind of a file it is so let's see what some common signatures are. Open an rtf file (Word can make these). What are the first 10 hex digits you see?

b. Open a pdf file - what are the first 10 hex digits you see? Some files also have trailers that tell the computer that the file has ended. What is the trailer for a pdf file in hex?

c. Open the trent.gif file available in the Assignment 2 zipped folder on Blackboard. What are the first 10 hex digits you see (i.e. the signature)?

d. Let's try one last type of file (and ASCII text file). Open COIS2750H_A2.txt and then determine the signature for this type of file.

e. A good way to see if a file has been altered is to d o a checksum. Open the file 4550out-s19.doc posted to Blackboard in Hex Workshop. Go to Tools and then Generate Checksum. Select CRC (32 bit) (or CRC-32 in the 010 Editor) as your algorithm, select Entire Document, and generate the checksum. How many digits are there in the hex checksum? What are the first 8 digits of the hex checksum? D o another checksum but this time select MD4 (128 bit) (or MD4 in 010 editor) as the algorithm. How many hex digits are there in this checksum? What are the first 8 hex digits?

f. Now let's see what effect changing the content of the file has on the checksum. Make a copy the 4550out-s19.doc file and rename it test.doc (in case we need it in court). Perform this copy from the Operating System (do not use "Save As" from within MS Word). Let's first check out the values of the checksums. Run the CRC (32 bit) and MD4 (128 bit)? algorithms on test.doc and compare them to the results from Part (e). What are the first 8 digits of each checksum and how much did the checksums change?

g. Now let's see what happens when we change the contents of our file copy. From within MS Word, change the first letter of the document text from upper case to lower case (i.e. Computing to computing), save it and then open test.doc in the hex editor. What are the first 8 digits of the hex checksum using CRC (32 bit) and what are the first 8 digits in hex using MD4 (128 bit)? How much did the checksums change from Part (f)?

h. Now let's try to recover corrupted files using our hex editor. Try to open the corrupted1.jpg file. Now use your hex editor and try to figure out why it doesn't open. Make the needed changes needed to open the file. What did you do to fix the image? Describe the picture. (Hint: use your hex editor to open similar image file types and check their signatures).

i. Now try to open the corrupted2.gif file. Use your hex editor and try to figure out why it doesn't open. Make the needed changes needed to open the file. What did you do to fix the file? Describe the contents of the file.