Computer Science 530 - Assignment #1 -- Fall 2006

Due: Thursday, Otober 5, 2006, 11:00 p.m.

1. To ensure authenticity of data, one can use a public key algorithm (say RSA) to encrypt the entire message with the private key. This way only one entity can send the message but anyone can check its authenticity. Do you see any drawbacks with the approach? Identify and explain such drawbacks and a workaround to address the limitation.
2. To achieve better confidentiality than DES, we use Triple DES with the encrypt-decrypt-encrypt sequence. Do you think that with this sequence of encrypt - decrypt - encrypt, as used for triple DES
   1. The encryption would be any stronger than just encrypting the message once. (yes / no)
   2. Why? (not to exceed 3 lines)
3. Consider the following scenario. A submarine is about the depart mainland of a country before a long mission. To ensure a high level of confidentiality a 512MB long one-time pad key was generated using the readings of vibrations generated by a motor engine and sent with the submarine. A copy of that was kept at the mainland for decryption purposes. Whenever communication was to take place the data would be XORed with the key and sent. Based on this arrangement, answer the following questions as true or false and a reason for the same (not to exceed 3 lines for each, in most cases one line is enough)
   1. Since we are using a simple operation like XORing the message and key, the confidentiality provided by this scheme is weaker than say a public key scheme like RSA.
   2. The amount of communication that can be carried out confidentially would be limited even though the key may be this large.
   3. Since we are using provably secure encryption, the integrity provided by this XOR scheme is stronger than a public key scheme like RSA.
   4. It would have been a better scheme if instead of using the motor engine readings say a C compiler was used.

INSTRUCTION:

The report must be submitted by 11:00 p.m. on October 5, 2006. The report should be approximately 3 pages, or roughly 1200 to 1500 words. To submit your report you will use the DEN Blackboard assignent submission mechanism. You will use this method regardless of whether you are an on-campus student or a DEN student.

How to submit Assignment #1:

• STEP 1. Please login to DEN, and select csci530.
• STEP 2. Please select "Assignment" in the menu.
• STEP 3. Please select "view/Complete Assignment #1".
• STEP 4. Please select "File To Attach" to attach your report. (NOTE: PDF, MS WORD, ASCII TEXT ONLY! Other formats are NOT acceptable.)
• STEP 5. Please select "Submit" button. (If you select *SAVE* button instead of *submit*, then the TA cannot view your report for grading.)

It is the individual student's responsibility to follow the submission instruction. Submissions that do not follow this instructions, e.g., submitted late, or only "Saved" and not submitted. may be penalized or may not be graded at all. Note that the submission box for the assignment may dissapear from the class web site at 11PM on October 5th, i.e. the submission deadline.

GUIDELINE:

This is a lot to cover in so few words - so our advice is to write a first pass at your answer that is longer, and then edit out material that is redundant or not to the point. The use of tables can be very effective in conveying your ideas in a small area, but the tables must be integrated with your textual discussion, and not the only item in your submission.