Security and Cryptography (CSS 322)

Midterm Exam

You can see your total score as well as the scanned PDF of your exam from this page. The original questions and my set of answers are also available (for them you'll need username/password: css322/steveslectures).

Most questions I try to be generous when marking, looking for important keywords in your answers. However in some questions I am more strict: I look for clear explanations. The following questions for example:

• Question 1 (b) and (c): you need a good explanation to obtain full marks.
• Question 4(a) (unconditional security): its important to mention that even with unlimited resourses the attacker cannot break the cipher. Answers like "unbreakable", "very secure", "it cannot be broken" did not receive full marks.
• Question 5(b) (passive/active): the difference is that active modifies system resources. Answers like "hard to detect, easy to prevent" were given 0 marks.
• Question 8(c) (Eulers theorem): you need to show that 1961 is divisible by 37 and 53 and then use that to calculate the totient, i.e. 36 times 52 = 1872.

Statistics

• Mean: 24
• Stdev: 10
• All scores in descending order:

1	42
2	41.5
3	40.5
4	38.5
5	37
6	36
7	35.5
8	33.5
9	33.5
10	33
11	33
12	31.5
13	30.5
14	28
15	27
16	26.5
17	26
18	25.5
19	25
20	24
21	23
22	23
23	22.5
24	22
25	21.5
26	20.5
27	20.5
28	20
29	20
30	16.5
31	16.5
32	16.5
33	14
34	12.5
35	10.5
36	10
37	8.5
38	8
39	5.5
40	1