Basic Terms :: Review – Questions & Answers
Part A
CIS341
1. T/F: An unavailable system is at least as bad as no system at all.
True
2. T/F: There is not difference between masquerading and delegation.
False
(3-9) Identify the key computer security terms described below:
3. Trustworthiness of data or resources
integrity
4. Verifying the integrity of a data source.
authentication
5. Concealment of information or resources.
confidentiality
6. Potential violation of security (potential attack).
threat
7. Statement of what is, and what is not, allowed
security policy
8. Ability to use information or resource desired.
availability
9. Method, tool or procedure for enforcing security policy
security mechanism
(10-12) List the three security services.
10.
confidentiality
11.
integrity
12.
availability
(13-14) Identify the security/integrity mechanisms described below:
13. Maintain integrity by blocking unauthorized attempts to change data and attempts to change data in unauthorized ways.
prevention mechanisms
14. Report that data's integrity is no longer trustworthy.
detection mechanisms
(15-18) Identify the security threats described below:
15. Acceptance of false data.
deception
16. Interruption or prevention of correct operation.
disruption
17. Unauthorized control of some part of the system.
usurpation
18. Unauthorized access to information.
disclosure
Part B
(1 - 4) Identify the concepts described below:
1. The unencrypted message.
plaintext
2. The encrypted message.
ciphertext
3. A cipher system that uses the original characters of the message but rearranges their order.
transposition cipher
4. The probability that two randomly chosen letters from the ciphertext will be the same.
index of coincidence
6-7. A cryptosystem that uses the same key for encipherment and decipherment is known as a _____ or a _____ cryptosystem.
symmetric
single key
8. The _____ is also known as a shift cipher because the letters of the plaintext are replaced by letters further along in the alphabet.
Caesar cipher
9. The usual attack on transposition ciphers involves the use of _____ to identify common n-grams.
table of n-gram frequencies
10-11. The formula
f(i) = S0 £ c £ 25 f(c) * p(c - i)
gives the correlation of the frequency of each letter _____ with the character frequencies _____, assuming the ciphertext was produced by a shift cipher.
in the ciphertext
in English
12. When using this formula, f(i) is _____ when the frequency of occurrence in English matches the frequency of occurrence in the ciphertext.
highest
13. But the results of this analysis are only _____ since the frequencies of character occurrence in the plaintext may not match the frequencies of occurrence in normal English usage.
statistical
14. The _____ employs multiple shifts to produce the ciphertext.
Vigenere cipher
15-16. In this cipher the number of shifts used is referred to as its _____ or its _____.
period
key length
17. A Prussian cavalry office, _____, devised a method of decryption for the Vigenere cipher.
Kasiski
18. This method took advantage of _____ in the ciphertext.
repetitions of n-gram occurrences
19. The higher the value of n for a repetition discovered the greater the probability that the repetition _____ a coincidence.
was not
20. In addition, if a repetition is found k characters apart (and the repetition is not a coincidence), then k is a multiple of _____.
the period of the cipher
21. If we discover the cipher period, we can break the ciphertext into segments and use _____ to each segment individually.
Caesar cipher decryption methods
22-31. List and describe the components of the cryptosystem 5-tuple.
E: M x K ® C - set of enciphering functions
D: C x K ® M - set of deciphering functions
M - set of plaintexts
K - set of keys
C - set of ciphertexts