1. The multiplicative Inverse of 550 mod 1769 is –
d) Does not exist
2. It is desirable to revoke a certificate before it expires because –
a) the user is no longer certified by this CA
b) the CA’s certificate is assumed to be compromised
c) the user’s private key is assumed to be compromised
d) all of the mentioned
3. Suppose that A has obtained a certificate from certification authority X1 and B has obtained certificate authority from CA X2. A can use a chain of certificates to obtain B’s public key. In notation of X.509, the correct order of this chain is represented as –
a) X2 X1 X1 B
b) X1 X1 X2 A
c) X1 X2 X2 B
d) X1 X2 X2 A
4. Certificate extensions fall into 3 categories. Which one of the following is not a Certificate extensions category?
a) Subject and Issuer attributes
b) Key and Policy information
c) Certification path constraints
d) All of the above are Certificate extensions categories
5. A total of seven messages are required in the Public-Key distribution scenario. However, the initial five messages need to be used only infrequently because both A and B can save the other’s public key for future – a technique known as ____________
a) time stamping
6. Which of the following slows the cryptographic algorithm –
1) Increase in Number of rounds
2) Decrease in Block size
3) Decrease in Key Size
4) Increase in Sub key Generation
a) 1 and 3
b) 2 and 3
c) 3 and 4
d) 2 and 4
7. Which of the following statements are true.
i) In the CBC mode, the plaintext block is XORed with previous ciphertext block before encryption.
ii) The CTR mode does not require an Initialization Vector
iii) The last block in the CBC mode uses an Initialization Vector
iv) In CBC mode repetitions in plaintext do not show up in ciphertext
b) ii) and iv)
c) All the Statements are true
d) i) ii) and iv)
8. What is the number of possible 3 x 3 affine cipher transformations ?
9. The blowfish algorithm’s key expansion converts a key of at most 448 bits into several subkey arrays totaling ___ bytes.
10. For the group Sn of all permutations of n distinct symbols, what is the number of elements in Sn?
11. Which of the following statements are true with respect to the blowfish algorithm?
i) Provided key is large enough, brute-force key search is not practical, especially given the high key schedule cost
ii) Key dependent S-boxes and sub keys make analysis very difficult
iii) Changing both halves in each round increases security
iv) Blowfish has improved avalanche effects
a) i) ii) and iv)
b) ii) and iii)
d) All are true
12. Which one of the following modes of operation in DES is used for operating short data?
a) Cipher Feedback Mode (CFB)
b) Cipher Block chaining (CBC)
c) Electronic code book (ECB)
d) Output Feedback Modes (OFB)
13. Which of the following is the correct encryption statement representation for the XTS-AES mode?
a) E(K1,P) XOR T
b) E(K2,T) XOR P
c) E(K1,T XOR P) XOR P
d) E(K1,P XOR T) XOR T
14. The last two blocks of the XTS-AES mode are
a) padded as 10*
b) encrypted/ decrypted using ciphertext-stealing
c) padded as 10*1
d) padded and then swapped after encryption/ decryption