1. (4 points) which of the following attacks are passive attacks (one or more answers may be correct)?
A. Traffic analysis B. Denial of service C. Replay attack D. Masquerade
2. (12 points) Let PuA and PrA be Alice’s public and private keys, respectively, and PuB and PrB be Bob’s public and private keys, respectively. Assume that Alice sends Bob a message M.
a) If Alice wants to protect the confidentiality of M, then what key should Alice use to encrypt M?
b) If Alice wants to provide digital signature, then what key should Alice use to create the digital signature?
c) If Alice wants to protect the data integrity of M, then what key should Alice use to encrypt M?
3. (8 points) Suppose 4 people want to communicate securely with each other such that the communication of none of the possible pairs of people can be eavesdropped by the remaining persons. Answer the following questions:
a) If they use a symmetric cipher, how many symmetric keys would they need in total?
b) If they use a public-key cipher, how many public and private keys would they need in total?
4. [15 points] Encrypt the message “tomorrowfriday” using rail fence cipher with depth 4
5. [15 points] Decrypt the message “rnoxitrzsunwinooagry” using row transposition cipher and key: 35214
6. [7 points] Given the following permutation table (P table)
Assume that the input of the P table is 11000000 00000000 00000000 00000000, which bits of the output of the P table are 1?
7. [15 points] Consider the following S-box. Assume that the output of this S-box is 2, What are the four possible inputs to S-box?
8. [8 points] Compute Φ(55), where Φ is Euler totient function.
9. [16 points] Consider the following simple hash function H, which computes the hash code H(M) of a message consisting of n blocks b1, b2, …, bn.
hi = bi1 bi2 … bin
- hi: the ith bit of the hash code - bij: the ith bit of the jth block
Assume that the block size is 4-bits and Alice sends message M = 0110 1001 1101 0101 to Bob.
Answer the following two questions:
(1) (8 points) what is the hash code H(M)?
(2) (8 points) show that this hash function is not secure by creating another message M’ so that H(M’) = H(M).
