1. Explain the three major security objectives: availability, integrity and confidentiality. Which one is more important than the others in the following scenarios? a. Suppose your job is to maintain the security of the patient information/data system for the Moffitt center. b. What if you are managing Tampa’s emergency alert system? Reading: https://en.wikipedia.org/wiki/2018_Hawaii_false_missile_alert 2. Explain DDoS Attacks and their impact on the Internet. What are the possible countermeasures against such attacks? 3. Prove one-time pad is perfectly secure. 4. What are the properties of hash functions? 5. Explain meet-in-the-middle attacks against double-DES. 6. Suppose Alice designs a one-time pad variant: the plaintext is to no longer XOR, but bite-wise multiply the one-time key that is generated uniformly at random. For example: plaintext: 001101 key: 101110 ciphertext: 001100 Is Alice’s design good? 7. Alice design a new double-DES scheme. The scheme will first DES-encrypt a message using K1 to get an intermediate ciphertext, then DES-decrypt the intermediate ciphertext using K2 to get the final ciphertext. Is there any vulnerability in Alice’s design? 8. Suppose the sub-key generation function is to reverse all the bits of the key K (e.g., 0 1 1 1 ➔ 1 1 1 0), and the scrambling function is f = M XOR K’, where M is the second half of input bits and K’ is the sub-key (i.e., the reverse of the original key K). Now given the original K = 0011, and input bits 1111 0000, compute the output of the Feistel Cipher. 9. A and B want to ensure the integrity and authenticity of the messages between them, but they do NOT care about the confidentiality. Assume A and B share a key K. Answering two questions a. How can they achieve their goal only with symmetric key cryptography? b. How can they achieve their goal with hash function H? 10. Bob is assigned a task to design a way to allow encryption of files stored in the system: all files are stored in an encrypted form. If a block of a file is requested, the system should retrieve the block, decrypt it and return the plaintext to the host. Similarly, if a host writes a block to the storage system, the system should retrieve the right keying material, encrypt the block, and only save the ciphertext on disk. Consider the modes of operations discussed in class (i.e., ECB, CBC, CFB, CTR). Which one should be used in terms of read/write efficiency? Why? (You do NOT need to consider the key storage problem.) 11. Bob designed a new scheme to detect whether a message is modified by an attacker (protecting data integrity). The scheme is to append to each message a SHA-256 hash of that message. Explain the vulnerability of Bob’s design. 12. Is using the same key twice in one-time pad secure? Why? Please explain in detail. 13. A company is selling an artifact worth millions of dollars. Many interested buyers are in the bidding process, which works as follows. Each buyer sends the information of his/her final number (e.g., $1,000,000.00) to the company to show his/her commitment. And the number must be kept confidential from other buyers and even the company before the deadline. After the deadline, all numbers are released to all buyers and the company, then the buyer with the highest number wins. Design a HASH FUNCTION based scheme to secure the bidding process. Describe steps a buyer and/or the company should do.
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