1. Cryptanalysis on Monoalphabetic Cipher (20 marks)
A monoalphabetic substitution cipher generates the ciphertext below. Perform cryptanalysis
and find the plaintext. Note that the plaintext only includes meaningful English sentence(s).
Ciphertext
wep umpp rgmusfp br znj rwmpwfepk ngw wn s qsmyp powpzw agw sffnmkbzy wn ngm
srrgvcwbnz wep vswpmbsqr grpk smp cpmupfwqt rwmpwfesaqp.
SENG6250 System and Network Security School of Information and Physical Sciences Semester 2, 2022 Assignment 1 (100 marks, 10%) - Due: 21 August, 23:59 Aims This assignment aims to establish a basic familiarity with security primitives and attacks by analysing, demonstrating, designing solutions using cryptography. Questions 1. Cryptanalysis on Monoalphabetic Cipher (20 marks) A monoalphabetic substitution cipher generates the ciphertext below. Perform cryptanalysis and find the plaintext. Note that the plaintext only includes meaningful English sentence(s). Ciphertext wep umpp rgmusfp br znj rwmpwfepk ngw wn s qsmyp powpzw agw sffnmkbzy wn ngm srrgvcwbnz wep vswpmbsqr grpk smp cpmupfwqt rwmpwfesaqp. Ciphertext letter frequency a. Find the plaintext. (5 marks) b. Show your process of finding (at least) FIVE plaintext letters. (15 marks) 2. Block Cipher and Operation Modes (15 marks) Use an AES encryption calculator (e.g., https://www.hanewin.net/encrypt/aes/aes-test.htm) to demonstrate the Counter mode (CTR) with AES (CTR-AES). a. Create a 256-bit key and a 512-bit plaintext (all in hexadecimal). (2 marks) The key should start with your student ID. For example, if your student ID is C1234567, then your key can be: C1234567EDEEEFF0F2F3F4F5F7F8F9FAC1234567EDEEEFF0F2F3F4F5F7F8F9FA https://www.hanewin.net/encrypt/aes/aes-test.htm b. Specify a hexdecimal Initialisation Vector (IV). An IV cannot be a trivial string like all 0s or 1s. (1 marks) c. Demonstrate the process of each round in the CTR-AES. You can use the AES encryption calculator to show the block cipher encryption result without providing the encryption detail. (8 marks) d. Show the entire ciphertext of 512 bits. (2 marks) e. Please use the following format for your answers. (2 marks) Sample Format Entire Plaintext: XXXX…XXXX Key: XXXX…XXXX IV: XXXX…XXXX Round 1: Input of AES: XXXX…XXXX Output of AES: XXXX…XXXX Round 2: Input of AES: XXXX…XXXX Output of AES: XXXX…XXXX … Entire Ciphertext: XXXX…XXXX 3. Hash Functions (20 marks) a. Let ℎ be a secure one-way hash function. Given a set {??1,??2, ??3,??4, ??5}, such that ??1 = ℎ(??); ??2 = ℎ(??1); ??3 = ℎ(??2); ??4 = ℎ(??3); ??5 = ℎ(??4). Suppose ??3 is known, can we compute any of others in {??1,??2, ??4,??5}? If yes, show how; otherwise, explain why. (10 marks) b. Let (??,??) be an RSA public key, and (??, ??,??) be the corresponding private key. The public key (??,??) is known to everyone, but NO ONE knows the private key (??, ??, ??). Consider a message ??, 1) If 0 <>< ,="" can="" we="" use="" the="" rsa="" encryption="" algorithm="" as="" a="" one-way="" hash="" function?="" justify="" your="" answer="" (5="" marks)="" 2)="" if=""> ??, can we use the RSA encryption algorithm as a cryptographic hash function? Justify your answer. (5 marks) 4. ElGamal Cryptosystem (20 marks) Alice has a public and private key pair (??????, ??????) for ElGamal signature. Suppose that Alice signs a message for Bob every day. If Alice uses the same random number ?? in all signatures. Analyse the good (6 marks) and bad (14 marks) parts of this signing method. 5. Encryptions and Digital Signatures (25 marks) Alice has a public and private key pair (??????, ??????) for RSA cryptosystem. Bob also has his public and private key pair (??????, ??????) for the RSA cryptosystem. Suppose Bob wants to send a message ?? to Alice. There are the following two ways. Case 1: Bob uses ?????? to sign ?? and gets a corresponding RSA signature ????. Then, Bob uses ?????? to encrypt (??,????). The ciphertext on (??,????) is sent to Alice. Case 2: Bob uses ?????? to encrypt ?? and obtains the corresponding ciphertext ??. Then, Bob uses ?????? to sign ?? and obtains the signature ???? . The ciphertext ?? and the signature ???? are sent to Alice. a. Comparing two methods, what would be an advantage(s) of Case 1? (10 marks) b. Create/Find a scenario where we should use Case 2 rather than Case 1. Justify your answer. (15 marks) Submission All assignments must be submitted via Canvas (Assessment tab for SENG6250). If you submit more than once, then only the latest will be graded. Your submission should be a PDF file containing answers to all questions. The mark for an assessment item submitted after the designated time on the due date, without an approved extension of time, will be reduced by 10% of the possible maximum mark for that assessment item for each day or part day that the assessment item is late. Note: this applies equally to week and weekend days. Plagiarism A plagiarised assignment will receive a ZERO mark (and be penalised according to the university rules). Assignment 1 (100 marks, 10%) - Due: 21 August, 23:59