Reference no: EM132968003

SENG2250 System and Network Security - The University of Newcastle

Network Security School of Information and Physical Sciences

Aims
This assignment aims to establish a basic familiarity with security primitives and attacks by analysing, demonstrating solutions using cryptography.

Question 1. Block Cipher and Operation Modes

Use an AES encryption calculator to demonstrate the CBC mode with AES (CBC-AES).

a. Create a 128-bit key and a 512-bit plaintext (all in hexadecimal). (5 marks) The key should start with your student ID. For example, if your student ID is C1234567, then your key can be:

C1234567EDEEEFF0F2F3F4F5F7F8F9FA

b. Specify an Initialisation Vector (IV). An IV cannot be a trivial string like all 0s or 1s.

c. Demonstrate the process of each round in the CBC-AES. You can use the AES encryption calculator to show the block cipher encryption result without providing the encryption detail.
d. Show the entire ciphertext of 512 bits.
e. Please use the following format for your answers.

2. Brute-Force Attacks
Suppose that a language "X" has 32 different letters. Answer the following questions.
a. Alice wants to use a 10-letter password (case insensitive). Each password character is randomly selected from 32 possible letters. how many different passwords can be generated?
b. Suppose that an adversary can attempt passwords at a rate of two million per second. If an adversary can immediately know an attempted password's correctness, what is the expected time (i.e., average time) to reveal Alice's password generated above? Convert the time to the number of days.
c. Suppose that Bob uses a monoalphabetic substitution cipher (regarding the language "X") to encrypt a message. Assume the redundancy of the plaintext "X" is 6. how many ciphertext characters are needed to identify a unique key?

3. hash Functions
a. Let h be a secure one-way hash function. Given a set {v!, v", v#, v$, v%}, such that
v! = h(??); v" = h(v!); v# = h(v"); v$ = h(v#); v% = h(v$).
Suppose v# is known, can we compute any of others in {v!, v", v$, v%}? If yes, show how; otherwise, explain why.

b. Suppose ((e, n), d) is an RSA public and private key pair. The public key (e, n) is known to everyone, but NO one knows the private key d. Consider a message space M, for all m ∈ M, we have m < n. Can we use the RSA encryption algorithm as a cryptographic hash function for a message m? Justify your answer. (hint: RSA has a property: (m!m")& = m&m& m??d n)
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4. Cryptanalysis on Monoalphabetic Cipher

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
rm clmhrwvirmt grnv zh gsv ulfigs wrnvmhrlm nliv li ovhh vjfrezovmg gl gsv gsivv hkzgrzo wrnvmhrlmh dv ifm rmgl lmv izgsvi wruurcfog jfvhgrlm.

a. Find the plaintext.
b. Show your process of finding (at least) FIVE plaintext letters.

Attachment:- System and Network Security.rar