CSC327 · TU past paper
Cryptography 2080 question paper
The complete TU 2080 exam paper for Cryptography (CSC327), all 12 questions with solved model answers written to the mark scheme.
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- 1NumericalRSA AlgorithmHideAnswer
Discrete Logarithms and RSA Cryptosystem
- Primes: $p = 13$, $q = 7$ - Plaintext: $M = \text{'hi'}$ - Encoding: $a=0, b=1, \ldots, z=25$ All required data is present. --- Given a prime $p$, a primitive root (generator) $g$, and a value $y$, the discrete logarithm is the integer...
- 210 marksNumericalDouble DESHideAnswer
Write down the encryption and decryption process at 2-DES and 3-DES. Explain the Fiestal cipher structure. Divide $5x^2 + 4x + 6$ by $2x + 1$ over GF(7). [10]
--- 2-DES applies the DES algorithm twice with two independent keys $K1$ and $K2$ (each 56 bits, giving 112-bit effective key length). Encryption: $$C = E{K2}(E{K1}(P))$$ Plaintext $P$ is first encrypted with $K1$ to give an intermediate...
- 310 marksApplications of Hash FunctionsHideAnswer
What are the applications of hash functions? Discuss how SHA-1 algorithm generates hash value from a given message.[10]
--- A hash function maps a message of any length into a fixed-length hash value, which serves as an authenticator. Hash functions are fundamental tools in cryptography and play a vital role in secure information processing. - One-way pro...
- 45 marksNumericalSubstitution TechniquesHideAnswer
Show encryption and decryption of "csit" using hill cipher having key, [5]
- Plaintext: "csit" - Cipher method: Hill cipher - Key matrix: NOT provided in the question (the LaTeX/image key is missing). Missing data note: The actual key matrix is not readable in the question. Without the key, the exact ciphertext...
- 5Authentication SystemHideAnswer
Give the formal definition of authentication system. Describe about one way and mutual authentication system. [3257]
An Authentication System is a security measure put in place to secure data and systems by requiring additional input beyond username and password for users to access a system. Formally, an authentication system is defined as a 5-tuple:
- 65 marksCertificate Life Cycle ManagementHideAnswer
List the stage of certificate life cycle. What are the types of firewalls? [5]
--- A digital certificate (such as an X.509 certificate) issued by a Certificate Authority (CA) goes through the following stages during its life cycle: The entity (user, server, or organization) submits a request to the Certificate Auth...
- 75 marksMalicious LogicHideAnswer
What is malicious logic? How zombies are different from trojan horses? [5]
Malicious logic (also called malicious code or malware) refers to any hardware, software, or firmware that is intentionally included or inserted into a system for a harmful or unauthorized purpose. It is a set of instructions that causes...
- 85 marksNumericalNumber TheoryHideAnswer
How Miller Rabin test is used for primality testing? Show whether the number 561 passes the test. [5]
- Number to test: $n = 561$ - Test base (chosen): $a = 2$ Miller-Rabin is a probabilistic primality test based on the fact that for a prime $n$, the only square roots of $1 \pmod n$ are $\pm 1$. Algorithm: 1. Write $n - 1 = 2^k \cdot m$ ...
- 95 marksFinite FieldsHideAnswer
Show that the set of integers is Ring under addition and multiplication. [5]
A set R with two binary operations (+) and (×) is a Ring if for all a, b, c ∈ R the following axioms hold: Axiom Name ---------------- A1 a + b ∈ R Closure under addition A2 a + (b + c) = (a + b) + c Associativity of addition A3 a + b = ...
- 105 marksNumericalTransposition TechniquesHideAnswer
How substitution ciphers are different from transposition ciphers? Given a message M="CSIT PROGRAM IS A HOT CAKE", encrypt M using Rail Fence cipher with rail size 3. [5]
Feature Substitution Cipher Transposition Cipher --------- Basic idea Each plaintext character is replaced by another character/symbol Character identity is retained but its position is changed Operation Maps letters to other letters via...
- 115 marksIP SecurityHideAnswer
Describe about IPSec. List the five services of PGP. [5]
IPSec is a suite of protocols designed to provide security at the network layer (IP layer) of the Internet. It provides security services for IP datagrams by authenticating and/or encrypting each IP packet in a communication session. IPS...
- 125 marksDiffie-Helman Key ExchangeHideAnswer
How does meet in middle attack work in Diffie Helman key exchange protocol? Explain. [5]
In the Diffie-Hellman (DH) protocol, two parties (Alice and Bob) agree on public parameters: - A large prime q - A primitive root a of q Each party generates a private key and computes a public key, then exchanges public keys to derive a...