Information Security · Unit 4
Asymmetric Encryption
Exam-focused notes for Asymmetric Encryption (Information Security, BIT303): what the TU syllabus asks and how it has actually been tested, with 5 solved past questions from this unit.
What this unit covers
- RSA algorithm and key generation
- RSA encryption and decryption
- RSA numerical examples
- Diffie-Hellman key exchange protocol
- Public key cryptography principles
RSA algorithm and key generation
RSA Cryptosystem with p=11 and q=7
Consider p=11 and q=7 in a RSA cryptosystem.
i. What is a public key pair (e, n)?
ii. What is a private key pair (d, n)?
iii. What is ciphertext for M=6? [10]
- $p = 11$ (prime) - $q = 7$ (prime) - Message $M = 6$ --- $$n = p \times q = 11 \times 7 = 77$$ $$\phi(n) = (p-1)(q-1) = 10 \times 6 = 60$$ --- Choose $e$ with $1 < e < \phi(n)$ and $\gcd(e, \phi(n)) = 1$. Try $e = 7$: $$\gcd(7, 60) = 1 \quad \checkmark$$ ...
Full solved answer →Write the algorithm for RSA key generation with encryption and decryption. [5]
Note: No specific reference notes were found for this topic. The following answer is based on standard RSA cryptography as taught in BSc CSIT curriculum. --- RSA (Rivest-Shamir-Adleman) is a public-key (asymmetric) cryptosystem based on the mathematical dif...
Full solved answer →Diffie-Hellman key exchange protocol
Distinguish between threats and attack. Discuss some computer security strategy. Assume a prime number 23 and 9 as its primitive root. Alice select a private key 5 and Bob select the private key 6. Now find the secret key value that Alice and Bob shared using Diffie - Hellman protocol.[10]
Parameter Value ------ Prime number $p$ 23 Primitive root $g$ 9 Alice's private key $a$ 5 Bob's private key $b$ 6 All required data is present. --- Aspect Threat Attack --------- Definition A potential danger that could exploit a vulnerability An actual, de...
Full solved answer →Explain Diffie Hellman Key Exchange Protocol with suitable example. [5]
The question is descriptive. The only numeric inputs come from the standard example: - Prime $p = 23$ - Generator (primitive root) $g = 5$ - Alice's private key $a = 6$ - Bob's private key $b = 15$ --- The Diffie-Hellman (DH) Key Exchange, introduced by Whi...
Full solved answer →RSA encryption and decryption
RSA Encryption and Decryption
RSA is an asymmetric (public-key) cryptosystem. Encryption uses the receiver's public key and decryption uses the receiver's private key. Its security rests on the difficulty of factoring the product of two large primes. --- 1. Choose two large primes $p$ a...
Full solved answer →Make Unit 4 stick
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