# CS315 Assignment 2 Solution and Discussion

• `````` Assignment No. 02
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Semester: Fall 2019
Network Security-CS315 Total Marks: 20

Due Date: 28/11/2019

Instructions:

You need to use MS word document to prepare and submit the assignment on VU-LMS.
It should be clear that your assignment will not get any credit if:

 The assignment is submitted after due date.
 The assignment is not in the required format (doc or docx).
 The submitted assignment does not open or file is corrupt.
 Assignment is copied (partial or full) from any source (websites, forums, students, etc.).

Objective:

To enhance the knowledge about Cryptographic techniques involving symmetric and asymmetric algorithms.

Assignment

Question No.1: 10 Marks

Message authentication in “One-way Hash” function can be implemented with and without encryption. Considering the scenario where a message is authenticated without encryption between two stations, you are required to answer the following questions:

a) What will be component of the message sent from station A and received at station B?
b) What component of the message will ensure at receiving station that message is not corrupted?

Question No.2: 10 Marks

Cryptography is usually done by using Symmetric and Asymmetric encryption algorithms like Public-key encryption algorithms and Hash functions respectively. How would you differentiate Public-key encryption algorithms and Hash functions on the basis of following?

a) Mechanism of mathematical operations.
b) Number of keys being used for cryptography.

Best of Luck!

• b) Number of keys being used for cryptography.

Although symmetric key cryptography makes use of only one key, asymmetric key cryptography, also known as public key cryptography, utilizes two keys: a public key and a private key. The public key is used to encrypt data sent from the sender to the receiver and is shared with everyone.

Public and Private Key Concept in Encryption

1. Secret key cryptography (symmetrical encryption): Both the sender and receiver must use the same key to encrypt and decrypt messages being sent. This imposes a security risk as we need to deliver the key to the recipient of the message in a secure way to make him/her able to decrypt the message. If an intruder gets hold of the key somehow, he/she will be able to decrypt the secret message and thus compromise the whole operation.

2. Public key cryptography (asymmetrical encryption): In this method we use two keys, one for encryption and the second for decryption. A user will use his/her friend’s public key to encrypt the message. The receiver will use a private key (which should be kept secret) in order to decrypt this message when needed. The public key is used to encrypt plain text or to verify a digital signature, whereas the private key is used to decrypt cipher text or to create a digital signature. Messages encrypted with the public key can only be decrypted using the associated private key pair.

Source

• a) Mechanism of mathematical operations.

The “operations” are addition, subtraction, multiplication, division, exponentiation, and grouping; the “order” of these operations states which operations take precedence (are taken care of) before which other operations. … Exponents.

• b) What component of the message will ensure at receiving station that message is not corrupted?

that enable the master station to ensure that the message has not been corrupted during transmission. … At the receiving end, the modem converts the keying frequencies into d.c. pulses and the serial—parallel converter module reassembles the message into a parallel word including the … Each part system is completely independent of the others; thus they effectively operate in parallel. … To decrease this time, either the number of RTUs in the part system B vs [+] DT) \ // C \ RTU [T].

Book

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20

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