Mumbai University Solved Question Papers
Information and Network Security
Previous Year Question Paper with Solution
BSc CS · Sem 5
Mar 2026 Examination
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BSc CS Sem 5 Information and Network Security Mar 2026 Question Paper with Solutions
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First published on munotes.in on 17 October 2026.
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Model answers written and edited by the munotes.in editorial desk.
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The question paper reproduced here is the paper as set by the University of Mumbai at the Mar 2026 examination.
Contents
The questions below are the paper as the University of Mumbai set it at the Mar 2026 examination, in the order it was set.
MarksPage
MarksPage
The Paper as Set
The questions in this volume are the questions asked at the Mar 2026 examination, reproduced as the University of Mumbai set them, in the order it set them. Nothing has been reworded, added or left out. Only the answers are ours. See the original question paper.
Duration 2½ hours · Total marks 75 · 24 questions answered
Instructions printed on the paper
- N.B. (1) All questions are compulsory. (2) Figures to the right indicate marks. (3) Illustrations, in-depth answers and diagrams will be appreciated. (4) Mixing of sub-questions is not allowed.
How to use this volume
Solve the paper first, under exam conditions and against the clock. Then read the answers here and mark your own. Reading a solution before attempting the question feels productive and teaches very little, because recognising an answer is not the same as being able to write one.
SECTION I
Q.1
Attempt ANY FOUR from the following · 20 Marks
(a)What is an Active Attack in network security? Explain any three types of active attacks in detail.[5]
Answer
For full marks, cover: the definition of an active attack and how it differs from a passive one, three types explained in detail with an example each, and how active attacks are countered.
Active attack
An active attack is one in which the attacker modifies the data stream or creates a false stream, or disrupts the system. The X.800 security architecture divides attacks into passive attacks, which only read or observe, and active attacks, which change something. Active attacks are easier to detect than passive ones but hard to prevent completely, because of the wide variety of possible weaknesses, so the aim is to detect them and recover.
Types of active attack
The four classes are masquerade, replay, modification of messages and denial of service. Three are explained below.
1. Masquerade
One entity pretends to be a different entity. A masquerade usually includes one of the other forms: for example, authentication sequences are captured and replayed so that an entity with few privileges gains extra privileges by impersonating one that has them.
Example: an attacker sends an email that appears to come from the college's accounts office, asking students to "confirm" their fee payment on a fake site.
2. Replay
The attacker passively captures a data unit and retransmits it later to produce an unauthorised effect. The message itself is genuine, which is what makes replay dangerous.
Example: an attacker records the encrypted message "transfer Rs 5,000 to account X" and sends it again ten times. If the bank does not check freshness, it makes ten transfers. Countermeasures are timestamps, sequence numbers and nonces.
3. Modification of messages
Some portion of a legitimate message is altered, delayed or reordered to produce an unauthorised effect.
Example: "Allow Ravi to read the result file" is changed in transit to "Allow Raj to read the result file". Countermeasures are message authentication codes and digital signatures, which detect any change.
4. Denial of service (in brief)
Prevents or inhibits the normal use or management of communication facilities, for example by flooding a server with requests.
Countering active attacks
Since prevention cannot be complete, systems detect active attacks (integrity checks, MACs, signatures, sequence numbers, intrusion detection) and recover from any disruption or delay they cause.
Conclusion. An active attack modifies the data stream, creates a false one or disrupts service, unlike a passive attack, which only observes. Its types are masquerade (pretending to be another entity), replay (retransmitting a captured message), modification of messages (altering, delaying or reordering) and denial of service. They are hard to prevent, so they are detected with MACs, signatures, timestamps and sequence numbers and then recovered from.
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