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BSc CS Sem 5 Information and Network Security Mar 2025 Question Paper with Solutions

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Information and Network Security

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BSc CS · Sem 5

Mar 2025 Examination

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First published on munotes.in on 17 October 2026.

Published by munotes.in, Mumbai.

Model answers written and edited by the munotes.in editorial desk.

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The University does not publish an official answer key for this paper. The answers in this volume are model answers, written to show how a full-mark answer is built. They are a study aid, not an authority on what an examiner marked.

The question paper reproduced here is the paper as set by the University of Mumbai at the Mar 2025 examination.

The questions below are the paper as the University of Mumbai set it at the Mar 2025 examination, in the order it was set.

MarksPage

The Paper as Set

The questions in this volume are the questions asked at the Mar 2025 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.

Read the original question paper

SECTION I

Q.1

Attempt ANY FOUR from the following · 20 Marks

(a)Discuss the X.800 Security Services?[5]

Answer

For full marks, cover: what X.800 is, what it means by a security service, the five categories with all their specific services set out, the availability service, and how services relate to mechanisms.

X.800

ITU-T Recommendation X.800, the OSI Security Architecture, gives managers a systematic way to define security requirements. It organises security into attacks, mechanisms and services. A security service is a service provided by a protocol layer of communicating systems that ensures adequate security of the systems or of data transfers.

The five categories and their specific services

1. Authentication (the communicating entity is who it claims to be)

Peer entity authentication: used with a logical connection, to give confidence in the identity of the entities connected.
Data-origin authentication: in a connectionless transfer, assurance that the source of received data is as claimed.

2. Access control

Prevention of unauthorised use of a resource: who can have access, under what conditions, and what they may do.

3. Data confidentiality (protection of data from unauthorised disclosure)

Connection confidentiality: all user data on a connection.
Connectionless confidentiality: all user data in a single data block.
Selective-field confidentiality: selected fields within the data.
Traffic-flow confidentiality: the information that might be derived from observing traffic flows.

4. Data integrity (data received is exactly as sent by an authorised entity)

Connection integrity with recovery: detects modification, insertion, deletion or replay of any data on a connection, and attempts recovery.
Connection integrity without recovery: detection only.
Selective-field connection integrity: for selected fields.

Connectionless integrity: for a single connectionless block, with limited replay detection.
Selective-field connectionless integrity.

5. Non-repudiation (protection against denial by a party to the communication)

Non-repudiation, origin: proof that the message was sent by the specified party.
Non-repudiation, destination: proof that the message was received by the specified party.

Availability service

X.800 and RFC 4949 also treat availability as a property to protect: a system is accessible and usable on demand. An availability service protects it against denial-of-service attacks and depends on proper management of resources.

Services and mechanisms

Services are implemented by mechanisms: confidentiality by encipherment; integrity by data integrity mechanisms and digital signatures; authentication by authentication exchange and signatures; access control by access control mechanisms; non-repudiation by signatures and notarisation; traffic-flow confidentiality by traffic padding and routing control.

Conclusion. X.800 defines security services in five categories: authentication (peer entity and data origin), access control, data confidentiality (connection, connectionless, selective-field and traffic-flow), data integrity (with or without recovery, selective-field, connectionless) and non-repudiation (of origin and destination), with availability treated alongside, each implemented by mechanisms such as encipherment, signatures and access control.

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