IGNOU FREE BCOS-183 Computer Application in Business Solved Guess Paper 2025

1) Define integrity & non repudiation.

Integrity ensures that data remains accurate, unaltered, and trustworthy throughout its lifecycle. It prevents unauthorized modifications, whether intentional or accidental, by implementing security measures like hashing, checksums, and digital signatures. When data integrity is compromised, errors, corruption, or malicious tampering can occur, leading to misinformation and security risks.

Non-repudiation is a security principle that ensures a sender cannot deny having sent a message or performed an action, and a recipient cannot deny receiving it. This is achieved through cryptographic techniques such as digital signatures and timestamps, which provide verifiable proof of communication or transactions. Non-repudiation is essential for legal and forensic purposes, ensuring accountability in digital interactions.

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2) Explain any two classical ciphers.

1. Caesar Cipher

The Caesar cipher is a simple substitution cipher where each letter in the plaintext is shifted a fixed number of places down the alphabet. For example, with a shift of 3, ‘A’ becomes ‘D,’ ‘B’ becomes ‘E,’ and so on. Decryption reverses this process by shifting backward.

Example:

Plaintext: HELLO

Shift: 3

Ciphertext: KHOOR

The Caesar cipher is easy to break using frequency analysis since each letter maps directly to another in a predictable manner.

2. Playfair Cipher

The Playfair cipher is a digraph substitution cipher that encrypts letter pairs using a 5×5 grid containing a keyword. It replaces repeated letters and adjusts for odd-length messages.

Example Grid (Key: “MONARCHY”)

mathematica

CopyEdit

M O N A R

C H Y B D

E F G I/J K

L P Q S T

U V W X Z

Encryption Rules:

Same row: Replace each letter with the one to its right.

Same column: Replace each letter with the one below it.

Elsewhere: Form a rectangle and swap letters diagonally.

Example:

Plaintext: “HELLO” → “HE LO”

The Playfair cipher is more secure than the Caesar cipher but still vulnerable to frequency analysis of letter pairs.

 3) Explain one time password.

A One-Time Password (OTP) is a dynamically generated password that is valid for a single login session or transaction. Unlike static passwords, which remain the same until changed, OTPs enhance security by reducing the risk of password reuse and unauthorized access.

How OTP Works:

Generation: OTPs are created using algorithms based on time (Time-based OTP or TOTP) or a secret key (HMAC-based OTP or HOTP).

Delivery: OTPs are sent via SMS, email, authenticator apps, or hardware tokens.

Expiration: OTPs are time-sensitive, usually expiring within a few seconds or minutes.

Authentication: Users enter the OTP to verify their identity before accessing an account or completing a transaction.

Benefits of OTP:

Prevents unauthorized logins, even if the main password is compromised.

Adds an extra security layer in two-factor authentication (2FA).

Reduces phishing and brute-force attacks.

OTPs are widely used in banking, e-commerce, and secure online systems for enhanced security.

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4) What are active and passive attacks? Explain with suitable example.

Active and Passive Attacks in Cybersecurity

In the field of cybersecurity, attacks on a system or network can be broadly classified into active attacks and passive attacks based on the intent and method of exploitation.

1. Passive Attacks

A passive attack is a type of cyberattack where the attacker intercepts and monitors data without modifying it. The goal of a passive attack is usually to gather information, such as sensitive data, communication patterns, or encryption keys, without alerting the victim. Since the attacker does not alter the system, passive attacks are harder to detect.

Example of Passive Attack

Eavesdropping (Sniffing): A hacker listens to network communications to capture confidential information, such as login credentials or credit card details.

Traffic Analysis: Even if data is encrypted, attackers can analyze communication patterns and infer sensitive information.

Prevention Methods:

Using strong encryption protocols (SSL/TLS)

Implementing secure network configurations

Using VPNs to encrypt network traffic

2. Active Attacks

An active attack is a type of cyberattack where the attacker manipulates or alters the data, disrupts network operations, or gains unauthorized access to a system. These attacks can cause significant damage, including data loss, financial theft, or system downtime.

Example of Active Attack

Man-in-the-Middle (MITM) Attack: The attacker intercepts and alters communication between two parties to steal sensitive data.

Denial of Service (DoS) Attack: Attackers flood a server with excessive requests, making it unavailable for legitimate users.

Malware Attacks: Injecting malicious software, such as viruses, ransomware, or worms, into a system to steal or destroy data.

Prevention Methods:

Using firewalls and intrusion detection systems (IDS)

Keeping software and systems updated

Implementing multi-factor authentication (MFA)

Key Differences Between Active and Passive Attacks

Feature	Passive Attack	Active Attack
Intent	Eavesdropping or monitoring	Data modification or disruption
System Alteration	No	Yes
Detection	Difficult	Easier
Examples	Eavesdropping, Traffic analysis	MITM, DoS, Malware attacks

5) What do you mean DES in cryptography?

Data Encryption Standard (DES) is a symmetric-key encryption algorithm used for securing digital data. It was developed by IBM in the early 1970s and later adopted by the U.S. National Institute of Standards and Technology (NIST) in 1977 as a federal encryption standard. DES played a crucial role in the evolution of modern cryptography but has since been replaced by more secure encryption methods due to its vulnerabilities.

Key Features of DES

Symmetric-Key Algorithm

Uses a single key for both encryption and decryption.

Requires secure key distribution between sender and receiver.

Block Cipher

Operates on fixed-size blocks of data (64-bit blocks).

Encrypts data in chunks rather than one bit at a time.

Key Size

Uses a 56-bit key, though the total key length is 64 bits (8 bits are used for parity checking).

Due to advancements in computing power, a 56-bit key is now considered weak.

Feistel Structure

DES follows the Feistel network, dividing the data into two halves and processing it through 16 rounds of encryption.

Each round includes permutation and substitution operations to increase security.

Initial and Final Permutation

The plaintext undergoes an initial permutation before encryption.

After the 16 rounds, the ciphertext undergoes a final permutation.

How DES Works?

Key Generation

A 56-bit key is derived from the original 64-bit key.

The key is divided into two halves and processed through 16 rounds of key scheduling.

Encryption Process

The plaintext is divided into 64-bit blocks.

Each block undergoes initial permutation and 16 rounds of substitution and permutation using different subkeys.

The final output is the ciphertext.

Decryption Process

The same algorithm is used, but the subkeys are applied in reverse order.

Security and Limitations of DES

Brute Force Attacks: The small key size (56-bit) makes DES vulnerable to brute force attacks, where all possible keys are tested until the correct one is found.

Cryptanalysis: DES is susceptible to differential and linear cryptanalysis, which analyze encryption patterns to break the cipher.

Replacement by AES: Due to its vulnerabilities, DES was replaced by the Advanced Encryption Standard (AES) in 2001, which offers stronger security with key sizes of 128, 192, and 256 bits.

Variations of DES

Triple DES (3DES)

An enhanced version that applies DES encryption three times with different keys.

Increases security by extending the key size to 112 or 168 bits.

Used in financial transactions before being gradually phased out.

AES (Advanced Encryption Standard)

Official successor to DES.

Uses a block size of 128 bits and key sizes of 128, 192, or 256 bits.

More secure and widely adopted.

Conclusion

DES was an essential cryptographic standard that paved the way for modern encryption techniques. However, due to its small key size and vulnerability to attacks, it is no longer considered secure. Today, more advanced encryption algorithms like AES and RSA are used to ensure data confidentiality and security in digital communications.

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6) Explain the use Hash function in cryptography.

A hash function is a crucial component of cryptography, used to ensure data integrity, authentication, and security. It is a mathematical algorithm that takes an input (or message) and produces a fixed-size string of characters, typically a hexadecimal number. The output is called a hash value or digest. Hash functions play a vital role in digital security applications like password storage, digital signatures, and blockchain technology.

1. Properties of Cryptographic Hash Functions

A cryptographic hash function must have the following properties:

Deterministic: The same input always produces the same output.

Fast Computation: The hash function should quickly process input data.

Pre-image Resistance: It should be infeasible to determine the original input from its hash value.

Small Change Effect: A minor change in input should result in a significantly different hash (Avalanche effect).

Collision Resistance: No two different inputs should produce the same hash.

Second Pre-image Resistance: Given a hash, it should be computationally impossible to find another input with the same hash.

2. Uses of Hash Functions in Cryptography
3. a) Password Security

Hash functions store passwords securely. Instead of storing plain text passwords, systems store hashed versions. When a user logs in, the input password is hashed and compared to the stored hash. This prevents attackers from accessing real passwords even if they obtain the database.

1. b) Data Integrity and Verification

Hashing ensures that data has not been altered. When transferring files or messages, the sender generates a hash and sends it along with the data. The receiver rehashes the data and compares it with the original hash to verify integrity.

1. c) Digital Signatures and Certificates

Hash functions are used in digital signatures to verify the authenticity of documents and messages. The sender signs the hash of a message instead of the whole message. The receiver can validate the signature by hashing the message again.

1. d) Blockchain and Cryptocurrencies

In blockchain technology, hash functions are used to secure transactions and link blocks together. Every block contains the hash of the previous block, ensuring that any modification is detectable.

1. e) Message Authentication Codes (MACs)

Hash functions are used in MACs to ensure message authenticity. A sender and receiver share a secret key, and the message is hashed using this key to confirm that the message has not been tampered with.

1. f) Secure Random Number Generation

Hash functions help generate secure random numbers for cryptographic protocols like encryption keys, session tokens, and authentication mechanisms.

3. Popular Cryptographic Hash Functions

Several widely used cryptographic hash functions include:

MD5 (Message Digest Algorithm 5) – Now considered weak due to vulnerabilities.

SHA-1 (Secure Hash Algorithm 1) – Deprecated due to collision attacks.

SHA-256 and SHA-3 – Secure and widely used in modern cryptographic applications.

BLAKE2 and Argon2 – Used in password hashing for improved security.

Conclusion

Cryptographic hash functions are essential for digital security. They ensure password protection, data integrity, authentication, and the security of blockchain transactions. However, as computing power increases, older hash functions become vulnerable to attacks, necessitating the use of stronger algorithms like SHA-3 and BLAKE2.

7) What do you mean by Private and public key?

In cryptography, private and public keys are essential components of asymmetric encryption, also known as public-key cryptography (PKC). This encryption method involves two mathematically related keys: a public key, which is shared with others, and a private key, which is kept secret. These keys work together to encrypt and decrypt data, ensuring secure communication, authentication, and digital signatures.

1. Understanding Public and Private Keys
2. a) Public Key

A public key is an openly shared key used for encrypting messages or verifying digital signatures. It is accessible to anyone and does not need to be kept secret. However, it cannot decrypt the information it encrypts; only the corresponding private key can do that.

1. b) Private Key

A private key is a confidential key used for decrypting messages encrypted with the corresponding public key or signing digital documents. It must be kept secret because, if exposed, an attacker could decrypt messages or impersonate the owner.

2. How Public and Private Keys Work

Public and private keys function together in encryption and decryption. The relationship between these keys ensures secure communication without requiring both parties to share a secret key beforehand.

1. a) Encryption and Decryption

The sender encrypts a message using the recipient’s public key.

The recipient decrypts the message using their private key.

Since only the private key can decrypt the message, confidentiality is maintained.

For example, if Alice wants to send Bob a secure message, she encrypts it with Bob’s public key. Only Bob, who has the private key, can decrypt and read the message.

1. b) Digital Signatures

The sender (e.g., Alice) signs a document using her private key, generating a digital signature.

The receiver (e.g., Bob) verifies the signature using Alice’s public key.

If the signature is valid, Bob knows the document is from Alice and has not been altered.

This process ensures authentication, integrity, and non-repudiation.

3. Uses of Public and Private Keys
4. a) Secure Communication

Public-key cryptography is widely used in email encryption (e.g., PGP), secure messaging, and HTTPS connections, ensuring that messages can be sent securely over the internet.

1. b) Digital Signatures

Organizations use digital signatures to verify the authenticity of software, contracts, and emails. This prevents tampering and fraud.

1. c) Blockchain and Cryptocurrencies

In blockchain and cryptocurrency transactions (e.g., Bitcoin, Ethereum), public and private keys help secure digital wallets and verify transactions.

1. d) SSL/TLS in Web Security

Websites use SSL/TLS certificates, which rely on public-key cryptography, to establish secure connections between browsers and servers (HTTPS).

1. e) Authentication and Access Control

Public-private key pairs are used in SSH (Secure Shell) authentication and two-factor authentication (2FA) for secure access to servers and systems.

5. Examples of Public-Key Cryptography Algorithms

Several cryptographic algorithms use public and private keys:

RSA (Rivest-Shamir-Adleman) – Used in digital signatures, encryption, and SSL/TLS.

Elliptic Curve Cryptography (ECC) – More efficient than RSA, used in blockchain and modern cryptographic applications.

Diffie-Hellman Key Exchange – Used for secure key exchanges over insecure channels.

DSA (Digital Signature Algorithm) – Used in digital signatures.

Conclusion

Public and private keys form the backbone of modern cryptography. They provide secure communication, authentication, data integrity, and digital signatures. While the public key can be shared openly, the private key must remain confidential to ensure security. The use of public-key cryptography in applications like SSL/TLS, blockchain, digital signatures, and authentication makes it essential for securing online transactions and communications.

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8) What do you mean by hackers? Also explain ethical hacking.

1. Who Are Hackers?

A hacker is a person who uses their technical skills to gain unauthorized access to computer systems, networks, or data. Hackers exploit security vulnerabilities to steal, manipulate, or damage information. However, not all hackers are malicious; some use their skills for ethical and legal purposes.

2. Types of Hackers

Hackers are categorized based on their intent and actions:

1. a) Black Hat Hackers (Malicious Hackers)

These hackers engage in illegal activities such as stealing sensitive data, spreading malware, or conducting cyberattacks.

Their primary motive is financial gain, personal revenge, or political disruption.

Example: Hackers who conduct ransomware attacks demanding payment in cryptocurrency.

1. b) White Hat Hackers (Ethical Hackers)

These hackers work legally to improve cybersecurity.

They help organizations identify and fix security vulnerabilities.

Ethical hackers are often certified professionals working in cybersecurity roles.

1. c) Grey Hat Hackers

These hackers operate between ethical and unethical hacking.

They find security flaws without permission but do not exploit them for personal gain.

Sometimes, they report the issues to companies for rewards (bug bounties).

1. d) Script Kiddies

Amateur hackers who use pre-made hacking tools without deep technical knowledge.

They often hack systems for fun or to impress peers.

1. e) Hacktivists

Hackers who attack systems for political, social, or ideological reasons.

Example: Anonymous, a hacking group known for cyber protests against governments and corporations.

1. f) State-Sponsored Hackers

Government-backed hackers who engage in cyber espionage, surveillance, or cyber warfare.

Countries use them to gather intelligence or disrupt enemy operations.

3. What Is Ethical Hacking?

Ethical hacking is the practice of testing and securing computer systems by identifying vulnerabilities before malicious hackers can exploit them. Ethical hackers follow legal guidelines and work with organizations to improve cybersecurity.

4. Importance of Ethical Hacking

Protects sensitive data from cybercriminals.

Prevents financial losses caused by cyberattacks.

Enhances overall security by fixing system vulnerabilities.

Helps companies comply with cybersecurity regulations.

5. Ethical Hacking Process

Ethical hackers follow a structured approach to identify and fix security risks:

1. a) Reconnaissance (Information Gathering)

Collecting data about the target system to identify potential weak points.

Example: Scanning a company’s website for exposed vulnerabilities.

1. b) Scanning and Enumeration

Using tools to scan networks and systems for security flaws.

Example: Checking open ports or weak passwords.

1. c) Gaining Access

Attempting to exploit vulnerabilities to test security defenses.

Example: Penetration testing to simulate a cyberattack.

1. d) Maintaining Access

Testing if an attacker could stay inside a system undetected.

Example: Checking for hidden backdoors or security loopholes.

1. e) Covering Tracks and Reporting

Ethical hackers do not harm the system but report vulnerabilities to the organization.

They provide recommendations to improve security.

6. Ethical Hacking Certifications and Tools

To become a professional ethical hacker, individuals can earn certifications such as:

Certified Ethical Hacker (CEH)

Offensive Security Certified Professional (OSCP)

CompTIA Security+

Some common ethical hacking tools include:

Nmap – Network scanning tool

Metasploit – Penetration testing tool

Wireshark – Network traffic analyzer

John the Ripper – Password cracking tool

7. Conclusion

Hackers can be either malicious or ethical, depending on their intentions. Ethical hackers play a crucial role in strengthening cybersecurity by identifying and fixing vulnerabilities before criminals can exploit them. Organizations rely on ethical hackers to safeguard sensitive data, prevent cyberattacks, and ensure compliance with security standards.

9) Discuss Digital Signature.

A digital signature is a cryptographic technique used to authenticate digital messages, documents, and transactions. It ensures that the sender is genuine and that the message has not been altered during transmission. Digital signatures provide data integrity, authentication, and non-repudiation, making them an essential tool in cybersecurity, e-commerce, and legal transactions.

2. How Digital Signatures Work

Digital signatures rely on public-key cryptography (asymmetric encryption), which uses two keys:

Private Key – Used to create the digital signature.

Public Key – Used to verify the signature’s authenticity.

Step-by-Step Process of Digital Signature Creation & Verification

1. a) Signature Creation

The sender writes a message or creates a document.

A hash function (e.g., SHA-256) generates a unique hash value from the document.

The sender encrypts this hash using their private key, creating the digital signature.

The digital signature is attached to the original document before sending it.

1. b) Signature Verification

The receiver extracts the digital signature from the received document.

The receiver decrypts the signature using the sender’s public key, revealing the original hash.

The receiver independently computes the hash of the received document.

If both hashes match, the document is authentic and unchanged. If they do not match, the document has been altered.

3. Importance of Digital Signatures
4. a) Authentication

Confirms the identity of the sender.

Prevents impersonation or fraud in digital transactions.

1. b) Data Integrity

Ensures that the message or document has not been modified.

Even a small change in the document results in a completely different hash value, making tampering detectable.

1. c) Non-Repudiation

The sender cannot deny signing the document, as the digital signature is unique and linked to their private key.

Provides legal proof in disputes.

4. Applications of Digital Signatures
5. a) Secure Online Transactions

Used in banking, financial services, and e-commerce to authenticate transactions.

1. b) Digital Contracts & Legal Documents

Helps businesses sign contracts electronically with legally binding signatures.

Governments use digital signatures for secure document verification.

1. c) Email & Software Security

Ensures that emails and software updates are from trusted sources.

Prevents malware-infected software from being distributed.

1. d) Blockchain and Cryptocurrencies

Used in Bitcoin and Ethereum transactions to ensure secure and tamper-proof transactions.

1. e) Government & Tax Documents

Used in e-governance for tax filing, Aadhaar verification (India), and e-passports.

5. Digital Signature Algorithms

Several cryptographic algorithms are used for digital signatures:

RSA (Rivest-Shamir-Adleman) – One of the most widely used algorithms.

DSA (Digital Signature Algorithm) – A U.S. government standard.

ECDSA (Elliptic Curve Digital Signature Algorithm) – More secure and efficient than RSA, commonly used in modern cryptography.

EdDSA (Edwards-curve Digital Signature Algorithm) – Provides high security with efficient performance.

6. Legal Recognition of Digital Signatures

Many countries have laws recognizing digital signatures as legally valid:

Electronic Signatures in Global and National Commerce (ESIGN) Act (USA)

eIDAS (European Union)

Information Technology Act (India)

These laws make digital signatures legally enforceable for business contracts, financial transactions, and legal documents.

7. Differences Between Digital and Electronic Signatures

Feature	Digital Signature	Electronic Signature
Technology	Uses cryptographic encryption	Simple electronic mark or scan
Security	Highly secure (uses public-key cryptography)	Less secure (can be copied or forged)
Legality	Legally binding in many countries	May require additional verification
Use Case	Used in financial, legal, and government documents	Used for informal agreements

8. Conclusion

Digital signatures play a vital role in securing online transactions, documents, and communications. They ensure authentication, integrity, and non-repudiation, preventing fraud and cyber threats. As businesses and governments move towards digital operations, digital signatures provide a secure and legally recognized method for electronic authentication.

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10. How equation editor can help you write a professional document?

An Equation Editor is a tool used in word processing software to create and insert mathematical symbols, formulas, and equations. It is widely used in academic, scientific, and professional documents where precise mathematical notation is required. Tools like Microsoft Word’s Equation Editor, LaTeX, and MathType help users format complex mathematical expressions efficiently.

2. Importance of Equation Editor in Professional Documents

A professional document should be clear, well-structured, and visually appealing. The Equation Editor helps achieve this by allowing users to insert well-formatted equations, ensuring accuracy and readability.

3. Benefits of Using Equation Editor
4. a) Creates Professionally Formatted Mathematical Expressions

Helps write complex formulas neatly without using plain text.

Supports various mathematical symbols, including fractions, integrals, matrices, and summations.

Ensures consistency in formatting, making documents look polished and professional.

1. b) Enhances Clarity and Readability

Handwritten equations or poorly formatted text-based equations can be confusing.

The Equation Editor organizes mathematical expressions clearly, making them easier to understand.

1. c) Saves Time and Increases Efficiency

Instead of manually aligning symbols, the Equation Editor automatically formats them.

Provides predefined structures for common equations, reducing effort.

1. d) Supports Scientific and Technical Writing

Essential for writing research papers, engineering reports, financial documents, and physics equations.

Used in journals, textbooks, and academic theses to maintain a high standard of presentation.

1. e) Enables Dynamic Editing and Customization

Equations can be modified without retyping entire formulas.

Users can adjust font size, alignment, and positioning for better visual appeal.

1. f) Compatibility with Different File Formats

Equations created in Microsoft Word’s Equation Editor can be exported to PDF, LaTeX, or HTML.

Works well with PowerPoint and Excel, allowing seamless integration in presentations and reports.

4. Features of Equation Editor in Microsoft Word

Microsoft Word’s Equation Editor provides:

Built-in templates for fractions, exponents, limits, and derivatives.

Keyboard shortcuts for quick equation entry.

Professional notation for algebra, calculus, and physics equations.

Ink Equation feature, allowing users to write equations using a touchscreen or stylus.

5. Comparison: Equation Editor vs. LaTeX

Feature	Equation Editor (MS Word)	LaTeX
Ease of Use	User-friendly, WYSIWYG (What You See Is What You Get)	Requires coding knowledge
Flexibility	Limited customization	Highly customizable
Speed	Faster for simple equations	More efficient for long documents
Output Quality	Good for general use	Preferred for professional publishing

6. Applications of Equation Editor in Different Fields

Mathematics – Writing algebraic expressions, calculus equations, and trigonometric functions.

Physics & Engineering – Representing scientific formulas, circuit equations, and mechanics principles.

Finance & Economics – Writing statistical models, probability functions, and financial equations.

Education – Preparing lesson plans, study materials, and academic papers.

7. Conclusion

The Equation Editor is an essential tool for creating professional and well-structured documents in academics, research, and technical fields. It enhances readability, improves efficiency, and ensures accurate representation of mathematical expressions, making documents more credible and visually appealing.

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