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WorksheetsUNIT 1 MCQ QUESTIONS - Cryptography and Network Security
Total questions: 96
Worksheet time: 48mins
If the shift value (key) in a Caesar Cipher is 3, what will "HELLO" encrypt to?
KHOOR
EBIIL
GDKKN
JGNNQ
How many possible keys are there in a standard Caesar Cipher for English letters?
26
25
52
256
Choose the TRUE statement for Caesar Cipher?
It requires a large key
It is vulnerable to brute-force attacks
It uses complex mathematical operations
It is a symmetric-key algorithm
If "DMWWDFN" is a Caesar Cipher encryption with a shift of 3, what is the original plaintext?
ATTACK
GOODBY
HELLOO
ZUUCCH
What happens if a Caesar Cipher uses a shift of 0?
The ciphertext is reversed
The plaintext remains unchanged
The cipher becomes unbreakable
It turns into a Vigenère Cipher
Which historical figure is credited with using the Caesar Cipher?
Alan Turing
Julius Caesar
Alberti
Claude Shannon
What is the decryption of "XLI WXIQTIV" if the shift is 4?
THE RESULT
THIS CIPHER
THE SECRET
THE MESSAGE
Which attack method is most effective against a Caesar Cipher?
Frequency analysis
Known-plaintext attack
Brute-force attack
Man-in-the-middle attack
What is the result of applying a Caesar shift of 5 to the word "CRYPTO"?
HWDUYT
FQXTOS
GQYVPT
HTIZSR
Which attack is most effective against the Caesar Cipher?
Frequency analysis
Brute-force
Man-in-the-middle
Replay attack
What is the main weakness of the Caesar Cipher?
Too complex to use
Very few possible keys
Requires a long key
Only works for numbers
What mathematical concept is the Caesar Cipher based on?
Modular arithmetic
Prime factorization
Matrix multiplication
Differential calculus
How can frequency analysis help break a Caesar Cipher?
By comparing letter frequencies to standard English
By reversing the shift pattern
By using a dictionary attack
By analysing punctuation marks
If "L OYVRH BRX" is a Caesar Cipher output, what was the original phrase if the shift was 3?
I LOVE YOU
HELLO WORLD
GOOD NIGHT
SEE YOU LATER
Which attack is least effective against Caesar Cipher?
Brute force
Frequency analysis
Known plaintext attack
Quantum computing
What happens if you apply a Caesar shift of 26?
The message becomes unreadable
The message remains the same
The message reverses
The message turns to symbols
Why Caesar Cipher is considered insecure today?
It only works for uppercase letters
It has a very small key space
It cannot encrypt numbers
It requires internet access
Which of the following is a formal mathematical property of the Bell-LaPadula model?
Biba Integrity Axioms
Clark-Wilson Enforcement Rules
Simple Security Condition (ss-property)
Non-repudiation Principle
In Bell-LaPadula, what is the difference between the "Strong Tranquility Property" and the "Weak Tranquility Property"?
Strong Tranquility prevents any label changes, while Weak Tranquility allows some changes
Weak Tranquility enforces mandatory access control, while Strong Tranquility does not
Strong Tranquility applies only to subjects, while Weak Tranquility applies to objects
There is no difference; they are the same
Which security model is often contrasted with Bell-LaPadula due to its focus on integrity rather than confidentiality?
Biba Model
Brewer-Nash Model
Harrison-Ruzzo-Ullman Model
Take-Grant Model
What is the main criticism of the Bell-LaPadula model in modern computing environments?
It does not support role-based access control (RBAC)
It is too focused on confidentiality and ignores integrity/availability
It requires excessive computational power
It cannot be implemented in distributed systems
Which of the following is NOT a valid security level in the Bell-LaPadula model?
Unclassified
Secret
For Official Use Only (FOUO)
Private
How does the Bell-LaPadula model interact with Mandatory Access Control (MAC)?
It is an implementation of MAC
It replaces MAC with Discretionary Access Control (DAC)
It is incompatible with MAC
It only works with Role-Based Access Control (RBAC)
A hacker intercepts an encrypted email but cannot read it. Later, they steal the decryption key and access the email. Which security goal was initially maintained but later compromised?
Availability
Integrity
Confidentiality
Non-repudiation
An attacker alters the contents of a financial transaction during transmission, changing the recipient’s account number. Which security goal is directly violated?
Availability
Integrity
Confidentiality
Authentication
A Distributed Denial-of-Service (DDoS) attack floods a web server with fake requests, making it unavailable to legitimate users. Which security goal is most affected?
Confidentiality
Integrity
Availability
Authorization
Which of the following is a method to ensure confidentiality?
Regular data backups
Encryption
Firewall monitoring
Using strong usernames
An e-commerce platform requires digital signatures for transactions. Which security goal does this primarily support?
Confidentiality
Integrity
Non-repudiation
Availability
What happens if confidentiality is breached?
Systems slow down
Unauthorized users access sensitive data
Data becomes corrupted
Websites become unavailable
Which attack directly threatens confidentiality?
Denial-of-Service (DoS)
Man-in-the-Middle (MITM)
Brute Force Attack
Both b) and c)
Which of these is an example of a confidentiality control?
Two-factor authentication (2FA)
Data backups
Network redundancy
Regular software updates
What role does encryption play in confidentiality?
Ensures data is not modified
Makes data unreadable to unauthorized users
Prevents system crashes
Speeds up data transfer
Which principle ensures that only authorized users can view sensitive information?
Integrity
Availability
Confidentiality
Authentication
An attacker exploits a web form to dump a database of usernames and passwords. Which security goal is directly violated?
Integrity
Availability
Confidentiality
Authentication
A company stores backups in geographically separate locations. Which security goal is most reinforced?
Integrity
Availability
Confidentiality
Authorization
A bank restricts employees to accessing only the data required for their job roles. Which security goal does this best align with?
Confidentiality
Integrity
Availability
All of the above
A log file shows unauthorized changes to system timestamps. Which security tool could have prevented this?
Firewall
Intrusion Detection System (IDS)
Antivirus
VPN
A company disables USB ports to prevent data leaks but hinders employees’ file transfers. Which security principle is prioritized over convenience?
Integrity
Availability
Confidentiality
Scalability
A user downloads a free software crack from an untrusted website. Later, their computer starts running slowly, and files are encrypted. What type of malware is likely involved?
Spyware
Trojan Horse
Adware
Worm
A finance employee receives an email that appears to be from the CEO, urgently requesting a wire transfer to a foreign account. The money is later traced to a scammer. What type of attack is this?
CEO Fraud (BEC)
Phishing
Spear Phishing
Whaling
An attacker uses a program to systematically try millions of common passwords until they guess the correct one for an admin account. What type of attack is this?
Dictionary Attack
Rainbow Table Attack
Brute Force Attack
Credential Stuffing
A hacker exploits weak default credentials on a smart security camera, gaining access to the home network. What security risk does this highlight?
Weak Encryption
Default Passwords in IoT Devices
Insider Threat
Phishing
A nation-state hacker group infiltrates a government agency’s network, remains undetected for months, and steals classified data. What best describes this attack?
Advanced Persistent Threat (APT)
Ransomware Attack
Insider Threat
Phishing Campaign
In the context of watermarking, the modular inverse is used to:
Encrypt the watermark
Ensure reversibility in transform-domain embedding
Generate pseudorandom sequences
Compress the host signal
Why is the modular inverse crucial in reversible data hiding?
It prevents distortion in the extracted watermark
It allows perfect reconstruction of the original cover after extraction
It increases embedding capacity
It enhances robustness against attacks
In a multiplicative inverse-based watermarking scheme, survivability is improved by:
Using large prime moduli
Embedding multiple copies of the watermark
Applying error correction codes
All of the above
Which of the following is NOT a characteristic of steganography?
Hiding data inside files
Encrypting data
Concealing message existence
Using images/audio as cover
What is the main weakness of monoalphabetic substitution ciphers?
Predictable letter frequency
Slow encryption
Complex key generation
Multiple alphabets
Which cipher uses a keyword to determine the shift for each letter?
Vigenère cipher
Caesar cipher
Hill cipher
Transposition cipher
In Hill cipher, the key matrix must be:
Invertible modulo 26
Symmetric
Diagonal
Upper triangular
Which steganography method hides data in the least significant bit?
LSB substitution
Frequency masking
Spread spectrum
Transform domain
How does the Vigenère cipher differ from the Caesar cipher?
Uses multiple shift values
Uses one fixed shift
Uses matrices
Only rearranges letters
What kind of cipher is the Hill cipher?
Block cipher
Stream cipher
Substitution cipher
Transposition cipher
Which method is commonly used for steganography in images?
LSB
Frequency analysis
Caesar cipher
Hill cipher
What is the size of the key space for the Caesar cipher?
26
256
226
100
Assertion (A): Polyalphabetic ciphers reduce the effectiveness of frequency analysis. Reason (R): They vary shifts throughout the message.
Both A and R are true, and R explains A
Both A and R are true, but R doesn’t explain A
A is true, R is false
A is false, R is true
Which of the following is a substitution cipher?
Caesar cipher
Rail fence
Columnar transposition
Playfair cipher
How is the key used in the Vigenère cipher?
To determine shifts for each letter
To swap letters
To create matrix keys
To encrypt blocks
What is the main principle of the Hill cipher?
Linear algebra with matrices
Frequency substitution
Transposition
Bitwise operations
Assertion (A): Transposition ciphers increase security by scrambling letters. Reason (R): They do not change the letters themselves.
Both A and R are true, and R explains A
Both A and R are true, but R doesn’t explain A
A is true, R is false
A is false, R is true
Which steganography technique modifies image pixels to hide data?
LSB
Frequency masking
Spread spectrum
Public key cryptography
What is the relationship between key length and security in Vigenère cipher?
Longer keys improve security
Shorter keys improve security
Key length doesn't matter
Keys must be prime
Assertion (A): Monoalphabetic substitution ciphers are easy to break using frequency analysis. Reason (R): They have one-to-one character mapping.
Both A and R are true, and R explains A
Both A and R are true, but R doesn’t explain A
A is true, R is false
A is false, R is true
Which matrix property is required for Hill cipher decryption?
Determinant must be non-zero modulo 26
Matrix must be diagonal
Matrix must be symmetric
Matrix size must be odd
How does a columnar transposition cipher work?
Rearranges columns according to key
Substitutes letters with others
Encrypts with matrix multiplication
Uses XOR operations
What is a major challenge in steganography?
Avoiding detection
Generating keys
Encrypting data
Compressing images
Which cipher type is best against frequency analysis?
Polyalphabetic substitution
Monoalphabetic substitution
Caesar cipher
Transposition cipher
72. Assertion (A): The key in Hill cipher is a matrix. Reason (R): Matrices provide mathematical structure for encryption.
Both A and R are true, and R explains A
Both A and R are true, but R doesn’t explain A
A is false, R is true
A is true, R is false
Which transposition cipher involves writing message diagonally?
Rail fence
Columnar
Scytale
Caesar
Why is key management important in steganography?
To ensure correct extraction
To speed up encryption
To reduce file size
To improve compression
In a Hill cipher, a 2x2 key matrix is used. What is the size of the plaintext block?
1
2
4
Any size
What happens if a monoalphabetic cipher uses a frequency-balanced alphabet?
Frequency analysis becomes harder
It becomes polyalphabetic
Letters repeat
Transposition occurs
Why is randomness important in steganography?
To encrypt the image
To avoid detectable patterns
To change compression
To reduce message length
Which cipher changes positions but not characters?
Caesar
Hill
Transposition
Vigenère
Which of the following is a type of digital watermarking based on visibility?
Robust watermarking
Fragile watermarking
Visible watermarking
Frequency-domain watermarking
How many alphabets does the Vigenère cipher effectively use if the key is 5 letters?
5
26
1
Depends on the message
Which type of cipher best hides statistical patterns?
Monoalphabetic
Caesar
Vigenère
Transposition
Which is not a method of hiding data in steganography?
A) LSB
B) Text spacing
C) Frequency substitution
D) Columnar key shifting
Hill cipher’s decryption requires:
The inverse of the key matrix modulo 26
The determinant of the key matrix
The transpose of the key matrix
The sum of the key matrix elements
Why might steganography fail detection systems?
It compresses message
It leaves no visual clue
It uses hashes
It replaces whole content
In Vigenère cipher, repeating keys result in:
Increased strength
Repeating patterns
Message truncation
Irregular padding
What is the primary purpose of digital watermarking?
To enhance image quality
To embed hidden information in a digital signal
To compress media files
To encrypt data for security
Monoalphabetic cipher is vulnerable because:
Key is reused
Frequency patterns remain
It shifts letters
It hides key in LSB
Which cipher operates block-wise using matrix transformations?
Hill
Vigenère
Monoalphabetic
Caesar
You reverse columns in a message. What cipher method is used?
Substitution
Transposition
Vigenère
Stream cipher
Why are polyalphabetic ciphers more secure than monoalphabetic?
They encrypt binary
They use fewer characters
They avoid one-to-one mapping
They remove key
Steganography protects content by:
Making it unreadable
Encrypting it with Caesar
Hiding it from view
Randomizing pixels
In a monoalphabetic substitution cipher, if the letter 'E' in plaintext is replaced by 'Q', what kind of cipher is this?
Simple substitution
Transposition
Polyalphabetic substitution
Steganography
Least Significant Bit (LSB) insertion is used in:
Hashing passwords
Image steganography
Breaking encryption
Firewall protection
Which is NOT a data hiding method?
Audio steganography
Video steganography
SQL injection
Text steganography
What does survivability in cryptography ensure?
A) Data remains accessible even after an attack
B) Data is permanently deleted after an attack
C) Only authorized users can modify data
D) Encryption keys are never changed
Which technique helps maintain survivability in case of a key compromise?
Using a single encryption key forever
Key rotation
Disabling backups
Storing keys in plaintext
Redundancy in cryptographic systems helps with:
Slowing down performance
Ensuring data availability if one component fails
Making encryption weaker
Hiding data from auditors
What is a "fail-safe" mechanism in cryptography?
A system that shuts down completely if attacked
A system that continues functioning securely even after an attack
A system that deletes all data upon failure
A system that ignores security breaches
Which of these improves cryptographic survivability?
Single point of failure
Distributed key management
Weak passwords
No backup strategy
Self-healing cryptographic systems are designed to:
Automatically recover from attacks
Delete all encrypted data
Prevent any form of encryption
Only work in offline mode
