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CRYPTOGRAPHY solved MCQs


 

1) Which of the following is not a type of symmetric-key cryptography technique?

  1. Caesar cipher
  2. Data Encryption Standard (DES)
  3. Diffie Hellman cipher
  4. Playfair cipher

Answer: c) Diffie Hellman cipher

Explanation:

The Diffie Hellman uses a pair of asymmetric keys for encryption and decryption processes. All the rest mentioned cipher techniques use the same key for encryption as well as decryption.

2) Which of the following is not a principle of data security?

  1. Data Confidentiality
  2. Data Integrity
  3. Authentication
  4. None of the above

Answer: d) None of the above

Explanation:

All the first three options are the principles of data security. None of the mentioned characteristics fall apart form these principles. Therefore, the correct answer is none of the above.

3) Which of the following security attacks is not an active attack?
OR
Which of the following attacks is a passive attack?

  1. Masquerade
  2. Modification of message
  3. Denial of service
  4. Traffic analysis

Answer: d) Traffic analysis

Explanation:

In a passive attack, the attacker does not modify any part of the data. His attempt is only to obtain the information and not to modify it. From the mentioned options, this happens only in Traffic analysis in which the attacker monitors the pattern of transmission. The rest other options are examples of active attacks.

4) Which of the following options correctly defines the Brute force attack?

  1. Brutally forcing the user to share the useful information like pins and passwords.
  2. Trying every possible key to decrypt the message.
  3. One entity pretends to be some other entity
  4. The message or information is modified before sending it to the receiver.

Answer: b) Trying every possible key to decrypt the message.

Explanation:

Only option b) is the correct definition for brute force attack.

5) "A key is a string of bits used by a cryptographic algorithm to transform plain text into ciphertext." Which of the following is capable of becoming a key in a cryptographic algorithm?

  1. An integer values
  2. A square matrix
  3. An array of characters (i.e. a string)
  4. All of the above

Answer: d) All of the above

Explanation:

As the key can be any string of bits, all the mentioned options are capable of becoming a key in a cryptographic algorithm.


6) A mechanism used to encrypt and decrypt data.

  1. Cryptography
  2. Algorithm
  3. Data flow
  4. None of these

Answer: a) Cryptography

Explanation:

Cryptography is a mechanism used to encrypt and decrypt data.

7) To encrypt the plaintext, a cryptographic algorithm works in combination with a key...

  1. Word, number, or phrase
  2. Special Symbols
  3. Function Keys
  4. All of these

Answer: a) word, number and phrase

Explanation:

Word, number and phrase are used to encrypt the plaintext.

8) The plaintext encrypts to different cipher text with different keys

  1. True
  2. False

Answer: a) True

Explanation:

The plaintext is used to encrypt to different cipher text with different keys.

9) Conventional cryptography also known as ... encryption.

  1. asymmetric-key
  2. logical-key
  3. symmetric-key
  4. None of these

Answer: c) symmetric-key

Explanation:

Conventional cryptography also known as symmetric-key encryption.

10) The Data Encryption Standard (DES) is an example of a ...

  1. Conventional cryptosystem
  2. Asymmetric cryptosystem
  3. Caesar's cryptosystem
  4. All of these

Answer: a) Conventional cryptosystem

11) Public key cryptography is a ... cryptosystem

  1. Symmetric
  2. Asymmetric
  3. Symmetric & Asymmetric both
  4. None of these

Answer: b) Asymmetric cryptosystem

Explanation:

Asymmetric is a public key cryptography.

12) Security Goals of Cryptography are

  1. Confidentiality
  2. Authenticityn
  3. Data integrityn
  4. Non-repudiation
  5. All of these

Answer: e) All of these

Explanation:

Confidentiality, authenticity, data integrity and non-repudiation security are the key goals of cryptography.

13) A process of studying cryptographic system is known as Cryptanalysis

  1. True
  2. False

Answer: a) True

Explanation:

Cryptanalysis is a process of studying cryptographic system.

14) Cipher in cryptography is –

  1. Encrypted message
  2. Algorithm for performing encryption and decryption
  3. Both algorithm for performing encryption and decryption and encrypted message
  4. Decrypted message

Answer: b) algorithm for performing encryption and decryption

Explanation:

Cipher in cryptography is an Algorithm for performing encryption and decryption.

15) The private key in asymmetric key cryptography is kept by

  1. Sender
  2. Receiver
  3. Sender and receiver
  4. All the connected devices to the network

Answer: b) Receiver

Explanation:

The private key is kept by the receiver.

16) Which one of the following algorithms is not used in asymmetric-key cryptography?

  1. DSA algorithm
  2. Electronic code book algorithm
  3. Diffie-Hellman algorithm
  4. RSA algorithm

Answer: b) Electronic code book algorithm

Explanation:

The electronic code book algorithm is a block cypher method in which a block of data corresponds to each block of text in the encrypted message.

17) Which is the cryptographic protocol that is used to protect an HTTP connection?

  1. Resource reservation protocol
  2. SCTP
  3. TLS
  4. ECN

Answer: c) TLS (Transport Layer Security)

Explanation:

In order to prevent eavesdropping, tampering and message forgery, TLS has strong message authentication and key-material generation.

18) A key is a value that works with a cryptographic algorithm to produce a specific cipher text.

  1. True
  2. False

Answer: a) True

Explanation:

A key is a value that works with a cryptographic algorithm to produce a specific cipher text.

19) A Public key size and conventional cryptography’s secret key size are closely related with one another.

  1. True
  2. False

Answer: b) False

Explanation:

A Public key size and conventional cryptography’s secret key size are unrelated with one another.

20) ElGamal encryption system is an asymmetric key encryption algorithm.

  1. Public-key cryptography
  2. Private-key cryptography
  3. Both
  4. None of these

Answer: a) Public-key cryptography

Explanation:

The ElGamal encryption scheme in cryptography is an asymmetrical key encryption algorithm based on the Diffie-Hellman key exchange for public-key cryptography.


SET 2


1) We are provided the plain text “SUN”. You need to convert the given plain text into ciphertext under the Ceasar cipher encryption technique. Which of the following options is the correct ciphertext for the given text if the key is 2?

  1. UWP
  2. NUS
  3. WUP
  4. QSL

Answer: a) UWP

Explanation:

In the Caesar cipher technique, the encryption is performed as follows,

    E ( P , K ) = ( P + K ) mod 26

    Therefore, 
    E ( S , 2 ) = ( 18 + 2 ) mod 26 = 20 = U
    E ( U , 2 ) = ( 20 + 2 ) mod 26 = 22 = W
    E ( N , 2 ) = ( 13 + 2 ) mod 26 = 15 = P
    Hence, the ciphertext is "UWP".

2) Which of the following cannot be chosen as a key in the Caesar cipher?

  1. An integer
  2. An alphabet (A-Z or a-z)
  3. A string
  4. None of the above

Answer: c) A string

Explanation:

In Caesar cipher, we can choose a number or a character which when performed addition modulo operation with the given letters of the plain text gives us ciphertext. However, a string cannot be chosen for encryption in this case.

3) Which of the following cipher techniques include the involvement of matrix operations in their algorithms of encryption and decryption?

  1. Hill Cipher
  2. Playfair cipher
  3. Both a and b
  4. None of the above

Answer: c) Both a and b

Explanation:

The hill cipher includes a square matrix as the key, and in Playfair cipher, we create a 5X5 matrix using the given key string. Hence, both these ciphers include the use of matrices.

4) Which of the following ciphers is a block cipher?

  1. Caesar cipher
  2. Vernam cipher
  3. Playfair cipher
  4. None of the above

Answer: c) Playfair cipher

Explanation:

The Playfair cipher uses a block of plain text, each block containing 2 characters.

5) Which of the following ciphers uses asymmetric key cryptography?

  1. Rail Fence Cipher
  2. Data Encryption Standard (DES)
  3. Diffie Hellman Cipher
  4. None of the above

Answer: c) Diffie Hellman Cipher

Explanation:

The Diffie Hellman cipher uses asymmetric key cryptography. It uses a pair of keys, one private and one public.

6) "Cipher" is synonymous with "code",

  1. True
  2. False

Answer: a) True

Explanation:

In cryptography, the terms "cypher" and "code" are synonymous since they both refer to a sequence of processes that encrypt a message; nonetheless, the ideas are separate in cryptography, particularly classical cryptography.

7) Block ciphers accumulate symbols in a message of a ______.

  1. Fixed size
  2. Variable
  3. Integration
  4. All of the mentioned above

Answer: a) Fixed size

Explanation:

Block cyphers amass symbols in a message of a fixed size (the block), whereas stream cyphers operate on a stream of symbols that is constantly changing. When a cypher employs the same key for both encryption and decryption, the algorithm or cypher is referred to as a symmetric key algorithm. Asymmetric key algorithms, also known as cyphers, encrypt and decrypt data using a different key for each operation.

8) With symmetric key algorithms, the ____ key is used for the encryption and decryption of data.

  1. Different
  2. Same
  3. Both A and B
  4. None of the mentioned above

Answer: b) Same

Explanation:

When using symmetric key techniques, the same key is utilized for both the encryption and decryption of the information being transmitted. Asymmetric key algorithms, which encrypt and decrypt data using public and private keys, are used to protect sensitive information.

9) ____ is the message or data that can be readable by the sender.

  1. Edited
  2. Main Text
  3. Plain text
  4. All of the mentioned above

Answer: c) Plain text

Explanation:

Plain text is a message or data that may be read by the sender, the receiver, or any third party who happens to come across it. When plain text is altered by the application of certain algorithms or procedures, the resulting data or message is referred to as ciphertext.

10) In the case of symmetric key encryption, the secret key that both the parties possess can be anything such as a _______.

  1. Passcode or a password
  2. Developed code
  3. Network set
  4. None of the mentioned above

Answer: a) Passcode or a password

Explanation:

With symmetric key encryption, the secret key that both parties have access to can be anything, such as a passcode or a password, depending on the circumstances. Also, a random string of characters or numbers generated using a secure Random Number Generator (RNG) can be used to represent it.


SET 3

1) What is the block size of plain text in SHA- 512 algorithm?
  1. 512 bits
  2. 1024 bits
  3. 2048 bits
  4. None of the above

Answer: b. 1024 bits

Explanation:

The SHA- 512 algorithm uses blocks of plain text one at a time to encrypt them into ciphertext. The size of each block in the SHA- 512 algorithm is 1024 bits.

2) All the below-stated processes are performed in the AES (Advanced Encryption Standard) Algorithm. Which of the following process(s) are not performed in the final round of the AES?
  1. Substitution bytes
  2. Shift rows
  3. Mix columns
  4. Add round key

Options

  1. i.
  2. iii.
  3. All of the mentioned
  4. None of the mentioned

Answer: b. iii.

Explanation:

In the AES algorithm, the MIX COLUMN operation is performed in all the rounds except the final round of the algorithm.

3) What does IDEA stand for in the world of cryptography?
or
The IDEA word in the IDEA algorithm is the abbreviation for which of the following?

  1. Independent Decryption Environment Analysis
  2. International Defense Encryption Area
  3. International Data Encryption Algorithm
  4. None of the above

Answer: c. International Data Encryption Algorithm

Explanation:

The IDEA Algorithm stands for "International Data Encryption Algorithm".

4) How many sub-keys in the total are used by the IDEA for encrypting the plain text into ciphertext?

  1. 64 sub- keys
  2. 48 sub- keys
  3. 52 sub- keys
  4. Only one key and no subkeys

Answer: c. 52 sub- keys

Explanation:

There are a total of 8 rounds in the IDEA technique for encryption and each of them uses 6 keys. Apart from that, 4 extra keys are used in the final round that is the output transformation round. This gives us a total of 52 subkeys.
(8 x 6) + 4 = 52

5) "The number of rounds in the AES algorithm depends upon the key size being used."
Which among the following shows a correct relation between the size of the key used and the number of rounds performed in the AES algorithm?

  1. 128 key size: 10 rounds
  2. 192 key size: 12 rounds
  3. 256 key size: 14 rounds
  4. All of the above

Answer: d. All of the above

Explanation:

All the mentioned options display the correct relation between the number of rounds and the key size used in the AES algorithm.

6) Which of the following properties are the characteristic properties of a block cipher technique which differs from stream cipher?

  1. Avalanche effect
  2. Completeness
  3. Both a. and b.
  4. None of the above

Answer: c. Both a. and b.

Explanation:

Avalanche effect and Completeness are the two characteristic properties of Block ciphers which differ them from stream ciphers.

7) Encryption algorithms are divided into two categories based on the ______.

  1. Output type
  2. Input type
  3. Process type
  4. All of the mentioned above

Answer: b. Input type

Explanation:

Encryption algorithms are classified into two categories based on the type of input they receive: block cyphers and stream cyphers. Block cyphers are the most used type of encryption technique. This type of encryption technique takes as input a defined size of data, such as b bits, and outputs as output another block of data of the same size as the input.

8) Cipher block chaining or CBC is an advancement made on _____.

  1. Electronic Code Book
  2. Decrypted code
  3. System engineering
  4. All of the mentioned above

Answer: a. Electronic Code Book

Explanation:

Cipher block chaining, also known as CBC, is an improvement on the Electronic Code Book. The electronic code book is the most straightforward block cypher manner of operation. It is simpler since each block of input plaintext is directly encrypted, and the output is in the form of blocks of encrypted ciphertext.

9) A secure block cipher is suitable for the encryption,

  1. True
  2. False

Answer: a. True

Explanation:

A safe block cypher is a type of encryption that is ideal for encrypting only a single block of data at a time with a fixed key. As building blocks of various cryptographic protocols, block cyphers can be found in a variety of configurations, including universal hash functions and pseudorandom number generators.

10) Cipher Feedback Mode is given as feedback to the ____ of encryption with some new specifications.

  1. Next block
  2. Previous block
  3. Middle block
  4. All of the mentioned above

Answer: a. Next block

Explanation:

Cipher Feedback Mode is provided as feedback to the following block of encryption with some new specifications, and it is used as a feedback mechanism.

11) In cryptography, a product cipher combines two or more transformations,

  1. True
  2. False

Answer: a. True

Explanation:

As used in cryptography, the term "product cypher" refers to the combination of two or more transformations in such a way that the final cypher is more secure than the individual components and hence more resistant to cryptanalysis. Using the product cypher, we may combine a series of simple transformations such as substitution (S-box), permutation (P-box), and modular arithmetic into a more complex transformation.



SET 4

1) In the AES-128 algorithm there are mainly __________ similar rounds and _________ round is different from other round.

  1. 5 similar rounds having 2 pair ; every alternate
  2. 9 ; the last
  3. 8 ; the first and last
  4. 10 ; no

Answer: b. 9; the last

Explanation:

Basically, in the AES-128 there are 9 rounds and the last round is different from other rounds.

2) Which of the following modes of operation in DES is used for operating?
  1. Cipher Feedback Mode (CFB)
  2. Cipher Block chaining (CBC)
  3. Electronic code book (ECB)
  4. Output Feedback Modes (OFB)

Answer: c. Electronic code book (ECB)

Explanation:

Mainly, the Electronic codebook mode is used for operating on short data as the same key is used for each block in this algorithm. Thus convert in Plain Text lead to repetitions in Cipher Text in cryptography.

3) Using Rivest, Shamir, Adleman cryptosystem with p=7 and q=9. Encrypt M=24 to find ciphertext. The Ciphertext is:

  1. 42
  2. 93
  3. 114
  4. 103

Answer: c. 114

Explanation:

    Calculate n = p × q = 63
    Phi(n)=(p-1) x (q-1)=48
    Let e=5 , where gcd(e,phi(n))=1
    Plaintext M = 24
    Ciphertext = C ≡ M^e (mod n)
    = 24^5 mod 63 = 7962624 mod 161
    Ciphertext transmitted = 114.

4) International Data Encryption Algorithm (IDEA) was developed by

  1. Xuejia Lai and James Massey
  2. Xuejia Lai and Bruce Schneier
  3. Xuejia Lai and Carlisle Adams
  4. Xuejia Lai and Stafford Tavares

Answer: a. Xuejia Lai and James Massey

Explanation:

It is a symmetric key block cipher designed by James Massey of ETH Zurich and Xuejia Lai and in 1991 it firstly described it.

5) When do we compare the AES with DES, which of the following functions from DES does not have an equivalent AES function in cryptography?

  1. f function
  2. permutation p
  3. swapping of halves
  4. xor of subkey with function f

Answer: c. swapping of halves

Explanation:

Mainly, there is no equivalent to swapping of halves in the AES algorithm in cryptography.

6) Data encryption standard is a block cipher and encrypts data in blocks of size of _____ each.

  1. 16 bits
  2. 64 bits
  3. 32 bits
  4. All of the mentioned above

Answer: b. 64 bits

Explanation:

When using the Data Encryption Standard, data is encrypted in blocks of 64 bits apiece, which means that the data encryption standard requires 64 bits of plain text to be entered as input?

7) The process of decryption of an AES ciphertext is similar to the encryption process in the ______.

  1. Reverse order
  2. Next order
  3. Both A and B
  4. All of the mentioned above

Answer: a. Reverse order

Explanation:

The process of decrypting an AES ciphertext is quite similar to the process of encrypting it, except that it is done in the opposite order. Each round is comprised of the four processes, which are carried out in the opposite sequence of the previous round. Due to the fact that sub-processes in each round are carried out in reverse order, as opposed to a Feistel Cipher, the encryption and decryption algorithms must be developed separately, despite the fact that they are extremely closely connected.

8) AES stands for Advanced Encryption Standard,

  1. True
  2. False

Answer: a. True

Explanation:

Advanced Encryption Standard (AES) is an abbreviation for Advanced Encryption Standard. It was thought to be vulnerable to an exhaustive key search attack because of the increase in computational capacity. AES is an iterative cypher, as opposed to a Feistel cypher. Based on the ‘substitution–permutation network,' it is a powerful tool. It is made up of a sequence of connected operations, some of which require substituting certain inputs with specified outputs (substitutions), and others which entail shuffling bits around (permutations).

9) RSA algorithm is ____ cryptography algorithm.

  1. Systematic
  2. Symmetric
  3. Asymmetric
  4. None of the mentioned above

Answer: c. Asymmetric

Explanation:

The RSA algorithm is a symmetric cryptography algorithm that uses a random number generator. Asymmetric refers to the fact that it operates on two separate keys, namely the Public Key and the Private Key.

10) Amongst which of the following is / are true with reference to the rounds in AES –

  1. Byte Substitution
  2. Shift Row
  3. Mix Column and Key Addition
  4. All of the mentioned above

Answer: d. All of the mentioned above

Explanation:

The rounds in AES are as follows: Byte Substitution, Shift Row, Mix Column, and Key Addition (in order of appearance).


SET 5

1) Which possible Attacks in Quantum Cryptography can take place?

  1. Possible Attacks in Quantum Cryptography and Birthday Attack
  2. Birthday attack and Boomerang attack
  3. Brute force attack and Faked-State-Attack
  4. Possible Attacks in Quantum Cryptography and Faked-State Attack

Answer: d. Possible Attacks in Quantum Cryptography and Faked-State Attack

Explanation:

Photon Number Splitting (PNS) Attack:

As we know that it is not possible to send a single photon thus a pulse is sent. So, some of the photons from a pulse can be captured by Eve and after matching bits by Amit and Bobby, Eve can use the same polarizer as done by Bobby and thus get the key without being detected in cryptography.

Faked-State Attack:

Mainly, Eve uses a replica of Bob’s photon detector and thus captures the photons intended for Bobby and further passed it to Bobby. Thus, Eve knows about the encoded bit, Bobby thinks that he received it from Amit.

2) _____ and ______ protocol models can be extended to Entangled particles theory.

  1. SARG04 and HTTP
  2. FTP and SSP
  3. SARG04 and SSP
  4. HTTP and FTP

Answer: c. SARG04 and SSP

Explanation:

SARG04 and SSP protocol models can be extended to Entangled particles theory.

3) Study with quantum computers of future being expected to solve the discrete logarithmic problem and the popularly know cryptography methods such as AES, RSA, DES, quantum cryptography becomes which solution?

  1. Quantum Solution
  2. Foreseen Solution
  3. Cryptographic Solution
  4. Block Cipher Solution

Answer: b) Foreseen Solution

Explanation:

As we study already that with quantum computers of future being expected to solve the discrete logarithmic problem and the popularly know cryptography methods such as AES, RSA, DES, quantum cryptography becomes the foreseen solution in this.

4) Which two principles of quantum mechanics on which quantum cryptography are dependent?

  1. Heisenberg Uncertainty Principle and Photon Polarization Principle.
  2. Fundamental Principle and Bohr's Model Principle
  3. Momentum Principle and Photons Principle
  4. Planck's Principle and Fundamental Principle

Answer: a. Heisenberg Uncertainty Principle and Photon Polarization Principle.

Explanation:

Quantum mechanics on which quantum cryptography depends are Heisenberg Uncertainty Principle and Photon Polarization Principle.

5) How many elements are used in cryptography tools?

  1. 1
  2. 4
  3. 6
  4. 3

Answer: d. 3

Explanation:

It has 3 elements as first is sender and second is the receiver and third is the channel in fact which connects both sender and receiver.

6) Quantum cryptography is the science of exploiting quantum mechanical properties to perform _____.

  1. Cryptographic system
  2. Cryptographic tasks
  3. Decryption system
  4. None of the mentioned above

Answer: b. Cryptographic tasks

Explanation:

Quantum cryptography is the science of utilizing quantum mechanical phenomena to perform cryptographic tasks. The best-known example of quantum cryptography is quantum key distribution which gives an information-theoretically secure solution to the key exchange problem.

7) The greatest threat is to public cryptography or asymmetric algorithms used for ____.

  1. Digital signatures and
  2. Key exchange
  3. Both A and B
  4. None of the mentioned above

Answer: c. Both A and B

Explanation:

It is public cryptography, or asymmetric algorithms, that are under the greatest threat, as they are utilized for digital signatures and key exchange. For example, one of the most well-known quantum algorithms is the Shor algorithm, which may be used to break the RSA and Elliptic Curve methods once a universal quantum computer is available.

8) Amongst which of the following is/ are true with reference to step-by-step breakdown of the process of quantum cryptography,

  1. The sender sends a photon through a polarizer with randomly assigned polarizations and bit assignment
  2. Photon uses a beam splitter that can be horizontal, vertical, or diagonal to decode or read the polarization of each photon
  3. Receiver tells the sender the random assignments of a beam splitter for each photon in the same sequence it was sent
  4. All of the mentioned above

Answer: d. All of the mentioned above

Explanation:

Referring to the step-by-step breakdown of the quantum cryptography process, the first sender sends a photon through a polarizer with randomly assigned polarizations and bit assignments; the second sender sends a photon through a polarizer with randomly assigned polarizations and bit assignments; the third sender sends a photon through a polarizer with randomly assigned polarizations and bit assignments; the fourth sender sends a photon through a polar After decoding or reading the polarization of each photon with a beam splitter, which can be horizontal, vertical, or diagonal in orientation, the photon is returned to its sender, who is informed of the random assignments of a beam splitter for each photon in the same sequence as it was sent.

9) A quantum state is a superposition of classical states,

  1. True
  2. False

Answer: a. True

Explanation:

It is possible to apply a quantum state to a measurement or a unitary operation since it is a superposition of classical states that is expressed as a vector of amplitudes.

10) Post-Quantum Cryptography is a classical cryptographic scheme that is conjectured to be secure against ____.

  1. Quantum adversaries
  2. Quantum integration
  3. Quantum hash
  4. None of the mentioned above

Answer: d. Quantum integration

Explanation:

In cryptography, post-quantum cryptography is a classical cryptographic technique that is conjectured to be secure against attackers who possess quantum computing capabilities. The quantum adversary approach is one of the most adaptable lower-bound methods for quantum algorithms, and it is also one of the most widely used. The variants of this method are the same: spectral adversary and spectral adversary.


SET 6


1) In the AES-128 algorithm there are mainly __________ similar rounds and _________ round is different from other round.

  1. 5 similar rounds having 2 pair ; every alternate
  2. 9 ; the last
  3. 8 ; the first and last
  4. 10 ; no

Answer: b. 9; the last

Explanation:

Basically, in the AES-128 there are 9 rounds and the last round is different from other rounds.

2) Which of the following modes of operation in DES is used for operating?
  1. Cipher Feedback Mode (CFB)
  2. Cipher Block chaining (CBC)
  3. Electronic code book (ECB)
  4. Output Feedback Modes (OFB)

Answer: c. Electronic code book (ECB)

Explanation:

Mainly, the Electronic codebook mode is used for operating on short data as the same key is used for each block in this algorithm. Thus convert in Plain Text lead to repetitions in Cipher Text in cryptography.

3) Using Rivest, Shamir, Adleman cryptosystem with p=7 and q=9. Encrypt M=24 to find ciphertext. The Ciphertext is:

  1. 42
  2. 93
  3. 114
  4. 103

Answer: c. 114

Explanation:

    Calculate n = p × q = 63
    Phi(n)=(p-1) x (q-1)=48
    Let e=5 , where gcd(e,phi(n))=1
    Plaintext M = 24
    Ciphertext = C ≡ M^e (mod n)
    = 24^5 mod 63 = 7962624 mod 161
    Ciphertext transmitted = 114.

4) International Data Encryption Algorithm (IDEA) was developed by

  1. Xuejia Lai and James Massey
  2. Xuejia Lai and Bruce Schneier
  3. Xuejia Lai and Carlisle Adams
  4. Xuejia Lai and Stafford Tavares

Answer: a. Xuejia Lai and James Massey

Explanation:

It is a symmetric key block cipher designed by James Massey of ETH Zurich and Xuejia Lai and in 1991 it firstly described it.

5) When do we compare the AES with DES, which of the following functions from DES does not have an equivalent AES function in cryptography?

  1. f function
  2. permutation p
  3. swapping of halves
  4. xor of subkey with function f

Answer: c. swapping of halves

Explanation:

Mainly, there is no equivalent to swapping of halves in the AES algorithm in cryptography.

6) Data encryption standard is a block cipher and encrypts data in blocks of size of _____ each.

  1. 16 bits
  2. 64 bits
  3. 32 bits
  4. All of the mentioned above

Answer: b. 64 bits

Explanation:

When using the Data Encryption Standard, data is encrypted in blocks of 64 bits apiece, which means that the data encryption standard requires 64 bits of plain text to be entered as input?

7) The process of decryption of an AES ciphertext is similar to the encryption process in the ______.

  1. Reverse order
  2. Next order
  3. Both A and B
  4. All of the mentioned above

Answer: a. Reverse order

Explanation:

The process of decrypting an AES ciphertext is quite similar to the process of encrypting it, except that it is done in the opposite order. Each round is comprised of the four processes, which are carried out in the opposite sequence of the previous round. Due to the fact that sub-processes in each round are carried out in reverse order, as opposed to a Feistel Cipher, the encryption and decryption algorithms must be developed separately, despite the fact that they are extremely closely connected.

8) AES stands for Advanced Encryption Standard,

  1. True
  2. False

Answer: a. True

Explanation:

Advanced Encryption Standard (AES) is an abbreviation for Advanced Encryption Standard. It was thought to be vulnerable to an exhaustive key search attack because of the increase in computational capacity. AES is an iterative cypher, as opposed to a Feistel cypher. Based on the ‘substitution–permutation network,' it is a powerful tool. It is made up of a sequence of connected operations, some of which require substituting certain inputs with specified outputs (substitutions), and others which entail shuffling bits around (permutations).

9) RSA algorithm is ____ cryptography algorithm.

  1. Systematic
  2. Symmetric
  3. Asymmetric
  4. None of the mentioned above

Answer: c. Asymmetric

Explanation:

The RSA algorithm is a symmetric cryptography algorithm that uses a random number generator. Asymmetric refers to the fact that it operates on two separate keys, namely the Public Key and the Private Key.

10) Amongst which of the following is / are true with reference to the rounds in AES –

  1. Byte Substitution
  2. Shift Row
  3. Mix Column and Key Addition
  4. All of the mentioned above

Answer: d. All of the mentioned above

Explanation:

The rounds in AES are as follows: Byte Substitution, Shift Row, Mix Column, and Key Addition (in order of appearance).

SET 7

1) Basically, in SHA-512, the message is divided into blocks of size ___ bits for the hash computation.

  1. 1024
  2. 512
  3. 256
  4. 1248

Answer: a. 1024

Explanation:

As we study, the message is divided into blocks of size 1024 bits, and the output produced is a 512-bit message digest and uses the 512-bit buffer till 80 rounds.

2) When a hash function is used to provide message authentication, the hash function value is called to as:

  1. Message Field
  2. Message Digest
  3. Message Score
  4. Message Leap

Answer: b. Message Digest

Explanation:

We know that the hash function providing message authentication is referred to as massage digest in cryptography.

3) Which of the following are used to create a message digest by the network security protocols?

  1. RSA
  2. SHA-1
  3. DES
  4. MD5

Answer: b. and c. SHA-1 and MD5

Explanation:

  • RSA: Basically, it is an algorithm used to encrypt and decrypt messages.
  • SHA 1: Secure Hash Algorithm 1 is a cryptographic hash function in cryptography. It produces a 160 bit (20 bytes) hash value in cryptography.
  • DES: Data Encryption Standard is a symmetric key algorithm for encryption of electronic data in cryptography.
  • MD5: It is a widely used cryptographic hash function that produces a 128-bit hash value in cryptography.

4) What is the output of the N 1024-bit blocks from the Nth stage in this?

  1. 512 bits
  2. 1024 bits
  3. N x 1024bits
  4. N x 512 bits

Answer: a. 512 bits

Explanation:

We know that when we use SHA 512 we take 1024 bit plaintext into this algorithm and get the output as 512 bit which is fixed.

5) What is the output of a cryptographic hash function means?

  1. A variable set of bits
  2. A fixed set of bits, derived from one-way mathematical operations
  3. An output which may be easily discovered by an adversary
  4. Outputs of such functions are of no importance

Answer: b. A fixed set of bits, derived from one-way mathematical operations

Explanation:

The output of a cryptographic hash function means as a fixed set of bits, derived from one-way mathematical operations.

6) A hash function is a _____ that converts a numerical input value into another compressed numerical value.

  1. Abstract view
  2. Mathematical function
  3. Both A and B
  4. None of the mentioned above

Answer: b. Mathematical function

Explanation:

A hash function is a mathematical function that turns a numerical input value into another numerical input value that has been compressed. When using the hash function, the input can be of any length, but the result is always of a set length.

7) A cryptographic hash function must be deterministic,

  1. True
  2. False

Answer: a. True

Explanation:

Determinism is required in a cryptographic hash function, which means that the same message must always result in the same hash value. The hash value for any given message can be computed in a short amount of time. It is not possible to generate a message that contains the hash value of a given value. It is impossible to find two different messages that have the same hash value in the same manner.

8) _____ and encryption is two separate cryptographic processes.

  1. Hashing
  2. Decryption
  3. Processing
  4. None of the mentioned above

Answer: a. Hashing

Explanation:

The cryptographic methods of hashing and encryption are distinct from one another. A cryptographic hash function, on the other hand, is distinct. Because hashing is a one-way process, after we've hashed data, we won't be able to restore it to its original format.

9) Amongst which of the following is /are good for Hashes,

  1. Password protection
  2. Data integrity / file verification
  3. Digital signatures and virus signatures
  4. All of the mentioned above

Answer: d. All of the mentioned above

Explanation:

Despite the fact that hashing is not encryption, it is a type of cryptography that can be used for a variety of purposes, including password protection, data integrity / file verification, digital signatures, and virus identification.

10) Digital Signatures authenticates the sender by appending the original message with the ____ digest.

  1. Decrypted message
  2. Encrypted message
  3. Systematic approach
  4. None of the mentioned above

Answer: b. Encrypted message

Explanation:

A digital signature verifies the identity of the sender by attaching the original message together with the encrypted message digest to the end of the message. The sender encrypts the message using the private key in order to assure nonrepudiation, while the hash safeguards against data tampering and ensures integrity, as shown in the equation: digital signature=private sender's key (hash (message).

SET 8

) Which of the following is a mode of operation for the Block ciphers in cryptography?

  1. Electronic Code Book (ECB)
  2. Cipher Block Chaining (CBC)
  3. Counter (CTR) mode
  4. All of the above

Answer: d. All of the above

Explanation:

All the mentioned modes are followed by the block cipher techniques. Therefore, the correct answer is d. All of the above.

2) For which of the following should EBC (Electronic Code Book) process not be used for encryption?

  1. For large block sizes
  2. For fixed block sizes
  3. For small block sizes
  4. None of the above

Answer: c. For small block sizes

Explanation:

It is preferred that the block size in the EBC technique must be greater than 64 bits. If not, the text is padded to make it of the required length. This is due to some particular words and phrases that may be reused again often so that the same repetitive part of ciphertext can emerge as mixed.

3) Which of the following is the main disadvantage of the ECB (Electronic Code Book)?
or
Which of the following is the major drawback of ECB?

  1. It requires large block size
  2. Padding is done to make the plain text divisible into blocks of fixed size
  3. It is prone to cryptanalysis since there is a direct relationship between plain text and cipher text.
  4. None of the above

Answer: c. It is prone to cryptanalysis since there is a direct relationship between plain text and cipher text.

Explanation:

In ECB, there lies a direct relation between the plain text and the ciphertext. Therefore, it is easy for an outsider to break the encryption logic and steal the data.

4) Which of the following options is not correct according to the definition of the Cipher Block Chaining (CBC)?

  1. CBC is a mode of operation for stream ciphers.
  2. Initialization vector (IV) is used in CBC in the initial phase.
  3. It has better resistive nature towards cryptanalysis than ECB
  4. None of the above

Answer: a. CBC is a mode of operation for stream ciphers

Explanation:

CBC which stands for Cipher Block chaining is a mode of operation for block ciphers and not for stream ciphers.

5) Which of the following modes of operations can be followed for both stream ciphers as well as block ciphers?

  1. CBC (Cipher Block Chaining)
  2. ECB (Electronic Code Book)
  3. CFB (Cipher text Feed Back)
  4. All of the above

Answer: c. CFB (Cipher text Feed Back)

Explanation:

CFB is primarily a mode to derive some characteristics of a stream cipher from a block cipher on the cryptography in cryptoanalysis.

6) Amongst which of the following is/ are showing the goodness of electronic code book,

  1. Parallel encryption of blocks of bits is possible
  2. It is a faster way of encryption.
  3. Simple way of the block cipher.
  4. All of the mentioned above

Answer: d. All of the mentioned above

Explanation:

The electronic code book is the most straightforward block cypher manner of operation. It is feasible to do parallel encryption of blocks of bits in this manner. This is a straightforward implementation of the block cypher.

7) Cipher block chaining or CBC is an advancement made to electronic code book,

  1. True
  2. False

Answer: a. True

Explanation:

Cipher block chaining, often known as CBC, is an improvement on the ECB algorithm since the ECB algorithm breaches some security standards. After XORing the previous cypher block with the original plaintext block, the previous cypher block is sent on as input to the next encryption algorithm in the CBC scheme.

8) In Cipher block chaining mode, the current plaintext block is added to the ____.

  1. Previous ciphertext block
  2. Next ciphertext block
  3. Middle ciphertext block
  4. None of the mentioned above

Answer: a. Previous ciphertext block

Explanation:

If you are using CBC mode, the current plaintext block is added to the previous ciphertext block, and the result is then encrypted with the secret key. To put it another way, encryption is the opposite process of decryption, which consists in decrypting the current ciphertext and then adding the preceding ciphertext block to the result.

9) With reference to Cipher Feedback (CFB) Mode, amongst which of the following is /are true,

  1. Each ciphertext block gets 'fed back' into the encryption process
  2. Encrypt the next plaintext block
  3. Both A and B
  4. None of the mentioned above

Answer: c. Both A and B

Explanation:

As part of the Cipher Feedback (CFB) Mode encryption process, each ciphertext block is "fed back" into the overall encryption process in order to encrypt the next plaintext block. CFB mode requires an initialization vector to be used as the first random n-bit input block in order to function properly. It is not necessary to keep the initialization vector a secret.

10) An initialization vector (IV) or starting variable (SV) is a block of bits that is used by several modes to _____.

  1. Randomize the decryption
  2. Randomize the encryption
  3. Minimize and maximize the randomization
  4. None of the mentioned above

Answer: b. Randomize the encryption

Explanation:

An initialization vector, also known as a starting variable (SV), is a block of bits that is used by several encryption modes to randomize the encryption process and, as a result, to produce distinct ciphertexts even if the same plaintext is encrypted multiple times without the need for a more time-consuming re-keying process.


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