Cryptography Teacher Questions And Answers

21⟩ Is the following matrix the inverse matrix of the matrix used in the mix columns step? x3 + 1 x x x3 + 1 a) Yes b) No c) Can’t say d) Insufficient Information

a) Yes

Explanation: On multiplying this matrix with the mix columns matrix we get the identity matrix, this proves that it is an inverse matrix.

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22⟩ For an inputs key of size 128 bits constituting of all zeros, what is w(7) ? a) {62 63 63 63} b) {62 62 62 62} c) {00 00 00 00} d) {63 63 63 62}

a) {62 63 63 63}

Explanation: Applying the key algorithm we get,

w(0) = {00 00 00 00}; w(1) = {00 00 00 00}; w(2) = {00 00 00 00}; w(3) = {00 00 00 00};

w(4) = {62 63 63 63}; w(5) = {62 63 63 63}; w(6) = {62 63 63 63}; w(7) = {62 63 63 63}

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23⟩ Voice privacy in GSM cellular telephone protocol is provided by A. A5/2 cipher B. b5/4 cipher C. b5/6 cipher D. b5/8 cipher

A. A5/2 cipher

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24⟩ A straight permutation cipher or a straight P-box has same number of inputs as cipher Frames Outputs Bits

Outputs

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25⟩ In cryptography, what is cipher? A. algorithm for performing encryption and decryption B. encrypted message C. both (a) and (b) D. none of the mentioned

A. algorithm for performing encryption and decryption

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26⟩ For the case of Mixed Columns and Inverse Mixed Columns, is it true that b(x) = a-1(x)mod(x4 + 1) where a(x) = {03}x3 + {01}x2 + {01}x + {02} and b(x) = {0B}x3 + {0D}x2 + {09}x + {0E} a) True b) False. The expression for a(x) is wrong. c) False. The expression for b(x) is wrong. d) False. Both a(x) and b(x) are faulty.

a) True

Explanation: The statment is true and can be checked as it is similar to the matrix forms of mixed columns and inverse mixed columns.

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27⟩ On comparing AES with DES, which of the following functions from DES does not have an equivalent AES function? a) f function b) permutation p c) swapping of halves d) xor of subkey with function f

c) swapping of halves

Explanation: There is no equivalent to swapping of halves in the AES algorithm.

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28⟩ Tell me what can you use to defend against multiple login attempts?

You can create a lockout policy that locks accounts when a user has too many login attempts.

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29⟩ Explain Kerckhoff’s Principle for Cryptosystem?

In the 19th century, a Dutch cryptographer A. Kerckhoff furnished the requirements of a good cryptosystem. Kerckhoff stated that a cryptographic system should be secure even if everything about the system, except the key, is public knowledge. The six design principles defined by Kerckhoff for cryptosystem are −

The cryptosystem should be unbreakable practically, if not mathematically.

Falling of the cryptosystem in the hands of an intruder should not lead to any compromise of the system, preventing any inconvenience to the user.

The key should be easily communicable, memorable, and changeable.

The ciphertext should be transmissible by telegraph, an unsecure channel.

The encryption apparatus and documents should be portable and operable by a single person.

Finally, it is necessary that the system be easy to use, requiring neither mental strain nor the knowledge of a long series of rules to observe.

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30⟩ ElGamal encryption system is A. symmetric key encryption algorithm B. asymmetric key encryption algorithm C. not an encryption algorithm D. none of the mentioned

B. asymmetric key encryption algorithm

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31⟩ An asymmetric-key (or public-key) cipher uses 1 Key 2 Key 3 Key 4 Key

2 Key

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32⟩ 1. How many computation rounds does the simplified AES consists of? a) 5 b) 2 c) 8 d) 10

a) 5

Explanation: The simplified AES has only 2 rounds of computation.

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33⟩ On perform the Mix Columns transformation for the sequence of bytes “67 89 AB CD” we get output a) {08 55 FF 18} b) {28 45 EF 08} c) {28 45 FF 18} d) {25 35 EF 08}

b) {28 45 EF 08}

Explanation: Perform the mix columns transformation to obtain the output {28 45 EF 0A}.

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34⟩ Explain me what is Diffie-Hellman?

It is a method by which a key can be securely shared by two users without any actual exchange.

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35⟩ Cryptanalysis is used A. to find some insecurity in a cryptographic scheme B. to increase the speed C. to encrypt the data D. none of the mentioned

A. to find some insecurity in a cryptographic scheme

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36⟩ Which of the following is a faulty S-AES step function? a) Add round key b) Byte substitution c) Shift rows d) Mix Columns

b) Byte substitution

Explanation: The correct version in S-AES would be nibble substitution as 4 bits are taken at a time.

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37⟩ Explain me what is Cryptanalysis?

The art and science of breaking the cipher text is known as cryptanalysis.

Cryptanalysis is the sister branch of cryptography and they both co-exist. The cryptographic process results in the cipher text for transmission or storage. It involves the study of cryptographic mechanism with the intention to break them. Cryptanalysis is also used during the design of the new cryptographic techniques to test their security strengths.

Note − Cryptography concerns with the design of cryptosystems, while cryptanalysis studies the breaking of cryptosystems.

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38⟩ Do you know advanced Encryption Standard?

The more popular and widely adopted symmetric encryption algorithm likely to be encountered nowadays is the Advanced Encryption Standard (AES). It is found at least six time faster than triple DES.

A replacement for DES was needed as its key size was too small. With increasing computing power, it was considered vulnerable against exhaustive key search attack. Triple DES was designed to overcome this drawback but it was found slow.

The features of AES are as follows −

☛ Symmetric key symmetric block cipher

☛ 128-bit data, 128/192/256-bit keys

☛ Stronger and faster than Triple-DES

☛ Provide full specification and design details

☛ Software implementable in C and Java

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39⟩ Tell me what are MD2, MD4, and MD5?

MD2, MD4 and MD5 are 128 bit hashing algorithms

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40⟩ Tell me how can you defend against phishing attempts?

Phishing is usually done through email, so you can block some SMTP servers, senders, and educate users on phishing attempts.

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55 Cryptography Teacher Questions And Answers

21⟩ Is the following matrix the inverse matrix of the matrix used in the mix columns step? x3 + 1 x x x3 + 1 a) Yes b) No c) Can’t say d) Insufficient Information

22⟩ For an inputs key of size 128 bits constituting of all zeros, what is w(7) ? a) {62 63 63 63} b) {62 62 62 62} c) {00 00 00 00} d) {63 63 63 62}

23⟩ Voice privacy in GSM cellular telephone protocol is provided by A. A5/2 cipher B. b5/4 cipher C. b5/6 cipher D. b5/8 cipher

24⟩ A straight permutation cipher or a straight P-box has same number of inputs as cipher Frames Outputs Bits

25⟩ In cryptography, what is cipher? A. algorithm for performing encryption and decryption B. encrypted message C. both (a) and (b) D. none of the mentioned

27⟩ On comparing AES with DES, which of the following functions from DES does not have an equivalent AES function? a) f function b) permutation p c) swapping of halves d) xor of subkey with function f

28⟩ Tell me what can you use to defend against multiple login attempts?

29⟩ Explain Kerckhoff’s Principle for Cryptosystem?

30⟩ ElGamal encryption system is A. symmetric key encryption algorithm B. asymmetric key encryption algorithm C. not an encryption algorithm D. none of the mentioned

31⟩ An asymmetric-key (or public-key) cipher uses 1 Key 2 Key 3 Key 4 Key

32⟩ 1. How many computation rounds does the simplified AES consists of? a) 5 b) 2 c) 8 d) 10

33⟩ On perform the Mix Columns transformation for the sequence of bytes “67 89 AB CD” we get output a) {08 55 FF 18} b) {28 45 EF 08} c) {28 45 FF 18} d) {25 35 EF 08}

34⟩ Explain me what is Diffie-Hellman?

35⟩ Cryptanalysis is used A. to find some insecurity in a cryptographic scheme B. to increase the speed C. to encrypt the data D. none of the mentioned

36⟩ Which of the following is a faulty S-AES step function? a) Add round key b) Byte substitution c) Shift rows d) Mix Columns

37⟩ Explain me what is Cryptanalysis?

38⟩ Do you know advanced Encryption Standard?

39⟩ Tell me what are MD2, MD4, and MD5?

40⟩ Tell me how can you defend against phishing attempts?

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55 Cryptography Teacher Questions And Answers

21⟩ Is the following matrix the inverse matrix of the matrix used in the mix columns step? x3 + 1 x x x3 + 1 a) Yes b) No c) Can’t say d) Insufficient Information

22⟩ For an inputs key of size 128 bits constituting of all zeros, what is w(7) ? a) {62 63 63 63} b) {62 62 62 62} c) {00 00 00 00} d) {63 63 63 62}

23⟩ Voice privacy in GSM cellular telephone protocol is provided by A. A5/2 cipher B. b5/4 cipher C. b5/6 cipher D. b5/8 cipher

24⟩ A straight permutation cipher or a straight P-box has same number of inputs as cipher Frames Outputs Bits

25⟩ In cryptography, what is cipher? A. algorithm for performing encryption and decryption B. encrypted message C. both (a) and (b) D. none of the mentioned

27⟩ On comparing AES with DES, which of the following functions from DES does not have an equivalent AES function? a) f function b) permutation p c) swapping of halves d) xor of subkey with function f

28⟩ Tell me what can you use to defend against multiple login attempts?

29⟩ Explain Kerckhoff’s Principle for Cryptosystem?

30⟩ ElGamal encryption system is A. symmetric key encryption algorithm B. asymmetric key encryption algorithm C. not an encryption algorithm D. none of the mentioned

31⟩ An asymmetric-key (or public-key) cipher uses 1 Key 2 Key 3 Key 4 Key

32⟩ 1. How many computation rounds does the simplified AES consists of? a) 5 b) 2 c) 8 d) 10

33⟩ On perform the Mix Columns transformation for the sequence of bytes “67 89 AB CD” we get output a) {08 55 FF 18} b) {28 45 EF 08} c) {28 45 FF 18} d) {25 35 EF 08}

34⟩ Explain me what is Diffie-Hellman?

35⟩ Cryptanalysis is used A. to find some insecurity in a cryptographic scheme B. to increase the speed C. to encrypt the data D. none of the mentioned

36⟩ Which of the following is a faulty S-AES step function? a) Add round key b) Byte substitution c) Shift rows d) Mix Columns

37⟩ Explain me what is Cryptanalysis?

38⟩ Do you know advanced Encryption Standard?

39⟩ Tell me what are MD2, MD4, and MD5?

40⟩ Tell me how can you defend against phishing attempts?

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