Q. Which of the following is a natural candidates for stream ciphers?

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Q. Which of the following modes of operation does not involve feedback?

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Q. Which mode requires the implementation of only the encryption algorithm?

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Q. Which block mode limits the maximum throughput of the algorithm to the reciprocal of the time for one execution?

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Q. Which mode of operation has the worst “error propagation” among the following?

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Q. The counter value in CTR modes repeats are a regular interval.

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Q. Which of the following modes does not implement chaining or “dependency on previous stage computations”?

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Q. In OFB Transmission errors do not propagate: only the current ciphertext is affected, since keys are generated “locally”.

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Q. Which of the following can be classified under advantages and disadvantages of OFB mode?

i) Transmission errors
ii) A bit error in a ciphertext segment
iii) Cannot recover from lost ciphertext segments
iv) Ciphertext or segment loss

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Q. There is a dependency on the previous ‘s’ bits in every stage in CFB mode. Here ‘s’ can range from ___

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Q. Which of the following statements are true ?

i) In the CBC mode, the plaintext block is XORed with previous ciphertext block before encryption
ii) The CTR mode does not require an Initialization Vector
iii) The last block in the CBC mode uses an Initialization Vector
iv) In CBC mode repetitions in plaintext do not show up in ciphertext

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Q. Which of the following is false for ECB mode of operation?

i) The Plain text is broken into blocks of size 128 bytes
ii) Blocks can be swapped, repeated, replaced without recipient noticing
iii) Good for short data
iv) Encryption of each block is done separately using a randomly generated key for each block

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Q. Which one of the following modes of operation in DES is used for operating short data?

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Q. How many modes of operation are there in in DES and AES?

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Q. How many round keys are generated in the AES algorithm?

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Q. Which of the following are true ?

i) In the AES key expansion algorithm, the function g() operates on w i+3
ii) Perform a one-byte right circular rotation on the argument 4-byte word
iii) The round constant follows the formula RC[j] = RC[j − 1]

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Q. The inverse transformation matrix times the forward transformation matrix equals the identity matrix.

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Q. For a key 25D5 and PT input A479 what is the output we obtain after the “add round key” function?

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Q. How many step function do Round 1 and 2 each have in S-AES?

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Q. Which of the following is a faulty S-AES step function?

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