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

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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 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. 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 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. 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 modes does not implement chaining or “dependency on previous stage computations”?

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

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

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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 requires the implementation of only the encryption algorithm?

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

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

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Q. The XTS-AES mode was approved by NIST in

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Q. The XTS-AES mode is based on the concept of tweakable block cipher.

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Q. The purpose of a ‘tweak’ in XTS-AES mode is to

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Q. A tweak is used in XTS-AES mode to provide a different output for the same input PT and same key.

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Q. XTS-AES mode of operation is a better version of

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Q. What is the size of the XTS-AES key?

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Q. Which of the following represent the tweak?

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