Question

Which of these is not a characteristic of block ciphers?

(a) Variable key length / block size / number of rounds

(b) Mixed operators, data/key dependent rotation

(c) Key independent S-boxes

(d) More complex key scheduling

I had been asked this question during an interview.

I would like to ask this question from RC4 and RC5 topic in section Pseudorandom Number Generation and Stream Ciphers and More Block Ciphers of Cryptograph & Network Security

Answer 1

The correct answer is (c) Key independent S-boxes

The explanation is: Features seen in modern block ciphers are:

– Variable key length / block size / number of rounds

– Mixed operators, data/key dependent rotation

– Key dependent S-boxes

– More complex key scheduling

– Operation of full data in each round

– Varying non-linear functions.