UGC NET CSE | December 2014 | Part 2 | Question: 30

Question

How many distinct stages are there in $DES$ algorithm, which is parameterized by a $56$-bit key ?

• A. $16$
• B. $17$
• C. $18$
• D. $19$

Answer 1

DES(Data Encryption Standard) algorithm which is parameterized by a 56 bit key has 19 distinct stages including 16 rounds or repetition so ans is D

Comments

Please explain how to solve this

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The answer should be A.16 since, first, one before last and the last are just transpositions of bits and independent of keys.

Answer 2

19 stages

Comments

Why 19 stages? I know about 16 of them only

Answer 3

In DES, plain text (here, password) is encrypted in block of 64 bits, yielding 64 bits of cipher text. The algorithm which is parameterized by 56 bit key has 19 distinct stages.