Question

How many keys does the Triple DES algorithm use?

(a) 2

(b) 3

(c) 2 or 3

(d) 3 or 4

I got this question in an interview for internship.

The origin of the question is The Data Encryption Standard (DES) and It’s Strength topic in chapter Block Ciphers and the Data Encryption Standard of Cryptograph & Network Security

Answer 1

Correct option is (c) 2 or 3

To elaborate: For Triple DES we can either have 2 or 3 keys.

Using two keys: c = Ek1(Dk2(Ek1(m)))

Using three keys: c = Ek3(Ek2(Ek1(m))).