... Ciphertext-Only Attack Figure 3.4 Ciphertext-only attack 3.9 3 .1. 2 Continued Known-Plaintext Attack Figure 3.5 Known-plaintext attack 3 .10 3 .1. 2 Continued Chosen-Plaintext Attack Figure 3.6 Chosen-plaintext ... Z26* 3.2 .1 Continued Example 3.7 What is the key domain for any multiplicative cipher? Solution The key needs to be in Z26* This set has only 12 members: 1, 3, 5, 7, 9, 11 , 15 , 17 , 19 , 21, 23, ... pattern in the permutation: ( 01, 05, 09, 13 ), (02, 06, 10 , 13 ), (03, 07, 11 , 15 ), and (08, 12 ) In each section, the difference between the two adjacent numbers is 3. 51 ...