Week 5 - Symmetric Ciphers & DES

Week 5 - Symmetric Ciphers & DES

1. P10

   • Left Shift 1
     • P8
       • Left Shift 3
         • P8
           • K2
           • K2
       • K1
       • K1
       • 6,3,7,4,8,5,10,9
   • 3,5,2,7,4,10,1,9,8,6

2. IP

   • Fk
     • SW
       • Fk
         • IP - 1
           • 4,1,3,5,7,2,8,6
       • Switch Left with Right
     • Fk (L,R) = (L XOR F (R, Sk), R)
       • E / P = 4,1,2,3,2,3,4,1
         • E/P(R) XOR K1
           • Expand / Permutation
           • Row (1,4)
             • Col (2, 3)
               • Sboxes
                 • P4(SBoxes)
                   • Fk (L, R) = (L XOR Fk (R, Sk), R)
   • 2,6,3,1,4,8,5,7

3. IP - 1

   • Fk
     • SW
       • Fk
         • IP

4. ECB - Electronic Code Book

5. Cipher Block Chaining

6. DES is Strong and Fast, Widely Used

   • But is susceptible to brute force attack