1. Symmetric Key Block Ciphers

2. Classical Ciphers
Substitution
Transposition

3. Modern Cryptography Data Encryption Standard 1977
“New Directions in Cryptography” 1976

4. Ciphers Symmetric key block ciphers Public key ciphers Stream ciphers
Post-quantum ciphers

5. Stream Ciphers
Stream ciphers

6. Data Encryption Standard 1977
Horst Feistel (1915 – 1990)
Simplified DES: Wade Trapp and Lawrence Washington

7. Data Encryption Standard 1976

8. DES
DES
Simplified DES
64-bit block 56-bit key (8 parity bits) 8 S-boxes 6 x 4 16 rounds Feistel cipher
12-bit block 9-bit key 2 S-boxes 4 x 3 4 rounds Feistel cipher

9. Simplified DES – Feistel Cipher

10. Key and Message

11. Key Schedule
9 bits of key Use the 8 bits on the left for k Rotate to the left one bit Use the 8 bits on the left for k Rotate to the left 1 bit Use the 8 bits on the left for k Rotate to the left 1 bit Use the 8 bits on the left for k

12. Expansion Function and XOR

13. S-Box

14. DES Encryption

15. DES Decryption
Encryption
Decryption

16. DES Decryption
Encryption
Decryption

17. Secrecy of Algorithm
Backdoor?

18. 3DES 112-bit security

19. Security Level
Perfect Security Random key, as long as the message, and used only once. Computational Security Today 128

20. Block Cipher Modes

21. Block Cipher Modes

22. Skipjack/Clipper Chip
64-bit block
80-bit key
32 rounds
Unbalanced Feistel cipher
Skipjack/Clipper Chip
Skipjack declassified 1998
Clipper Chip

23. Substitution-Permutation Networks
Claude Shannon (1916 – 2001)

24. Claude Shannon
“A Mathematical Theory of Communication” 1948 “The Theory of Secrecy Systems” 1949

25. “The Theory of Secrecy Systems 1949
Diffusion: “… the statistical structure of [the message] which leads to its redundancy is dissipated into long range statistics.” P-box Confusion: “… make the relation between the simple statistics of [the ciphertext] and the simple description of [the key] a very complex and involved one.” S-box

26. SPN

27. PRESENT 2007
Many

28. PRESENT
64-bit block 80- or 128-bit key 1 S-box 4 x 4 31 Rounds Substitution-Permutation Network

29. Substitution Layer

30. Permutation Layer

31. Substitution and Permutation

32. Key Schedule

33. Advanced Encryption Standard 2001
Joan Daemen and Vincent Rijmen
Simplified AES: Mohammad Musa, Edward Schaefer, and
Stephen Wedig

34. AES (Rijandael) AES Simplified AES
128-bit block 128-bit, 192-bit, or 256-bit key 10, 12, or 14 rounds SPN
16-bit block 16-bit key 2 rounds SPN

35. S-Box

36. S-Box

37. Add Key

38. SN, SR, MC

39. S-AES

40. Simplify the Other AES Finalists
Serpent Twofish RC6 MARS