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

2. Symmetric key block ciphers Public key ciphers Stream ciphers Post-quantum ciphers

3. Horst Feistel (1915 – 1990) Simplified DES: Wade Trapp and Lawrence Washington

5. 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 Simplified DES

8. 9 bits of key 111 010 110 Use the 8 bits on the left for k1 1110 1011 Rotate to the left one bit 110 101 101 Use the 8 bits on the left for k12 1101 0110 Rotate to the left 1 bit 101 011 011 Use the 8 bits on the left for k3 1010 1101 Rotate to the left 1 bit 010 110 111 Use the 8 bits on the left for k4 0101 1011

12. Encryption Decryption

13. EncryptionDecryption

14. Backdoor?

16. Perfect Security Random key, as long as the message, and used only once. Computational Security Today 112

19. Skipjack declassified 1998 Clipper Chip 1993 -1996 64-bit block 80-bit key 32 rounds Unbalanced Feistel cipher

20. Claude Shannon (1916 – 2001)

21. “A Mathematical Theory of Communication” 1948 “The Theory of Secrecy Systems” 1949

22. Diffusion: “… the statistical structure of [the message] which leads to its redundancy is dissipated into long range statistics.” Wire crossing, 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

24. Many

25. 64-bit block 80- or 128-bit key 1 S-box 4 x 4 31 Rounds Substitution-Permutation Network

30. How do they know it’s secure?

31. Joan Daemen and Vincent Rijmen Simplified AES: Mohammad Musa, Edward Schaefer, and Stephen Wedig

32. 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 Simplified AES