1. Announcements: Quizzes returned tomorrow Quizzes returned tomorrow This week: Mon-Thurs: Data Encryption Standard (DES) Mon-Thurs: Data Encryption Standard (DES) HW 4 (assigned Thurs) is to implement DES HW 4 (assigned Thurs) is to implement DES Friday: Computer quiz on breaking ciphers in ch 2 Friday: Computer quiz on breaking ciphers in ch 2 Next week: Rijndael, start RSA Rijndael, start RSAQuestions? DTTF/NB479: DszquphsbqizDay 13

2. DES is a block cipher Interesting history in section 4.1. Mistrust of IBM, NSA? Mistrust of IBM, NSA? Full-scale version operates on 64-bit blocks TextASCII bit vector Block 1 (64 bits) DES Encoded 1 (64 bits) Encoded bit vector Block 2 (64 bits) DES Encoded 2 (64 bits) …

3. EDEN Today we look at a simpler version of DES that operates on 12-bit blocks. I hereby coin this simpler version EDEN: Easy Data Encryption Non-standard

4. EDEN Input (12 bits) L 0 (6)R 0 (6) f L 1 (6)R 1 (6) K 1 (8) f L 2 (6)R 2 (6) K 2 (8) Round 1 Round 2 Repeat for 8 rounds … The key, K i for round i is derived from a 9-bit key K. 1.Write L 1, R 1 2.We can decrypt by switching L and R and using the same procedure! (We need only to reverse the key sequence.) Example. This is a Feistel system.

5. The encryption function f EDEN’s f is similar to DES’s 3 components: Expanders Expanders XOR with key XOR with key S-boxes S-boxes Read about them now (p. 116) and fill out the worksheet. Could you implement this?

6. DES T&W, p. 125

7. The initial permutation 585042342618102605244362820124 625446383022146645648403224168 57494133251791595143352719113 615345372921135635547393123157 Reading permutation charts Say y = IP(x) Then y 1 = x 58, y 2 = x 50, …

8. Differences between DES & EDEN EDENDES 12-bit blocks 64-bit block Extra initial permutation IP (for efficiency in 1970’s?) 8 rounds 16 rounds E: 6  8 bits E: 32  48 bits 9 bit key: use 8/round 64-bit key: use 56/round Also contains extra permutations, a left-shift, and a reduction to 48 bits 2 S-boxes: 4  3 bits each 8 S-boxes: 6  4 bits each f ends by permuting the 32 bits

9. T&W, p. 126

10. HW4: DES Implementation I implemented EDEN in Java fairly quickly DES is obviously more complicated You’ll implement encryption and decryption. Correctness: Can use one to test the other. Can use one to test the other.Efficiency: In addition, it’d be nice to use a language that closer to the hardware for efficiency, like C. In addition, it’d be nice to use a language that closer to the hardware for efficiency, like C. I’m planning a competition to see whose implementation is quickest! I’m planning a competition to see whose implementation is quickest!