Announcements: Homework 2 returned Homework 2 returned Monday: Written (concept and small...

Announcements:Announcements: Homework 2 returnedHomework 2 returned Monday: Written (concept and small calculations) exam Monday: Written (concept and small calculations) exam

on breaking ch 2 cipherson breaking ch 2 ciphers HW 3 due date pushed back to TuesdayHW 3 due date pushed back to Tuesday ““Stuff You Don’t Learn In School” workshop next Stuff You Don’t Learn In School” workshop next

Saturday – register by Wednesday to get free food.Saturday – register by Wednesday to get free food.

Next 2 weeks:Next 2 weeks: Data Encryption Standard (DES)Data Encryption Standard (DES) HW 4 (posted Monday, due 1.5 weeks later) is to HW 4 (posted Monday, due 1.5 weeks later) is to

implement DESimplement DES Rijndael, start RSARijndael, start RSA

Questions?Questions?

DTTF/NB479: DszquphsbqizDTTF/NB479: Dszquphsbqiz Day 12Day 12

DES is a block cipherDES is a block cipher

History?History?Full-scale version operates on 64-bit blocksFull-scale version operates on 64-bit blocks

Text ASCII bit vector

Block1 (64 bits)

DES

Encoded1 (64 bits)

Encoded bit vector

Block2 (64 bits)

DES

Encoded2 (64 bits)

…

EDEN is a toy version of DES that operates on 12-bit EDEN is a toy version of DES that operates on 12-bit blocksblocks

EDEN is a term I coined:EDEN is a term I coined:EEasyasy

DDataata

EEncryptionncryption

NNon-standardon-standard

EDENEDENInput (12 bits)

L0 (6) R0 (6)

f

L1 (6) R1 (6)

K1(8)

f

L2 (6) R2 (6)

K2(8)

Round 1

Round 2

Repeat for 8 rounds

…

The key, Ki for round iis derived from a 9-bit key K.

1. Write L1, R1

2. We can decrypt by switching L and Rand using the sameprocedure! (We needonly to reverse the keysequence.) Example.

This is a Feistelsystem.

1.1. ExpandersExpanders2.2. XOR with keyXOR with key3.3. S-boxesS-boxes

Read p. 116 to help with Q1-4.Read p. 116 to help with Q1-4.

Could you implement this? Could you implement this?

EDEN’s encryption function f has the same three EDEN’s encryption function f has the same three types of components as DES’ ftypes of components as DES’ f

1-4

DES has the same structure as EDEN DES has the same structure as EDEN except it uses initial permutations (IP)except it uses initial permutations (IP)

Trappe &Washington, p. 125Trappe &Washington, p. 125

The initial permutation table tells at which position in The initial permutation table tells at which position in the input to find the output bitthe input to find the output bit

5858 5050 4242 3434 2626 1818 1010 22 6060 5252 4444 3636 2828 2020 1212 44

6262 5454 4646 3838 3030 2222 1414 66 6464 5656 4848 4040 3232 2424 1616 88

5757 4949 4141 3333 2525 1717 99 11 5959 5151 4343 3535 2727 1919 1111 33

6161 5353 4545 3737 2929 2121 1313 55 6363 5555 4747 3939 3131 2323 1515 77

Reading permutation tablesSay y = IP(x)Then y[1] = x[58], y[2] = x[50], …

Differences between DES & EDENDifferences between DES & EDENEDENEDEN DESDES

12-bit blocks12-bit blocks 64-bit blocks64-bit blocks

Extra initial permutation IP (for Extra initial permutation IP (for efficiency in 1970’s?)efficiency in 1970’s?)

8 rounds8 rounds 16 rounds16 rounds

E: 6E: 68 bits8 bits E: 32E: 3248 bits48 bits

9 bit key: use 8/round9 bit key: use 8/round 64-bit key: use 56/round64-bit key: use 56/round

Also contains extra permutations, Also contains extra permutations, a left-shift each round, and a a left-shift each round, and a reduction to 48 bits each roundreduction to 48 bits each round

2 S-boxes: 42 S-boxes: 43 bits each3 bits each 8 S-boxes: 68 S-boxes: 64 bits each4 bits each

f ends by permuting the 32 bitsf ends by permuting the 32 bits

T&W, p. 126T&W, p. 126

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