Permuted Choice #2 14 17 11 24 1 5 3 28 15 6 21 10 23 19 12 4 26 8 16 7 27 20 13 2 41 52 31 37 47 55 30 40 51 45 33 48 44 49 39 56 34 53 46 42 50 36 29.

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Presentation transcript:

Permuted Choice # (note, some numbers missing: 9, 22...) Left shift is 1 or 2 depending on round number

Important Function

DES/TDEA Initial Permutation (IP) –Transposes the input block using table: 58, 50, 42, 34, 26, 18, 10, 2, 60, 52, 44, 36 28, 20, 12, 4 62, 54, 46, 38, 30,… 57, 49, 41, 33,… 61, 53, 45 i.e. Bit 58 goes to position 1, 50 to 2, 42 to 3, … Maybe makes it easier to load text into a DES chip?

LRKey Key’L’R’ P-Box S-Box Expansion shift Compression

DES/TDEA Expansion Permutation –Expand R 32 bit half to 48 bits –Main purpose: one bit affects two substitutions creating a rapidly increasing dependency of output to input bits (avalanche effect) –E-box: For each 4 bit input, 32, 1, 2, 3, 4, 5, 4, 5, 6, 7, 8, 9, 8, 9, 10, 11, 12, 13, 12, 13, 14, 15, 16, 17, 16, 17, 18, 19, 20, 21, 20, 21, 22, 23, 24, 25, 24, 25, 26, 27, 28, 29, 28, 29, 30, 31, 32, 1

S-Boxes (6 bit to 4 bit) S S bit input and 4-bit output (table translation) S S

S-Box Design No output bit of S-box should be too close to a linear function of the input bits If L and R bits are fixed, and 4 middle bits varied, each possible 4 bit result is obtained once. 2 inputs vary in 1 bit, output varies in 2 bits 2 inputs vary in 2 middle bits, the output varies in at least 2 bits 2 inputs are different on 1 st 2 bits, and same on last 2 bits, the output is different A few more esoteric ones….

DES/TDEA P-Box Permutation –Output of S-Box is permuted –Map each input bit  output position –No bits used twice and bits ignored (straight permutation) 16, 7, 20, 21, 29, 12, 28, 17, 1,15, 23, 26, 5, 18, 31, 10 2, 8, 24, 14, 32, 27, 3, 9, 19, 13, 30, 6, 22, 11, 4, 25