DATA ENCRYPTION STANDARD (DES) -Sheetal Thapaliya

Outline History Key Generation Encryption Decryption Strength of DES Ultimate

History In 1971, IBM developed an algorithm, named LUCIFER which operates on a block of 64 bits, using a 128-bit key Walter Tuchman, an IBM researcher, refined LUCIFER and reduced the key size to 56-bit, to fit on a chip.

History In 1977, the results of Tuchman’s project of IBM was adopted as the Data Encryption Standard by NSA (NIST).

DES – Block Diagram

DES – Basic Information Block size of 64 bit Usable Key size 56 bit Input = Plain text and Key Plain text: 0000 0001 0010 0100 0101 0110 0111 1000 1001 1010 1011 1101 1110 1111 Key: 00010011 00110100 01010111 01111001 10011011 101111100 11011111 11110001 Output = Cipher No. of round = 16

Key Generation Input= 56 (or 64 bit) Output = 16 subkey of 48 bit Uses Permuted Choice (PC-1) table

Key Generation

Key Generation

Key Generation Generate other C0 and D0 by Left Circular Shift

Key Generation

Key Generation C1D1 = 111000 1100110 0101010 1011111 1010101 0110011 00111100 0011110 K1 = 000110 110000 001011 101111 111111 000111 000001 110010

Key Generation

EnCRYption Input= 64 bit Output = 64 bit Key Size = 32 bit

Encryption Block Diagram

Encryption – IP (initial Permutation)

Encryption : Divide plain text

Encryption: The f function Block Diagram

Encryption : Calculation of f Size Rn-1 = 32 bit Size of Kn = 48 bit Thus Expand Rn-1 using E Bit-Selection Table

Encryption: Calculation of f E bit Selection Table

Encryption: Calculation of f S-Box Input = 6 bit X 8 = 48 bit Output= 4 bit X 8 = 32 bit Eg.: 011000  0101

Encryption: Calculation of f S-Box 010001 1100 011111 ?

Encryption: Calculation of f S-Box

Encryption: Calculation of f Output of S-BOX

Encryption: Calculation of f Last step: Permulation

Encryption: Final Calculation of R1 Repeat this step upto 16 round Final block : L16 R16 Reverse to get : R16 L16

Encryption: Final Permutation

Encryption: Final Permutation

Thank you