Implements DES Encryption Program for Secure Data Assignment

Assignment Task

You are to write a program that Implements encryption in simplified DES system described in section

The program will consist of at least two methods. - encrypt(plaintext, key): The plaintext is an integer in the range 0 to 4095 (12 bits) and the key an integer in the range 0 to 511 (9 bits). It returns the ciphertext, which is a 12-bit integer.

A main method or section that prompts the user for a plaintext value and a key value and then prints the ciphertext.

A good approach to writing this is to implement each step in a round as a method. To support this, here is the pseudocode for the various steps along with a method for creating the key schedule.

Note that all variables and parameters are of type integer.

generateKeySchedule(key)

subkeys = integer array of length 4

subkeys[0] = (key & 0b111111110) >> 1;

subkeys[1] = ((key & 0b011111111) << 0>> 9);

subkeys[2] = ((key & 0b001111111) << 1>> 8);

subkeys[3] = ((key & 0b000111111) << 2>> 7);

return subkeys

expand(r)

bit1 = (r & 0b100000) >> 5

bit2 = (r & 0b010000) >> 4

bit3 = (r & 0b001000) >> 3

bit4 = (r & 0b000100) >> 2

bit5 = (r & 0b000010) >> 1

bit6 = (r & 0b000001) >> 0

expandedR = (bit1 << 7>

(bit4 << 3> return expandedR

s1box(n)

s1values = [[0b101, 0b010, 0b001, 0b110, 0b011, 0b100, 0b111, 0b000],

[0b001, 0b100, 0b110, 0b010, 0b000, 0b111, 0b101, 0b011]]

fourBitValue = n & 0b1111

rowIndex = fourBitValue >> 3

columnIndex = fourBitValue & 0b111

return s1values[rowIndex][columnIndex]

s2box(n)

s2values = [[0b100, 0b000, 0b110, 0b101, 0b111, 0b001, 0b011, 0b010],

[0b101, 0b011, 0b000, 0b111, 0b110, 0b010, 0b001, 0b100]]

fourBitValue = n & 0b1111

rowIndex = fourBitValue >> 3

columnIndex = fourBitValue & 0b111

return s2values[rowIndex][columnIndex]

f(r, key)

r = expand(r)

r = r ^ key

rLeft4bits = (r & 0b11110000) >> 4

rRight4bits = (r & 0b1111) >> 0

s1 = s1box(rLeft4bits)

s2 = s2box(rRight4bits)

return (s1 << 3>

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