Question

Need to finish the des_round method JAVA

1. expands 6-bit r-input to 8-bits.  The 8 bits should be: (1) (2) (4) (3) (4) (3) (5) (6) of original 6-bit input
2. generates round key based on the master key and round number
3. passes the expanded_r and round key to f(), which:
   3a. XORs them together;
   3b. Splits result into two 4-bit sequences
   3c. Refer to the 2 S-Boxes (row = bit 1; column = bits 2-4) to get two 3-bit outputs
   3d. Concatenates together to single 6-bit output
4. XORs result of f() with original left-input. This result is the right part of output
5. Combine with original right-input (which is the left part of the output)

import java.util.ArrayList;
import java.util.Collections;

public class DESMethod
{
private static int sbox1[][] = {
{0b101, 0b010, 0b001, 0b110, 0b011, 0b100, 0b111, 0b000}, // row 0
{0b001, 0b100, 0b110, 0b010, 0b000, 0b111, 0b101, 0b011} // row 1
};
private static int sbox2[][] = {
{0b100, 0b000, 0b110, 0b101, 0b111, 0b001, 0b011, 0b010}, // row 0
{0b101, 0b011, 0b000, 0b111, 0b110, 0b010, 0b001, 0b100} // row 1
};

public static void main(String[] args)
{   
int input = 0b011100100110;
int masterkey = 0b010011001;
int round = 4;

int result = des_round(input, masterkey,round);
}

//des_round() -- Performs a single round of simplified DES algorith on given input pt,  for round, using masterkey.
public static int des_round(int pt, int masterkey, int round)
{
//isolate the left and right halves of the input
//use bitwise AND operation to isolate the bits we want (upper 6 for left, lower 6 for right)
int l_in = (pt & 0b11111100000) >> 6; //need to right shift 6 spots so result is in lower 6 bits
int r_in = (pt & 0b000000111111);
  

//Print out results of the round (the round input, the round key, and the round output

  
}

}

Answer 1

import java.util.ArrayList;
import java.util.Collections;

public class DESMethod {
    private static int sbox1[][] = { { 0b101, 0b010, 0b001, 0b110, 0b011, 0b100, 0b111, 0b000 }, // row 0
            { 0b001, 0b100, 0b110, 0b010, 0b000, 0b111, 0b101, 0b011 } // row 1
    };
    private static int sbox2[][] = { { 0b100, 0b000, 0b110, 0b101, 0b111, 0b001, 0b011, 0b010 }, // row 0
            { 0b101, 0b011, 0b000, 0b111, 0b110, 0b010, 0b001, 0b100 } // row 1
    };

    public static void main(String[] args) {
        int input = 0b011100100110;
        int masterkey = 0b010011001;
        int round = 4;

        int result = des_round(input, masterkey, round);
        System.out.println(result);
    }
    
    static int getKeyForRound(int key, int round) {
        if(round == 1) {
            return (key & 0b111111110) >> 1;
        }
        int firstBit = key & 0b100000000;
        key = key << 1;
        key = key | (firstBit >> 8);
        return getKeyForRound(key, round - 1);
    }
    
    static int expanded_r(int x) {
        String s = Integer.toBinaryString(x);
        while(s.length() < 6) {
            s = "0" + s;
        }
        s = s.substring(0, 2) + s.charAt(3) + s.substring(2, 4) + s.charAt(2) + s.substring(4);
        return Integer.parseInt(s, 2);
    }

    //des_round() -- Performs a single round of simplified DES algorith on given input pt,  for round, using masterkey.
    public static int des_round(int pt, int masterkey, int round) {
        //isolate the left and right halves of the input
        //use bitwise AND operation to isolate the bits we want (upper 6 for left, lower 6 for right)
        int l_in = (pt & 0b111111000000) >> 6; // need to right shift 6 spots so result is in lower 6 bits
        int r_in = (pt & 0b000000111111);

        //Print out results of the round (the round input, the round key, and the round output
        int roundKey = getKeyForRound(masterkey, round);
        int erIn = expanded_r(r_in);
        
        int xored = erIn ^ roundKey;
        int s1 = (xored & 0b11110000) >> 4;
        int s2 = (xored & 0b00001111);
        
        int l_out = r_in;
        int r1 = (s1 & 0b1000) >> 3;
        int c1 = s1 & 0b0111;
        int r2 = (s2 & 0b1000) >> 3;
        int c2 = s2 & 0b0111;
        
        int r_Out = l_in ^ ((sbox1[r1][c1] << 3)| (sbox2[r2][c2]));
        return (l_out << 6) | r_Out;
    }

}

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