S-DES.java

package cybersecurity;

public class S_DES {
	//int key[]= {0,0,1,0,0,1,0,1,1,1};
	int key[]= {1,0,1,0,0,0,0,0,1,0};   //extra example for checking perpose
	int P10[]= {3,5,2,7,4,10,1,9,8,6};
	int P8[]= {6,3,7,4,8,5,10,9};
	
	int key1[]=new int[8];
	int key2[]=new int[8];	
	
	int []IP= {2,6,3,1,4,8,5,7};
	int []EP= {4,1,2,3,2,3,4,1};
	int []P4= {2,4,3,1};
	int []IP_inv= {4,1,3,5,7,2,8,6};
	
	int[][]S0= {
			{1,0,3,2},
			{3,2,1,0},
			{0,2,1,3},
			{3,1,3,2}
	};
	int[][]S1= {
			{0,1,2,3},
			{2,0,1,3},
			{3,0,1,0},
			{2,1,0,3}
	};
	
	
//	this function basically generates the key(key1 and key2)
//	using P10 and P8 with (1 and 2)left shifts
	
	void key_generation()
	{
		int key_[]=new int[10];
		
		for(int i=0;i<10;i++)
		{
			key_[i]=key[P10[i]-1];
		}
		
		int Ls[]=new int[5];
		int Rs[]=new int[5];
		
		for(int i=0;i<5;i++)
		{
			Ls[i]=key_[i];
			Rs[i]=key_[i+5];
		}
		
		int []Ls_1=shift(Ls,1);
		int []Rs_1=shift(Rs,1);
		
		for(int i=0;i<5;i++)
		{
			key_[i]=Ls_1[i];
			key_[i+5]=Rs_1[i];
		}
		
		for(int i=0;i<8;i++)
		{
			key1[i]=key_[P8[i]-1];
		}
		
		int []Ls_2=shift(Ls,2);
		int []Rs_2=shift(Rs,2);
		
		for(int i=0;i<5;i++)
		{
			key_[i]=Ls_2[i];
			key_[i+5]=Rs_2[i];
		}
		
		for(int i=0;i<8;i++)
		{
			key2[i]=key_[P8[i]-1];
		}
		
		System.out.println("Your Key-1 :");
		
		for(int i=0;i<8;i++)
			System.out.print(key1[i]+" ");
		
		System.out.println();
		System.out.println("Your Key-2 :");
		
		for(int i=0;i<8;i++)
			System.out.print(key2[i]+" ");
			
	}
	
//	this function is use full for shifting(circular) the array n position towards left
	
	int[] shift(int []ar,int n)
	{
		while(n>0)
		{
			int temp=ar[0];
			for(int i=0;i<ar.length-1;i++)
			{
				ar[i]=ar[i+1];
			}
			ar[ar.length-1]=temp;
			n--;
		}
		return ar;
	}
	
//	this is main encryption function takes plain text as input
//	uses another functions and returns the array of cipher text 
	
	int[] encryption(int []plaintext)
	{
		int []arr=new int[8];
		
		for(int i=0;i<8;i++)
		{
			arr[i]=plaintext[IP[i]-1];
		}
		int[] arr1=function_(arr,key1);
				
		int []after_swap=swap(arr1,arr1.length/2);

		int []arr2=function_(after_swap,key2);
		
		int []ciphertext=new int[8];
		
		for(int i=0;i<8;i++)
		{
			ciphertext[i]=arr2[IP_inv[i]-1];
		}
		
		return ciphertext;
	}

	//decimal to binary string 0-3

	String binary_(int val)
	{
		if(val==0)
			return "00";
		else if(val==1)
			return "01";
		else if(val==2)
			return "10";
		else
			return "11";
	}
	
//	this function is doing core things like expansion
//	then xor with desired key then S0 and S1 substitution
//	P4 permutation and again xor 
//	we have used this function 2 times(key-1 and key-2) during encryption and
//	2 times(key-2 and key-1) during decryption
	
	int [] function_(int [] ar,int []key_)
	{
		
		int []l=new int[4];
		int []r=new int[4];
		
		for(int i=0;i<4;i++)
		{
			l[i]=ar[i];
			r[i]=ar[i+4];
		}
		
		int[]ep=new int[8];
		
		for(int i=0;i<8;i++)
		{
			ep[i]=r[EP[i]-1];
		}
		
		for(int i=0;i<8;i++)
		{
			ar[i]=key_[i]^ep[i];
		}
		
		int []l_1=new int[4];
		int []r_1=new int[4];
		
		for(int i=0;i<4;i++)
		{
			l_1[i]=ar[i];
			r_1[i]=ar[i+4];
		}
		
		int row,col,val;
		
		row=Integer.parseInt(""+l_1[0]+l_1[3], 2);
		col=Integer.parseInt(""+l_1[1]+l_1[2], 2);
		val=S0[row][col];
		String str_l=binary_(val);
		
		row=Integer.parseInt(""+r_1[0]+r_1[3], 2);
		col=Integer.parseInt(""+r_1[1]+r_1[2], 2);
		val=S1[row][col];
		String str_r=binary_(val);
		
		int []r_=new int[4];
		for(int i=0;i<2;i++)
		{
			char c1=str_l.charAt(i);
			char c2=str_r.charAt(i);
			r_[i]=Character.getNumericValue(c1);
			r_[i+2]=Character.getNumericValue(c2);
		}
		int[]r_p4=new int[4];
		for(int i=0;i<4;i++)
		{
			r_p4[i]=r_[P4[i]-1];
		}
		
		for(int i=0;i<4;i++)
		{
			l[i]=l[i]^r_p4[i];
		}
		
		int []ouptput=new int[8];
		for(int i=0;i<4;i++)
		{
			ouptput[i]=l[i];
			ouptput[i+4]=r[i];
		}
		return ouptput;
	}
	
//	this function swaps the nibble of size n(4)
	
	int []swap(int []aray,int n)
	{
		int[] l=new int[n];
		int[] r=new int[n];
		
		for(int i=0;i<n;i++)
		{
			l[i]=aray[i];
			r[i]=aray[i+n];
		}
		
		int [] output=new int[2*n];
		for(int i=0;i<n;i++)
		{
			output[i]=r[i];
			output[i+n]=l[i];
		}
		
		return output;
	}
	
//	this is main decryption function 
//	here we have used all previously defined function 
//	it takes cipher text as input and returns the array of
//	decrypted text
	
	int [] decryption(int []ar)
	{
		int []arr=new int[8];
		
		for(int i=0;i<8;i++)
		{
			arr[i]=ar[IP[i]-1];
		}
		
		int[] arr1=function_(arr,key2);
				
		int []after_swap=swap(arr1,arr1.length/2);

		int []arr2=function_(after_swap,key1);
		
		int []decrypted=new int[8];
		
		for(int i=0;i<8;i++)
		{
			decrypted[i]=arr2[IP_inv[i]-1];
		}	
	
		return decrypted;
	}
	
	public static void main(String[] args) {
	
		
		S_DES obj=new S_DES();
		
		obj.key_generation();									//call to key generation function
		
		//int []plaintext= {1,0,1,0,0,1,0,1};
		int []plaintext= {1,0,0,1,0,1,1,1};   					//extra example for checking perpose
		
		System.out.println();
		System.out.println("Your plain Text is :");
		for(int i=0;i<8;i++)									//printing the plaintext
				System.out.print(plaintext[i]+" ");
		
		int []ciphertext=obj.encryption(plaintext);
		
		System.out.println();
		System.out.println("Your cipher Text is :"); 			//printing the cipher text
		for(int i=0;i<8;i++)
				System.out.print(ciphertext[i]+" ");
		
		int []decrypted=obj.decryption(ciphertext);
		
		System.out.println();
		System.out.println("Your decrypted Text is :");			//printing the decrypted text
		for(int i=0;i<8;i++)
				System.out.print(decrypted[i]+" ");
	}

}