des.java

import java.util.*;

class Main{
	private static class DES{
		//constants
		int[] IP = { 58,50,42,34,26,18,10,2,60,52,44,36,28,20,12,4,62,54,46,38,30,22,14,6,64,56,48,40,32,24,16,8,57,49,41,33,25,17,9,1,59,51,43,35,27,19,11,3,61,53,45,37,29,21,13,5,63,55,47,39,31,23,15,7};
		int[] IP1 = { 40,8,48,16,56,24,64,32,39,7,47,15,55,23,63,31,38,6,46,14,54,22,62,30,37,5,45,13,53,21,61,29,36,4,44,12,52,20,60,28,35,3,43,11,51,19,59,27,34,2,42,10,50,18,58,26,33,1,41,9,49,17,57,25};
		int[] PC1 = { 57,49,41,33,25,17,9,1,58,50,42,34,26,18,10,2,59,51,43,35,27,19,11,3,60,52,44,36,63,55,47,39,31,23,15,7,62,54,46,38,30,22,14,6,61,53,45,37,29,21,13,5,28,20,12,4};
		int[] PC2 = { 14,17,11,24,1,5,3,28,15,6,21,10,23,19,12,4,26,8,16,7,27,20,13,2,41,52,31,37,47,55,30,40,51,45,33,48,44,49,39,56,34,53,46,42,50,36,29,32};
		int[] EP = { 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}; 
		int[] P = { 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};
		int[][][] sbox = {
			{{14,4,13,1,2,15,11,8,3,10,6,12,5,9,0,7},{0,15,7,4,14,2,13,1,10,6,12,11,9,5,3,8},{4,1,14,8,13,6,2,11,15,12,9,7,3,10,5,0},{15,12,8,2,4,9,1,7,5,11,3,14,10,0,6,13}},
			{{15,1,8,14,6,11,3,4,9,7,2,13,12,0,5,10},{3,13,4,7,15,2,8,14,12,0,1,10,6,9,11,5},{0,14,7,11,10,4,13,1,5,8,12,6,9,3,2,15},{13,8,10,1,3,15,4,2,11,6,7,12,0,5,14,9}},
			{{10,0,9,14,6,3,15,5,1,13,12,7,11,4,2,8},{13,7,0,9,3,4,6,10,2,8,5,14,12,11,15,1},{13,6,4,9,8,15,3,0,11,1,2,12,5,10,14,7},{1,10,13,0,6,9,8,7,4,15,14,3,11,5,2,12}},
			{{7,13,14,3,0,6,9,10,1,2,8,5,11,12,4,15},{13,8,11,5,6,15,0,3,4,7,2,12,1,10,14,9},{10,6,9,0,12,11,7,13,15,1,3,14,5,2,8,4},{3,15,0,6,10,1,13,8,9,4,5,11,12,7,2,14}},
			{{2,12,4,1,7,10,11,6,8,5,3,15,13,0,14,9},{14,11,2,12,4,7,13,1,5,0,15,10,3,9,8,6},{4,2,1,11,10,13,7,8,15,9,12,5,6,3,0,14},{11,8,12,7,1,14,2,13,6,15,0,9,10,4,5,3}},
			{{12,1,10,15,9,2,6,8,0,13,3,4,14,7,5,11},{10,15,4,2,7,12,9,5,6,1,13,14,0,11,3,8},{9,14,15,5,2,8,12,3,7,0,4,10,1,13,11,6},{4,3,2,12,9,5,15,10,11,14,1,7,6,0,8,13}},
			{{4,11,2,14,15,0,8,13,3,12,9,7,5,10,6,1},{13,0,11,7,4,9,1,10,14,3,5,12,2,15,8,6},{1,4,11,13,12,3,7,14,10,15,6,8,0,5,9,2},{6,11,13,8,1,4,10,7,9,5,0,15,14,2,3,12}},
			{{13,2,8,4,6,15,11,1,10,9,3,14,5,0,12,7},{1,15,13,8,10,3,7,4,12,5,6,11,0,14,9,2},{7,11,4,1,9,12,14,2,0,6,10,13,15,3,5,8},{2,1,14,7,4,10,8,13,15,12,9,0,3,5,6,11}}
		};
		int[] shiftBits = {1,1,2,2,2,2,2,2,1,2,2,2,2,2,2,1};

		String hextoBin(String input){
			int n = input.length() * 4;
			input = Long.toBinaryString(Long.parseUnsignedLong(input, 16));
			while(input.length()< n)
				input = "0"+input;
			return input;
		}

		String binToHex(String input){
			int n = (int)input.length() / 4;
			input = Long.toHexString(Long.parseUnsignedLong(input, 2));
			while(input.length()< n)
				input = "0"+input;
			return input;
		}

		String permutation(int[] sequence, String input){
			String output = "";
			input = hextoBin(input);
			for(int i = 0; i < sequence.length; i++)
				output += input.charAt(sequence[i] - 1);
			output = binToHex(output);
			return output;
		}

		String xor(String a, String b){
			long t_a = Long.parseUnsignedLong(a, 16);
			long t_b = Long.parseUnsignedLong(b, 16);
			t_a = t_a ^ t_b;
			a = Long.toHexString(t_a);
			while(a.length() < b.length())
				a = "0" + a;
			return a;
		}

		String leftCircularShift(String input, int numBits){
			int n = input.length() * 4;
			int perm[] = new int[n];
			for(int i = 0; i < n-1; i++)
				perm[i] = (i+2);
			perm[n-1] = 1;
			while(numBits --> 0)
				input = permutation(perm, input);
			return input;
		}

		String[] getKeys(String key){
			String keys[] = new String[16];
			key = permutation(PC1, key);
			for(int i = 0; i < 16; i++){
				key = leftCircularShift(key.substring(0,7), shiftBits[i]) + leftCircularShift(key.substring(7,14), shiftBits[i]);
				keys[i] = permutation(PC2, key);
			}
			return keys;
		}

		String sBox(String input){
			String output = "";
			input = hextoBin(input);
			for(int i = 0; i < 48; i+=6){
				String temp = input.substring(i, i+6);
				int num = i / 6;
				int row = Integer.parseInt(temp.charAt(0)+""+temp.charAt(5), 2);
				int col = Integer.parseInt(temp.substring(1,5), 2);
				output += Integer.toHexString(sbox[num][row][col]);
			}
			return output;
		}

		String round(String input, String key){
			//fk
			String left = input.substring(0,8);
			String temp = input.substring(8,16);
			String right = temp;
			temp = permutation(EP, temp);
			temp = xor(temp,key);
			temp = sBox(temp);
			temp = permutation(P, temp);
			left = xor(left,temp);
			//s
			return right+left;
		}

		String encrypt(String plainText, String key){
			int i;
			String keys[] = getKeys(key);
			plainText = permutation(IP, plainText);
			for(i = 0; i < 16; i++){
				plainText = round(plainText, keys[i]);
			}
			plainText = plainText.substring(8,16)+plainText.substring(0,8);
			plainText = permutation(IP1, plainText);
			return plainText;
		}

		String decrypt(String plainText, String key){
			int i;
			String keys[] = getKeys(key);
			plainText = permutation(IP, plainText);
			for(i = 15; i > -1; i--){
				plainText = round(plainText, keys[i]);
			}
			plainText = plainText.substring(8,16)+plainText.substring(0,8);
			plainText = permutation(IP1, plainText);
			return plainText;
		}
	}
	public static void main(String args[]){
		Scanner in = new Scanner(System.in);
		System.out.printf("Enter plainText:(64- bit hexadecimal): ");
		String text = in.nextLine();
		System.out.printf("Enter key:(64-bit hexadecimal): ");
		String key = in.nextLine();
		DES cipher = new DES();
		text = cipher.encrypt(text, key);
		System.out.println("cipherText: "+text);
		text = cipher.decrypt(text, key);
		System.out.println("plainText: "+text);
	}
}