Simplified DES in JAVA

                                                       Simplified DES

A simplified variant of the Data Encryption Standard (DES). Note that Simplified DES or S-DES is for educational purposes only. It is a small-scale version of the DES designed to help beginners understand the basic structure of DES.

Here is the code I used for encryption and decryption.......

// SimplifiedDES.java

import java.io.*;

import java.lang.*;

class SDES

       {

        public int K1, K2;

        public static final int P10[] = { 3, 5, 2, 7, 4, 10, 1, 9, 8, 6};

        public static final int P10max = 10;

        public static final int P8[] = { 6, 3, 7, 4, 8, 5, 10, 9};

        public static final int P8max = 10;

        public static final int P4[] = { 2, 4, 3, 1};

        public static final int P4max = 4;

        public static final int IP[] = { 2, 6, 3, 1, 4, 8, 5, 7};

        public static final int IPmax = 8;

        public static final int IPI[] = { 4, 1, 3, 5, 7, 2, 8, 6};

        public static final int IPImax = 8;

        public static final int EP[] = { 4, 1, 2, 3, 2, 3, 4, 1};

        public static final int EPmax = 4;

        public static final int S0[][] = {{ 1, 0, 3, 2},{ 3, 2, 1, 0},{ 0, 2, 1,

                                                              3},{ 3, 1, 3, 2}};

        public static final int S1[][] = {{ 0, 1, 2, 3},{ 2, 0, 1, 3},{ 3, 0, 1,

                                                              2},{ 2, 1, 0, 3}};

       

       public static int permute( int x, int p[], int pmax)

       {

         int y = 0;

         for( int i = 0; i < p.length; ++i)

          {

            y <<= 1;

            y |= (x >> (pmax - p[i])) & 1;

        }

         return y;

       }

       

       public static int F( int R, int K)

       {

          int t = permute( R, EP, EPmax) ^ K;

          int t0 = (t >> 4) & 0xF;

          int t1 = t & 0xF;

          t0 = S0[ ((t0 & 0x8) >> 2) | (t0 & 1) ][ (t0 >> 1) & 0x3 ];

          t1 = S1[ ((t1 & 0x8) >> 2) | (t1 & 1) ][ (t1 >> 1) & 0x3 ];

           t = permute( (t0 << 2) | t1, P4, P4max);

         return t;

       

  }

  public static int fK( int m, int K)

        {

            int L = (m >> 4) & 0xF;

            int R = m & 0xF;

            return ((L ^ F(R,K)) << 4) | R;

        }

       

  public static int SW( int x)

  {

   return ((x & 0xF) << 4) | ((x >> 4) & 0xF);

  }

       

       

        public byte encrypt( int m)

       

        {

         System.out.println("\nEncryption Process Starts........\n\n"); 

          m = permute( m, IP, IPmax);

         System.out.print("\nAfter Permutation : ");

          printData( m, 8);

          m = fK( m, K1);

          System.out.print("\nbefore Swap : ");

          printData( m, 8);

          m = SW( m);

          System.out.print("\nAfter Swap : ");

          printData( m, 8);

          m = fK( m, K2);

          System.out.print("\nbefore IP inverse : ");

          printData( m, 8);

          m = permute( m, IPI, IPImax);

          return (byte) m;

       

        }

       

       

        public byte decrypt( int m)

       

        {

          System.out.println("\nDecryption Process Starts........\n\n");

          printData( m, 8);

          m = permute( m, IP, IPmax);

          System.out.print("\nAfter Permutation : ");

          printData( m, 8);

          m = fK( m, K2);

          System.out.print("\nbefore Swap : ");

          printData( m, 8);

          m = SW( m);

          System.out.print("\nAfter Swap : ");

          printData( m, 8);

          m = fK( m, K1);

          System.out.print("\nBefore Extraction Permutation : ");

          printData( m, 4);

          m = permute( m, IPI, IPImax);

          System.out.print("\nAfter Extraction Permutation : ");

          printData( m, 8);

          return (byte) m;

       

        }

       

        public static void printData( int x, int n)

         {

           int mask = 1 << (n-1);

           while( mask > 0)

           {

           System.out.print( ((x & mask) == 0) ? '0' : '1');

           mask >>= 1;

           }

        }

       

       

       

        public SDES( int K)

      {

          K = permute( K, P10, P10max);

          int t1 = (K >> 5) & 0x1F;

          int t2 = K & 0x1F;

          t1 = ((t1 & 0xF) << 1) | ((t1 & 0x10) >> 4);

          t2 = ((t2 & 0xF) << 1) | ((t2 & 0x10) >> 4);

          K1 = permute( (t1 << 5)| t2, P8, P8max);

          t1 = ((t1 & 0x7) << 2) | ((t1 & 0x18) >> 3);

          t2 = ((t2 & 0x7) << 2) | ((t2 & 0x18) >> 3);

          K2 = permute( (t1 << 5)| t2, P8, P8max);

       

        }

       

      }

// Main operations

      public class SimplifiedDES

      {

       

        public static void main( String args[]) throws Exception

        {

         DataInputStream inp=new DataInputStream(System.in);

         System.out.println("Enter the 10 Bit Key :");

          int K = Integer.parseInt(inp.readLine(),2);

          SDES A = new SDES( K);

          System.out.println("Enter the 8 Bit message To be Encrypt  : ");

          int m = Integer.parseInt(inp.readLine(),2);

          System.out.print("\nKey K1: ");

          SDES.printData( A.K1, 8);

          System.out.print("\nKey K2: ");

          SDES.printData( A.K2, 8);

          m = A.encrypt( m);

          System.out.print("\nEncrypted Message: ");

          SDES.printData( m, 8);

          m = A.decrypt( m);

          System.out.print("\nDecrypted Message: ");

          SDES.printData( m, 8);

       

        }

       

    }


Output:

Output :

D:\javapgm>java SimplifiedDES

Enter the 10 Bit Key :

1011011010

Enter the 8 Bit message To be Encrypt  :

10110110

Key K1: 11110101

Key K2: 01100011

Encryption Process Starts........

After Permutation : 01111001

before Swap : 00001001

After Swap : 10010000

before IP inverse : 10000000

Encrypted Message: 01000000

Decryption Process Starts........

01000000

After Permutation : 10000000

before Swap : 10010000

After Swap : 00001001

Before Extraction Permutation : 1001

After Extraction Permutation : 10110110

Decrypted Message: 10110110