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
