sdes.java

S-DES的编程实现 S-DES的加密使用8位明文和10位密钥做为输入

// simplified DES
//
// R. Perry, Jan. 2002

public class SDES
{
 // subkeys
 //
  public int K1, K2;

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

 // permute bits
 //
  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;
  }

 // F function
 //
  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;
  }

 // fK function
 //
  public static int fK( int m, int K)
  {
    int L = (m >> 4) & 0xF;
    int R = m & 0xF;

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

 // switch function
 //
  public static int SW( int x)
  {
    return ((x & 0xF) << 4) | ((x >> 4) & 0xF);
  }

 // encrypt one byte
 //
  public byte encrypt( int m)
  {
    m = permute( m, IP, IPmax);
    m = fK( m, K1);
    m = SW( m);
    m = fK( m, K2);
    m = permute( m, IPI, IPImax);

    return (byte) m;
  }
 
 // decrypt one byte
 //
  public byte decrypt( int m)
  {
    m = permute( m, IP, IPmax);
    m = fK( m, K2);
    m = SW( m);
    m = fK( m, K1);
    m = permute( m, IPI, IPImax);

    return (byte) m;
  }
 
 // print n bits in binary
 //
  public static void printb( int x, int n)
  {
    int mask = 1 << (n-1);

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

 // constructor - initializes K1 and K2
 //
  public SDES( int K)
  {
    K = permute( K, P10, P10max);

   // 5-bit parts of K
   //
    int t1 = (K >> 5) & 0x1F;
    int t2 = K & 0x1F;

   // LS-1
   //
    t1 = ((t1 & 0xF) << 1) | ((t1 & 0x10) >> 4);
    t2 = ((t2 & 0xF) << 1) | ((t2 & 0x10) >> 4);

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

   // LS-2
   //
    t1 = ((t1 & 0x7) << 2) | ((t1 & 0x18) >> 3);
    t2 = ((t2 & 0x7) << 2) | ((t2 & 0x18) >> 3);

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

}