Implementation of S-DES

Problem Statement: 

Implementation of S-DES

Reference for understanding functions of algorithm: 

 https://www.brainkart.com/article/Simplified-Data-Encryption-Standard-(S-DES)_8343/

If the above link doesn't work. Try using google cached responses for the link.

Code:

	import java.awt.datatransfer.StringSelection;
	import java.io.DataInputStream;
	/*
	* Link For reference: https://www.brainkart.com/article/Simplified-Data-Encryption-Standard-(S-DES)_8343/
	*/ // https://www.brainkart.com/article/Simplified-Data-Encryption-Standard-(S-DES)_8343/
	public class SDES {
	public int K1,K2;
	//Note: below matrics will be provided in lab(PICT)..
	//For performing P10 permutation
	public static final int P10[] = { 3, 5, 2, 7, 4, 10, 1, 9, 8, 6};
	public static final int P10max = 10;
	//10 to 8 bit permutation
	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;
	//Performing initial permutaion
	public static final int IP[] = { 2, 6, 3, 1, 4, 8, 5, 7};
	public static final int IPmax = 8;
	//performing final permuttaion(Inverse of initial permutation)
	public static final int IPI[] = { 4, 1, 3, 5, 7, 2, 8, 6};
	public static final int IPImax = 8;
	//expansion/permutation operation:Used in F1 Function
	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}};
	/*
	* Generic Function to perform all permutations
	*/
	public static int permute(int x, int p[], int pmax) {
	int y=0;
	//System.out.println(Integer.toBinaryString(x));
	/*
	String binary=Integer.toBinaryString(x);
	StringBuffer br=new StringBuffer(new String(new char[10]).replace("\0", "0"));
	*/
	for(int i=0;i<p.length;i++) {
	// br.setCharAt(i, binary.charAt(p[i]-1));
	y=y<<1;
	y=y|(x>>(pmax-p[i]))&1;
	}
	//System.out.println("Final :"+Integer.toBinaryString(y));
	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);
	}
	/*
	* Ciphertext = IP-1 (fK2 (SW (fk1 (IP (plaintext))))
	*/
	public byte encrypt( int m)
	{
	System.out.println("\nEncryption Process Starts........\n\n");
	m = permute( m, IP, IPmax);
	System.out.print("\nAfter Initial Permutation(IP) : ");
	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;
	}
	/*
	* Plaintext = IP-1 (fK1 (SW (fk2 (IP (ciphertext)))))
	*/
	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;
	}
	}
	/*
	*
	* K1 = P8 (Shift_1 (P10 (Key)))
	K2 = P8 (Shift_2 (shift_1 (P10 (Key))))
	*/
	public SDES( int K) //COnstructor generates key k1 & k2 used for encyption
	{
	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);
	}
	@SuppressWarnings("deprecation")
	public static void main( String args[]) throws Exception
	{
	DataInputStream inp=new DataInputStream(System.in);
	System.out.println("Enter the 10 Bit Key :"); //1011011010
	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); //10110110
	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);
	}
	}

view raw SDES.java hosted with ❤ by GitHub

	/*
	*
	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
	*/

view raw SDES_output.txt hosted with ❤ by GitHub

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