sdes

#include <stdio.h>
int l[4],r[4],keys[2][8],ct[8];
void sbox(int sip[],int p[],int sbno,int i)


    {
    	int sbox[2][4][4]={1,0,3,2,3,2,1,0,0,2,1,3,3,1,3,2,0,1,2,3,2,0,1,3,3,0,1,0,2,1,0,3};
    	int rw,c,sop;
    	rw = sip[3]+sip[0]*2;
    	c = sip[2]+sip[1]*2;
    	sop = sbox[sbno][rw][c]; //sop gives decimal value of S-Box Output
    	for(;sop!=0;sop/=2)
    		p[i--]=sop%2;
}
void cmp_fun(int round)


    {
    	int EP[]={4,1,2,3,2,3,4,1},i,epd[8];
    	int slip[4],srip[4];
    	int p[4]={0},p4[]={2,4,3,1},np[4];
    	for(i=0;i<8;i++) // E/P Permutation
    		epd[i]=r[EP[i]-1];
    	for(i=0;i<8;i++)//Performing XOR with Key
    		if(i<4)
    			slip[i] = epd[i]^keys[round][i]; // Using Key _ 1=>0
    		else
    			srip[i-4] = epd[i]^keys[round][i];
    	sbox(slip,p,0,1);//Calling SBox 1, 0->SBOX 1
    	sbox(srip,p,1,3);//Calling SBox 1, 1->SBOX 2
    	for(i=0;i<4;i++) //P4 permutation
    		np[i]=p[p4[i]-1];
    	for(i=0;i<4;i++)
    		l[i] = l[i]^np[i];
}
void left_shift(int keyip[],int nob)


    {
    	int t1,t2,i;
    	while(nob>0)


        	{
        		t1=keyip[0],t2=keyip[5];
        		for(i=0;i<9;i++)
        			if(i<4)
        				keyip[i] =keyip[i+1];
        			else if(i>4)
        				keyip[i] = keyip[i+1];
        		keyip[4]=t1,keyip[9]=t2;
        		nob--;
        	}
    }
    void gen_keys()


        {
        	int key[10],i,keyip[10];
        	int p10[]={3,5,2,7,4,10,1,9,8,6},p8[]={6,3,7,4,8,5,10,9};
        	printf("Enter Key :");
        	for(i=0;i<10;i++)
        		scanf("%d", &key[i]);
        	for(i=0;i<10;i++) // Permutation P10
        		keyip[i] = key[p10[i]-1];
        	left_shift(keyip,1);	 // Left Shifting (Array,No of bts)
        printf("\nKey1 :");
        	for(i=0;i<8;i++){ 			//Permuting P8 on key1
        	 keys[0][i] = keyip[p8[i]-1];// Key1 Generated!!
        	 printf("%d",keys[0][i]);
        	}
        	left_shift(keyip,2);// Generating Key2 . .
        	printf("\nKey2 :");


            	for(i=0;i<8;i++){
            		keys[1][i] = keyip[p8[i]-1];// Key2 Generated!!
            		printf("%d",keys[1][i]);
            	}
        }
        void En_De(int pt[],int c)


            {
            		int ip[]={2,6,3,1,4,8,5,7},ipi[]={4,1,3,5,7,2,8,6},t[8],i;
            	for(i=0;i<8;i++)// Performing Permutation on input bits!!
            		if(i<4)
            			l[i]=pt[ip[i]-1];
            		else
            			r[i-4] = pt[ip[i]-1];
            	cmp_fun(c);//Round 0+1 using key 0+1
            	for(i=0;i<4;i++) //Swapping left & right
            		r[i]=l[i]+r[i],l[i]=r[i]-l[i],r[i]=r[i]-l[i];
            	printf("\n\n");
            	cmp_fun(!c); // Round 1+1 wid key1+1 wid swapped bits
            	for(i=0;i<8;i++)
            		if(i<4)	t[i]=l[i];
            		else	t[i]=r[i-4];
            	for(i=0;i<8;i++)
            		ct[i] = t[ipi[i]-1];
        }
        void main()


            {
            	int pt[8]={0},i;
            	printf("Enter plain text binary bits:");
            	for(i=0;i<8;i++)
            		scanf("%d",&pt[i]);
            	gen_keys(); // Generating Keys key1 & key2
            	En_De(pt,0);
            		printf("\nCipher Text :");
            			for(i=0;i<8;i++)
            				printf("%d",ct[i]);
            	//Decrypting - - -
            	En_De(ct,1);
            		printf("\nPlain Text (After Decrypting):");
            				for(i=0;i<8;i++)
            				printf("%d",ct[i]);
        }