Implementation of Simplified Data Encryption Standard (SDES) v1

#include<fstream.h>
#include<conio.h>
#include<string.h>
#include<math.h>


char result[11];
char input_to_sbox[5];
char sbox0[4][4],sbox1[4][4];
char key1[9];
char key2[9];
char key[10];

void xor(char *str1,char *str2)
{

if(strlen(str1)!=strlen(str2))
{
cout<<"X-or can be done with same length numbers only!!!";
return;
}

for(int i=0;i<strlen(str1);i++)
{
if(str1[i]==str2[i])
result[i]='0';
else
result[i]='1';
}
result[i]=NULL;
}

int convert_to_decimal(char *str)
{

if(strlen(str)!=2)
return -1;

if (strcmp(str,"00")==0)
return 0;

if (strcmp(str,"01")==0)
return 1;

if (strcmp(str,"10")==0)
return 2;

if (strcmp(str,"11")==0)
return 3;

return -1;
}

void convert_to_binary(int num)
{

if(num==0)
strcpy(result,"00");

if(num==1)
strcpy(result,"01");

if(num==2)
strcpy(result,"10");

if(num==3)
strcpy(result,"11");

}


void s_box(int s_box_no)
{
int row,column;

char temp1[3];
char buff[4];
strcpy(buff,input_to_sbox);
//strset(buff,'\0');

/*if(strlen(buff)!=4)
return "ERROR";*/

temp1[0]=input_to_sbox[0];
temp1[1]=input_to_sbox[3];
temp1[2]=NULL;

row=convert_to_decimal(temp1);

temp1[0]=input_to_sbox[1];
temp1[1]=input_to_sbox[2];
temp1[2]=NULL;

column=convert_to_decimal(temp1);

//cout<<"Row:"<<row<<"Columm"<<column;


int tmp;
if(s_box_no==0)
{
tmp=sbox0[row][column]-48;
convert_to_binary(tmp);
//cout<<"SBox0:"<<result;
}
else
{
tmp=sbox1[row][column]-48;
convert_to_binary(tmp);
//cout<<"SBox1:"<<result;
}
}



void fk(char *input,char* key)
{
char temp[9],buff[2];

if(strlen(input)!=4 || strlen(key)!=8)
{
cout<<"Wrong input!!!";
return;
}
//Expansion and Permutation E/P
temp[0]=temp[6]=input[3];
temp[1]=temp[7]=input[0];
temp[2]=temp[4]=input[1];
temp[3]=temp[5]=input[2];
temp[8]=NULL;

xor(temp,key); //Xor with key...
strcpy(temp,result);

input_to_sbox[0]=temp[0];
input_to_sbox[1]=temp[1];
input_to_sbox[2]=temp[2];
input_to_sbox[3]=temp[3];
input_to_sbox[4]=NULL;

char str1[2],str2[2];

strset(result,'\0');
s_box(0);
result[2]='\0';
strcpy(str1,result);

input_to_sbox[0]=temp[4];
input_to_sbox[1]=temp[5];
input_to_sbox[2]=temp[6];
input_to_sbox[3]=temp[7];
input_to_sbox[4]=NULL;

strset(result,'\0');
s_box(1);
result[2]='\0';
strcat(str1,result);

result[0]=str1[1];
result[1]=str1[3];
result[2]=str1[2];
result[3]=str1[0];
result[4]=NULL;

//strcpy(result,s_box_result);
}

void generate_sub_keys(char key[])
{

int k1_order[]={0,6,8,3,7,2,9,5};
int k2_order[]={7,2,5,4,9,1,8,0};

for(int i=1;i<=8;i++)
{
key1[i-1]=key[k1_order[i-1]];
key2[i-1]=key[k2_order[i-1]];
}
key1[8]=key2[8]=NULL;
}//void generate_sub_keys()


void ip(char str[])
{

result[0]=str[1];
result[1]=str[5];
result[2]=str[2];
result[3]=str[0];
result[4]=str[3];
result[5]=str[7];
result[6]=str[4];
result[7]=str[6];
result[8]=NULL;

}

void ip_inverse(char str[])
{

result[0]=str[3];
result[1]=str[0];
result[2]=str[2];
result[3]=str[4];
result[4]=str[6];
result[5]=str[1];
result[6]=str[7];
result[7]=str[5];
result[8]=NULL;

}

int convert_to_dec(long int bin)
{
int n=0,c=0,temp;

while(bin>0)
{
temp=bin%10;
bin/=10;
n+=pow(2,c)*temp;
c++;
}
return n;
}

void getachar(int ch,int len=8)
{
long int n,dec,temp,bin=0,c=0,counter=0;
char str[10],tmp_str[10];

//cout<<"Enter a Character:";
//dec=getche();
dec=ch;
while(dec>0)
{
temp=dec%2;
dec/=2;
bin+=pow10(c)*temp;
c++;
}

n=bin;

strset(tmp_str,'\0');
strset(str,'\0');

while(n>0)
{
temp=n%10;
n/=10;
tmp_str[counter]=temp+48;
counter++;
///cout<<'\t'<<temp;
}
tmp_str[counter]=NULL;
strrev(tmp_str);

counter=len-counter;

for(int i=0;i<counter;i++)
str[i]='0';

str[i]=NULL;

strcat(str,tmp_str);

strcpy(result,str);
}

void main()
{

char in_file_path[50],out_file_path[50];
char ch,choice;
char plain_text[9],cipher_text[9];
char l[5],r[5];
char buff[9];
char pass[25];
int i,tmp;

strcpy(sbox0[0],"1032");
strcpy(sbox0[1],"3210");
strcpy(sbox0[2],"0213");
strcpy(sbox0[3],"3132");

strcpy(sbox1[0],"0123");
strcpy(sbox1[1],"2013");
strcpy(sbox1[2],"3010");
strcpy(sbox1[3],"2103");

//strcpy(key,"1010101101");

menu:
clrscr();
cout<<"Enter Your Option..."<<endl;
cout<<"Encrypt a File ??? 1"<<endl;
cout<<"Decrypt a File ??? 2"<<endl;
cout<<"Quit ??? 3"<<endl;

choice=getch();

switch(choice)
{

case '1':

cout<<"Enter the file to be Encrypted:";
cin>>in_file_path;

cout<<"Enter a name for the Encrypted file:";
cin>>out_file_path;


cout<<"Enter Password(key):";
cin>>pass;

tmp=0;
cout<<endl<<"Pass:";
for(i=0;i<strlen(pass);i++)
{
cout<<pass[i];
tmp+=(int)pass[i];
}

tmp%=1024;

getachar(tmp,10);

strcpy(key,result);

ifstream in_file(in_file_path);



if(!in_file)
{
cout<<"File not Found!!!\a";
getch();
goto menu;
}

ofstream out_file(out_file_path);

while(in_file.get(ch)!=NULL)
{
//cout<<ch;

long int n,dec,temp,bin=0,c=0,counter=0;
char str[9],tmp_str[9];

dec=ch;

while(abs(dec)>0)
{
temp=dec%2;
dec/=2;
bin+=pow10(c)*temp;
c++;
}

n=bin;

strset(tmp_str,'\0');
strset(str,'\0');

while(abs(n)>0)
{
temp=n%10;
n/=10;
tmp_str[counter]=temp+48;
counter++;
///cout<<'\t'<<temp;
}
tmp_str[counter]=NULL;
strrev(tmp_str);

counter=8-counter;

for(i=0;i<counter;i++)
str[i]='0';

strcat(str,tmp_str);
strcpy(plain_text,str);
bin=0;

//cout<<endl<<"Plain Text:"<<plain_text;
/*
cout<<"Enter The 8-bit Plain Text:";
cin>>plain_text;
cout<<"Enter The 10-bit Key:";
cin>>key;
*/

//strcpy(key,"1100111001");

//*************************Start of Encryption********************************

//Generate Sub keys k1 and k2...
generate_sub_keys(key);

// Initial Permutation...
ip(plain_text);

strcpy(plain_text,result);

l[0]=plain_text[0];
l[1]=plain_text[1];
l[2]=plain_text[2];
l[3]=plain_text[3];
l[4]=NULL;

r[0]=plain_text[4];
r[1]=plain_text[5];
r[2]=plain_text[6];
r[3]=plain_text[7];
r[4]=NULL;

fk(r,key1);//Fk1...
strcpy(buff,result);

xor(buff,l);// Xor with left...

//Switch the blocks...
strcpy(buff,result);
strcpy(l,r);
strcpy(r,buff);

fk(r,key2);//Fk1...
strcpy(buff,result);

xor(buff,l); // Xor with left...
strcpy(buff,result);
strcpy(l,buff);

strcpy(cipher_text,l);
strcat(cipher_text,r);

//cout<<"Cipher before IP-1:"<<cipher_text;

ip_inverse(cipher_text);
strcpy(cipher_text,result);

//cout<<endl<<"Cipher Text:"<<cipher_text;
bin=0;
for(i=7;i>=0;i--)
bin+=pow(10,7-i)*((int)cipher_text[i]-48);

//cout<<endl<<bin;

dec=convert_to_dec(bin);
//cout<<(char)dec;

out_file.put(dec);

}//while(in_file.get(ch)!=NULL)...

out_file.close();
break;

case '2':

cout<<"Enter the file to be Decrypted:";
cin>>in_file_path;

cout<<"Enter a name for the Decrypted file:";
cin>>out_file_path;

cout<<"Enter Password(key):";
cin>>pass;

tmp=0;
cout<<endl<<"Pass:";
for(i=0;i<strlen(pass);i++)
{
cout<<pass[i];
tmp+=(int)pass[i];
}

tmp%=10241;

getachar(tmp,10);

strcpy(key,result);

ifstream in_file_de(in_file_path);

if(!in_file_de)
{
cout<<"File not Found!!!\a";
getch();
goto menu;
}
ofstream out_file_de(out_file_path);

long int dec=0,bin=0;

while(in_file_de.get(ch)!=NULL)
{
//*************************Start of Decryption********************************
dec=ch;
if(dec<0)
dec+=256;
getachar(dec);

result[8]=NULL;
strcpy(cipher_text,result);
generate_sub_keys(key);
ip(cipher_text);
strcpy(cipher_text,result);

l[0]=cipher_text[0];
l[1]=cipher_text[1];
l[2]=cipher_text[2];
l[3]=cipher_text[3];
l[4]=NULL;

r[0]=cipher_text[4];
r[1]=cipher_text[5];
r[2]=cipher_text[6];
r[3]=cipher_text[7];
r[4]=NULL;

fk(r,key2);//Fk1...
strcpy(buff,result);

xor(buff,l);// Xor with left...

//Switch the blocks...
strcpy(buff,result);
strcpy(l,r);
strcpy(r,buff);

fk(r,key1);//Fk1...
strcpy(buff,result);

xor(buff,l); // Xor with left...
strcpy(buff,result);
strcpy(l,buff);

strcpy(cipher_text,l);
strcat(cipher_text,r);

//cout<<"Cipher before IP-1:"<<cipher_text;

ip_inverse(cipher_text);
strcpy(plain_text,result);

//cout<<endl<<"Plain Text:"<<plain_text;
bin=0;
for(i=7;i>=0;i--)
bin+=pow(10,7-i)*((int)plain_text[i]-48);

//cout<<endl<<bin;

dec=convert_to_dec(bin);

cout<<endl<<"The Decrypted char is:\'"<<(char)dec<<'\''<<endl<<"Its Ascii is:"<<dec;


out_file_de<<(char)dec;
//*************************End of Decryption**********************************
}//while..
out_file_de.close();
in_file_de.close();
break;

case '3':
break;

default:
goto menu;

}//switch(choice)...


}//main()...