Implementation of Simple Data Encryption Standard (SDES) in C++
Algorithm:
Step 1: Start the program. Step 2: Declare the necessary variables and functions.
Step 3: Get the plain text from the user
Step 4: Generate the key for encrypting the plain text.
Step 5: Encrypt the plain text using the generated key.
Step 6: Display the encrypted text.
Step 7: Terminate the program. Source code: #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], key2[9], 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(t emp1); temp1[0]=input_to_sbox[1 ];
temp1[1]=input_to_sbox[2 ]; temp1[2]=NULL; column=convert_to_decim al(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,coun ter=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_p ath[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,coun ter=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<<'\''<<en dl<<"Its Ascii is:"<<dec;
out_file_de<<(char)dec; //******************** *****End of Decryption************* ********************* }
out_file_de.close(); in_file_de.close(); break; case '3': break; default: goto menu; } } Output: S-DES
Do you want to use the predetermined key(y/n)? y Please specify plain text(10 BITS) : ben
PlainText = 00000000 [ +0 in decimal] Key = 0000100000 [ +32 in decimal] Encrypt Cipher Text = 00101011 [+43 in decimal] Decrypt Decrypted Ciphertext = 00000000 [ +0 in decimal S-DES
Do you want to use the predetermined key(y/n)? n
Viva Questions:
1. How many keys are used for encryption and decryption in S-DES? For the encryption of the plain text in S-DES two keys are used. 2. Define encryption and decryption? Encryption is the process for converting the plain text into hidden text that cannot be understood my others. Decryption is the process of converting the cipher text into plain text. 3. Define symmetric and asymmetric encryption? In symmetric encryption the same key is used for both encryption and decryption. Whereas in asymmetric encryption different key is used for encryption and decryption. 4. What type of encryption is S-DES? S-DES is a symmetric encryption. 5. What is the size of
the keys in SDES? Two 8-bit keys are used for encryption & decryption in SDES.
