Note: This source code has an Error. If you want a completely correct code, you'll have to ask me in the comments. I was under the impression that repeated letters are replaced with padding character(say X), instead of being inserted, while coding this. Hence the code reflects this output. I never really got around to change the code and fix this so since you've got a starting hint to write code for this cipher, Take it as a fun exercise to correct that mistake. Your debugging skills are being tested! :D
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#include <iostream>
#include <string>
using namespace std;
class Playfair
{
string keyword;
string ukey; //unrepeated keyword
string plain;
string cipher;
string generic="ABCDEFGHIKLMNOPQRSTUVWXYZ";
char pftable[5][5]; // 5x5 matrix table
public:
void setKey(string keyword)
{
this->keyword = keyword;
//Capitalize all characters and replace all j with i in keyword
for(int i=0;i<(int)keyword.length();i++)
{
keyword[i]=toupper((char)keyword[i]);
if(keyword[i]=='J'){keyword[i]='I';}
}
//find unrepeated characters in keyword
int x=0,itrepeated=0;
cout<<endl<<"Tracing the processes of playfair Cipher"<<endl;
for(int i=0;i<(int)keyword.length();i++)
{
for(int j=0;j<i;j++)
{
if (keyword[i]==keyword[j])
{
itrepeated++;
cout<<"Discard Repeated Character->";
}
}
if (itrepeated==0)
{
cout<<"Store Non-Repeated Character to ukey("<<x<<")-";
ukey+=keyword[i]; //Note to self: don't use ukey[x] index on this part since ukey is unallocated pointer
x++;
}
cout<<keyword[i]<<"--> obtained from keyword("<<i<<") "<<endl;
itrepeated=0;
}
cout<<endl<<"Length of keyword("<<keyword<<") = "<<keyword.length()<<"; removing repetitions("<<ukey<<") = "<<ukey.length()<<endl;
//Now its time to put this ukey in matrix form of 5x5
//Inserting into matrix
cout<<endl<<"Inserting unrepeated keyword into playfair table in matrix form 5x5::";
//First inserting ukey[k]
int a=-1,b=0;
for(int i=0;i<(int)ukey.length();i++)
{
if(i%5==0){cout<<endl;b=0;a++;}
pftable[a][b]=(char)ukey[i];
cout<<pftable[a][b]<<"["<<a<<"]"<<"["<<b<<"]"<<" "; //JUST TRACING (Uncomment this line to see trace result)
b++;
}
x=0;
itrepeated=0;
for(int i=0;i<(int)generic.length();i++)
{
for(int j=0;j<(int)ukey.length();j++)
{
if(generic[i]==(char)ukey[j])
{
itrepeated++;
break;
}
}
if(!itrepeated)
{
if(((int)ukey.length()+x)%5==0){cout<<endl;b=0;a++;}
pftable[a][b]=(char)generic[i];
cout<<pftable[a][b]<<"["<<a<<"]"<<"["<<b<<"]"<<" ";// JUST TRACING (Uncomment this line to see trace result)
x++;
b++;
}
itrepeated=0;
}
//At this point, keyword is properly formatted into the 5x5 matrix
}
void setPlain(string plain)
{
this->plain = plain;
}
void setCipher(string cipher)
{
this->cipher = cipher;
}
int * MapThisLetter(char Char2m)
{
static int r[2];
r[0]=0;
r[1]=0;
for(int i=0;i<5;i++){
for(int j=0;j<5;j++){
if(pftable[i][j]==Char2m){
cout<<pftable[i][j];
r[0]=i;
r[1]=j;
break;
}
}
}
return r;
}
void encrypt()
{
int *position;
bool flag=0;
int indexx1;
int indexy1;
int indexx2;
int indexy2;
for(int i=0;i<(int)plain.length();i++)
{
plain[i]=toupper((char)plain[i]);
if(plain[i]=='J'){plain[i]='I';}
}
cout<<endl<<endl<<"Now mapping each letter to its corresponding cipher character from the playfair table:"<<endl;
for(int i=0;i<(int)plain.length();i++)
{
position=MapThisLetter(toupper((char)plain[i++]));
indexx1=*(position);
indexy1=*(position+1);
cout<<"["<<indexx1<<","<<indexy1<<"] & ";
if(((char)plain[i-1]==(char)plain[i]) || (i>=(int)plain.length() && (int)plain.length()%2!=0)){
position=MapThisLetter('X');
indexx2=*(position);
indexy2=*(position+1);
cout<<"["<<indexx2<<", "<<indexy2<<"]";
flag=1;//Indicates (a letter has been replaced with X) OR (a position has been padded with X)
}// breaks at last line if odd length plaintext is entered
if(!flag){
position=MapThisLetter(toupper((char)plain[i]));
indexx2=*(position);
indexy2=*(position+1);
cout<<"["<<indexx2<<", "<<indexy2<<"]";
}
//at shis point we already have x1,y1 and x2,y2 available for two letters of plaintext at a time.
//now we apply certain conditional comparisions
if(indexx1==indexx2){
//if x1==x2 i.e. when horizontal match then right shift
indexy1=(indexy1+1)%4;
indexy2=(indexy2+1)%4;
cout<<" maps to: "<< pftable[indexx1][indexy1]<<"["<<indexx1<<", "<<indexy1<<"] & "<< pftable[indexx2][indexy2]<<"["<<indexx2<<", "<<indexy2<<"] respectively"<<endl;
}
else if(indexy1==indexy2){
//if y1==y2 i.e when vertical match then down shift
indexx1=(indexx1+1)%4;
indexx2=(indexx2+1)%4;
cout<<" maps to: "<< pftable[indexx1][indexy1]<<"["<<indexx1<<", "<<indexy1<<"] & "<< pftable[indexx2][indexy2]<<"["<<indexx2<<", "<<indexy2<<"] respectively"<<endl;
}
else{
//exchange x1 and x2 in boxes
indexy1=indexy1+indexy2;
indexy2=indexy1-indexy2;
indexy1=indexy1-indexy2;
cout<<" maps to: "<< pftable[indexx1][indexy1]<<"["<<indexx1<<", "<<indexy1<<"] & "<< pftable[indexx2][indexy2]<<"["<<indexx2<<", "<<indexy2<<"] respectively"<<endl;
}
cipher+=pftable[indexx1][indexy1];
cipher+=pftable[indexx2][indexy2];
if(flag){//this flag is TRUE IF (selected both string are same) or (odd End-of-line has been reached)
if((char)plain[i-1]==(char)plain[i]){flag=0;}//reseting the flag to Not-END-of-Line IFF selected both letters are the same
if(flag){break;} //no resetting; break IF odd End-of-line is padded with character X at the last position
}
}
}
void decrypt()
{
int *position;
bool flag=0;
int indexx1;
int indexy1;
int indexx2;
int indexy2;
cout<<endl<<endl<<"Now mapping each letter to its corresponding cipher character from the playfair table:"<<endl;
for(int i=0;i<(int)cipher.length();i++)
{
position=MapThisLetter(toupper((char)cipher[i++]));
indexx1=*(position);
indexy1=*(position+1);
cout<<"["<<indexx1<<","<<indexy1<<"] & ";
if(((char)cipher[i-1]==(char)cipher[i]) || (i>=(int)cipher.length() && (int)cipher.length()%2!=0)){
position=MapThisLetter('X');
indexx2=*(position);
indexy2=*(position+1);
cout<<"["<<indexx2<<", "<<indexy2<<"]";
flag=1;//Indicates (a letter has been replaced with X) OR (a position has been padded with X)
}// breaks at last line if odd length plaintext is entered
if(!flag){
position=MapThisLetter(toupper((char)cipher[i]));
indexx2=*(position);
indexy2=*(position+1);
cout<<"["<<indexx2<<", "<<indexy2<<"]";
}
//at shis point we already have x1,y1 and x2,y2 available for two letters of plaintext at a time.
//now we apply certain conditional comparisions
if(indexx1==indexx2){
//if x1==x2 i.e. when horizontal match then LEFT shift
indexy1=(indexy1-1)%4;
indexy2=(indexy2-1)%4;
cout<<" maps to: "<< pftable[indexx1][indexy1]<<"["<<indexx1<<", "<<indexy1<<"] & "<< pftable[indexx2][indexy2]<<"["<<indexx2<<", "<<indexy2<<"] respectively"<<endl;
}
else if(indexy1==indexy2){
//if y1==y2 i.e when vertical match then UP shift
indexx1=(indexx1-1)%4;
indexx2=(indexx2-1)%4;
cout<<" maps to: "<< pftable[indexx1][indexy1]<<"["<<indexx1<<", "<<indexy1<<"] & "<< pftable[indexx2][indexy2]<<"["<<indexx2<<", "<<indexy2<<"] respectively"<<endl;
}
else{
//exchange x1 and x2 in boxes
indexy1=indexy1+indexy2;
indexy2=indexy1-indexy2;
indexy1=indexy1-indexy2;
cout<<" maps to: "<< pftable[indexx1][indexy1]<<"["<<indexx1<<", "<<indexy1<<"] & "<< pftable[indexx2][indexy2]<<"["<<indexx2<<", "<<indexy2<<"] respectively"<<endl;
}
plain+=pftable[indexx1][indexy1];
plain+=pftable[indexx2][indexy2];
if(flag){//this flag is TRUE IF (selected both string are same) or (odd End-of-line has been reached)
if((char)cipher[i-1]==(char)cipher[i]){flag=0;}//reseting the flag to Not-END-of-Line IFF selected both letters are the same
if(flag){break;} //no resetting; break IF odd End-of-line is padded with character X at the last position
}
}
}
string getPlainText()
{
return plain;
}
string getCipherText()
{
return cipher;
}
};
int main()
{
Playfair playfair;
int choice=1;//just for testing first choice
string plain,cipher,keyword,ukey;
cout<<"Playfair:: Enter 1 for Encryption or, 2 for Decryption-";
cin>>choice;
if(choice == 1)
{
/* encryption */
cout<<"Enter keyword-";
cin>>keyword;
cout<<"Enter plain text-";
cin>>plain;
playfair.setKey(keyword);
playfair.setPlain(plain);
playfair.encrypt();
cout<<endl<<"Finally, we have the Cipher text = "<<playfair.getCipherText()<<endl;
}
else if(choice == 2)
{
/* decryption */
cout<<"Enter key-";
cin>>keyword;
cout<<"Enter cipher text-";
cin>>cipher;
playfair.setKey(keyword);
playfair.setCipher(cipher);
playfair.decrypt();
cout<<endl<<"Finally, we have the Plain text = "<<playfair.getPlainText()<<endl;
}
return 0;
}
Try it yourself!
Note: I was under the impression that repeated letters are replaced with padding character(say X) while coding this. Hence the code reflects this output. I never really got around to change the code and fix this so please Take it as a fun exercise to correct that mistake. Your debugging skills are being tested! :D
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