Added Play Fair Cipher In CPP

algorithms/PlayFairCipher/cpp/PlayFairCipherDecryption.cpp

@@ -0,0 +1,282 @@
+//Playfair Cipher
+//CODE BY JATIN DHALL
+//A playfair cipher has a 5X5 playfair matrix which is used for encryption as well as decryption
+#include <iostream>
+#include <cstring>
+#include <cctype>
+#include <algorithm>
+#include <iterator>
+#include <vector>
+#include <unordered_set>
+
+using namespace std;
+
+char playfairMatrix[5][5];  
+string alphabets = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+
+// Function to remove all spaces from a given string
+string removeSpaces(string str)
+{
+    str.erase(remove(str.begin(), str.end(), ' '), str.end());
+    return str;
+}
+
+vector<char> getVectorFromString(string str)
+{
+    vector<char> res;
+    vector<char>::iterator it;
+    for(int i=0;i<str.length();i++)
+    {
+        // std::find function call
+        it = std::find (res.begin(), res.end(), str.at(i));
+        if (it != res.end())
+        {
+            continue;
+        }
+        else
+            res.push_back(str.at(i));
+    }
+    return res;
+}
+
+void dispKeyMatrix()
+{
+    cout<<"Key Matrix is :-"<<endl;
+    for(int i=0;i<5;i++)
+    {
+        for(int j=0;j<5;j++)
+        {
+            cout<<playfairMatrix[i][j]<<" ";
+        }
+        cout<<endl;
+    }
+}
+
+void dispPairVectors(vector<pair<char,char>> pairs)
+{
+    for(int i=0;i<pairs.size();i++)
+    {
+        cout<<pairs.at(i).first<< " "<<pairs.at(i).second<<endl;
+    }
+}
+
+void createPlayFairMatrix(string key)
+{
+    int lengthKey = key.length();
+
+    int count = 0,count1 = 0;
+    int flag = 0;
+
+    string alphabets = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+
+    vector<char> result = getVectorFromString(key);
+
+    //Creating the 5x5 Matrix
+    for(int i=0;i<5;i++)
+    {
+        for(int j=0;j<5;j++)
+        {
+            if(count < result.size())
+            {
+                playfairMatrix[i][j] = toupper(result.at(count));
+                alphabets.erase(remove(alphabets.begin(), alphabets.end(), toupper(result.at(count))), alphabets.end());
+                if(toupper(result.at(count)) == 'I')
+                {
+                     alphabets.erase(remove(alphabets.begin(), alphabets.end(), toupper('J')), alphabets.end());
+                }
+                else if(toupper(result.at(count)) == 'J')
+                {
+                     alphabets.erase(remove(alphabets.begin(), alphabets.end(), toupper('I')), alphabets.end());
+                }
+                cout<<"Count : "<<count<<" CHAR : "<<result.at(count)<<" Alphabets : "<<alphabets<<endl;
+                count++;
+            }
+            else if(count1 < alphabets.length())
+            {
+                playfairMatrix[i][j] = toupper(alphabets.at(count1));
+                if(alphabets.at(count1) == 'I')
+                {
+                     alphabets.erase(remove(alphabets.begin(), alphabets.end(), toupper('J')), alphabets.end());
+                }
+                else if(alphabets.at(count1) == 'J')
+                {
+                     alphabets.erase(remove(alphabets.begin(), alphabets.end(), toupper('I')), alphabets.end());
+                }
+                cout<<"Count : "<<count1<<" CHAR : "<<alphabets.at(count1)<<" Alphabets : "<<alphabets<<endl;
+                count1++;
+            }
+        }
+    }
+
+    dispKeyMatrix();
+}
+
+vector<pair<char, char>> CipherText_To_Pairs(string text)
+{
+    vector<pair<char,char>> pairs;
+    cout<<"The length of the text is : "<<text.length()<<endl;
+    if(text.length() % 2 == 0){ //If text length is even, then nothing to worry about, but if the text lenght is odd then, 
+    //the last letter gets left out, so we have to increase the length by 2 and add 'X' as the last character
+        for(int i=0;i<text.length();i=i+2)
+        {
+            char a1 = toupper(text.at(i));
+            char a2 = toupper(text.at(i+1));
+            if(a1 == a2)
+            {
+                a2 = 'X';
+            }
+            pairs.push_back(make_pair(a1,a2));
+        }
+    }
+    else
+    {
+        for(int i=0;i<text.length() + 1;i=i+2)//If the text length is 5, then at the last iteration, i = 4, hence i<5+1 (6)
+        {
+            char a1 = toupper(text.at(i));
+            char a2;
+            if(i == text.length() - 1) // If the text length is 5, then in this loop,i at the last iteration would be 4, hence 5-1 = 4
+            {
+                a2 = 'X';
+            }
+            else{
+                a2 = toupper(text.at(i+1));
+            }
+            if(a1 == a2)
+            {
+                a2 = 'X';
+            }
+            pairs.push_back(make_pair(a1,a2));
+            cout<<a1<<" "<<a2<< " "<<i<<endl;
+        }
+    }
+
+    cout<<"The Pairs Formed from the text are :- "<<endl;
+    dispPairVectors(pairs);
+    return pairs;
+}
+
+pair<int,int> IndexInMatrix(char c)
+{
+    pair<int,int> res;
+    for(int i=0;i<5;i++)
+    {
+        for(int j=0;j<5;j++)
+        {
+            if(playfairMatrix[i][j] == c || c == 'I' && playfairMatrix[i][j] == 'J' || c == 'J' && playfairMatrix[i][j] == 'I')
+            {
+                res = make_pair(i,j);
+                return res;
+            }
+        }
+    }
+    return res;
+}
+pair<char,char> generalCase(pair<char,char> substring) //When the letters are not in the same row or column etc.
+{
+    pair<int,int> coord1,coord2;
+    pair<char,char> plainstring;
+    coord1 = IndexInMatrix(substring.first);
+    coord2 = IndexInMatrix(substring.second);
+
+    plainstring = make_pair(playfairMatrix[coord1.first][coord2.second],playfairMatrix[coord2.first][coord1.second]);
+
+    return plainstring;
+}
+
+pair<char,char> sameRow(pair<char,char> substring) // When the letters are on the same row of the playFair Matrix
+{
+    pair<int,int> coord1,coord2;
+    pair<char,char> plainstring;
+    coord1 = IndexInMatrix(substring.first);
+    coord2 = IndexInMatrix(substring.second);
+
+    int c1,c2,c3,c4;
+    c1 = coord1.first;
+    c2 = coord1.second-1;
+    c3 = coord2.first;
+    c4 = coord2.second-1;
+
+    if(c2<0)
+    {
+        c2 = 4;
+    }
+    else if(c4<0)
+    {
+        c4 = 4;
+    }
+    plainstring = make_pair(playfairMatrix[c1][c2],playfairMatrix[c3][c4]);
+
+    return plainstring;
+}
+
+pair<char,char> sameColumn(pair<char,char> substring) // When the letters are on the same column of the playFair Matrix
+{
+    pair<int,int> coord1,coord2;
+    pair<char,char> plainstring;
+    coord1 = IndexInMatrix(substring.first);
+    coord2 = IndexInMatrix(substring.second);
+
+    int c1,c2,c3,c4;
+    c1 = coord1.first-1;
+    c2 = coord1.second;
+    c3 = coord2.first-1;
+    c4 = coord2.second;
+
+    if(c1<0)
+    {
+        c1 = 4;
+    }
+    else if(c3<0)
+    {
+        c3 = 4;
+    }
+
+    plainstring = make_pair(playfairMatrix[c1][c2],playfairMatrix[c3][c4]);
+    return plainstring;
+}
+
+string PlayFairDecode(vector<pair<char,char>> result)
+{
+    string decodedString = "";
+    pair<int,int> coord1,coord2;
+    pair<char,char> substring,decodedPair;
+
+    cout<<"The Encoded Pairs are :-"<<endl;
+    for(int i=0;i<result.size();i++)
+    {
+        substring = result.at(i);
+        coord1 = IndexInMatrix(substring.first);
+        coord2 = IndexInMatrix(substring.second);
+
+        if(coord1.first == coord2.first){decodedPair = sameRow(substring);}
+        else if(coord1.second == coord2.second){decodedPair = sameColumn(substring);}
+        else{decodedPair = generalCase(substring);}
+
+        decodedString += decodedPair.first; 
+        decodedString += decodedPair.second;
+
+        cout<<decodedPair.first<<" "<<decodedPair.second<<endl;
+    }
+
+    return decodedString;
+}
+
+//Driver Code
+int main()
+{
+    string text;
+    cout<<"Enter the Text you want to Decode using PlayFair Cipher : ";
+    getline(cin,text);
+    text = removeSpaces(text);
+    string key;
+    cout<<"Enter the Key : ";
+    getline(cin,key);
+    key = removeSpaces(key);
+
+    createPlayFairMatrix(key);
+
+    vector<pair<char,char>> result =  CipherText_To_Pairs(text);
+
+    string decodedString = PlayFairDecode(result);
+    cout<<"The Decoded String is : "<<decodedString<<endl;
+}