├── README.md
├── caesarCipher.cpp
├── eulerTotient.cpp
└── playfairCipher.cpp


/README.md:
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1 | # css - Cryptography and Security Systems
2 | 


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/caesarCipher.cpp:
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  1 | #pragma GCC optimize("Ofast")
  2 | #pragma GCC optimize("unroll-loops")
  3 | 
  4 | #include <bits/stdc++.h>
  5 | 
  6 | using namespace std;
  7 | 
  8 | typedef long long int           ll;
  9 | typedef unsigned long long int  ull;
 10 | typedef long double             ld;
 11 | 
 12 | typedef pair<ll,ll>             pll;
 13 | typedef vector<ll>              vll;
 14 | typedef vector<pll>             vpll;
 15 | typedef map<ll, ll>             mll;
 16 | typedef map<char, ll>           mcl;
 17 | 
 18 | #define inf                 1<<30
 19 | #define mx9                 1000000007
 20 | #define test(t)             int t; cin >> t; while(t--)
 21 | #define f(i, a, b)          for(int (i) = (a); (i) < (b); ++(i))
 22 | #define all(a)              (a).begin(), (a).end()
 23 | #define endl                "\n"
 24 | #define ff                  first
 25 | #define ss                  second
 26 | #define pb                  push_back
 27 | #define deb(x)              cout << #x << ": " << x << endl;
 28 | #define deb2(x,y)           cout << #x << ": " << x << " ~ " <<  #y << ": " << y << endl;
 29 | #define deba(arr)           cout << #arr << " ~ [ "; for(auto n: arr) cout << n << " "; cout << "]" << endl;
 30 | #define debap(arr)          cout << #arr << " ~ [ "; for(auto n: arr) cout << n.first << "-" << n.second << " "; cout << "]" << endl;
 31 | #define fast                ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
 32 | 
 33 | void solve()
 34 | {
 35 |     mcl mapChar;
 36 |     map<ll, char> cntMap;
 37 |     ll cnt = 0;
 38 |     for (char c = 'a'; c <= 'z'; c++) {
 39 |         mapChar[c] = cnt;
 40 |         cntMap[cnt] = c;
 41 |         cnt += 1;
 42 |     }
 43 | 
 44 |     // STARTS
 45 |     ll type;
 46 |     cin >> type;
 47 |     ll toBeEncrypted = 1;
 48 |     ll toBeDecrypted = 2;
 49 | 
 50 |     if(type == toBeEncrypted) {
 51 |         // Encryption
 52 |         string input;
 53 |         cin >> input;
 54 | 
 55 |         ll key;
 56 |         cin >> key;
 57 | 
 58 |         string decrypted = "";
 59 |         ll encryptedLength = input.length();
 60 |         f(i, 0, encryptedLength) {
 61 |             if(input[i] == ' ')
 62 |                 continue;
 63 |             decrypted += (cntMap[(mapChar[input[i]] + key) % 26]);
 64 |         }
 65 |         cout << decrypted << endl;
 66 |     } 
 67 |     else {
 68 |         // Decryption
 69 |         string input;
 70 |         cin >> input;
 71 | 
 72 |         ll key;
 73 |         cin >> key;
 74 | 
 75 |         string encrypted = "";
 76 |         ll decryptedLength = input.length();
 77 |         f(i, 0, decryptedLength) {
 78 |             if(input[i] == ' ')
 79 |                 continue;
 80 |             ll curr = mapChar[input[i]] - key;
 81 |             if(curr < 0) {
 82 |                 curr += 26;
 83 |             }
 84 |             encrypted += (cntMap[curr]);
 85 |         }
 86 |         cout << encrypted << endl;
 87 |     }
 88 |     cout << endl;
 89 | }
 90 | 
 91 | int main()
 92 | {
 93 |     fast;
 94 |     #ifndef ONLINE_JUDGE
 95 |         freopen("input.txt", "r", stdin);
 96 |         freopen("output.txt", "w", stdout);
 97 |     #endif
 98 |     test(t)
 99 |         solve();
100 |     return 0;
101 | }
102 | 
103 | /*
104 | 6
105 | 
106 | 1
107 | abc
108 | 5
109 | 
110 | 1
111 | abc
112 | 1
113 | 
114 | 1
115 | tushar
116 | 8
117 | 
118 | 2
119 | fgh
120 | 5
121 | 
122 | 2
123 | bcd
124 | 1
125 | 
126 | 2
127 | bcapiz
128 | 8
129 | */
130 | 
131 | /*
132 | fgh
133 | bcd
134 | bcapiz
135 | abc
136 | abc
137 | tushar
138 | */


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/eulerTotient.cpp:
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  1 | #pragma GCC optimize("Ofast")
  2 | #pragma GCC optimize("unroll-loops")
  3 | 
  4 | #include <bits/stdc++.h>
  5 | 
  6 | using namespace std;
  7 | 
  8 | typedef long long int           ll;
  9 | typedef unsigned long long int  ull;
 10 | typedef long double             ld;
 11 | 
 12 | typedef pair<ll,ll>             pll;
 13 | typedef vector<ll>              vll;
 14 | typedef vector<pll>             vpll;
 15 | typedef map<ll, ll>             mll;
 16 | typedef map<char, ll>           mcl;
 17 | 
 18 | #define inf                 1<<30
 19 | #define mx9                 1000000007
 20 | #define test(t)             int t; cin >> t; while(t--)
 21 | #define f(i, a, b)          for(int (i) = (a); (i) < (b); ++(i))
 22 | #define all(a)              (a).begin(), (a).end()
 23 | #define endl                "\n"
 24 | #define ff                  first
 25 | #define ss                  second
 26 | #define pb                  push_back
 27 | #define deb(x)              cout << #x << ": " << x << endl;
 28 | #define deb2(x,y)           cout << #x << ": " << x << " ~ " <<  #y << ": " << y << endl;
 29 | #define deba(arr)           cout << #arr << " ~ [ "; for(auto n: arr) cout << n << " "; cout << "]" << endl;
 30 | #define debap(arr)          cout << #arr << " ~ [ "; for(auto n: arr) cout << n.first << "-" << n.second << " "; cout << "]" << endl;
 31 | #define fast                ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
 32 | 
 33 | bool isPrime(int n)
 34 | {
 35 |     // Corner cases
 36 |     if (n <= 1)
 37 |         return false;
 38 |     if (n <= 3)
 39 |         return true;
 40 | 
 41 |     if (n % 2 == 0 || n % 3 == 0)
 42 |         return false;
 43 | 
 44 |     for (int i = 5; i * i <= n; i = i + 6)
 45 |         if (n % i == 0 || n % (i + 2) == 0)
 46 |             return false;
 47 | 
 48 |     return true;
 49 | }
 50 | 
 51 | ll formula(ll n) {
 52 |     if (n == 1) {
 53 |         return 1;
 54 |     }
 55 |     ll curr = n;
 56 |     mll mp;
 57 |     f(i, 2, sqrt(n) + 2) {
 58 |         if(isPrime(curr)) {
 59 |             mp[curr] += 1;
 60 |             curr = 1;
 61 |         }
 62 |         while(curr % i == 0) {
 63 |             curr /= i;
 64 |             mp[i] += 1;
 65 |         }
 66 |         if(curr == 1) {
 67 |             break;
 68 |         }
 69 |     }
 70 |     ld ans = n;
 71 |     for(auto it: mp) {
 72 |         ld abc = (ld)(1 - (ld)(1.0 / it.ff));
 73 |         ans *= (abc);
 74 |     }
 75 |     return ans;
 76 | }
 77 | 
 78 | ll eulerTotient(ll n) {
 79 |     if(n == 1) {
 80 |         return n;
 81 |     }
 82 |     if(isPrime(n)) {
 83 |         return n - 1;
 84 |     }
 85 |     ll curr = n;
 86 |     mll mp;
 87 |     f(i, 2, sqrt(n) + 2) {
 88 |         if(isPrime(curr)) {
 89 |             mp[curr] += 1;
 90 |             curr = 1;
 91 |         }
 92 |         while(curr % i == 0) {
 93 |             curr /= i;
 94 |             mp[i] += 1;
 95 |         }
 96 |         if(curr == 1) {
 97 |             break;
 98 |         }
 99 |     }
100 | 
101 |     ll ans = 1;
102 |     // debap(mp)
103 |     for(auto it: mp) {
104 |         f(i, 0, it.ss)
105 |             ans *= eulerTotient(it.ff);
106 |     }
107 |     return ans;
108 | }
109 | 
110 | void solve()
111 | {
112 |     ll n;
113 |     cin >> n;
114 |     // deb(n)
115 |     cout << formula(n) << endl;
116 | }
117 | 
118 | int main()
119 | {
120 |     fast;
121 |     #ifndef ONLINE_JUDGE
122 |         freopen("input.txt", "r", stdin);
123 |         freopen("output.txt", "w", stdout);
124 |     #endif
125 |     test(t)
126 |         solve();
127 |     return 0;
128 | }


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/playfairCipher.cpp:
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  1 | #pragma GCC optimize("Ofast")
  2 | #pragma GCC optimize("unroll-loops")
  3 | 
  4 | #include <bits/stdc++.h>
  5 | 
  6 | using namespace std;
  7 | 
  8 | typedef long long int           ll;
  9 | typedef unsigned long long int  ull;
 10 | typedef long double             ld;
 11 | 
 12 | typedef pair<ll,ll>             pll;
 13 | typedef vector<ll>              vll;
 14 | typedef vector<pll>             vpll;
 15 | typedef map<ll, ll>             mll;
 16 | typedef map<char, ll>           mcl;
 17 | 
 18 | #define inf                 1<<30
 19 | #define mx9                 1000000007
 20 | #define test(t)             int t; cin >> t; while(t--)
 21 | #define f(i, a, b)          for(int (i) = (a); (i) < (b); ++(i))
 22 | #define all(a)              (a).begin(), (a).end()
 23 | #define endl                "\n"
 24 | #define ff                  first
 25 | #define ss                  second
 26 | #define pb                  push_back
 27 | #define deb(x)              cout << #x << ": " << x << endl;
 28 | #define deb2(x,y)           cout << #x << ": " << x << " ~ " <<  #y << ": " << y << endl;
 29 | #define deba(arr)           cout << #arr << " ~ [ "; for(auto n: arr) cout << n << " "; cout << "]" << endl;
 30 | #define debap(arr)          cout << #arr << " ~ [ "; for(auto n: arr) cout << n.first << "-" << n.second << " "; cout << "]" << endl;
 31 | #define fast                ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
 32 | 
 33 | void solve()
 34 | {
 35 |     string input;
 36 |     cin >> input;
 37 | 
 38 |     string key;
 39 |     cin >> key;
 40 | 
 41 |     // MATRIX 
 42 |     char matrix[5][5];
 43 |     vector<char> matrixVector;
 44 |  
 45 |     mcl mapCharCnt;
 46 |     f(i, 0, key.length()) {
 47 |         char currChar = key[i];
 48 |         if(currChar == 'j') {
 49 |             currChar = 'i';
 50 |         }
 51 | 
 52 |         if (!mapCharCnt[currChar]) {
 53 |             matrixVector.pb(currChar);
 54 |             mapCharCnt[currChar] += 1;
 55 |         }
 56 |     }   
 57 | 
 58 |     for(char c = 'a'; c <= 'z'; c++) {
 59 |         if(mapCharCnt[c] || c == 'j') {
 60 |             continue;
 61 |         }
 62 | 
 63 |         matrixVector.pb(c);
 64 |         mapCharCnt[c] += 1;
 65 |     }
 66 | 
 67 |     // deba(matrixVector)
 68 | 
 69 |     map<char, pair<ll, ll>> coordinates;
 70 | 
 71 |     ll k = 0;
 72 |     // cout << "~ matrix ~" << endl;
 73 |     f(i, 0, 5) {
 74 |         f(j, 0, 5) {
 75 |             matrix[i][j] = matrixVector[k++];
 76 |             coordinates[matrix[i][j]] = {i, j};
 77 |             // cout << matrix[i][j] << " ";
 78 |         }
 79 |         // cout << endl;
 80 |     }
 81 |     // cout << endl;
 82 | 
 83 |     // ENCRYPTION
 84 | 
 85 |     string bogusChar = "x";
 86 |     ll inputLen = input.length();
 87 |     f(i, 0, input.length() - 1) {
 88 |         string curr = input;
 89 |         if(input[i] == input[i + 1]) {
 90 |             input = curr.substr(0, i + 1);
 91 |             input += bogusChar;
 92 |             input += curr.substr(i + 1, inputLen);
 93 |             inputLen += 1;
 94 |         }
 95 |     }
 96 |     
 97 | 
 98 |     // Length check
 99 | 
100 |     if(input.length() % 2) {
101 |         input += bogusChar;
102 |     }
103 | 
104 |     deb(input)
105 |     
106 |     string encrypted = "";
107 | 
108 |     f(i, 0, input.length() - 1) {
109 |         ll firstChar = input[i];
110 |         ll secChar = input[i + 1];
111 | 
112 |         ll firstCharX = coordinates[firstChar].ff;
113 |         ll firstCharY = coordinates[firstChar].ss;
114 | 
115 |         ll secCharX = coordinates[secChar].ff;
116 |         ll secCharY = coordinates[secChar].ss;
117 | 
118 |         // deb2(firstCharX, firstCharY)
119 |         // deb2(secCharX, secCharY)
120 | 
121 |         if(firstCharX == secCharX) {
122 |             ll first = firstCharY + 1;
123 |             ll sec = secCharY + 1;
124 |             first %= 5;
125 |             sec %= 5;
126 |             encrypted += matrix[firstCharX][first];
127 |             encrypted += matrix[secCharX][sec];
128 |         }
129 |         else if(firstCharY == secCharY) {
130 |             ll first = firstCharX + 1;
131 |             ll sec = secCharX + 1;
132 |             first %= 5;
133 |             sec %= 5;
134 |             encrypted += matrix[first][firstCharY];
135 |             encrypted += matrix[sec][secCharY];
136 |         } 
137 |         else {
138 |             encrypted += matrix[firstCharX][secCharY];
139 |             encrypted += matrix[secCharX][firstCharY];
140 |         }
141 |         i += 1;
142 |     }
143 |     cout << "encrypted: " << encrypted << endl << endl;
144 | }
145 | 
146 | int main()
147 | {
148 |     fast;
149 |     #ifndef ONLINE_JUDGE
150 |         freopen("input.txt", "r", stdin);
151 |         freopen("output.txt", "w", stdout);
152 |     #endif
153 |     test(t)
154 |         solve();
155 |     return 0;
156 | }
157 | 
158 | /*
159 | 
160 | 3
161 | abc
162 | college
163 | hammer
164 | college
165 | tushar
166 | nankani
167 | 
168 | */


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