Added encoder function

Fixed XOR operator
TODO - Add boilerplate from syllabus file, then merge with main branch

Codes/CRC.cpp

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+#include <iostream>
+#include <cstring>
+using namespace std;
+
+string XOR(string data, string key) {
+    // Dividend is data
+    // Divisor is the primary key, i.e. the key
+    string result = "";
+    int dataLen = data.length();
+    int keyLen = key.length();
+
+    // Perform XOR operation
+    for (int i=0; i<keyLen; i++) {
+        if (i < dataLen) {
+            // Only perform XOR if within the length of data
+            if (data[i] == key[i]) {
+                result += '0';
+            }
+            else {
+                result += '1';
+            }
+        } else {
+            // If data length exceeded, append the key
+            result += key[i];
+        }
+    }
+    return result;
+}
+
+string encoder(string data, string key) {
+    int keyLen = key.length();
+
+    // Append n-1 zeroes to the data
+    string dataWithZeroes = data + string(keyLen-1, '0');
+
+    // Perform XOR operation with the key
+    string remainder = XOR(dataWithZeroes, key);
+
+    // Get the remainder (last n-1 bits)
+    string crc = remainder.substr(remainder.length() - (keyLen-1));
+
+    // Append the CRC to the original data
+    return data + crc;
+}
+
+int main() {
+    string data, key;
+
+    cout << endl << "Enter data:\t";
+    getline(cin, data);
+    cout << "Enter primary key:\t";
+    getline(cin, key);
+
+    string messageToSend = encoder(data, key);
+    cout<<endl<<"--------------------"<<endl;
+    cout<<"Message to be sent:\t"<<messageToSend;
+    cout<<endl<<"--------------------"<<endl;
+
+    return 0;
+}
+
+// TODO:
+// - Check if input data is actually binary

README.md

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+# Computer Networks and Security
+
+This Git repository is a comprehensive resource for the Computer Networks and Security (CNS) course under the SPPU 2019 syllabus. It includes materials on fundamental concepts such as network architectures, protocols, and technologies, as well as practical implementations of client-server applications and insights into the data link layer and routing protocols. The repository also covers the application layer's role and essential network security topics, providing students with the knowledge and skills needed to master the course outcomes effectively.
+
+---