From 1c3e9f70b1640b3b2efa4e8c8b6cfbc2ba43986d Mon Sep 17 00:00:00 2001
From: Kshitij <kshitijk@tuta.io>
Date: Sun, 11 Aug 2024 21:55:12 +0530
Subject: [PATCH] Added recevier side checking for sent data.

---
 Codes/CRC.cpp | 49 ++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 44 insertions(+), 5 deletions(-)

diff --git a/Codes/CRC.cpp b/Codes/CRC.cpp
index 2e1a9d7..c8bb556 100644
--- a/Codes/CRC.cpp
+++ b/Codes/CRC.cpp
@@ -43,6 +43,35 @@ string encoder(string data, string key) {
     return data + crc;
 }
 
+string performDivision(string data, string key) {
+    int keyLen = key.length();
+
+    // Initialize with the data to be divided
+    string temp = data.substr(0, keyLen);
+
+    // Perform XOR operations on each segment
+    for (int i = keyLen; i < data.length(); i++) {
+        if (temp[0] == '1') {  // Only perform XOR if the leading bit is 1
+            temp = XOR(temp, key);
+        }
+        temp = temp.substr(1) + data[i];  // Shift left and add the next bit
+    }
+
+    // Perform the final XOR operation
+    if (temp[0] == '1') {
+        temp = XOR(temp, key);
+    }
+
+    // Extract the remainder (last keyLen-1 bits)
+    return temp.substr(temp.length() - (keyLen - 1));
+}
+
+// Function to check the correctness of received data
+bool checkData(string data, string key) {
+    string remainder = performDivision(data, key);
+    return (remainder.find('1') == string::npos); // No '1' means remainder is all zeros
+}
+
 int main() {
     string data, key;
 
@@ -51,13 +80,23 @@ int main() {
     cout << "Enter primary key:\t";
     getline(cin, key);
 
+    cout<<endl<<"Original data:\t"<<data;
+    cout<<endl<<"Key:\t"<<key;
     string messageToSend = encoder(data, key);
-    cout<<endl<<"--------------------"<<endl;
+    cout<<endl<<"----------------------------------------"<<endl;
     cout<<"Message to be sent:\t"<<messageToSend;
-    cout<<endl<<"--------------------"<<endl;
+    cout<<endl<<"----------------------------------------"<<endl;
+
+    string receivedData;
+    cout<<endl<<"HINT: Received data should be the same as message to be sent.";
+    cout<<endl<<"Enter received data:\t";
+    getline(cin, receivedData);
+
+    if (receivedData == messageToSend) {
+        cout<<"The received data is correct."<<endl;
+    } else {
+        cout<<"The received data appears to be tampered."<<endl;
+    }
 
     return 0;
 }
-
-// TODO:
-// - Check if input data is actually binary