// MD5 Padding
 
#include <iostream>
#include <vector>
#include <bitset>
using namespace std;
 
// Converts a decimal number to an 8-bit binary string
string decToBinary8(int n) {
    return bitset<8>(n).to_string();
}
 
// Converts a 64-bit integer to little-endian byte-wise binary strings
vector<string> lengthTo64BitLittleEndian(uint64_t bitLength) {
    vector<string> res;
    for (int i = 0; i < 8; i++) {
        res.push_back(decToBinary8(bitLength & 0xFF)); // Get the least significant byte
        bitLength >>= 8; // Shift right by 8 bits
    }
    return res;
}
 
int main() {
    string inp;
    cout << "Give the original message to check: ";
    getline(cin, inp);
 
    vector<string> inputChain;
    cout << "\n1. Original message in binary:\n";
    for (char c : inp) {
        string binChar = decToBinary8((int)c);
        inputChain.push_back(binChar);
        cout << binChar << " ";
    }
 
    int originalBits = inp.size() * 8;
    cout << "\n\n2. Total message length in bits: " << originalBits << endl;
 
    // Padding starts with '1' bit followed by '0's
    vector<string> paddingChain;
    paddingChain.push_back("10000000"); // First '1' bit (0x80)
 
    // Calculate padding length: make total (message + padding) ≡ 448 mod 512
    int totalBitsBeforeLength = originalBits + 8; // +8 for the initial 0x80 byte
    int paddingBitsNeeded = (448 - totalBitsBeforeLength % 512 + 512) % 512;
    int paddingBytes = paddingBitsNeeded / 8;
 
    for (int i = 0; i < paddingBytes; i++) {
        paddingChain.push_back("00000000");
    }
 
    cout << "\n3. Padding bytes (including 0x80): " << paddingChain.size() << endl;
    cout << "Padding in binary:\n";
    for (string p : paddingChain) {
        cout << p << " ";
    }
 
    // Message length in 64-bit little-endian format
    vector<string> lengthChain = lengthTo64BitLittleEndian(originalBits);
    cout << "\n\n4. 64-bit message length in little-endian binary:\n";
    for (string l : lengthChain) {
        cout << l << " ";
    }
 
    // Combine everything
    cout << "\n\n5. Final message in binary (message + padding + length):\n";
    for (string s : inputChain) cout << s << " ";
    for (string s : paddingChain) cout << s << " ";
    for (string s : lengthChain) cout << s << " ";
 
    cout << "\n\nTotal final size in bits: " << inputChain.size()*8 + paddingChain.size()*8 + 64 << endl;
 
    return 0;
}

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